UCSF

ABSTRACT

Introduction: Condylar growth direction and rotation affect the type of occlusion that forms, especially in the vertical dimension. It stands to reason that condylar morphology would be positively correlated with vertical facial dimension. The first objective of this study was to evaluate the reliability of novel three-dimensional semi-automated landmark computer software on mapping the head of the mandibular condyle. The second objective was to evaluate qualitatively how condylar morphology differs three-dimensionally according to skeletal vertical pattern and mandibular morphology in healthy adults who had had cone beam computed tomography scans (CBCT).

Methods: A convenience sample of 606 (423 females and 183 males) patient CBCT DICOM scans without identifiers was obtained from DDI Imaging Center in Sacramento. Due to inclusion and exclusion criteria, a total of 242 (169 females and 73 males) scans were eligible for the study. DICOM scans were loaded into the Anatomage InVivo software (Anatomage, San Jose, CA) to create lateral cephalograms. The lateral cephalograms were then loaded into Dolphin Imaging (Dolphin, Chatsworth, CA) and traced to determine MP-SNº and chin angle (Id-Pg-MPº). Subjects were selected at random from the 242 to create three groups of 10 subjects based on their MP-SNº. Subjects who were more than one standard deviation below the norm were assigned to the brachyfacial group, while subjects who were more than one standard deviation above the norm were assigned to the dolichofacial group. Those in between were assigned to the mesofacial group. Those 30 subjects were also divided by mandibular symphyseal morphology according to the chin angle (Id-Pg-MPº). Each subject’s condyles were landmarked using Stratovan’s Checkpoint software (Davis, CA). A Procrustes analysis was then used to generate an average condylar shape for each of the six groups from which to evaluate shape differences.

Results: Checkpoint proved to be a reliable method of placing landmarks on the condyle with a low coefficient of variation of 1.81% (SD/mean). The Bland-Altman indicated a mean difference of 0.344mm on average measurements of 55.232. Qualitative analysis of the Procrustes averages revealed morphological differences between the three skeletal vertical pattern groups. The brachyfacial average showed a moderate anterior lean from the sagittal, anterior convexity from the axial, and medial lean from the coronal views. The dolichofacial average showed a mild anterior lean from the sagittal, anterior concavity from the axial, and a symmetrical half-dome shape from the coronal. Counter to expectations, the obtuse chin angle group average displayed morphology similar to the brachyfacial average while the acute chin angle group average displayed morphology similar to the dolichofacial average.

Conclusions: Checkpoint is reliable software to landmark the TMJ. There are differences in average morphologies between all groups. Larger sample sizes and objective quantitative methods are needed for future research.