Abstract

Tooth agenesis (hypodontia) was studied in two samples of nonsyndromic subjects possessing either maxillary canine-first premolartransposition (Mx.C.Pl; N=43, M9:F34) orpalatal displacement of the maxillary canine (PDC; N=58, M21 :F37). Agenesis of permanent teeth was identified by x-ray film analysis. Significantly elevated tooth-agenesis frequencies were noted in both samples. Statistically significant differences between the Mx.C.Pl and PDC samples were found in locations of absent teeth, indicating site-specificity of tooth agenesis associated with these canine malpositions. In Mx.C.Pl, agenesis of third molars (M3) occurred at a near-normal rate (19%) while maxillary lateral incisor (12) agenesis showed a thirteen-fold increase (26%). In PDC, the prevalence rate for associated M3 agenesis was 40%, twice the normal rate, while I2 agenesis was 3%, a slight elevation of no statistical significance. These new findings may warrant a hypothesis of anteroposterior site-specific shift in the occurrence of tooth agenesis, associated genetically or epigenetically with distinct anomalies of maxillary canine position and possibly other abnormalities.