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UBC Theses and Dissertations

Changes in the occlusal curves secondary to serial sextractions compared to late premolar extractions and controls Feldman, Esther


Objectives: To determine the relationships between tooth tipping and occlusal curvature patterns in serial extraction (SE) cases versus late premolar extraction (LPE) cases and controls. Methods: Mandibular dental casts and cephalometric radiographs were collected from 90 subjects (30 Class I controls, 30 SE cases, 30 LPE cases) at 3 time points: baseline (T0) for controls and SE, after natural drift/pre orthodontics (T1) for controls, SE, and LPE, and after comprehensive orthodontic treatment (T2) for the SE and LPE groups. The casts were scanned and rendered as virtual models. 12 cusp tips (4 incisors and 2 first molars) were digitized and the occlusal curves were measured using Rhinoceros by fitting a sphere to the landmarks (least-squares method). Radiographs were digitized and the long axes of the central incisor, canine, and first molar were landmarked and related to palatal plane to determine the direction and amount of tipping. Results: The SE group differed significantly from the other two groups at T1, with smaller radii in 2/3 outcomes. From T0-T1, the SE group showed a tendency for the incisor and canine to tip distally, while the molar tipped mesially. From T1-T2, the SE group had smaller radii versus LPE and demonstrated mesial tipping of the incisor and canine angulations, with the molar tipping distally. Conclusions: SE cases tend to have steeper occlusal curves (smaller radii), post tooth drift and after orthodontic treatment as compared to the other groups. In general, orthodontic treatment, post SE, involved incisor and canine proclination, as well as molar uprighting. SE is unlikely to save more than 4-6 months of active treatment due to the time needed to correct the increased occlusal curvature that results from this procedure.

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