Influence of Tooth Crown Sizes on Risk of Malocclusion

The etiology of malocclusion frequently is labeled “multifactorial” because some indefinite set of problems occurred during development to produce the skeletodental disharmonies in a given patient. Objective: This study focused on the effect of tooth size as a predisposing factor. Methods: Full-mouth casts of male American white dental students were sorted into those with naturally occurring good occlusions (n = 24) and those with a history of comprehensive orthodontic treatment (n = 55). Mesiodistal crown dimensions of the permanent teeth (omitting second and third molars) were measured in a standardized fashion. Data were analyzed with factorial ANOVA and multivariable ANOVA. Results: Males with histories of orthodontic treatment had significantly larger mesiodistal crown diameters. The largest percentage differences were in the anterior segments, especially the upper lateral incisor (7% larger). Of note, none of the cases had a Bolton discrepancy; all teeth were within normal limits. Given the positive intercorrelations among tooth sizes, it is expected that multiple tooth types would yield comparable results—in this case, most crown sizes were larger in the malocclusion group. This statistical redundancy was taken into account using MANOVA, where the intergroup difference was highly significant. Conclusions: Most malocclusions—particularly dentoalveolar problems—develop from some interplay of multiple developmental factors. The present study shows that tooth size per se is one predisposing condition that results in the common situation of excessive tooth size for the available arch size. Prior studies have, likewise, tested for a tooth-size difference, but several have combined males and females, so the inherent sexual dimorphism (on the order of 4-6%) can easily confound the intended test. Differences in sex ratios among groups can enhance or attenuate the true effect of size—which probably accounts for the variable results in the literature. Supported by the UT Alumni Endowment for Research.