Is there geometric morphometric evidence for the selection against impaction? A comparative cross-sectional study of specific tooth-agenesis patterns.

OBJECTIVES

Reductions in tooth number and facial prognathism may reflect shared genetic and evolutionary mechanisms but have been inconsistently reported by traditional cephalometric analyses. This study aimed to assess whether common patterns of dental agenesis are associated with craniofacial morphology using geometric morphometric methods.

DESIGN

This retrospective comparative cross-sectional study included 538 patients aged 10-19 years from a French orthodontic population. Individuals with hypodontia (n = 269), restricted to third molars, maxillary lateral incisors, or second premolars, were matched by age and sex with controls without agenesis (n = 269). Craniofacial morphology was assessed on lateral cephalograms using 18 landmarks and 87 semilandmarks. Multiple linear regression and Procrustes MANOVA were applied to evaluate differences in size and shape, adjusting for sex and age.

RESULTS

No significant association was found between agenesis status and craniofacial size in the overall configuration as well as in the cranial base, maxilla, and mandible. A significant sex effect was detected in the mandible, with smaller centroid size in males (p = 0.012). Multivariate regression on shape confirmed allometric effects across all configurations. Procrustes MANOVA detected a significant effect of sex on overall shape (p = 0.003), but neither age nor hypodontia reached significance.

CONCLUSION

In this large geometric morphometric study, no generalized or localized alterations in craniofacial morphology were detected, even in third molar agenesis, suggesting that the anthropological significance of hypodontia should be regarded with caution.