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The relationship between systematic metabolism and the structure and deposition of human jaw bone

University of British Columbia

The high rate of resorption of the residual ridge in an edentulous jaw may be related to the continuous process of systemic and local bone remodelling in the body throughout life. The aim of this study was to determine the relationship between the histological appearance and deposition of bone in edentulous jaws and the systemic bone metabolism in humans. A convenient sample of 21 apparently healthy patients scheduled for endosseous oral implants (a Ia modem Brânemark) as they presented for treatment volunteered for the study. Prior to surgery, one gram of tetracycline per day was ingested by the patients to label new fronts of bone deposition. The patients were instructed to take the tetracycline for two days starting 22 days before surgery, and again for another two days after a 14 day interval. The two layers of tetracycline accumulation in the bone were used to estimate the daily quantity of bone formation during the 22 day period. A sample of blood was withdrawn from each patient before surgery and assayed using a radioimmunoassay to detect serum osteocalcin, a non-collagenous bone protein that reflects the metabolic activity of bone formation. Along with the blood, a sample of urine was obtained to measure the concentration of Type I collagen cross-linked N telopeptide that reflects the metabolic activity of bone resorption. A cylindrical core of bone (2x3mm) was taken from each of the 54 implant sites with a surgical trephine as the bone was prepared to receive the implants. Static and dynamic histomorphometric parameters of cortical bone were measured using the “point-counting” method. There was no apparent correlation between systemic metabolism and the histological appearance or turnover of jaw bone. The histomorphometric parameters measured on each specimen of bone showed substantial variations both between and within patients, while the porosity of the bone decreased from the anterior to the posterior parts of both jaws. Women presented relatively lower values for osteocalcin and higher values for Type I collagen cross-linked N-telopeptide, which supports the view that women are at greater risk of bone loss. Moreover, there was a direct correlation between the values of osteocalcin and Type I collagen cross-linked N-telopeptide, verifying the supportive role of both assays as markers of bone turnover. It seems that inter- and intra-variation is an intrinsic and widespread characteristic in the structure of jaw bone, and this phenomenon is not necessarily indicative of bone metabolic disorders. We estimated from the variance in bone structure that a sample size of 125 subjects would be necessary in order to offer sufficient statistical power for stochastic contrasts of jaw porosity. Many (45%) of the specimens had woven bone, which suggests that the residual ridges have been subjected to abnormal mechanical stress. Nevertheless, all of the implants that have been exposed intraorally appear to have integrated successfully in the jaws despite the porous structural characteristic of the bone. The widespread variation in normal porosity and the limited number of subjects in the study may be the reason why we could not find any relationship between the jaw bone and systemic bone metabolism. However, the fact that the release of products of bone turnover in the serum and urine did not reflect either the histological appearance or the osteogenic activity of the specimens of bone suggests that the influence of systemic metabolism is less accentuated in the jaws than in other bones (e.g. iliac crest).

Thesis/Dissertation

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2009-02-27

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http://hdl.handle.net/2429/5257

Dental Science

University of British Columbia

UBCV

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