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American Journal of Orthodontics and Dentofacial Orthopedics, 2007-07-01, Volume 132, Issue 1, Pages 126-126, Copyright © 2007 American Association of Orthodontists

Introduction: A common concept in orthodontics is that brachyfacial patients have shorter, thicker muscles of mastication and denser cortical bone in the mandible compared with their dolicofacial counterparts. The goal of this study was to look at retrospective data acquired from live patients by using the CB MercuRay and iCAT cone-beam computerized tomography (CBCT) systems.

Methods: The collected CBCT scans were used to determine differences in cortical plate thicknesses, mandibular heights, and widths in patients with high-, average-, and low-angle facial types. A total of 113 scanned patients were deemed acceptable. Of these subjects, 44 were included in the average facial angle group, 35 in the high group, and 34 in the low group. Computerized tracings of lateral cephalometric films evaluated the facial height index and the mandibular plane angle. Cross-sectional slices of the mandible were rendered between the dentition at 13 locations. Each section was then measured in 8 areas including 1 height, 2 width, and 5 cortical plate thicknesses. An ANOVA with a post-hoc Bonferroni statistical analysis was used with a significance level of P <.0167.

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Results and Conclusions: Although few thicknesses of the cortical plates were statistically significant among the facial vertical dimension groups, nearly all measurements for the low-angle subjects were greater than those in the high-angle group. Mandibular height in the high-angle group was shorter posteriorly than in the other groups, and became even greater toward the symphysis. Width measurements in the brachyfacial group were greater than in the dolicofacial subjects. No differences were found in cortical plate thickness between the sexes, although mandibular height and upper width were greater in males. There was a trend for subjects aged 10 to 20 years and over 50 years of age to have smaller cortical bone thicknesses.