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Mandibular dental changes following serial and late extraction of mandibular second premolars

University of British Columbia

Introduction: 15% of the general population are affected by severe dental crowding where conventional orthodontic treatment involves permanent dentition extractions. An alternative treatment method involves serial extraction in the mixed dentition. There is currently limited research on second premolar serial extraction. Objectives: To determine the changes in occlusal curves and dental tipping that occur from mandibular second premolar serial extraction and early extraction of deciduous mandibular second molars with missing mandibular second premolars. Methods: Records were collected from 85 subjects at 3 timepoints: T0, baseline for the control and serial extraction patients; T1, after extraction and physiologic drift but prior to orthodontic treatment for serial extraction patients, and pre-treatment for the late premolar extraction patients; and T2, after comprehensive orthodontic treatment. Three occlusal curves were measured on digitized mandibular casts by placing best fit spheres at specified landmarks. The long axes of the lower first molar, first premolar, canine and central incisor to the palatal plane were measured on digitized cephalometric radiographs to determine the direction and amount of tipping. Results: At T0, there were no significant differences between groups. At T1, there was significant steepening of Monson’s Sphere and the Curve of Wilson between early and late extraction groups. At T2, the differences in Monson’s sphere and the Curve of Wilson were fully corrected. At T1, there were significant differences in the tipping of lower 6’s, 4’s and 3’s between the early extraction groups compared to the late extraction and control groups. There was no difference in lower incisor tipping between any group. At T2, the differences in tipping were fully corrected. Conclusions: Serial extraction of lower second premolars, or lower deciduous second molars when second premolars were missing, produced steeper occlusal curves and significant tipping of mandibular first molars, first premolars and canines after extraction and physiologic drift (T1). The tipping of teeth and accentuated occlusal curves of Monson’s sphere and the Curve of Wilson were fully corrected following comprehensive fixed orthodontic treatment (T2). Serial extractions involving lower second premolars or lower deciduous second molars did not cause any significant lingual tipping of lower incisors following physiologic drift.

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2018-08-14

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/66771

Craniofacial Science

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/