A Biometric Comparison of Skeletal Class III Orthodontic Patients

Racial and gender variability in mesiodistal crown diameters has diagnostic and therapeutic implications when predicting the sizes of unerupted canines and premolars. Recent concerns have been raised regarding variations of tooth size relationships that may exist among different malocclusion groups. Objectives: This study compared biometric data from skeletal Class III malocclusions compared to Angle Class I/II malocclusions. Methods: Diagnostic records were selected using the following criteria: Skeletal Class III, acceptable radiographs and models. Power analysis determined that a sample size of 100 subjects for each race and gender would be needed in order to detect significant differences at a=0.05 and b=0.80. The University of Kentucky Analysis was used for age, race, and gender-specific cephalometric norms. Teeth were measured using digital calipers. Subjects were compared to a control group of 352 class I/II subjects. Our preliminary Class III sample consists of 26 patients who meet these criteria. Caucasian female = 8, Caucasian male = 15, Black female = 1, Black male = 2. Results: Statistical analysis was performed using the SAS/STAT program. Two and three way ANOVA showed no significant correlations between gender, race, and skeletal class. Statistically significant differences of tooth size for #4, #3, #12, and #14 were found between class I/II and class III; the average difference in size for I/II vs. III: -0.29 (p=0.01), 0.44 (p<0.01), -0.25 (p=0.01), and 0.33 (p=0.01), respectively. Initial regression analyses showed that a more accurate prediction of the sizes of unerupted premolars and canines may be established using the average of the sum of #8, 9 & #19, 30, compared to the sum of the lower incisors. Conclusion: Preliminary findings suggest a tooth size difference between malocclusion types and that the lower incisors may not be the most accurate predictors of the sizes of unerupted premolars and canines.