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Treatment of acute arthrogenous pain in the human temporomandibular joint with an oral orthopaedic applicance Tobias, David Leonardo 1994

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TREATMENT OF ACUTE ARTHROGENOUS PAIN IN THE HUMANTEMPOROMANDIBULAR JOINT WITH AN ORALORTHOPAEDIC APPLIANCEbyDAVID LEONARDO TOBIASUniversity of British Columbia, Vancouver, Canada,University of British Columbia, Vancouver, Canada,A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTERS OF SCIENCEB.Sc.,D.M.D,19781984inTHE FACULTY OF GRADUATE STUDIES(Department of Oral Biology)We accept this thesis as conforming to therequired standardIIVERSITY OF BRITISH COLUMBIASeptember 1994® David L. Tobias, 1994In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. it is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.(Signature)Department of_____________________The University of British ColumbiaVancouver, CanadaDate_______DE6 (2/88)ABSTRACTThe biomechanical events that accompany functional loading of thehuman mandible are poorly understood. Computer simulations has emerged as anindirect way to demonstrate the principles of jaw mechanics. The modelling ofcondylar load distributions for various clenching tasks has lead to the observationsthat deviations in form and osteoarthritic changes as most commmonly found in thecentral and lateral regions of the articulation reflect habitual compressive loading ofthe temporomandibular joints.Speculation has existed that compressive stresses as measured duringsimulated unilateral tooth clenching, offer a functional correlate for regional differencesin articular pathology. It has been suggested due to the indirect measuring of theeffects of these loads, that well-known progressive deterioration of the discs andarticular surfaces are largely brought about by persistent non-working sidecompression of the temporomandibular joint structures. This in the short term isbelieved to lead to arthralgia of sufficent magnitude that patients often seek treatmentby dental clinicians.In the first study, an existing 3D FEM model of the human mandible,modified to include an opposing oral orthopaedic device, was utilized to test for theeffect of two clenching tasks on the compressive stresses measured at the level of thecondylar heads when an orthopaedic dental appliance with unilateral occlusal contactswas placed between the teeth. It was found that the level of compressive stress in thecontralateral side is twice that of the working side joint.A clinical study was then performed in order to test the hypothesis thatin acute articular pathology, the use of an orthopaedic appliance designed to reducethe load to the painful joint can positively influence the resolution of arthrogenous painin the short term. Specifically, it was proposed that this could be achieved with anappliance designed with unilateral occiusal support.A group of patients diagnosed with unilateral articular pathology wererandomized into two treatment groups, one was treated with a conventional flatappliance, the other with unilateral occlusal contacts removed from the sidecontralateral to the painful joint. In both cases, a VAS was used to assess pain in bothjoints with and without the mechanical stimulus provided by biting on a forcetransducer placed between the teeth. Patients were followed for 3 weeks after initialtesting. It was found that painful symptoms improved in the range, as measured bythe VAS, and in the degree of pain for subjects treated with the unilaterally supportedappliance, It was also discovered that the range and magnitude of the bite forceincreased concomittantly with the reduction in painful symptoms.IIICollectively the studies suggest that muscle activity is sensitive todifferences in occiusal support offered by an intra-oral appliance, and that such adevice can be used to modify articular loading and/or to control muscle use in sucha way as to speed up the resolution of painful intrarticular symptoms in TMJ patients.ivTABLE OF CONTENTSABSTRACT iiTABLE OF CONTENTS vLIST OF FIGURES viiACKNOWLEDGEMENT viiiINTRODUCTION 1Introduction to the Thesis 1Review of the LiteratureClassification of Temporomandibular Joint Disorders 6Etiology of Temporomandibular Joint Disorders 12Management of Temporomandibular Joint Disorders 21Orthopaedic Appliance Therapy 27Pain 36Articular Pain 37Innervation of the TMJ 39Biomechanics of the TMJ 47Articular Loading 47Articular Stability 59STATEMENT OF THE PROBLEM 65METHODS AND MATERIALS 67Biomechanical Model 67VClinical Study 71The Measurement of Oral Bite Forces 71Experimental Measurement of Pain 73Methodology of Clinical Study 75RESULTS 79Model Predictions 79Clinical Study 80DISCUSSION 91CONCLUSIONSCLOSING COMMENTS AND DIRECTIONS FOR FUTURE RESEARCH 103BIBLIOGRAPHY 106APPENDIX 128viLIST OF FIGURESFigure 1 Level of pain during the past week 83Figure 2 Level of pain at time of examination 84Figure 3 Level of pain during an ipsilateral clench 86Figure 4 Level of pain during a contralateral clench 87Figure 5 Level of pain in the contralateral joint during a ipsilateral clench 89Figure 6 Bite forces 90viiACKNOWLEDGEMENTI wish to dedicate this thesis to my teacher and friend Dr. W.W.Wood,without whose inspiration and encouragement this body of work would not have beencorn pleted.My never ending admiration goes to my wife Rosalind and my childrenEmily, Max and Sam for their patience, support and understanding for the many hoursI disappeared from home in order to complete this work.I am forever indebted to my supervisor and teacher Dr. Alan Hannamfor his friendship, his never ending fountain of intellectual stimulation and his constantguidance and encouragement.To my advisory committee my thanks for your counsel. To my friendsand colleagues Dr’s. Tom Korioth and Geerling Langenbach my thanks for yourgenerous advice and contribution to this work.Finally, I wish to thank my father, friend and mentor for his inspirationand unfailing support.viiiINTRODUCTIONThe human masticatory apparatus can be lookedi upon as abiomechanical system of complex interrelated components made up of muscles,bones, ligaments, nerves and teeth, all of which play a role in the proper function andhealth of the being. The mandible is analogous to a limb that crosses the midline withover 27 muscles influencing its action with tendons and ligaments of inmeasurablenumbers and complexity affecting its functions. Muscles are recruited as required tomove the bony components against gravity with the aid of other passive forces andfunction to provide forces, directed in such a manner as to maintain the articulationof the temporomandibular joint in an optimum position to withstand loads, and toprovide mobility.The craniomandibular articulation with its component parts is vital indetermining general posture and movement. One can easily speculate, that withchanges in morphology, excessive muscle tensions, parafunctional movements,persistent loading of connective or bony tissues and/or with trauma, the wholearticulation can progressively destabilize or break down, leading to the malfunction ofthis most crucial apparatus.Temporomandibular disorders (TMD) is a broad term that encompassesa variety of clinical conditions that involve the stomatognathic system.1Although TMD has been viewed as one syndrome, current thought increasinglysupports the view that what is now termed as TMD or by some CMD(Craniomandibular Disorders) is a variety of disorders often of multifactorial etiology,and presenting with overlapping signs and symptoms. Unfortunately, many studiesin the past have not differentiated between the broad terms for classification of thesedisorders and what is now believed to be a subgroup of these, temporomandibularjoint disorders. The signs and symptoms of these disorders manifest themselves inthe masticatory musculature, the temporomandibular joints, teeth and periodontalstructures, and cervical musculature. They are a major cause of non-dental pain in theorofacial region and have been seen to develop post trauma to the head, post-motorvehicle accidents, and appear commonly following excessive levels of oralparafunctional activities, often exacerbated by stress and cognitive influences.Most commonly, these disorders are treated by general dentalpractitioners, by means of intra-oral appliances, which are designed to alter toothcontacts, joint forces, and masticatory muscle use. The appliance therapy is oftensupplemented by analgesics, anti- inf lammatories, habit modification education,physical therapy and a variety of biofeedback and behavioral altering techniques.Oral orthopaedic appliances, commonly referred to as splints, have beenused with a good measure of success.2The reduction of painful symptoms with appliance therapy has been reportedcommonly to reach levels of 70% of clinical success.Standard appliances are usually worn during the day and/or night, andare designed to balance forces between the jaws. Research in the past has notmanaged to explain the biological reason for the reported improvement in symptoms.It is not known whether their beneficial effects occur because these devices activelyreduce force on the affected joint, change its movement patterns, or because toothcontact is altered and thus muscle activity is influenced, or simply because theappliance changes the habits and modifies the behaviour in the affected individual.Loading that exceeds the physiological limits of the temporomandibularjoints and its associated structures may present itself initially as arthrogenous pain andpain to the muscles of mastication, the pre-auricular area, and angle of the lower jaw.Pain is often aggravated by chewing and jaw movement. Complaints of restricted jawopening are commom, as well as distressing joint sounds described as clicking orpopping.Tissues of the temporomandibular joint react to functional demands byalterations in the soft and hard tissues. The role of articular mechanics in theprogression of change in the joint has been implied but not proven.3Loading demands beyond the physiological limits of the tissues of the joint often leadto remodelling. This constitutes the adaptive processes that the form can undergounder function.As the biomechanics of the temporomandibular joints and theconcommittant musculature are complex and not fully understood, and vary with theanatomy and physiology of each individual, it is difficult to predict the effects that astandard design appliance has on any one person. Knowledge of the actual changewhich may be responsible for the beneficial results would clearly improve treatmentplanning and predictability of success. The increased level of prediction for eachtreatment approach could in turn, speed up the resolution of the disorder.Research in jaw mechanics suggests that the forces in the joints arenormally compressive, but can be altered by tooth contact patterns, and the way thejaw muscles are recruited and activated. Recent studies that have looked at theinfluence of mechanics on the temporomandibular joint and the possible effects on itsfunction, suggest a probable role of joint biomechanics on symptomatology. Thus, itseems theoretically possible to increase or decrease temporomandibular joint forcesby altering the appropriate combination of tooth contacts, and by encouragingparticular patterns of masticatory muscle use.4An increased level of success both in terms of improved predictability asto the treatment approach , and improvement in the speed of recovery fromsymptoms, as well as a decrease in the magnitude of the pain, by articulardecompression would be a desirable effect from an oral orthopaedic appliance.Thus any novel oral appliance, designed specifically to reduce loadingin an acutely-painful temporomandibular joint, could resolve arthrogenous pain moreeffectively than conventionally-designed ones reported previously in the literature, andwould be a useful clinical approach for managing specific clinical temporomandibulardisorders.5CLASSIFICATION, ETIOLOGY AND MANAGEMENTOF TEMPOROMANDIBULAR JOINT DISORDERSCLASSIFICATION OF TEMPOROMANDIBULAR DISORDERSTemporomandibular disorders are a major cause of non dental pain inthe orofacial region. Their most frequent symptom is pain, usually localized around themuscles of mastication, the preauricular area, and the temporomandibular joint. Thepain is commonly aggravated by excursive movements of the jaw and mastication.There is also often what has been described as clicking, popping, grating and crepituscoming from inside the joint complex. Patients usually complain of earaches,headaches, jaw aches, toothaches and facial pain. Often a history of trauma iselicited, and of parafunctional activities such as bruxing or clenching, and of stress.Definition of the disorders has undergone substantial changes in the lastfew years. The term TMD itself has come to be regarded as too broad, becauseindividuals with TMD present with quite distinct variations in signs and symptoms, andprobably have various mechanisms underlying their disease.The term “TMJ” has become regarded in the popular press as the“disease” of the 70’s, 80’s and 90’s, due to the increased attention this complex6articulation has attracted from the profession. Due to the ever increasing costs tosociety and to the need to bring health care costs under control, and with theproliferation of diagnostic and therapeutic devices, there have been major efforts madeto improve the diagnostic and managem ent guidelines existing for this multifactorialdisorder. A historical review can be found in the Guidelines for Classification,Assessment and Management of Temporomandibular Disorders by McNeill, (McNeill1993) and in Dworkin (1992).Laskin (1969), described what is now considered to be a specificsubgroup category within TMD called Myofascial Pain Dysfunction Syndrome (MPD).MPD was proposed for use by clinicians for diagnostic and treatment planningpurposes and for researchers for the purpose of defining subject groups. For thediagnosis to be made, four positive and two negative signs had to apply.The positive inclusionary signs were:- Unilateral pre-auricular pain.- Muscle pain on palpation.- Joint noises (clicking, popping).- Limited mandibular opening.The negative exclusionary signs were:- No joint tenderness upon palpation of the external auditory meatus.- No clinical, radiographic, or biochemical evidence of organic disease.7All patients with TMD, but not categorized as MPD, were consideredarthritic patients (McNeil 1993). The operational definitions for eliciting a positive ornegative sign were not provided, nor were there clear descriptions on the amount ofpressure needed to palpate a muscle or an objective measure of pain considered. Italso unfortunately did not differentiate between intra-articular or so called internalderangements of the discs and muscular problems. It did serve nevertheless for manyyears as the operational definition for temporomandibular disorders.During the late 70’s, based on a conference convened to establishguidelines for the clinical diagnosis of TMD (Laskin et al. 1983), a nomenclaturesystem suggested by Bell (1982) was decided upon. Bell’s system also lacked clearoperational definitions and reproducibility or validity testing, but it did serve as anexpansion on Laskin’s. It suggested five subgroups:- Acute Muscle Disorders- Disc Interference Disorders- Inflammatory Disorders- Chronic Mandibular Hypomobilities- Growth DisordersIn 1985, Eversole and Machado (1985) proposed another classificationsystem for TMD. This system specified three main categories:- Myogenic Facial Pain.8- Internal Derangements.- Degenerative Joint Disease.This simplification eliminated the subgroupings made by Bell for musclepain and simplified the disc derangements categories. As this system was proposedfor research as well as clinical purposes, specific exclusionary and inclusionary criteriawere developed. Unfortunately, again no operational definitions for the examinationswere given. It also has proven to be too exclusionary, since for example, a myogenicfacial pain could not present with joint sounds. These exclusions make it difficult tocategorize patients into the proposed subgroups. Nevertheless, it has been shown tocapture the more acceptable grouping for TM dysfunction (i.e., muscle disorders andpain, joint disorders and pain and arthritis).The problem of multiple diagnoses and how to deal with these whenattempting to define a presumably homogenous reasearch population has not reallybeen solved. Although individual clinicians are succesful in diagnosing the simplerforms of TMD, the management of the more complex and more chronic problemsoften require a multidisciplinary approach. To facilitate this approach Dworkin (1992)suggested a multiaxial diagnostic system that develops concurrent physical,psychological and social conditions along two axes, and the newly proposed ResearchDiagnostic Criteria (RDC), (Dworkin Ed. 1992) has been an attempt to do just this.9The base for the two axes are a clinical examination and a chronic pain disablilty andpsychological-based questionnaire. This classification has gone a long way inproviding some operational definitions and criteria to aid in the examination andevaluation of the multifactorial presentation of signs and symptoms for a heterogenousgroup of patients. The parameters that are suggested for use by researchers have notyet been fully validated, but at least give some guidance in how best to group patientsand what tests to use, and the method doesn’t ignore the multidimensional aspect ofthese disorders.For clinician’s use, the clinical diagnostic nomenclature systems detailedby Clark et al. in 1989 and MoNeill et al. in 1993 continue to be used, and be of usein the assessment and treatment of individual cases for they are generally consistentwith patient symptomatic presentations.The presence of multiple symptoms thus remains an issue. To someextent, researchers have ignored the underlying sources of the disorders and havefocused unduly on the multiplicity of symptoms and signs for this multifactorialdisorder. Researchers need to continue addressing the issue of symptom overlap andcontinue developing a system which allows multiple attributions to distinct subgroups,as well as scoring specific symptoms when multiple signs and symptoms exist. Onlyin this way can the relative strength of each subgroup be assessed.10The pooling of heterogenous groups has unfortunately caused muchconfusion. Clinicians have not been concerned with the problems of forminghomogenous groups and since they have been mostly involved in the treatment ofthese disorders, the criteria available in the past has not proven very helpful in thestudy of the disorder. All too often the broader term of TMD has been equated with,what is now accepted as a subgroup of the classification, TMJ disorders.For research purposes, the refinement of existing clinical methodologyand the addition of more objective methods to quantify signs and symptoms can onlybenefit any study that deals with repeated measurements over a period of time.Methods need to be tested for reliability and validity and compared to some TMGoldStandard”, which to date continues to be the examination and history that cliniciansare most adept at.Data on sensitivity, specificity, and predictive values exist, for someexaminations and questionnaires, but further work is needed before these can be usedboth as research and clinical tools in order to facilitate the communication betweenresearchers and clinicians.In summary, the definition of TMD and its various subgroups hasprogressed steadily since the concept of MPD was brought forward by Laskin.11Fortunately clinicians are more routinely observed to describe their patients in a moredetailed fashion, and rarely is the broad concept of “Temporomandibular Disorder”considered a sufficient diagnosis. “TMJ” continues to simply be the anatomical namefor the articulation, not an unknown disease entity, and temporomandibular jointdisorders is increasingly studied as a disease entity in itself.ETIOLOGY OF TEMPOROMANDIBULAR JOINT DISORDERS-Early Theories of Etiology-Since the beginning of this century a variety of etiologic factors havebeen suggested as the cause of pain and dysfunction in the temporomandibulararticulation system. One of the earliest proposed and most persistent theories, wasthat temporomandibular joint disorders are caused by abnormal structure both of theteeth and jaws. Ever since the pioneering work by Edward Angle (1900), who todayis credited with describing the essential features of a “normal” occlusion, dentists haveregarded abnormal structure as a major etiologic factor in temporo-mandibulardisorders. Costen (1934) described a more specific structural joint disorder, when hepostulated that ear and temporomandibular joint pain were signs and symptomscaused by the compression of vascular and neural elements, specifically the chordatympani nerve and tympanic plate, due to displacement of the mandibular condyles.Most structural abnormality theories of the first half of the century, centered on12occlusal abnormalities due to lack of teeth, malpositions of teeth and the so calledabnormal occlusions. The structural occlusal model only became succesfullychallenged in the 50’s by Sicher, in the late 1960’s by the multifactorial model oftemporo-mandibular dysfunction of Laskin (1969) and by a new structural ormorphological concept, that of the disc displacement model (See Clark (1991) for anhistorical perspective).Theories by the middle to late 1970’s became more multifactorial inapproach and allowed for joint and muscle abnormalities. These could be induced bytrauma, parafunctional habits, hypermobility of tissues and of course malocciusionsof the jaws.-Current Theories-It is interesting to note, that to this day, the occlusal abnormality theoryhas survived, even though evidence exists to the contrary (Helm and Petersen 1989).While clearly, others feel that the scientific evidence available does not warrant therejection of the hypothesis that occiusal factors are part of a causal complex ofcraniomandibular disorders. (Kirveskari and Alanen 1993). It nevertheless has beenestablished that many patients with naturally occuring, so called occlusalabnormalities, do not present with signs or symptoms of temporomandibular jointdisorders, while others with ideal occlusions exhibit disease.13Unfortunately, the evidence for the prevalence of other etiologic factorssuch as trauma, joint laxity, parafunctional habits, stress related behaviours and otheranatomic susceptible abnormalities needs to be more convincingly presented.Temporomandibular joint disorders are diverse and often multifactorial,and most probably a universal etiology does not exist. According to McNeill (1983),there are certain factors that increase risk and are therefore predisposing. Others maycause the onset of signs and symptoms and can be referred to as initiating factors.Still others that enhance the progression of TMJ disorders and are called perpetuating.Any of these factors under different circumstances may serve any of these roles.Many factors are thought to affect the dynamic balance or equilibriumbetween the different components of the masticatory system. Loss of structuralintegrity, altered function, or biomechanical overloading in the system can compromiseadaptability and increase the likelihood of dysfunction by disrupting this equilibrium.(Parker 1990, McNeill 1993). The exact prevalence of the various etiologic factors hastherefore not been firmly established. (Clark 1991). For the purposes of this reviewhowever, etiologic agents or factors in TMD are divided into 4 major groups: Trauma;Anatomic or Biologic; Systemic Pathophysiologica I and Psychosocial Factors.14Trauma.The best estimates indicate that long lasting effects from an injury ortrauma account for 10 to 30% of TMD patients. A history of trauma can be elucidatedfrom a majority of adults suffering from TMD signs or symptoms, compared to a muchsmaller number in non-patients (Pullinger et aL 1985). Katzberg (1985), reported ahistory of trauma in 26% of paediatric patients. Commonly, blows to the mandibleduring sports injuries and abuse during artistic performance were reported by Howard(1990). latrogenic trauma from dental procedures, as well oral intubation associatedwith the administration of general anaesthesia has also been implicated. (Harkins andMarteney 1985, Taylor and Way 1968). Evidence also exists for the presence oftemporomandibular joint symptoms after motor vehicle accidents (Kronn 1993 andBraun et al. 1992) and for signs of altered function of the temporomandibular jointafter cervical extension-flexion injuries, the so-called Whiplash injuries, even thoughthe mechanism whereby these injuries develop remains controversial (Weinberg andLapointe 1987, Howard et al. 1991).Another form of trauma associated with joint disorders has beenhypothesized to originate from adverse loading of the system due to parafunctionalhabits. Tooth clenching and grinding, lip biting, and abnormal posturing of the jaw allare common in asymptomatic individuals but have been suggested as initiating and/orperpetuating factors joint disorders ( see Travell and Simons 1983,Faulkner 1990,15Rugh and Harlan 1988, and Scharer 1974). Parafunctional habits have been mostfrequently assessed by self-reporting, questionnaires and tooth wear. These havebeen critized for being too subjective and relying primarily on memory and verbalreports. Limitations of such measures were recently reviewed by Marbach et al.(1990).Anatomic or Biologic FactorsThese comprise the developmental and genetic factors, encompassingskeletal malformations, past alterations to the dentition or what historically have beenviewed as malocclusions.Historically as was mentioned above, the profession has viewedmalocclusions as a primary etiologic factor for temporomandibular joint disorders.Interferences in occlusions (both non-working and working) plus centric discrepancies,have commonly been associated with these disorders. However, reviews of theliterature fail to support tooth position discrepancies as a common etiologic factor (SeeMarbach 1990, De Laat et al. 1986, Seligman 1991 among others).Changes in the structure of the component parts of the articulation havebeen associated with the loss of occiusal support and lack of molar teeth. Studies ofskeletal remains, (Granados 1979, Whittaker 1989) and of patients with osteoarthrosis,16(Akerman et al. 1988, Tegelberg 1987, Kopp 1977 to name a few), have correlatedloss of molar support with bony changes. The highest correlation with osteoarthrosisseems to be increasing age however, not the lack of teeth (Whittaker et al. 1990).Studies of living, apparently normal populations, have not shown anassociation between tooth loss and tern porm andibu lar joint disorders (Helkimo 1974,Kirveskari and Alanen 1985, Wilding and Owen 1987, Pullinger at al. 1990, amongothers). The loss of moderate changes in vertical dimension (5mm) does not seemto be enough cause for TMD symptoms (Rivera-Morales and MohI 1990). In a studycomparing a control group to well-defined diagnostic groups rather than to specificsymptoms, Selligman and Pullinger (1989) found selective occlusal variablessomewhat associated with some TMJ disorders.In a further review of the role of intercuspal relationships in TMD, thesame authors in 1991 concluded that in skeletal anterior open bites, reduced overbiteand increased overjet were all associated with osteoarthrosis but they lacked thespecific parameter to define a patient population. Therefore, they concluded that therewas no evidence that overbite and overjet play a role in the pathophysiology ofnonarthrotic disorders. They also found a relationship between unilateral retrudedcontacts and the lack of a centric slide with the presence of disc displacements. Alsothere was no relationship between crossbites and the presence of disease.17This review should be consulted for a more detailed look at the skeletal and occlusalrelationships to TMD. Nevertheless, the association remains between anatomicalfactors such as an altered condylar positions with concomitant capsular alterations,but not as the cause of the pathophysiology (Selligman and Pullinger 1991).Systemic PathoDhysiolog ical FactorsThese can include degenerative, endocrine, neoplastic, vascular andmetabolic disorders, which can act simultaneously at a central or local level (Byrd andStein 1990, Hagberg et al. 1990). Degenerative muscle changes can result fromankylosis and lack of use of the articulation (El-Labben et al. 1990).It has also been suggested for all joints that the lack of intra-articularlubrication and alterations in synovial fluid viscosity may initiate disc derangementsand clicking (ToIler 1961). The content and make up of synovial fluid has beenimplicated in the modulation of pain in inflammation of the TMJ (Israel 1989, Quinnand Bazan 1990).Systemic joint laxity has been suggested as a contributing factor to TMJdisorders. It has been reported more prevalent in females and a correlation has beenmade with the number of lax joints and the appearance of a craniomandibular disorder(Westling 1989, 1990, 1992, Bucking ham et al 1991, Bates 1984). Other studieshowever have found no relationship (Chun et al.1990, Blasberg et al. 1991).18If true, this together with hormonal cyclical changes could help explain some of theincreased incidence of TMJ disorders in females (Olson et al. 1988), but further workis needed to confirm it.Other factors include the arthritides. Of these, the most common isosteoarthrosis (Kopp 1977). The distinction between an adaptive response by intraarticular tissues to increased joint loads and the pathologic one is somewhat blurred.(A discussion of loading and its efects can be found elsewhere). Studies haveevaluated enzymatic and other metabolic by-products in degeneration of the TMJ(Kopp 1983, Israel 1989). On the other hand, there is strong evidence thatrheumatoid arthritis affects the temporomandibular articulation (Akerman et al. 1988)and that it can be modulated by injections of glucocorticosteroids (Wenneberg 1991),suggesting that inhibition of the degenerative process may be achieved by a reductionin the inflammatory process.Histologic changes have been observed on condylar cartilage as aresponse to functional loads (Hansson and Oberg 1977, Hansson and Nordstrom1977 among others) as has the remodelling of the articular tissues (Baldioceda et al.1990, Luder 1993). The presence of changes in the structure of the temporomandibularjoint with age is as expected with all aging tissues. Nevertheless, the presence orabsence of intra-articular changes, be it disc derangement and/or bony remodellingcannot be ruled out as normal anatomic variation in aging individuals, nor can it be19said that it is found solely as a result of the systemic pathophysiologica I factorsreviewed above.Psychosocial FactorsThese factors include individual, social and societal variables that impacton the behaviour and the ability of the patient to function and adapt to change. Therehas been some evidence that patients who suffer from temporomandibular disordersexperience more anxiety than controls and that many of the symptoms expreseed maybe somatizations of emotional disturbances (Gerschman et al. 1987, McCreary et al.1991). These patients often have a history of other stress-related disorders (Gold etal. 1975).The role of stress and mediating cognitive variables, ie: the feeling ofcontolling one’s own life situation, may be important in the etiology and progressionof temporomandibular disorders (Stockstill and Callahan 1991).While the relationship of psychosocial disorders to TMD is still not clear,clinical reports suggest that the psychosocial conflicts and distress of pre-existingpsychiatric conditions may be a contributing factor to the etiology of TMD, and mayexacerbate and/or affect the adaptive capabilities of the individuals to thetemporomandibular disorder (Lipowski 1988).20Psychosocial factors may predispose certain individuals to TMD and may alsoperpetuate the disorder once chronicity is established. Careful consideration ofpsychosocial factors therefore seems important to the diagnostic evaluation of TMDpatients (McNeill 1993).MANAGEMENT OF TEMPOROMANDIBULAR DISORDERSIncreasingly the management of patients with TMD attempts to deal withthese patients in a similar manner to those of other orthopaedic or rheumatologicdisorders. Its primary goals are to reduce pain, decrease adverse loading, and restorenormal function.To achieve these goals the clinician tries to develop a multidisciplinaryapproach. Often there is a need for the rehabilitation program to incorporatetreatments for both the physiological as well as the psychological component of thedisorder, and to decrease or remove all contributing factors that can be ascertainedfrom a history and examination.-Reversible TherapiesIt is important in planning treatment to remember that TMD can betransient and self-limiting. The progression of a mild form of the disorder to a more21serious condition has not been shown to be the natural course of TMD (Greene andLaskin 1983, Fricton 1991). The body has powerful healing and remodellingcapabilities that cannot be ignored (Nickerson and Boering 1989). This conservativeapproach to therapy has resulted repeatedly in positive treatment outcomes (Fricton1991, Carlsson 1985, Randolph et al. 1990, Okeson et al. 1986 to name a few).The conservative approach to the management of TMD dependsprimarily on the education of the patient with regard to the various treatmentapproaches, as well as addressing etiological, contributing and/or perpetuating factorsthat may be playing a role. This approach towards self car& depends largely onmotivation and cooperation by the patient. The prevention of further injury to thetemporomandibular system, as in other musculoskeletal injuries, depends on rest andallowing healing to proceed without further insult (Randolph et al. 1990, Hodges 1990).Self-care instructions emphasize habit modification, avoidance of heavy chewing (softdiet), awareness of parafunctional activities of the tongue, lips and jaw, and mild formsof physiotherapy and exercise (Danzig and VanDyke 1983, Curl 1993).Changing persistent maladaptive habits also play an important part incognitive behavioral intervention. This sometimes requires a structured programme ofbehaviour modification that may involve lifestyle changes and often needs to beindividualized (Rugh 1988).22Biofeedback is an example of structured therapy designed to alterbehaviour that has been used alone and in conjunction with other therapies, to alterbruxing behaviours and muscle tonic activity (Solberg and Rugh 1972, Rugh andJohnson 1981, Pierce and Gale 1988).Psychotherapy can also be part of a multidisciplinary approach to TMDtherapy. This is especially the case in chronic pain patients, where symptoms mayserve as a somatic metaphor that both expresses and resolves pre-existing orconcurrent psychological conflicts (Levinson 1990). When TMD is part of the patient’scoping mechanism, treatment efforts with cognitive-behavioral management orpharmacologic therapy will not be sufficient to resolve the conflict. The aid of a skilledpsychotherapist is an integral part of management.Pharmacotherapy has been shown to be an important adjunct to aid inpatient comfort and rehabilitation. Nevertheless, its use needs to be controlled formisuse and abuse since relying on narcotics or analgesics for TMD patients may leadto tolerance and dependency (Ready 1979). The most effective agents for themanagement of TMD in acute conditions include analgesics, non-steroidalinflammatories, corticosteroids and muscle relaxants. In addition, anti-depressants areused in some chronic pain patients (Gregg and Rugh 1988, McNeill 1991).23Physical therapies are most commonly used as adjuncts to othertreatments (Clark 1990). These involve posture training (Curl 1993, Hackney 1993),exercise and relaxation (Carlson et al. 1991), mobilization and manipulation (VanDyke1990, Minagi et al. 1991). Agents often used in conjunction to the above arethermotherapy, utilizing surface heat or by means of cryotherapy or coolant therapy(Nelson 1988, Burgess et al. 1988, Travell 1952, Travell and Simons 1983);Electrotherapy in the form of electrogalvanic stimulation (EGS) (Murphy 1983), ortranscutaneous electrical stimulation (TENS) (Binder 1981, Gold et al. 1983, Wessbergetal. 1981, Moystad 1990); Acupuncture (Johansson etal. 1991, Raustia 1985); Lasertherapy (Hanson 1989, Bezuur 1988); and Ultrasound (Esposito 1984). For detailedreviews of these modalities the reader should consult Okeson 1993 and McNeill 1993.Orthopaedic appliance therapy is primarily regarded as a reversible modality. It isreviewed in detail later.-Irreversible TherapiesOcciusal therapy and its role in establishing a cause and effectrelationship to TMD has been a subject of much debate. Although dental treatmentper se may be necessary for patients with TMD, many believe that it is infrequentlynecessary for the purpose of directly treating TMD (McNeill 1991).24As reported above there is little evidence, that normal and natural occiusal variationis a direct cause of TMD (Seligman and Pullinger 1991). Controlled studies have failedto show an association between occiusal interferences and TMD.Occiusal adjustment has been reported to be effective in reducingsymptoms of TMD (Magnusson 1983), but it has not been shown to be more effectivethan reversible modalities. (Wenneberg 1988). Limited occiusal adjustment may beindicated where certain interferences apparently provoke acute symptoms, especiallyas a result of dental restorative interventions (Scharer 1966). Occlusal adjustment isnot viewed as a preventive modality for TMD (Goodman 1976).It has been suggested that restorative therapy, since it is an irreversibletreatment option, should never be regarded as an initial form of therapy (McNeill1993), and the benefits of occlusal restorative therapy has been questioned(Plasmans et al. 1988). However, once symptoms are under control, its role could beconsidered. It would seem intuitively obvious that a stable occlusion and an optimumplatform for the even distribution of forces and loading stresses to the teeth and joints,might be a desirable biomechanical state for the continuation of health for the teethand articulation (Hannam 1984, Hylander 1985, Faulkner et al. 1987).Orthodontic therapy, and in the extreme, orthognathic surgery, can beviewed as improving occlusal stability and thus providing more optimum surfaces to25distribute the stress. Their use as a treatment modality has to be viewed in the samemanner as any occlusal therapy. When used after repositioning appliance therapy,orthodontic therapy has not been proven to be any more succesful than appliancetherapy alone (Bradley 1989). In fact, orthodontic therapy in itself has been viewed aspossibly destabilizing the stomatognathic system (Greene 1982). In contrast with thisview, some long term studies have shown the risk factor of orthodontics itself to benegligible (Kremenak et at. 1992).Surgery is considered an appropriate an effective form of managementfor specific temporomandibular disorders. The American Association of Oral andMaxillofacial Surgeons has set criteria in order to maximize the potential for succesfuloutcomes in surgical therapies of the TMJ. These have been reviewed by McNeiII(1993). Arthroscopy, a commonly used mode for lavage and visualization of the jointmay in the future be superceded by arthrocentesis as a conservative surgical therapy(Nitzan et al. 1991).Arthrotomy, and in general open surgical techiques are today only usedfor advanced disease states, such as ankylosis, neoplasias, persistent painful discderangements and severe osteoarthrosis. Discoplasty and discectomy whenperformed have been considered to be succesful (McCarty and Farrar 1979) forinternal derangements, but the measure of success has not been made clear.26Afloplastic prostheses presently seem to be contraindicated due to tissue rejectionproblems and material breakdown, and condylectom ies are presently performedinfrequently. (For a review see McNeiIl 1993).ORTHOPAEDIC APPLIANCE THERAPYThe occiusal appliance, commonly referred to as a splint, is a removabledevice most often made out of acrylic, that fits over the occiusal surfaces of the teethin either the maxillary or mandibular arch creating a prosthetic surface that allows forvarying tooth contacts with the opposing arch.These appliances, in a variety of designs, have been commonlyaccepted as part of the primary form of therapy for temporomandibular disorders.Since the etiology and interrelationships of these disorders are often ill-defined andcomplex, the initial therapy is commonly reversible and non-invasive. There is a broadset of clinical experiences by enumerable practitioners dating back decades to justifythe use of these types of appliances.A critical review by Clark (1984) found their effectiveness to vary depending on themasticatory disorder being treated. In general there appears to be a 70 percent rateof “clinical success” with their use.27The precise effect and role of these appliances has yet to be defined.Several theories have been brought forward to explain how the interocclusalappliances actually work.-The Ocol usal Disengagement Theory-This is based on the premise that the appliance provides the patient withan ideal occlusal scheme that eliminates any occlusal disharmonies, abnormal muscleactivity and stabilizes the TMJ’s (Ramfjord and Ash 1971, Posselt 1968). The designof the appliance is such that it is most often adjusted into a centric relation position,when the posterior teeth are in contact with the appliance, with posterior separationand anterior contact only on protrusive and canine rise during lateral disclusive pathsof mandibular movement. It is often referred to as the full arch stabilization splint.The occusal disengagement theory is based primarily on malocclusionsas the primary etiology for TMD. Most studies use the splint in combination with othertherapies, usually occlusal adjustments and/or prosthetic rehabilitation and counselling(Franks 1965, Zarb 1975, Agerberg and Carlsson 1974, Magnusson and Carlsson1980, Suvineen and Reade 1989) . Few studies have utilized the stabilization splintas the sole mode of therapy (Goharian and Neff 1980, Greene and Laskin 1972,Carraro and Caffesse 1978). However, its “clinical success” cannot be considered asproof that the occiusal disengagement theory is correct.28The resoon cf atjedie s,ç*zmatok as is caTimoly rpoited,may be the result of force redistribution, occlusal stabilization, relaxation of muscleactivity or simply habit modification or by the appliance working as a placebo.The stabilization type splint has been used to treat bothtemporomandibular intra-articular pain and muscle dysfunctions. The differentiationbetween these diagnostic categories has often been blurred. The success rates havevaried in part, due to poor control as to the diagnostic criteria for temporomandibularjoint disorders. Even so in studies that have looked at the short term effectiveness tosuch a therapy, intra-articular pain seem to respond better than TMJ sounds ormandibular movement limitations (Tsuga et al. 1989, Caffesse 1978).-Lack of Vertical Dimension Theory-This theory is based on the concept that an interocclusal splint canrestore the previously lost vertical dimension, thus restoring muscles and thearticulation to a more “advantageous” position. The design of the appliance is oftensimilar to the stabilization splint, but more care is placed in increasing the thicknessand height of the appliance, thus supposedly reestablishing the original vertical. Thistreatment has been commonly suggested for patients with loss of posterior occlusalsupport and muscle hyperactivity.29Since the measurement of vertical dimension is often difficult to make quantitatively,the application of this approach is guarded (Rugh 1981). The adaptation of humansto changes in muscle length has been shown to be quite good (Goldspink 1976,Hellsing 1984). Nevertheless, some claims have been made for the use of varyingsplint heights to treat certain muscle symptoms (Manns et al. 1983). It is alsopertinent to add that any interocclusal device increases the vertical dimension : thusa change in symptomatology would be expected for this reason alone, if this theorywere the only factor involved in affecting temporomandibular symptomatology. Theeffect in any case may prove to be only temporary (Jaffe 1991).-Mandibular Realignment TheoryIt has been theorized that by changing the relationship of the two jawswith an interocclusal appliance, various musculoskeletal symptoms improve as themuscles achieve a “neuromuscular balance”. The assumption lies in the malrelatioshipthat is said to exist between the jaws causing this imbalance. Jaw manipulatingtechniques can be utilized to achieve this new jaw position (Celenza et al. 1978).Another approach to mandibular realignment is a muscle determined positiondetermined by trancutaneous low frequency electrical stimulation of the elevatormusculature (Jankelson 1979). No studies of treatment of TMJ pain have been doneusing this approach, and there are no specific biological descriptions of what isprecisely meant by “neuromuscular imbalance”.30-Temporom andibula r Repositioning Theory-Similarities exist between this approach and the one mentionedpreviously. Both assume that the mandibular position is incorrect. This approachattempts to alter the actual position of the condyle in the fossa (Weinberg 1979,1980). This method is contemplated when a change in the position of the condyles ispresumed to be necessary in order to attempt the correction of an intracapsulardisplacement of the disc, If succesful it is expected that the altered disc-condylerelationship will alleviate the clicking joint. The basic premise of this theory is that thedisc repositioning actually occurs, which after a period of healing or readaptationallows the mandible to return to a non-treatment position. Alterations of disc-condylepositions have a guarded prognosis due to the possible remodelling changes that canoccur in the joints (McNamara 1979, Mongini 1980), and the possible need forpermanent alterations to the tooth to tooth relationships that need to follow in orderto stabilize the jaws long term.-Cognitive Awareness and/or Placebo theoryThe term placebo has been applied to many types of substances usedin a variety of different ways. The most common definition refers to a material thatdoes not contain any active medicine and is pharmacologically inert, a ‘pure placebo’.An orthopaedic appliance can be categorized as such a device.31An ‘impure placebo’, refers to any substance or device used as placebo that is notbelieved to be totally inert. It is also important to note that it has been known that youcan demonstrate objective physiological changes in patients given placebos.The cognitive awareness theory is based on the concept that aninterooclusal appliance of any design will alter behaviour. This change in behaviour,whatever this may be, is enough to alter abnormal muscle activity, parafuntional jawmovement or jaw loading forces. Greene and Laskin (1972) as well as Rubinoff et al.(1987) found that a non-occluding splint proved just as succesful as an occludingone, in ameliorating symptoms, suggesting that cognitive awareness may play asignificant role in the effectiveness of intra-oral appliances.The modification or altering of one’s behaviour is a general theory thathas been shown to apply to most succesful therapeutic interventions (Rugh andSolberg 1976).ORTHOPAEDIC APPLIANCE (SPLINT) TYPES-The Stabilization SplintThis is the most commonly used intra-oral device by dental practitionersfor the treatment of temporomandibular joint disorders. It is adjusted for use in32condylar positions ranging from centric occlusion, to habitual and hinge positions. Aswe have seen above, it is used in the treatment of masticatory dysfunction,temporomandibular joint pain, clicking joints, bruxism, and in the treatment of disordersof incoordination and limitation of jaw movement. It has been used most succesfullyfor the treatment of muscle related disorders (Okeson 1993). In addition, myogenouspain disorders seem to respond best to part time use (often night-time wear), whileintracapsular disorders are better managed by continous use (Wilkinson et al. 1992).-The Anterior Repositioning Splint-This intraoral device incourages the mandible to be positioned in a moreanterior tooth relationship. Its presumed goal is a “better” condyle-disc relationship sothat the coordination of jaw movement can proceed without pain and joint noises.However, the elimination of joint sounds has not been shown to position the condyledisc complex necessarily in the intermediate zone. Arthrography (Tallents et al. 1986),and CT scanning (Manco and Messing 1986), have shown that even with the absenceof sounds, the position of the complex is not as thought pior to the repositioning.Lundh and Westesson (1989) followed a group of patients treated with a repositioningappliance long term, and found that pain and clicking were mostly eliminated by theuse of this type of appliance initially, but the clicking returned in 74% of cases.Okeson (1988) retro-spectively looked at 40 patients treated with a repositioning splintfor eight weeks and then phased out with a step-back procedure. 80% of patients33presented free of pain and clicking at eight weeks. Thirty months later 66% had areturn of joint sounds, with 23% reporting joint pain. The author concluded that ifresolution of pain is the primary objective, repositioning has a good long termprognosis, but a repositioning splint is of limited value in the permanent elimination ofjoint sounds. Similar conclusions were reported by Clark et al. (1988).-Bite Planes- (Anterior).This appliance is worn over the maxillary teeth and provides contact onlyfor the mandibular anterior teeth. It leaves the posterior teeth out of contact, in orderto eliminate their influence on the function of the masticatory system. Has also beencalled a re-programming appliance usually used for brief periods in anticipation ofocclusal adjustment. It has been recommended for use in the treatment of muscledisorders by Ramfjord and Ash (1983), Posselt (1968) and others that have believedthe primary etiology of the disorders to be malocclusion based. The main drawbackto an anterior bite plate is the uncontrolled supra-eruption of the posterior teeth.- Bite Planes - (Posterior).This appliance type is usually fabricated for the mandibular posteriorteeth. It has been commonly referred to as the GeIb Splint (GeIb 1977). It has beenadvocated for use in cases of severe loss of vertical dimension and jaw repositioning.34Once again, long term use is not advocated due to the potential for supra-eruption ofteeth and/or intrusion of the occluding teeth.-Pivot Appliances-This appliance covers one arch and usually provides a single posteriorcontact on each side. It was originally designed with the idea that it would lessen intraarticular pressure and unload the temporomandibular joints in order to help treat noisyjoints (Posselt 1968). It has been shown to actually produce the opposite effect by Itoet al. (1986). Bilateral pivots tended to intrude the condyles in the fossa in a superiorand anterior direction, and did not cause distraction of the joints.-Soft Appliances-This splint is fabricated from resilient materials adapted to either themaxillary or mandibular teeth. It’s most common application is as a protective devicefor the prevention of traumatic injuries of the teeth or jaws during sports. They havebeen advocated for use by clenchers and bruxers with the belief that the softnessallowed for the more even distribution of loads to the joints (Posselt 1968). In fact,Okeson (1987) showed that their use increased nocturnal masseteric activity.35The anecdotal reporting of the reduction in symptoms in some patients using softappliances, could be explained by the cognitive awareness theory.In summary, it is accepted that a patient’s resolution of symptoms is dueto many of the factors outlined above. That a majority of TMD patients benefit by areduction in symptom atology, is reason enough to consider this form of reversibletherapy for these patients. Complications, and iatrogenic sequelae of appliancetherapy can be prevented with proper use and design. Appliances probably shouldnot be designed to allow tooth movement unless desired. They should also behygienic and easily tolerable in order to promote compliance.PAINPain is the most common symptom of disease or injury that compelspatients to seek medical or dental attention. The treatment of pain is associated withenormous costs to society. As for its effects on our health and lifestyle, chronicpathologic pain serves no clear biological benefit to humans, yet imposes emotional,physical, and social stresses to the sufferer and society. In contrast, acutesymptomatic pain serves a distinct biological function, since it warns the subject thatsomething is amiss. Pain as an experience is complex. It includes sensations evoked36by noxious stimuli and the reactions to such stimuli. Pain sensation refers to the abilityto discriminate the quality, location, intensity and duration of the stimulus. Humanreactions to these sensations vary from individual to individual. Attentional, cognitive,motivational and emotional variables modify the behaviour elicited by the noxiousstimulus. This multidimensionality of pain has evolved in great part from the landmarkwork of Meizack and Wall (1965). The reaction to pain may depend on the meaningof the situation in which pain occurs. Cultural backgrounds influence individualreactions and responses. Level of stress, anxiety, past experience and memory affectthe response to the noxious stimulation.ARTICULAR PAIN MECHANISMSIn humans the control mechanism for musculoskeletal pain in general,has been studied mostly on the processing of superficial nociceptive information fromsuch tissues as skin. Small-diameter, slow conducting primary afferent fibers areusually associated with the responses to noxious stimuli. Articular tissues are not onlyinnervated by nociceptor fibers that transmit pain, but also by larger diameter fibers,(group II and III) primary afferents. The latter are associated with low thresholdreceptors (e.g. Ruffini- like, Pacicinian- like, Golgi tendon organs). These low-thresholdreceptors respond to non-noxious mechanical stimuli or movements and areconsidered to play a role in perceptual and reflex responses related to articularmovements. While most work has been directed at limb joints, some is available on37the TMJ. There is reasonable evidence that articular receptors do play a role in thedetection of joint movements, but controversy exists about the extent of theircontribution to joint position sense (Burke et al. 1988, Clark et al. 1989, Dubner et al.1978).Recently the view has been substantiated that group Ill and IV primaryafferents, and perhaps Group II, are also involved in responses to noxious stimulationof articular tissues. These afferents terminate in the peripheral tissues as free nerveendings, and they can be activated by mechanical or chemical means, or even non-noxious low threshold distortions of the articular tissues. These studies have alsodocumented the progressive increase in activity as the intensity of the stimulusincreases (Mense 1986, Schaible and Schmidt 1988).Enhancement of articular afferent activity has also been demonstratedin experimentally induced arthritis, and this activity has been shown to becounteracted by analgesics. These responses to peripheral mechanisms maycontribute to our ability to code the intensity of articular pain, the hyperalgesia andallodynia that can occur in a traumatized or inflammed joint, and to the spontaneouspain and to symptoms and signs related to movement that are commonly observedclinically (Guibaud 1988). There has been some evidence that sensitization ofafferents supplying limb and trunk muscles may occur, when the activation thresholdis lowered by chemicals such as bradykinin or prostaglandins (Mense 1986).38Sympathetic afferents supplying articular tissues, may also be playinga modulatory role. This has been suggested in inflammatory conditions and in painassociated with arlicular tissues (Basbaum and Levine 1991).INNERVATION OF THE TEMPOROMANDIBULAR JOINTThe temporom andibu lar joint differs from most other joints in the body,in that its condyle not only rotates but also translates. It is technically considered aginglymoarthrodial joint (Bell 1990). It is a compound synovial joint formed by themandibular condyle fitting into the squamous portion of the temporal bone. A pliablewater-filled intra-articular disc composed of dense fibrous connective tissue separatesthe two bony surfaces and divides the joint into two synovial compartments. The discemerges at its periphery with a capsular sheath that surrounds the joint, that gets itssupport from peripheral ligamentous attachments particularly at its medial and lateralborders. Three of the masticatory muscles have projections on to the disc. The parsprofunda of the masseter muscle, the superior head of the lateral pterygoid and thetemporalis muscle. The articular disc starts in fetal developm ent, as a structure withvascular elements but its central portion becomes compressed and loses itsvascularization as development progresses embryological ly.39-Peripheral Innervation-The mandible in the adult is a single bone that crosses the midline of thebody, having arisen laterally and fused in the midline, and has at both its ends thesetwo articulating surfaces. Thus, afferent inputs from the TMJ’s to the central nervoussystem probably are associated with integrative processes that differ from other joints.Sensory and motor branches of the Fifth Cranial nerve supply the muscles that movethis joint as well the joint itself. The innervation was first detailed by Thilander in 1961.The central portion of the disc was found to be avascular and not innervated. Thisportion is believed to receive the load and compressive forces of mastication andmovement as it cushions this joint in function.Studies carried out on human and animal tissues have producedcontradictory results as to the innervation of the disc and capsule. However, most ofthese were carried out by metallic impregnation that can produce inconsistent results(Thilander 1961, Bernick 1962, Wink 1992). Recently, immunohistochemicaltechniques that detect neurospecific structural or neuroactive peptides has allowed formore specific markers of neural elements . Thus, some evidence has surfaced latelythat, not only is there innervation of the capsular and perivascular fibers, but fiberswere indentified in areas of the joint disc previously considered avascular . The TMJdoes contain free nerve endings, but specialized receptors have not been found inabundance. The afferents supplying these receptors are nearly all less than 1Om in40diameter and are carried primarily in the branches of the auriculotemporal nerve. Therichest innervation has been found in the posterolateral aspect of the capsule of thejoint (Morani et al. 1994). Conclusive evidence as to the organization of theinnervation in the articular disc and articulating surfaces has been scant. In autopsyspecimens nerve fibers were reported penetrating the disc from the pericapsulartissues, and structures resembling Pacinian corpuscles and Golgi tendon organs havebeen identified (Wink et al. 1992).Few studies have concentrated on the properties of nociceptor afferentssupplying the TMJ. Group Ill and IV afferents do supply the tissues of the joint, as wellas larger, faster conducting afferents. Recordings have been made, from theseapparently low threshold non-nociceptive afferents in responses to jaw movement andchanges in position. (Klineberg 1971, Kawamura and Abe 1974, Lund and Matthews1981). However, the data has not been conclusive. Nociceptive input clearly can beexpected to exist from the temporomandibular joint as it does from limbs, but itsevidence has proven elusive.In the last few years it has become clear that primary afferent nervefibers responding exclusively to noxious stimuli are found innervating the face andextremities. Dissatisfaction with specificity theory that argued that pain was a primaryor specific sensation with its own specialized receptors and pathways plus its inabilityto explain some of the characteristics of clinical pain, led to central summation41theories that proposed that stimulus intensity and summation were the criticaldeterminants of pain (Sessle and Wu 1991).Some studies have also shown that neuropeptides with aprobable trophic function are released in synovial fluids (Larsson et al. 1989, Mappet at. 1990). These neuropeptides can modulate the production of immunoglobulins,stimulate T lymphocytes, and induce production of PGE-2 and collagenases insynovial cells. Many of the neuropeptides are believed to be involved invasoregulatory and inflammatory mechanisms. Thus, it is conceivable that somenerves observed in the TMJ capsule may be responsible for the release of some ofthese peptides. The identification of prostaglandins and leukotrienes in the synovialfluid of painful and dysfunctional TMJ’s has been presented by Quinn and Bazan(1990).The output of the transmission neurons is also known to be influencedby descending control mechanisms from the brain that relate to cognitive, motivational,and affective processes.-Central Afferent ProjectionsThe central projection sites within the trigeminal brainstem sensorynuclear complex from deep craniofacial tissues have not been fully explained.42Those of large diameter jaw muscle afferents whose cell bodies are located in thetrigeminal mesencephalic nucleus have been well documented (Dubner et al. 1978,Capra 1987). Bulk labelling of these afferents has resulted in labelling of the rostralcomponents of the trigeminal brainstem as well as in its subnucleus caudalis. Theprojection of small diameter afferents from the TMJ has not been examined.Nonetheless, we could speculate that deeper structures, like an articulating joint, mayalso project to each subdivision of the trigeminal brainstem complex.-Central Neuronal MechanismsNeurones in the dorsal horn of the spinal cord are responsive to non-noxious mechanical stimulation of limb joints, but can also be activated by noxiousarticular stimuli, from bilateral joints. It is also becoming clear that both nociceptivespecific (NS) and wide dynamic range neurons (WDR) in the spinal dorsal hornreceive nociceptive inputs from articular tissues and that, like spinal dorsal hornneurones activated by noxious stimulation of muscle, they receive convergent inputsfrom afferents supplying superficial tissues (Menetrey et al. 1980, Schaible et al.1 987a). The convergence of superficial and deep inputs on the same neurone isconsidered an integral mechanism underlying the hyperalgesia, poor localization, andreferral that characterize many conditions manifesting pain from joints and other deepstructures.43With respect to TMJ afferents inputs, it has been documented in the ratand cat subnucleus caudalis (Sessle 1987), that a substantial population of caudalisneurones receive TMJ nociceptive inputs. Upon a variety of stimuli, TMJ afferents arepreferrentially excited by cutaneous nociceptive (WDR and NS) neurones. Theseneurones are predominantly located in laminae I-Il and V-Vl of the subnucleuscaudalis. In view of findings by Sessle and others that cutaneous or intraoralnociceptive neurones also exist in more rostral components of the trigeminal braistemcomplex, some of which receive jaw muscle afferent inputs, it is likely that rostralneurones also contribute to brainstem mechanisms underlying deep craniofacial pain.It suggests that the caudalis neurones responsive to the TMJ andcraniofacial muscles afferent inputs, represent critical neural elements underlying thetransmission of acute orofacial pain, and that these deep nociceptive inputs showconsiderable convergence in transmitting deep nociceptive information. Theconvergence of mechanosensitive fields is consistent with the view of pain referralmechanisms. These probably contribute to the apparent spread of pain to adjacenttissues from the site of injury or inflammation which is often reported incraniomandibular injuries (Sessle and Wu 1991).44-Thalam ocortical Projections-The role of the thalamus and cerebral cortex in nociceptive mechanismspertaining to pain perception is poorly understood. Only limited information is knownabout the thalamocortical processing of deep nociceptive information. Some activitycan be evoked in the cat ventromedial and basal thalam us from the stimulation offorelimb and hindlimb afferents. Noxious mechanical or algesic stimulation of joints ormuscles, as well as cutaneous noxious stimuli, activates single neurones in theventrobasal thalamus and its immediately sorrounding regions and in the SIsomatosensory cortex (Guibaud 1991).A major input to the posterior thalamus originates from the dorsalcolumn-medial lemniscal system and the rostral components of the trigemirialbrainstem complex that transmit primarily non-nociceptive information from the spinaland orofacial regions. Another important input is the spinothalamic tract, whichoriginates in the spinal dorasal horn: its trigeminal analogue is the thalamic projectionfrom subnucleus caudalis. Axons originating in caudalis represent a major portion ofthe input of the trigeminal to the posterior thalamus. (For further review of theneurobiology of facial and dental pain Sessle 1987 should be cosulted).45SUMMARYPain by its nature is a subjective symptom. Its conscious perception isgenerally evoked by noxious stimuli and described as a multidimensional processinvolving both a subjective evaluation of the sensory aspects of the stimulus (intensity,duration, location) as well as the emotional or affective component to that stimulus.In the temporomandibular joint and its associated structures, pain is notalways due to joint pathology or traumatic injury. Since the TMJ capsule has beenshown to be supplied with free nerve endings, it is not surprising that pain mayemanate from this joint. The most common symptoms of TMJ pathology are limitationof movement and tenderness on palpation. Pain in the joint has been known to bereferred to other areas of the head and neck.The detailed mechanisms underlying acute and especially chronic painhave yet to be clarified. This is partly a reflection of the multidimensional nature ofpain, since we now do understand it as a multifactorial experience encompasssingsensory-discriminative, affective, cognitive and motivational dimensions. Themechanisms involved in our understanding of pain are receptor specificity, centralconvergence and summation, inhibition, and descending control.46BIOMECHANICS OF THE TEMPOROMANDIBULAR JOINT ARTICULATIONARTICULAR LOADINGFor over a century, researchers analyzing the mechanics of themammalian mandible, have looked at the forces developed in varying planes, and howthey relate to mandibular function with the thought that the mandible, acts as leverduring mastication with the mandibular condyle acting as a fulcrum (Hylander 1975)For the human temporomandibular joint (TMJ), several investigators havecommented upon the possibility of differential mechanical loading within the joint, withthe stress bearing portion being located along the articular surfaces of the eminenceof the temporal bone and the head of the mandibular condyle (Mofett 1964, Oberg1971). It has become evident that forces reactive to functional demands are in partdirected through the articulation of the jaw and these are unevenly dissipated throughthe tissues (Hylander 1979). The evidence for differential loading appeared originallyfrom studies by Moffet et al. (1964), who demonstrated how the lateral aspect of thejoint remodels differently than the medial aspect with increased function. Thesepatterns have been seen as highly indicative of possible differences in mechanicalloading of the articular components of the temporomandibular joint.47Degenerative studies have also suggested differential loading within thejoint. Oberg et al. (1971) noted that the majority of disc perforations were found on thelateral aspect of the joint. Since arthrotic changes are often related to local mechanicalfactors, these data seem to support the view that the central and lateral aspect of theTMJ experiences more load and stress, and therefore more remodelling change thanthe medial aspect.Knowledge of the distinct microheterogenous regional specialization ofproteoglycans, the distribution of complex collagens and of the fibrillar orientation inthe extracellular matrix of the disc, has elucidated much about the possible reactionsto forces acting on this tissue and has helped in the formulation of a model for itsmechanical function (Mills et al. 1994).There are various reasons for the preponderance of stresses to belocated on the lateral or posterolateral aspect of the TMJ. One is related to thedistortions that the mandible goes through during the power stroke in chewing. Themandibular corpus of primates has been shown by Thilander (1979) to evert at itslower border and invert at the coronoid process, causing the lateral aspect of thecondyle to get pressed against the articular eminence during differential occlusalloading.48These observations have been replicated in modelling studies, wheremeasurements of the rotational deformations with simulated tooth clenching tasks ina computerized simulation were observed, and the rotational distortion was shown tooriginate at the rami, due to the action of the elevator muscles, and manifested in thedental arch and at the condyles (Korioth and Hannam 1994).MohI (1988), advanced another reason for the increased loading of thelateral aspect of the TMJ. He suggested that the lateral pole of the condyle, due to itsangulation and position with relation to the transverse axis of rotation, traversesdifferently at its medial and lateral poles during the power stroke in mastication.Another, perhaps more important explanation for differential loading, is related to themediolateral translation of the condyle relative to its position in the fossa duringunilateral mastication. In these instances the ipsilateral condyle exhibits a lateral shift,commonly referred to as Bennett’s shift, during the opening phase of mastication. Thisin turn, is followed by a medial shift of the same condyle from this lateral positionduring the closing phase. The medial shift is therefore correlated with the occurenceof the power stroke and with it, the increase in condylar reaction force. While, at theipsilateral condyle its position is shifted to a more lateral one, relative to the eminence.This presumably causes the lateral and central part of the condyle and its disc, to bepressed against the more lateral portion of the fossa, while the contact is reducedbetween the medial portion of the condyle and its eminence.49This would suggest, that in the early phase of the power stroke inmastication, the lateral aspect of the ipsilateral joint may experience more stress thanits medial aspect. Once centric occlusion is reached, the stress bearing surface of thejoint no longer oppose each other in a steep medial-to-lateral gradient of increasingreaction force. Instead, the TMJ reaction force will be more evenly distributed alongthe articulating surfaces.-Condylar Forces-In vivo animal experiments have measured condylar forces during jawfunction. Force transducing devices were attached on bony surfaces in thesuboondylar region (Hylander 1979), or directly on top of the condyles (Brehnan et al.1981 and Boyd et al. 1990). Metallic prostheses have been implanted in the ramusnear the joint (HohI and Tueck 1982), and hydrostatic synovial fluid pressure has beenanalyzed within the superior aspect of the TMJ space (Roth et al. 1984 and Ward etal 1990).The forces recorded by Hylander in primates were correlated withmovement of the mandible, to distinguish between compressive and tensile strains.During mastication, the condyle was found to be loaded compressively. Forces weregenerally greater on the balancing side temporomandibular joint, than on the working50side. Changing bite positions altered the level of force. The condyle was also shownto be loaded during opening jaw movements.The vast majority of studies have suggested the TMJ to be load bearingand higher forces to be transmitted through the balancing side articulation duringunilateral mastication (Brehnan 1981, Thilander 1979, HohI 1982, Roth 1984, Ito 1986,Boyd 1990, Ward 1990, Korioth 1994, Ferrario 1994). Some differences in the resultsare believed to be due to difficulties in detecting the chewing or biting side (especiallyfrom animal experiments), a crucial point in the correct interpretation of the data, sincethe ratio of bicondylar force distribution is dependent on the bite point location (Boyd1990), others to the ratio and resultant of masticatory muscle forces (Ito 1986,Ferrario 1994).Condylar forces have been estimated to be between 250-350 Newtonsduring intercuspal clenching (Koolstra et al. 1988 and Nelson 1986). The greaterforces are being transmitted bilaterally through the TMJ’s during intercuspal and incisalclenches, and through the balancing side articulation during unilateral isometric molarbiting as well as left group function clenching tasks. However, the inclusion of a molarcontact on the balancing side of a clench decreases the total amount of forces actingon the balancing side condylar region (Korioth and Hannam 1994).51The site and number of occlusal contacts, and the direction ofapplication, influence the activity of the masticatory musculature during clenching(Williamson and Lundquist 1983, Shupe et al. 1984, MacDonald and Hannam 1984,Belser and Hannam 1985, Manns et al 1987). The degree of muscle activity has beenshown to be sensitive to differences in occiusal support throughout the arch (Woodand Tobias 1984). The differential removal of contacts on a bite plane, significantlyaltered the general distribution of muscle activity. When one balancing contact wasleft intact, the general activity remained much the same. It was apparent that themandibular condyle of the balancing side may have been dispersing the load that waspreviously transmitted by the balancing tooth contact.The Finite Element Model (FEM) of Korioth and Hannam (1994)predicted this relationship as well and confirmed the importance of a balancing sidemolar contact in “stress-breaking or splinting” the balancing side TMJ during simulatedclenching activities.Further substantiation can be attributed to the clinical findings of Minagiet al. (1990), where the authors attribute the lack of balancing tooth contacts to theprevalence of joint sounds. They hypothesized that the presence of balancing contactswas protective to the the tempo romandibular joint in certain occlusions. This has beencorroborated by condylar movement observations made by Hagiwara et al. (1994).52Condylar forces during maximum clenching in the intercuspal posftion have beenestimated to be around 250-350 Newtons and 250 Newtons for incisal clenching(Koolstra 1988, Nelson 1986). Forces are assymetrical during unilateral clenching withvalues being reported during first molar clenching perpendicular to the occiusal plane,at 25/15% of total muscle force (Faulkner 1987). The reason for this assymetry andthe functional significance of morphological variation in the muscles of mastication hasbeen reviewed by Weijs (1989). Miller (1991) should also be consulted for a reviewof the function and form of masticatory musculature.Evidence presented above increasingly supports the assumption, sincedirect measurements in the human have not been possible, that during normalfunctioning there is symmetrical loading of the dentition and the joints. The magnitudeof these loads changes with varying muscle recruitments for each particular task. Thebite forces and the loads these muscles produce are usually directed at angles thatallow a ustablell resistance by the anatomy. That is, during tooth clenching, condylarforces are developed which are more or less perpendicular to the temporal eminencewhen the jaw finishes the power stroke with teeth together, and roughly parallel to theocclusal plane or slightly more anterior to it, during rest when the condylar head is inthe Iossa.53-Bite Forces-Bite forces in vivo have been shown to vary considerably betweenpopulations. So called IiprimitiveN peoples eat less refined diets and thus rely moreheavily on the use of their dentitions for the trituration of their foods. They have beenshown to have stronger maximal bite force values than so called developed” societies(CarIsson 1974).Maximal bite forces vary in vivo considerably. Typically though, theyrange from 300-450 Newtons in the molar region, and about 1/3 of that strength in theincisor region. Helkimo (1977) showed gender differences in the mean values for biteforce in a Scandinavian population, with women having about 2/3 the strength of men.Values for bite force are seen to decrease with increasing age partially due, it isbelieved, on the age-dependent deterioration of the dentition seen in thosepopulations.In general, bite force does not seem to be closely related to generalmuscle force and skeletal dimensions (Linderholm and Wennstrom 1970). However,bite force is reported to be associated with a long mandibular corpus and a smallgonion angle (Ringquist 1973).54The exertion of a maximal bite force is affected when the mandible is placedin eccentric positions. Bite forces measured with the mandible in extreme lateral,retrusive or protrusive positions reduce the overall level of the bite force (Molin 1972,Leff 1966). Mechanical advantage is an important contributing factor to the forcedeveloped by a muscle. Subjects with a so called “long face’ have a relatively largemandibular plane angle and a shorter ramus and develop lower molar biting forces ascompared to normal subjects (Throckmorton et al.1980 and Proff it et al. 1983).Another factor is tooth anatomy. It could also be that molars by havinga larger occlusal table have a larger supportive area closer to the action of themuscles (Carlsson 1974). The vertical separation between the jaws is also important.Manns et al. (1979) have reported that an intermaxillary distance of 15 to 20mm ofjaw opening, is the optimal masseter muscle length and thus at this opening theoptimal bite force can be generated. Hellsing and Hagberg (1990) reported differencesin maximal bite force with changes in head angulation and hyoid bone to mandiblerelationships. They found that the force increased with an altered head position.Peripheral feedback either from the periodontal ligaments, intradental,or joint and/or muscle receptors affects the control of bite forces. Lund and Lam arre(1973) reported that anaethesia around the teeth reduced the force of maximal jawclosing contractions by 40%. In contrast, Hellsing (1980) showed an increase in themaximal bite force in both anaethetized and non anaesthetized subjects.55He also concluded that elevator muscle vibration did not influence maximum biteforce. Lately, Teenier and Throckmorton (1991) showed there was no change in thevoluntary maximal bite force levels or the levels of integrated EMG levels inanaesthetized subjects.It has also been observed that in patients with reduced periodontalligament support, due to periodontal disease or at its extreme due to loss of teeth andtherefore wearing dental prostheses, that the level of bite force is decreased (Laurell1985, Williams et al. 1985, Lundquist et al. 1986). This is in contrast to patients withimplanted prostheses where the level of bite force has been seen to return to a preedentulous level or even surpass it (Haraldson et al. 1979).Patients with disturbances of the craniomandibular system such as painfrom muscles or joints are reported to have lower maximal bite force values thanhealthy subjects (Helkimo et al. 1975, Molin 1972). In the patient group studied, as thepain subsided the bite forces increased. They also observed no significant differencesbetween the affected and non affected sides.In patients with a history of clenching and grinding habits it was foundby Helkimo and Ingervall (1978) that these patients differed from the norm becausethey achieved lower levels of bite force than the controls.56In a measure of endurance with a 50-Newton bite force in patientssuffering from temporomandibular joint disorders, it was observed by Stegenga et al.(1992) that TMJ pain was the main reason for the cessation of the biting effort, incontrast to control subjects who ceased biting due to muscle fatigue.-Masticatory Forces-Several techniques have been developed over the years to measure thehuman masticatory force. The instruments used for this purpose are referred to asgnathodynamometers. The earliest of these date back to the late 19th century (SeeKlaffenbach 1936). The level of biting force needed to crush different types of nutswas measured by these biting instruments. These were made of spring steel arms,which were held between the teeth by the subjects with varying degrees of comfort.Rugh and Solberg (1972) in their review, looked at the historical use ofbite blocks to measure forces and credit G.V. Black in 1895 for recognizing that biteforces, were dependent on the degree of separation between the jaws, and for notingthat the force was not being exerted equally across the occlusal surface of the teeth.Major advances were made by the late 1940’s, as variable inductanceand wire strain gauges became available. Howell and Manly in 1948 developed avariable inductance type of gauge, with interchangeable bite plates, in order to attempt57to deal with the interocclusal separation at the time of measurement, which wasshown to affect the level of attainable force, at varying degrees of jaw separation.Biting forces were applied to a spring steel plate that moved a silver foil near aninductance coil, as the inductance changed a meter type circuit changed the variationin inductance to a DC current, which then indicated the level of biting force.Later, small strain gauges were mounted within a single tooth. Anderson(1956), Scott and Ash (1970). Strain gauges have been placed under artificial teeth,Brudevold (1951), Yurkstas and Curby (1953), Atkinson and Sheperd (1967) andothers.Strain gauges have been placed inside acrylic bite blocks in order to measure forcedistribution and the effect of varying the position of the bite point on muscle forces(Kikuchi et al. 1994).Most commonly the indirect measurement of bite force has beenperformed using bite forks (Haraldson et al.1979, Helkimo and Ingervall 1978, Rughand Solberg 1972) to mention a few. The masticatory force is highest when the foodis initially crushed between the teeth and the values are highest for hard foods suchas nuts and carrots (Carlsson 1974). Levels of force can reach as high as 400Newtons during normal mastication (Hagberg 1987).58ARTICULAR STABILITYThere is little literature regarding the stability of this joint and itssupporting structures and constraints. It therefore remains unclear to what extent theconfiguration of the articular fossa and the condylar head and disc, under loaded andnon-loaded conditions, contributes to mobility and/or stability of the articulation. It maybe hypothesized that the less the joint elements are congruent, the less stable thesystem would be (Osborn 1985).Mandibular movements are controlled by muscles, their innervation, andby biomechanical constraints such as the hard and soft tissue anatomy of the joint andthe dentition. Osborn (1985) suggests that during jaw movement, and especiallyduring mastication, the function of the disc is to not only spread the forces exerted onthe articulation, but also to limit the movement of the condylar head into the retrodiscaltissues and the temporal bone. Thereby, allowing the articulating surfaces as well asthe disc, sufficient freedom to rotate and slide in the fossa and down the eminence.He believes that in reality the disc destabilizes the condyle by keeping the incongruentbony surface slippery by its low coefficient of friction, and it is the annulus, to whichboth theanterior and posterior thickened bands contribute, which maintains stability and whichcan do so without muscle action.59Williams and Warwick (1980) in their review of joint function state thatjoints are maximally stressed at the limits of their movement and it is in this positionthat the surfaces become congruent and ‘closely packed’, and in this way able toresist further movement.Osborn sees the temporomandibular joint as an exception. It is notbraced and closely packed when maximally loaded but it is held “balanced” by itssupporting ligaments and musculature as the stresses are placed on it in order toachieve stability (Osborn 1989).Hesse and Hansson (1988) have suggested that close-packing onlyoccurs in joints when the supporting ligaments have been stretched to their limit andare taut. This is not the case when teeth intercuspate and transmit loading forcesduring mastication or hyperfunction in humans.The mechanics of the other soft tissues found intra-articularly would leadus to question the idea of the articulation as ever close-packed. Scapino (1991) hasexpressed, that upon articular loading we find retrodiscal compression and venouscollapse, and during opening, reduced retrodiscal pressures cause the expansion ofloose connective tissue fibers and venous spaces, with blood being drawn into thearticular region. This venous cushion would impart a viscoelastic damping to the60loading stresses placed on the articulation and provide for some give as loads wereplaced on it thus destabilizing any close packing tendencies.Others have viewed stability, and the role the disc plays in it, as theability of the condylar head and soft tissues to remain statically positioned in the fossaas compressive forces pass through the articulation. Okeson (1993) has lately viewedthe purpose of the disc, as an interpositional medium of dense fibrous connectivetissue that protects, and stabilizes the condyle in the fossa.At first these apparently different views seem to contradict each other,but actually with further understanding the views expressed above are not thatdissimilar. There is common support in the literature for the role elevator muscles andthe supporting ligaments play, and these are widely understood to play a major roleas the stabilizers of the temporomandibular joint articulation. Optimum joint positionbeing achieved only when the articular discs are properly interposed between thecondyles and the articular fossae. An unstable joint then would include one, in whichthe disc and intra-articular tissues fail to provide the articulating surfaces with thenecessary support required, for loaded condylar motion.The role of the musculature in generating compressive forces on thearticulation has been discussed above, It is not difficult then, to presume that thesemuscle forces generated by the elevator musculature contribute to the apposition of61the condylar head, in the fossa, with interpositional fibrous damping being providedby the disc and the retrodiscal connective tissues.During jaw opening the role of the musculature is less clear. We havediscussed above that some view the role of the ligaments as restraining elementsduring jaw opening. Osborn (1989) has expressed that the temporomandibularligament restrains the condyle against the eminence during opening and mastication,and that the sphenomandibular ligament, even though may exhibit some slack withthe teeth in contact, restrains the size of the gape during maximum opening.The musculature of the jaw is expected to have passive muscle tensionas the muscles are lengthened during opening, with each muscle exerting increasesin tension depending on their attachemnt position relative to the jaw movement. Somemuscles can be expected to be lenghthened more than others, and also have differenttrajectories of movement during different functions (Goto et al. 1994). The varyingtensions generated by these muscles have not been directly measurable.Lately, computer assisted models have been used to study the dynamicchanges in jaw muscle tension and the effect of jaw movements on articularcompression. The forces generated are directed approximately perpendicular to therear slope of the articular eminence, and seem to peak at maximum jaw opening, witha total compressive thrust of 40-50 Newtons. This seems to indicate that in a normal62joint during voluntary jaw movements, the system has a capability to produce sufficientmuscle tension to mainatain appositional articular loading during jaw opening and mayplay a significant role, in stabilizing the temporomandibular joint. (Langenbach andHannam, in press)SUMMARYIn order to understand the craniomandibular system, increasing effortshave been made to understand muscle contraction, jaw motion, masticatory and jointforces, as part of the theoretical framework used to diagnose and manage disordersof the craniomandibular system.Biomechanical models have combined the anatomy of the system, withtheir primary function of developing tension, to discover the direction of forcesdeveloped by the muscles of mastication, relating these to loading patterns andchanges observed to occur in the system under function.FEM models have confirmed the prediction that the mandibular condylesare load bearing, with greater force magnitudes being transmitted bilaterally duringintercuspal and incisal clenching, as well as through the balancing side articulationduring unilateral clenching. In symmetrical biting, contact positions that lie anterior to63the canine region cause compressive condylar reaction forces, while more posteriormolar biting locations create higher tooth forces.During asymmetrical unilateral occlusal tasks, higher condylar reactionforces on the non-working or balancing side will occur. On the working side, thecondylar reaction forces will tend to decrease and may even cause the workingcondyle to distract or decompress for posterior tooth contacts.Bite force measurement has provided a variable that can be related tofactors such as the state of the occlusion, the type of dental treatment undertaken,condition and function of the articulation and its related musculature. The intraoralmeasurement of these forces has proven most reliable with the use of strain gaugesattached to a bite fork.Individuals of varying anatomy and morphology can produce similarbiting forces. Joint stability increases for more distant bite locations, and thedifferential activity of working and balancing jaw muscles helps to ensure themoderation of intra-articular forces while accounting for higher bite forces.In applying biomechanical principles to loading forces on the bony jawelements, studies have tried to show a correlation between muscle forces and thecounteracting role played by the teeth, the state of the occlusion, the role of the disc64and connective tissue components, that play a part in the proper fuctioning of thisarticulation and perhaps try to point to why and how the system does reach itsphysiological limit, and break down.STATEMENT OF THE PROBLEMThe etiology of human temporomandibular joint disorders is due to anumber of factors. Of these the role of adverse articular mechanics in the progressionof change in the joint has been implied but not proven. It has been observed thatloading beyond the physiological limits of the soft and hard tissues of the joint maylead to acute inflammation in the short term and remodelling, in the long term. It ispossible that loading which exceeds the physiological limits of the structures, underclenching, grinding, abusive habits or primary trauma leads to disordered conditionsthat often present themselves initially as smatognath ic pain. Evidence exists for asignificant innervation in pericapsular connective tissues. It has been shown that thetrigeminal subnucleus receives nociceptive information from components in the TMJ,and one could infer that afferent input from pain fibers may also be important withrespect to referred pain from the joint. Afferent input in humans is cognitivelyperceived, and can be expressed verbally as pain.65Although, it has proven difficult to measure directly loads within thehuman temporomandibular joint, model simulations support the suggestion that higherloads occur in the area of the joint during clenching tasks and that the contralateralor balancing side of a clench measures even higher loading patterns. In patients withmissing posterior tooth support, the load in the joints is higher than with contactspresent. Pain may ensue that can often be moderated by providing prostheticappliances which reestablish these posterior contacts.Interocclusal orthopaedic appliances or splints have been used routinelyfor the treatment of temporomandibular joint disorders because of their ease of use,and when properly managed, because of their efficacy. The value of such orthopaedicinterocclusal appliances have been evaluated in a number of studies in the past, andthus various theories have been proposed with regard to the method of action ofdifferent appliances, but at present no conclusive testing of these theories has beenpresented.In the present thesis, it is hypothesized that in acute articular pathology,the use of an orthopaedic appliance designed to reduce the load to the painful jointcan positively influence the resolution of arthrogenous pain in the short term.Specifically, it is proposed that this could be achieved with an appliance designed withunilateral occlusal support.66METHODS AND MATERIALSIn order to test the hypothesis two separate studies were carried out,one on a computer to verify the biomechanical effect of the test device, and the othera clinical study to test the hypothesis on patients suffering from an articular disorder.BIOMECHANICAL MODELThe first study made use of an existing computer model of the mandible.The model was based on a technique known as finite element modelling (FEM). Afreshly dissected human mandible was imaged with the aid of computerizedtomography (CT) scans at 2mm intervals. The outer and inner cortical outlines wereretraced, digitized and assembled into a three dimensional finite element mesh withavailable software (1-DEAS 6, SDRC, Milford, OH). The simulations were carried outon a unix based Hewlett Packard 9000 series, 380 mini-corn puter work station. Thismodel was developed by Korioth (1993) and the full description of the process canbe found elsewhere. (Some details of this model are described below for clarification).Finite element modeling is an advanced numerical technique developedfor engineering structural analysis. It subdivides the complex geometry of acomplicated structure like the human jaw into a mesh of smaller elements. Theseelements are then interconnected at specified points (nodes) on the element67boundaries with defined degrees of freedom. The use of mathematicalfunctions allowsfor the generation of a series of equilibrium equations (one per nodal degree offreedom) that, when summed across the entire geometry and solved simultaneously,define the structure in question.The reconstructed mandible was divided into multiple interconnectedelements. The structure of the temporomandibular joints was modelled as a twolayered cap” in which the first layer consisted of the combined thicknesses of thearticular fibrocartilages, and the second consisted of the temporal cortical bone. Thispermitted analysis of the stress distribution on the condyles and allowed for sometheoretical buffering effect of the articular disc against the temporal bone.In collaboration with Korioth, the FE model was used to simulate twoclenching tasks on an acrylic appliance that was modelled with similar characteristicsto an orthopaedic maxillary occlusal splint. This appliance was assigned the materialproperties of heat cured acrylic and it optionally opposed all mandibular cusps. Themodel was loaded with multiple force vectors and rigidly restrained from movementat the maxillary teeth and the endosteal surface of the temporal bone. Groups ofparallel vectors simulated nine pairs of masticatory muscles (superficial and deepmasseter; anterior, middle and posterior temporalis; medial pterygoid; superior andinferior lateral pterygoid; and anterior digastric), assumed to be directly attached to thebony surface. Their directions were derived algebraically as unit vectors from single68vectors of muscular attachment available in the literature. The magnitude of the totalmuscle force exerted by each muscle during isometric contraction was given by theproduct of a Weighting Factor (representing maximum possible tension) and a ScalingFactor (representing muscle activation levels. The orthogonal vector force componentswere subsequently proportioned between the nodes comprising a specific area ofmuscle attachment. (see Korioth and Hannam 1994).The two occlusal tasks modelled clenching in the intercuspal position(ICP) with clenching with and without contralateral tooth contact against the acrylicappliance. The contact of the cusps tips opposing the acrylic splint were either evenlydistributed across the arch (Bilateral Contacts), or removed on one side from theincisor region to the last distal contact. (Unilateral Contacts). The ensuing compressivestresses (negative sign), also termed Minimum Principal Stresses, were then analyzedfor each task and for each joint and expressed in MegaPascals.(See page following for colour photocopy of Model)69FE model of a human jaw with overlaying intraoral orthopaedic acrylic splint. Modelwas made in collaboration with Korioth (Korioth, 1994).70CLINICAL STUDYTwo methods of assessment were used in the clinical part of the study,and are reviewed here.THE MEASUREMENT OF ORAL BITE FORCESBite force measurements were made in order to standardize the level ofmasticatory force exerted and to replicate the mechanical stimuli directed to thetemporomandibular joints for each subject at each assessment session.Instruments that measure human forces are known asGnathodynamometers. The earliest efforts at estimating the force required to crushcertain food stuffs dates back to the 19th century. Black (1895) and other earlypioneers in the years that followed, developed gnathodynamometers using spring steelarms which the subjects bit upon. As many others have since, he encountered avariety of problems. (See review by Rugh and Solberg 1972). The thickness of themetal, its ease of use, the recognition that biting forces depended on the separationbetween the teeth, the calibration and the method used to record the level of biteforce contributed to a variety of designs.71For the purposes of this study a thin bite plate of sufficient strength andplastic properties to withstand high clenching forces was required. The instrumentdescribed below is modelled after a design by Rugh and Solberg (1972) whichconsisted of a cantilever bridge and strain gauge arrangement with a bite platethickness of 1.5mm before the placement of balsa wood bite pads which were addedfor stabilization of the cuspal contacts. Construction was simplified by using a set ofASH articulating forceps, modified to form a dual cantilever bridge arrangement. Smallstrain gauges were mounted on both sides of one of the forceps handles. The twingauges provided for temperature compensation and doubled the gauge factor. Apositioning bar was placed at the edge of the bite pad in order to keep the orientationof the bite force as perpendicular to the ocolusal plane as possible, and in order toreproduce the location of the occlusal force on the dental arch. Several materials weretried to cushion and stabilize the occlusal contact points. Cotton wood sticks were cutto fit the occluding surfaces, and were cemented into place and soaked in waterbefore use in order to soften the wood. The force transducer was attached to anAmmeter in order to measure the bite force in Newtons. It was calibrated with anInstron Tensile Tester, and found to be linear. (Calibration chart in Appendix 1).72EXPERIMENTAL MEASUREMENT OF PAINThe level of symptoms elicited by the clenching effort at eachassessment session, for each subject, was recorded in order to obtain an objectivemeasure of the level of pain that the clenching effort exerted on thetemporomandibular joints.In many studies, only the presence or absence of pain has beenreported (Clark 1984). When pain has been assessed, the use of rating scales orvisual reports are most frequently used. The most commonly used measure in studiesof experimental and clinical pain in humans has been the subjective verbal report.Thehuman subject is unique, in that he or she can provide introspective verbal reports ofpain. Both verbal and non-verbal scales have been developed to evaluate differentaspects of pain perception. The evolution of these approaches traces back to themore traditional ordinal scales, which asked patients to rate their pain as mild,moderate or severe, to the present approach of using numerical scales thatincorporate the principles of cross modality matching (Stevens 1975). In suchexperiments, subjects are asked to match the level of a modality, such as line length,elapsed time, handgrip force, or in this case occlusal force, with various levels ofstimuli from another modality (sound, light, weight, etc. ). This provides for a bias-freeratio of data that allows for parametric analyses of the responses to the stimuli.73A seminal verbal test that became a standard for the multi-dimensionalmesurement of pain was the McGill pain Questionnaire. This classification schemewas described by Melzack (1975) and others since, to distinguish among different painsyndromes and to be sensitive to some therapeutic manipulations. Other verbalscales, such as the Verbal Descriptor Checklist, allows for a quantitative measurementof the sensory and affective dimensions of pain by using words that share acommonality across different pain syndromes. Numerical values, previously assignedto the descriptors by a comparable population using cross modality matchingtechniques, result in a scale with ratio characteristics. Thus, allowing a parametric,multidimensional assessment of the subjects painful experience. (Gracely, McGrathand Dubner 1978), (Heft, Gracely and Dubner 1984), (Duncan, Bushnell and Lavigne1989).One of the most widely used non-verbal measurement techniques is thevisual analogue scale (VAS). This measure is a form of cross modality matching. Itconsists of a horizontal line, of predetermined length, with each end representing anextreme state for the criterion under consideration, defined by appropriate opposingwords or phrases. The subject is asked to mark his or her status somewhere betweenthese two extremes, by placing a mark on a 10-cm line. It has been found preferablenot to mark intermediate reference points on such a scale as this influences theresponses and their uniform distribution and cluster around the reference points arelost. This technique is valid and reliable as a measuring tool for both clinical and74experimental pain (Price 1983). A review of the assessment of pain in thetemporomandibular joint can be found in Stegenga et al. (1993). The VAS format usedin this study is shown on Appendix 2.METHODOLOGY OF CLINICAL STUDYThe clinical study involved the recruitment of two groups of subjects whowere either symptom less (Normals) or diagnosed with primarily a unilateral jointdisorder. All were females between the ages of 25 and 45. This selection was due tothe predominance of TMJ disorders in women. They were recruited either byresponding to a posting requesting volunteers for this research study (Normals) or bypresenting with temporomandibular joint symptoms at one of two clinics; A Universitybased clinic that specilalizes in treating patients with craniomandibular symptoms, andthe private dental clinic of the author. (This constituted the Treatment Group).The clinical examination and history taking procedure was common toall subjects. It consisted of the history questionnaire and examinations forms asdiscussed by Widmer from La Resche (1992), following the guidelines set by Dworkinet al. (1992), for a set of standardized research diagnostic criteria fortemporomandibular disorders or RDC/TMD. The relevant criteria are summarized inAppendix 3.75These criteria are intended primarily for research purposes, allowing standardizedmethods for gathering relevant data and making possible comparison of findingsamong different investigators. The diagnostic system is nonhierarchical and allows forthe possibility of multiple diagnoses for a given subject. For the purposes of this studythe most important clinical condition for inclusion in the treatment group was thepresence of primarily unilateral arthralgia (an Axis I Group Ill diagnosis). Any sign ofdisc displacement or Group II diagnosis did not rule the subject ineligible, if in additionto the displacement and or disc incongruency, arthralgia was present in one joint. Thehistory of the symptoms at the time of examination varied from three days to threeweeks and had to be of acute origin, that is, of sudden onset and persistent. As willbe discussed later, subjects suffering from Axis I, group I, (muscle disorders) primarilywere excluded from the study, as were patients suffering from bilateralcranioman dibular symptomatology.Normal subjects, (comprised of 6 subjects) who were the “normalcontrols”, showed an absence of symptoms upon history taking and examination.These subjects were asked to clench maximally on the gnathodynamometer’s bitepads and to maintain this clench for 2 to 3 seconds. Immediately upon performing thetask, the measurement of the bite force was recorded for both sides of the arch, aswas the measure of any sensation elicited, (or its absence) for each joint. The articularsensation was measured with the aid of the visual analogue scale, which required the76subjects to assess their sensation by marking a position on a straight line withpredetermined end-points at 10mm of length.Patients affected with disorders (12 subjects) were randomly assignedinto Groups I and Il (Treatment Groups) in order to test the efficacy of two treatmentappliances. They followed the the same protocol as above with regards to clenchingon the force transducer and notating their discomfort on a VAS scale. The treatmentapproach varied by the type of occlusal appliance used. As these were symptomaticpatients, with a history of an acute onset unilateral arthralgia, Group I subjectsreceived a conventional maxillary oral orthopaedic appliance commonly used in thetreatment of temporomandibular joint disorders. This appliance was a flat-plane,occiusally balanced appliance (Intra-oral Splint) which was worn 24 hours a dayexcept at meals. At 3 sessions following the initial placement of the appliance(approximately one week apart) these patients were asked to return for follow upassessment, at which time the pain and force measurement protocol was repeatedand the splints adjusted as necessary.Group II subjects, (comprised of 6 subjects) underwent an identicalprotocol to the other treatment group. They were provided with a modified orthopaedicappliance after ascertaining which side (temporomandibular joint) was the onepresenting with painful symptoms. A unilateral occiusal support on this appliance wasmaintained or augmented on the side of the arthralgia and removed from the77contralateral side. This was done with the use of cold-cure acrylic and acrylic burs asused conventionally when adjusting occlusal appliances. The altered occlusal schemewas expected to reduce the load and possible compression that the painful joint washypothesized to be under during the treatment period. This altered occlusal balancewas maintained during the 3-4 week treatment period. At 3 sessions following theinitial placement of the appliance, these patients were also re-assessed for theirsymptoms. The level of arthralgia was measured after each clenching effort on thegnathodynamometer (force transducer), as was the level of bite force for eachclenching effort. At the completion of the treatment period the appliances werepermanently modified to the more conventional, balanced bilateral contact design,providing equal support to both joints. This is necessary to prevent any unwarrantedtooth movement. In this group if the pain worsened during treatment, the subject’streatment protocol was modified immediately to the conventionally designed applianceand the subject’s treatment reassessed.All subjects in Group I and II were treated for the time necessary for theresolution of all symptoms, or until such time that they decided to discontinue anyfurther treatments. Their treatments and pain control were handled in the most ethicaland professional manner possible. All subjects were asked to abstain from analgesicsand anti-inflammatory medications and alternative treatments during the study period.If this was not possible, they were removed from the study and treated for theirsymptoms in the conventional manner. If it was deemed necessary to place any78subject on additional treatment, this was undertaken following the study period.Patients were asked to keep a record of appliance use during the treatment period.Figures presented in the results illustrate the level of pain immediatelyafter performing the clenching task on the force transducer plotted against the pretreatment session and the 3 post-treatment sessions.RESULTSMODEL PREDICTIONSThe compressive stresses at the site of the condylar heads during thesimulated intercuspal clench, as analyzed by the IDEAS software for this study, arepresented in the Table below.BILATERAL CONTACTS UNILATERAL CONTACTSRight Condyle Left Condyle Right Condyle Left CondyleTotal -151 -140 -230 -115Max. -8.1 -7.1 -12.2 -6.5Avg. -3.7 -3.4 -5.6 -2.8Measurements are in MPa (1 Mpa = lxlOE÷06 Nm2). Negative sign indicatescompressive stress. Data in Table reports the compressive stresses as measured bythe FE model for the two clenching tasks.79The data clearly supported the view that the location of occlusal contactsaffects the magnitude of compressive stress on the supporting condyle. There was adramatic (two-fold) increase in the compressive stresses experienced by the condylarhead on the side contralateral to the contacting side. In other words, when the rightocclusal contacts were removed from contacting the acrylic splint, the condyleexperienced a marked increase in compressive stress. It was also noted that theworking side (Left) condyle experienced LESS compression when the occlusal patternwas modified from bilateral to unilateral support. It is presumed that the addition ofthe acrylic material interposed between the two arches absorbed some of the stressesat the tooth contact locations. This also decreased the condylar load levels whencompared with clenching activities without the interposed acrylic as presented byKorioth and Hannam (1994).CLINICAL STUDYThe level of pain at the start of the examination of the normal group, asmeasured by the VAS scale, was zero.The “normal” control group (6 subjects) did not present with any notationon the VAS scale above the level of 1 for right and left sided tasks. These valueswere typical of asymptomatic subjects. Repeated attempts at eliciting pain intensitylevels above 1 for either joints were unsuccesful, related to the clenching tasks80(the mechanical stimulus) on the force transducer. The absence of symptoms helpedto confirm grouping these subjects in the asymptomatic control group.The levels of bite force varied between 100 Newtons and 200 Newtons,well within the normal ranges for these individuals as reported by other workers.Repeated tries at the clenching task (during the same sitting), were of similar levelsfor left and right sided clenching on the gnathodynamometer.All the patients receiving treatment, either with the conventional balancedappliance or the unilaterally contacting appliance, benefited to some extent fromwearing the orthopaedic device over the 3 to 4 week treatment period. The differencein pain levels (as notated on the VAS), infers that those provided with the unilaterallycontacting appliance showed the most profound change in their symptoms over thistreatment period.The data are presented as scatter plots in Figures 1 through 5, whichrepresented the pain intensity reported on the VAS scale as plotted against the PREOPERATIVE and 3 POST-OPERATIVE sessions. They highlight the variance in thesymptomatology of both treatment groups from the PRE-OP SESSION, that is thelevel of perceived pain in and around the temporomandibular joint before the deliveryof any appliance, through the 3 POST-OP SESSIONS at which each re-assessmentof symptoms was performed.81Figure 1 depicts the level of pain in both treatment groups in responseto the first question on the VAS scale, viz. “Rate the intensity of the usual pain duringthe last week.” Both groups showed an overall decrease in symptoms over thetreatment period. What is most striking here is the change in variance from the pre-opto the 3rd session post-op, in the new appliance group. The range in symptoms at thestart of the treatment was similar for both groups; From 2.5 to 7.8 in Group I and 2.2to 8.6 in Group II. This range, decreased most markedly in Group II, so much so, thatfor all 6 subjects the total range in the VAS at the end of the treatment period was 1.5to 3.0. This was in marked comparison to Group I, where the range stayed the same,though decreased in terms of pain intensity.Figure 2 depicts the change in symptoms perceived at the time ofquestioning. This rating of the pain was in answer to the question: ‘Rate the intensityof the pain at present.’The VAS range was virtually unchanged when the 1st POST-OPassessment was compared with the level at the PRE-OP session in the figures above.But here again, the change in the range of the level of pain for all subjects notablychanged especially for Group II, the group treated with the “new” appliance, by the 3rdPOST-OP visit. The pain level in most cases dropped to less than half that perceivedat the start of the treatment for this Group. This change was not as striking for theconventionally treated group.82Co>>CsCCsCCCs0CO>>‘InCCsCCCs0Figure 1 depicts the level of pain (in VAS) during the past week for both treatmentgroups (a: bilateral and b: unilateral contacts), plotted against the 4 assessmentsessions.KGa) USUAL PAIN DURING THE PAST WEEKBilateral contactsI . 0 -I- ACH WK TB CS TWb)Pre-op 1St post 2nd post 3rd post10864201086420Unilateral contactsAA ML DC MRAWM SJPre-op 1st post 2nd post 3rd post83Co>>a,0CC0Cl)>a,CCC(aa-KGPre-op 1st post 2nd post 3rd posta) PAIN AT PRESENTBilateral contactso I-OH WK TB Cs TW1086420b) Unilateral contactspML DC MR108420I IFigure 2 depicts the pain at the time of examination (in VAS) for both treatmentgroups (a: bilateral and b: unilateral contacts), plotted against the 4 assessmentsessions.AAAWM sJPro-op 1st post 2nd post 3rd post84Figure 3 depicts the level of pain perceived on the painful joint when thesubject clenched on the side ipsilateral to the painful joint. For the group treatedconventionally, the level of pain was not markedly changed when the load and stresson the joint was directed ipsilaterally. However, the effect on the unconventionallytreated group was most noticeable. The change in the level of pain elicited by theclenching effort was similar to that recorded when these subjects were required to ratethe level of pain “at present”, without it being triggered by the clenching task.The most striking change in the level of pain perceived, was found whenthe subjects were required to clench on the side opposite to the painful joint (Figure4). This task was designed to elicit the greatest level of load to the painful joint.Consistent with the hypothesis that a clenching effort on the side contralateral to ajoint causes the greatest load on that joint. The level of pain for the six subjects inGroup II was highest for this task. All subjects were able to elicit pain levels in thepainful joint higher than their ‘resting’ level of pain. The range however was low here,levels measuring from 5.2 to 8.6 at the P RE-OP SESSION and from 0.5 to 3.2 at theend of the treatment period. The change in the elicited level of pain was moredramatic than the one depicted in Figure 2b. This might be expected, since the levelof pain was enhanced by the clenching task.85Co>>‘(0C0CC0Co>(0C0CC(50PAIN IPSILATERAL TO CLENCHBilateral contactsI oCH WK TB CSATW KGPre-op 1st post 2nd post 3rd posta)1086420b)1086420Pre-opFigure 3 depicts the level of painto the painful joint (a: bilateralassessment sessions.Unilateral contactsI 0 AAA ML DC MR WM SJ1st post 2nd post 3rd post(in VAS) elicited by the clench on the ipsilateral sideand b: unilateral contacts), plotted against the 486Co>>.CCC0PAIN IPSILATERALICONTRALATERAL CLENCHBilateral contactspOH WK TB CS TW KCa)108Co60C0.E.C0020 — APro-op 1st post 2nd post 3rd postb) PAIN IPSILATERALICONTRALATERAL CLENCHUnilateral contactsI pAA ML DC MR WM SJ1086’4.20I I IPro-op 1st post 2nd post 3rd postFigure 4 depicts the level of pain (in VAS) elicited by the clench on the contralateralside to the painful joint (a: bilateral and b: unilateral contacts), plotted against the 4assessment sessions.87Finally, it was observed that when the clenching effort was directedipsilateral to the painful joint but the pain level measured at the opposite joint, the levelof pain to that joint also decreased noticeably for some Group II subjects (Figure 5).Suggesting that not all symptom atology was strictly unilateral. In addition, a clenchingeffort on the side of the painful joint apparently produced an excerbation of the normalloading and stress that the joint undergoes in normal function. Subjects in Group I didnot exhibit such a marked change in symptoms for either the ipsilateral clench or thecontralateral clench.The force levels as measured by the gnathodynamometer (forcetransducer) were collated for all patients treated with appliances and as shown onFigure 6. The most salient feature was the general level of increase in the clenchingeffort that occured as the treatment progressed. This was true for both Groups I andII. As with the pain levels, the amount of clenching effort increased most dramaticallywhen the measure was recorded while the subjects clenched on the side opposite thepainful joint.88Co>CCC0.Co>>‘0C0CC00a) PAIN CONTRALATERAL TO IPSILATERAL CLENCHBilateral contactsI ACH WK TB CS TW KC10864.2b)0 .—. Pre-op 1st post 2nd post 3rd postUnilateral contactsI AAA ML DC MR WM SJ10864.0-Preop 1st post 2nd post 3rd postFigure 5 depicts the level of pain at the contralateral joint (in VAS) elicited by theclench on the ipsilateral side to the painful joint (a: bilateral and b: unilateral contacts),plotted against the 4 assessment sessions.89Pre Op 1st PostFigure 6 depicts the level of bite force as measured by the gnathodynamometer forall subjects during the study period. One unit of bite force equals about 20 N.FORCE ON SIDE OPPOSITE TO PAINFUL JOINT(All Subjects)5410 I I I2nd Post 3rd PostTreatment sessions90DISCUSSIONMandibular condylar forces during jaw function have been measured invivo in experimental animals. Transducers have been placed on bony surfaces in thesubcondylar region (Hylander 1979) or directly on top of the condyles (Brehnan et al1981 and Boyd et al. 1990). Metallic prostheses have been implanted in the ramusof the baboon near the TMJ (HohI and Tucek 1982), and hydrostatic synovial fluidpressure has been measured within the superior compartment of the joint (Ward etat. 1990). Computerized models of the mandible (Korioth and Hannam 1994, Ferrarioand Sforza 1994) support the view of the temporomandibular joint as a loaded joint.During unilateral mastication higher loads are transmitted through thebalancing side articulation than through the working side articulation, even though thelatter authors suggest that with a change in the ratio of the muscles this imbalancecan be altered, perhaps unconciously, as a compensation for the altered jointconditions. One must also be cautious when comparing models, due to differencesin the calculation of the condylar reaction forces. Ferrario and Sfoza only accountedfor the EMG potentials recorded over the masseter and temporalis when calculatingreaction forces, in contrast to the EMG data used in the Korioth model, which madeuse of muscle data as presented by MacDonald (1982) for 9 pairs of muscles. Thisdifference alone may have affected their conclusions. Nevertheless, condylar loaddistribution may be altered by cognitive influences.91Miller (1991) has presented data regarding the average muscle activation levelsassociated with various occlusal devices to predict changing loading patterns.The results obtained in the present modelling study confirmed thedependency of condylar load distribution on the type of clenching task. Thesimulations support the notion that higher loads and stresses are observed on thecondyles contralateral to the clenching effort. The patterns of stress distribution arealso task dependent as was found by Korioth and Hannam (1994) for bilaterallysymmetrical tasks, with the force distribution patterns differing between sides. Thiscould be related to the asymmetry of the muscle forces loading the mandible, as therecruitment of the different muscles changes with the level of occlusal support. Onlythe superior aspects of the condylar surfaces were taken into account when analyzingthe data, but the complete model came into play for the calculation of thesecompressive stresses including its inherent bending and rotational deformations.These results attest to the usefulness of the FE technique for modellingforces on 3-D surfaces, and for developing a biomechanical justification for thehypothesis. At present there are no other methods for obtaining such a confirmationin the human temporomandibular joint.The site and number of occlusal contacts affects the levels of muscleactivity. Wood and Tobias (1984) showed that with the removal of six contacts on one92side of the arch of an occlusal splint, muscle activity decreased by 21%, with theauthors suggesting that the balancing condyle absorbed the load previously taken bythe balancing side contacts. One would expect the articular loads to decrease as themuscular activity decreased, due to the lack of contacts on the balancing side. Thisnotion is supported by the model’s predictions of higher loads in the contralateral orbalancing side of a clench, and is not in conflict with a change in this imbalance beingpossible with a changing muscular balance or by changing cognitive influences.The differences in the compressive stresses presented in the modellingstudy for both clenching tasks, attest to the possible biomechanical effect that anappliance designed to alter the location of occlusal contacts and with it, the directionand level of the muscular effort must have when placed intra-orally between themandible and the skull. It is interesting to speculate on the possible effect theappliances designed to alter the biomechanical environment may have on theresolution of temoporomandibular joint disorders. It must be remembered that for thisstudy the muscle forces were equal for both tasks simulated by the model. Thestructure, muscle architecture, and muscle recruitment were kept the same, but thereis as wide variation in the architectural anatomy of patients who seek dental treatment.These anatomical and physiological differences may sum with different patterns ofmuscle use, to create load and stress characteristics that differ markedly for each taskand possibly for each individual.93The recruitment of subjects for the clinical study, proved to be achallenge due to the need to include only subjects who suffered primarily fromunilateral joint arthralgia. Efforts were made at the outset to keep both treatmentGroups similar with respect to histories and diagnoses in order to test the twoorthopaedic appliance designs, but in retrospect Group I, the conventional treatmentgroup, ended up with a slighly different profile from Group II. Both groups did have apreponderance for unilateral joint symptoms, but as was discovered later, the degreeof the myalgias contributing to the overall symptomatology of 2 subjects in Group Icould have affected the comparison. If one looks at Figures 3a and 3b one canobserve that for subjects TW and KC the level of articular pain was nearly nonexistent during the performance of the clenching tasks. By POST-OP SESSION 2, asis evident in Figure 2a, it was found that these two subjects had recovered mostremarkably from their symptoms. It might be postulated that these subjects did nothave a preponderance of arthralgia, but were suffering from both arthrogenous andmyogenous symptoms, which in turn improved drastically with the reduction in activitythat was possibly influenced by the conventional flat plane orthopaedic device.A more optimum design for the random assignment of the patients toboth treatment groups, would in retrospect have included the blinding of the examiner,since bias may have crept in, in the assignment of suitable patients to each treatmentgroup. In addition, the presence of symptoms bilaterally could also have been due totenderness in the lateral pterygoid muscle. At present there is no reliable method that94can be used to differentiate pain emanating from the lateral pterygoid muscle whichlies in close apposition to the joint and intracapsular pain. Anaesthetizing differentiallythe capsule of the joint and the muscle could prove beneficial in the future, in orderto mutually exclude the influence of each structure on the symptomatology.The improvement of symptoms in the conventional treatment group could also beexplained by any of the theories presented in the review of the literature above, forthe use of these appliances, most significantly the cognitive and behavioralmodification aspect of treating these disorders.In a recent study by Linde and Isacsson (1990) an attempt was madeto differentiate by clinically apparent signs, patients with disc displacement versuspatients with myogenic craniomandibular disorders. They pointed out that signs of TMJtenderness appear in 1% to 13% of the general population, while they appear in 36%to 55% in patients with nonspecifled CMD. In their own study, they found that a tenderTMJ was present in 33% of the patients they examined with primarily myogenic CMD.This difficulty in recruiting a pure sample of TMJ sufferers is not new. It may be, asthey suggest, that some myogen ic CMD patients have crepitation and some restrictionin condylar translation and arthralgia because of some sub-clinical joint pathosis.Another possibility, may be our present inability using the CMD/RDC criteria fordiagnosis and evaluation, to separate clearly enough these two sub-groups of CMDpatients.95It is known from the work of Sessle (1987), that caudalis neuronesresponsive to the temporomandibular joint and craniofacial muscle afferent inputs,represent critical neuronal elements underlying the transmission of acute orofacialpain, and that these deep nociceptive inputs show considerable convergence intransmitting nociceptive information. The convergence of mechanosensitive fields isconsistent with the view of pain referral mechanisms. Thus the possibility oflmistakingH arthralgia for myalgia is quite plausible and relevant to this study.Expressing the results presented above in terms of a range instead ofa mean or a specific stastistical test was a decision mitigated on the problemsencountered in the size of the sample. With the present results it is expected that wewill be able to more closely plan for a statististically valid sample in the future, sincethe range of our symptoms will allows us to plan for the optimum sample size. Interms of the variation in symptoms between visits, this may have been due to thesomewhat irregular intervals of time between visits that occured due to schedulingdifficulties, and this could have clouded the data. Given the constraint of possibleiatrogenically caused tooth movement possible with a unilaterally supported oralorthopaedic appliance, a two test period of pre-determined length maybe all that isneeded to show significant changes in pain levels which would in turn facilitate thestatistical analysis and the regular scheduling of assessment sessions.96Flat occiusal appliances such as those conventionally used by mostdental clinicians can produce exactly the opposite effect that is desired. While it is wellestablished that in most cases the use of a flat-plane occlusal appliance decreasesmuscle activity, the design of itself cannot guarantee that a patient will graduallydecrease muscle effort, in some cases, muscle activity during clenching on full-archbilaterally supported appliances can actually increase, compared to clenching onnatural teeth (Miller 1991). It is quite possible and perhaps a common occurrence inGroup I subjects, that the effect of the appliance worn 20 plus hours a day, is toproduce higher levels of muscle activity, with increasing loads to bothtemporomandibular joints than is hypothetically desired. In contrast, the lack ofocclusal contacts on the side contralateral to the painful joint, as in Group II subjects,may reduce muscular activity as suggested by Wood and Tobias (1984). If so, thetheoretical suggestion that the compressive stresses on the painful joint would bereduced (or perhaps even turned into traction of the joint) is understandable. Thisintroduces a new hypothesis for muscle activation, based on the number and locationof occlusal contacts.It is sobering to consider the effects that may occurr when patients inthe alternative treatment group clench and function while wearing the “new appliance”.From the biomechanical perspective, standard appliances can be predicted to havedifferent effects on muscle an articular symptoms. An appliance could have a profoundeffect on pain in one subject, yet a similar design in another with identical symptoms97could have a far less profound effect because it simply does not affect the local tissuemechanics. Customization of the so-called Hnew appliance to reduce the apparentload and compressive stress to the painful joint may be justified, at least provisionally,according to our results, and could contribute to a reduction in inflammation broughtabout by intracapsular changes. This could be achieved by asymmetric ramps on theappliances, or anterior bite blocks of varying thicknesses, or by behavioral modificationbrought about by functionally altering the use of these appliances in combination withthe above. Clearly, efforts to modify muscle use will require more than just alteredocclusal conditions, since these cannot be maintained for extended periods of timedue to the propensity of teeth to move. Nevertheless, the combination of such abiomechanical approach together with altered behavioral activity could prove usefulin a staged treatment protocol, especially over the short term.The intracapsular causes of pain have been reviewed earlier. Bradykininsand excessive particulate debris produce the release of prostagland ins and othermediators. The subintimal tissue of the synovial membrane is highly innervated, andearly inflammatory changes may lead to a loss of lubricating ability of the hyaluronicacid and chondroitin sulfate present inside the joint, causing increased friction (Moses1991). Lavage of the TMJ space has proven succesful in the short term (Quinn 1989).Inflammation and pain probably continues until there isa reduction in joint overloading.It is interesting to speculate on the possible findings that assays on Group Ill patientswould show at the start of treatment and at the conclusion of a specific treatment98period. It is perhaps this combination of the change in the biomechanical milieutogether with a change in the local mediating factors that may lead to more effectivelong term success in treating patients with TMJ arthralgia.Another important factor in the measurement of efficacy of a treatmentapproach is the amount and level of compliance. Patient compliance while takingmedicines can be assessed directly, but the degree of use of an appliance, and themanner of its use, are very important in the assessment of efficacy. In this study,patient compliance was monitored by the manner in which the appliance was handledat each re-assessment visit and also by the thoroughness, frequency and quality ofthe notes found in the patient diaries. Attendance at each assessment session alsoserved as a measure of compliance. However, the difference between groups couldnot be measured with respect to the level of compliance.Erskine et al. (1990) have suggested that when pain is experienced asacute, as in these two subject groups, it is considered relatively novel, and theaccuracy of recall for its intensity is greater than that when pain is either chronic orwhen the patient has episodic experiences of pain. It is evident from Figures la and1 b that the memory of the pain was unaffected, from pain perceived to exist over theprevious week.The studies of Helkimo et al. (1975) and Molin (1972), suggest thatpatients with disturbances of the craniomandibular system, such as joint and muscle99pain, have lower maximal bite force capabilities than healthy subjects. This was againborne out in the present study. What appears most evident is that as pain decreases,the level of the bite force increases. What was not shown was a difference betweenthe sides for the level of the bite force. Molin also failed to show a difference in thelevel of bite force between the affected side and the non-affected side.An incidental finding during this study was the re-appearance of contactson the occiusal appliances in the side from which they were removed. This wasnoticed often during the re-assessment sessions for Group II subjects. a simpleexplanation for this would be the possible change in oral habits that may have occuredduring the study period. In addition, some evidence exists for condylar repositioningalterations that may be occuring with altered appliance designs (Hagiwara 1994), pIusthe possible phenomenon described by Scapino’s (1991), where during articularloading there is compression of the retrodiscal tissues with venous collapse followedby blood being drawn in once the retrodiscal pressures are decreased. This“decompression” of the painful joint was most interesting since it appeared to coincidewith a reduction in symptomatology.The term placebo has been applied to many types of substances usedin a variety of different ways. The most common definition refers to a material thatdoes not contain any active medicine and is pharmacologically inert. This has alsobeen called a TMpure placebo”. An “impure placebo” refers to any substance or device100used as placebo that is not believed to be totally inert. Orthopaedic appliances canresult, as with any treatment, in effects deemed to be placebo-like in nature. Greenand Laskin (1972) have suggested that 40% of patients suffering from TM disordersrespond favorably to placebos. A positive placebo may result simply from a positivedoctor-patient relationship. Reassurance that the appliance provided for the treatmentwill be effective may be the most significant factor influencing the placebo effect. Inthis study attempts were made to remove this effect by providing all treatmentsubjects with an appliance for which the difference in treatment approach was notmade obvious to them, It is conceivable nevertheless, that the clinician providing thetreatment inadvertently treated both treatment groups differently. Although this wasbelieved not to be the case, one way to avoid the problem in the future could be theblinding of the clinician as to the treatment approach or by having several trainedoperators.101CONCLUSIONS1) The FEM model of the human mandible supported the hypothesis that the sidecontralateral to the working side of a static clench exhibits the highercompressive stress at the condylar head.2) Patients diagnosed to be suffering from unilateral temporomandibular jointarthralgia and randomized into two treatment groups received a unilaterallysupported oral orthopaedic appliance and were found to have a smaller rangeof painful symptoms and seemed to show a more dramatic improvement insymptoms than the conventional appliance treatment group, as measured bya VAS.3) Bite force measurements increased in magnitude as the level of the paindecreased for both patient groups.4) Future studies are indicated on a larger sample of patients to confirm theefficacy of short term unilateral appliance use in a clinical environment.102CLOSING COMMENTS AND DIRECTIONS FOR FUTURE RESEARCHThe comparison of benefit to risk considerations for two or moretreatment modalities is not trivial and a decision not easily made. This is partlybecause most factors that affect benefits or risks are either not major considerationsin specific situations or are so similar between alternatives therapies that they do notgreatly impact the benefit to risk concept or decisions based on this concept. It is notoften the case that a single factor is the sole basis for choosing a treatment approachfor a particular patient. It is also true that not all patients need to have the samefactors influencing the decision for the use of a specific approach.The term benefit includes numerous concepts beyond that of a treatmentefficacy. Efficacy relates to how well a treatment achieves its objectives, in acomparative way (eg., treatment A improves symptoms better than treatment B) or ina non comparative way (Treatment A improves patients’ disease measures). Benefitsalso include quality of life considerations at the individual patient level or at thecollective patient level . For a society, benefits should more often be considered interms of the improved public health and improved utilization of resources, money andtime. There are different types of risks in comparing two treatment approaches. Apatient’s failing to improve could be viewed as a type of risk, since the alternativetreatment or no treatment at all might have provided the patient with a greaterlikelihood of improvement.103In the use of appliances there is often relative risks that should be considered. Theterm risk usually refers to the probability that a given experience yields a deleteriousreaction. Under carefully controlled conditions the use of a unilateral appliance neednot involve any risk. Even a patient’s failing to improve on by its treatment could beviewed as a type of risk, since the alternative treatment might have provided thepatient with a greater likelihood of achieving a therapeutic effect. This was not thecase in this study.Present treatment modalities for TMJ arthralgias may not be trulybeneficial in shortening the long term resolution of the disease or disorder, but needto be considered a benefit in the short term reduction of the symptoms associated withthe disorder. The benefit of considering the biomechanical approach to the treatmentof this painful condition may be the enhanced capability of this treatment approachto reduce intracapsular inflammation and ensuing pain. The overall long term effecton the resolution of the symptom atology as compared to a conventional appliancemay not be any greater but the quality of life in the short term may be positivelyaffected.Future considerations are the continuation of this study with perhapsgreater emphasis being paid to the recruitment of patients with reproducibly similarsymptomatologies. The diagnostic criteria available unfortunately still relies on aclinical diagnosis as the gold standard in assessing patients with CMD.104There is an increasing need to develop more objective tests, such as synovial fluidassays, or muscle biopsies, that may enable clinicians to rule out or rule in, thepresence of synovitis mediating factors or muscle disorders in treating TMJ disorders.An additional aspect that needs to be considered is the level of muscleactMty that may be occuring during the use of these appliances. It would prove mostinteresting in the future to be able to monitor the changes in muscle activity during thetreatment period. This would allow more precise correlation of the level of muscsculareffort during function or parafunction with the observed symptoms at re-assessmentsessions.In addition, further studies could involve the monitoring of articularchanges via the use of recording dental and condylar positions. 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The equation shows the relationshipbetween both axes.DLT FORCE TRANSDUCERCalibration - Run 140030020010000 100 200 300Instron Load Cell (N)128Appendix 2 Questionnaire used to measure pain levels during all four sessions.VAS QUESTIONNAIRERate the intensity of the USUAL PAIN during the LAST WEEK by placing a (I)somewhere on the line below.INo pain Most intensepain imaginable.Rate the intensity of the PAIN at present.No pain Most intensepain imaginable.Rate the intensity of the PAIN on the RIGHT JOINT while clenching on the RIGHTSIDE.I INo pain Most intensepain imaginable.Rate the intensity of the PAIN on the LEFT JOINT while clenchingon the RIGHT SIDE.I INo pain Most intensepain imaginable.Rate the intensity of the PAIN on the RIGHT JOINT while clenchingon the LEFT SIDE.I INo pain Most intensepain imaginable.Rate the intensity of the PAIN on the LEFT JOINT while clenchingon the LEFT SIDE.I INo pain Most intensepain imaginable.129Appendix 3 Research diagnostic criteria for TMD disorders (Axis I)I. MUSCLE DIAGNOSESa. Myofascial painb. Myofascial pain with limited openingII. DISC DISPLACEMENTSa. Disc displacement with reductionb. Disc displacement without reduction, with limited openingc. Disc displacement without reduction, without limited openingIII. ARTHRALGIA, ARTHRITIS, ARTHROSISa. Arthralgiab. Osteoarthritis of the TMJc. Osteoarthrosis of the TMJFrom: Dworkin (1992)RDC (Ed) L. LeResche et al.130


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