Relation of the mandibular body and ramus in Treacher Collins syndrome

Treacher Collins syndrome is associated with a clockwise mandibular deformity (Plast Reconstr Surg 2008;121:77e-84e). We hypothesize that the Treacher Collins mandible exhibits a more obtuse relation between the body and the ramus compared with unaffected subjects. The purpose of this study was to objectively analyze the body-ramus relation in Treacher Collins compared with control subjects and to investigate the effect of age.

This was a retrospective analysis involving three-dimensional computed tomography (CT) scans. Demographic and CT scan information was obtained for Treacher Collins and control subjects. Measurements were performed on the IDXrad platform. The ramus body angle (RBA) was defined as the intersection of the anterior ramus with the tangent from the alveolar process of the mandible. The mandibular plane angle (MPA) was measured in standard fashion. Left and right hemimandibles were analyzed. Statistical analysis involved the paired t-test (P < 0.005 significance). Subgroups based on age, younger than 3 years and older than 12 years, were then compared, within and between groups.

Three-dimensional CT scans were identified in 18 Treacher Collins (36 sides) and 24 control (48 sides) subjects. The MPA was excluded in 6 Treacher Collins and 2 control hemimandibles for absent centric occlusion. The Treacher Collins group consisted of 7 females and 11 males, ranging in age from 0.66 to 204 months (mean, 91.6 months). The control cohort included 13 females and 11 males, aged 0.26 to 204 months (mean, 111.5 months). The mean RBAs for the Treacher Collins and comparison groups were 150.28 and 114.2 degrees (P < 0.0001). The mean MPAs were 38.25 and 31.9 degrees for the Treacher Collins group and control subjects, respectively (P < 0.0001). In children younger than 3 years, the RBAs were 154.40 and 119.36 degrees, and for patients older than 12 years, the RBAs were 148.40 and 111.75 degrees for the Treacher Collins group and control subjects (both P < 0.0001). Comparing Treacher Collins younger than 3 years with those older than 12 years, the mean RBAs were not statistically different at 154.40 and 148.40 degrees (P = 0.1869). Among control subjects younger than 3 years compared with older than 12 years, the RBAs approached significance, but not statistically at 119.36 and 111.75 degrees (P = 0.0122). Notably, among control subjects, the MPA did statistically flatten with increasing age, showing 37.36 and 29.50 degrees (P = 0.0011).

The clockwise relation of the mandibular body relative to the ramus is objectively documented in Treacher Collins subjects. This relation persists despite increasing age, in distinction to control subjects where the mandibular plane flattens in adolescence.