Semester

Spring

Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

School of Dentistry

Department

Orthodontics

Committee Chair

Tim Tremont

Committee Co-Chair

Chris Martin

Committee Member

Peter Ngan

Committee Member

Bryan Weaver

Abstract

Background Objectives: The occlusal plane has been given much attention throughout the orthodontic literature. Studies have shown that the occlusal plane inclination varies relative to vertical and sagittal skeletal discrepencies. The Six Elements of Orofacial Harmony does not address the occlusal plane inclination as a parameter in diagnosis and treatment planning despite its spatial influence on the position of the chin. The occlusal plane inclination is considered a critical factor in treatment planning for orthognathic surgery. The objective of this study was to systematically evaluate the inclination of the occlusal plane (Op°) relative to various skeletal and dental cephalometric parameters. Methods: A sample of 105 pretreatment cephalometric radiographs, in subjects with a range of skeletal and dental morphological characteristics, was appraised. Differences in the Op° and AP measurements of pogonion relative to the GALL were evaluated among the various anteroposterior, vertical, and soft tissue facial convexity groups were compared. Correlation coefficients evaluating relationships among the cephalometric measurements were calculated. A stepwise regression analysis was performed to further elucidate the variables which contribute to changes in the Op°. Results: The occlusal plane inclination was most significantly correlated with SN-MPº, MPº, Pog'GALL, Pog-GALL, Pogc'- GALL, TVL-Pog, and S-Go. The regression analysis indicated that SN-MPº, PPº, Element IV Md Ant, PP-Msc, PP-1, Mp-Mic, Sn'-Me', SNº, Element IV Mx Ant and Co-Gn are good predictors of Opº. There were statistically significant differences among all vertical groups for the mean Opº. The mean Opº was found to differ among Class II and III skeletal profiles and convex and concave soft tissue facial convexities. Conclusions: Opº varies relative to sagittal and vertical jaw dimensions. There is a strong relationship between the occlusal plane inclination and the vertical dimension. Hyperdivergent profiles tend to have steeper occlusal plane inclinations. Hypodivergent profiles tend to have flatter occlusal plane inclinations. There is a tendency towards steeper occlusal planes in Class II skeletal subjects and a flatter occlusal plane in Class III skeletal subjects. There is a tendency towards steeper occlusal planes in subjects with convex profiles and flatter occlusal planes in patients with concave profiles. The occlusal plane inclination is highly correlated with the measurement of soft tissue pogonion to the GALL. There is a strong correlation between the occlusal plane inclination and maxillary incisor inclination. The occlusal plane inclination should be considered when diagnosis and treatment planning to maximize dental and facial esthetics.

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