Morphological changes of dental and basal arch forms in skeletal class II malocclusions before and after extraction treatment

Abstract

Objective To study the variation of the dental and basal arch forms before and after orthodontic treatment of patients with skeletal class Ⅱ malocclusion by tooth extraction. Methods The mandibular dental casts of 25 skeletal class Ⅱ patients were laser scanned before and after treatment. The facial axis (FA) points, which were used to represent the dental arch, and the WALA point, which were used to represent the basal bone, were identified for each tooth from the right first molar to the left first molar. We constructed the curve with points of projection of the FA and WALA point on the reference plane, and compared the curve of dental arch and basal bone before and after treatment. Results The width of anterior middle and posterior of the basal arch increased (0.835±1.259) mm, (1.700±1.280) mm and (2.170±1.227) mm, respectively. While the dental arch had a wider width (1.110±1.566) mm in posterior segment but a narrower one in anterior (3.345±2.907) mm. Conclusions The width of middle and posterior of basal bone represented by WALA ridge becomes wider after orthodontic treatment with tooth extraction in patients with skeletal class Ⅱ malocclusion, while the dental arch turns to a new form, which is more coordinated to the basal bone. Key words: Skeletal class Ⅱ malocclusions; Extraction; Dental and basal bone arch form; WALA ridge; Curve fitting