EC Dental Science

Objective: To evaluate lower incisor dentoalveolar compensation and related mandible symphysis morphology among patients with class II division 1, class I and class III malocclusions with different facial vertical skeletal patterns.

Subjects and Methods: Lower incisor extrusion and inclination, mandibular symphyseal height (LH), buccal (LA) and lingual (LP) symphyseal bony cortex depth were measured in 199 lateral cephalometric x-rays of adult patients without prior orthodontic treatment (Class II division 1 n = 66, Class I n = 71, Class III n = 62). A principal component analysis (PCA) considered both sagittal and vertical facial patterns.

Results: A response pattern for the lower incisor behavior inside its symphyseal environments were identified. The IMPA in Class II division 1 malocclusion exceeded 93º and negatively correlated with the mandibular plane in Class III. The increase of mandibular plane had a negative correlation with LA and LP for class I, II division 1 and III groups. Still, no significant differences were found in class II division 1 patient for LH. According to the PCA, close to 70% of the analyzed samples showed evidence that dentoalveolar compensation of II division 1 behaves differently than class I and III when vertical facial patterns were considered. In class II division 1, all the groups showed a similar pattern. LA and LP were reduced in long-face patterns, but LH didn’t increase.

Conclusion: In class II division 1 malocclusion, the lower incisor was usually proclined, while the increase of the mandibular plane was related to a decrease in lower incisor inclination and extrusion. Symphyseal morphology and the lower incisor position did not respond in a consistent, precise mechanism of dental compensation, unlike in other malocclusions, suggesting a skeletal alteration in the morphology of the jawbone.

Keywords: Lower Incisor; Mandibular Symphysis; Dentoalveolar Compensation

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