Early recognition of mandibular growth pattern using geometric morphometrics

Abstract

OBJECTIVE: The objective of this study is to determine the earliest time point in growth when a difference in mandibular shape of dolichocephalic and brachycephalic subjects is distinguishable. MATERIALS & METHODS: 11 dolichocephalic and 14 brachycephalic subjects were selected using lateral cephalograms from the Forsyth/Moorrees Twin Study using a method described by Rocky Mountain Orthodontics. 23 landmarks outlining the mandible were identified on the lateral cephalograms of each subject from their earliest age (5-8 years) to their latest (16-18 years) using TPSdig software. The 2 dimensional coordinates for each landmark were then exported to TPSUtil. From TPSUtil, the TPS data was then converted to a .csv file in Microsoft Excel and imported into MorphoJ for analysis. Primary morphometric analysis consisted of generalized Procrustes analysis, principal component analysis, and discriminant function analysis. RESULTS: The first 5 principal components for both facial types accounted for the majority of the variance. Discriminant function analyses were not significant for any phenotype or age group pairing, suggesting that the overall shape difference was too small to be detected between groups and over time starting at age 7. A plot of the Procrustes coordinates for the brachycephalic group versus the dolichocephalic group revealed that there were differences in shape between the two phenotypes, but this difference was statistically insignificant. CONCLUSIONS: The mandible increases in size with age, with minimal change in shape. Mandibular shape is established by the age of 7. The difference in mandibular shapes of the two phenotypes was not statistically significant.