Class III cases are more prone to have impacted upper canines and microdontic upper lateral incisor. Any evidence and why? I am an orthodontics trainee.

Not as a firm general rule. Evidence suggests that maxillary canine impaction is associated with small/peg-shaped or missing maxillary lateral incisors, but evidence that skeletal Class III itself causes or consistently has higher rates of these anomalies is limited and mainly based on retrospective orthodontic samples.

• A small retrospective study comparing skeletal Class III with Class I patients reported a higher prevalence of impacted maxillary canines in the Class III group. Another retrospective study found bilateral maxillary canine impaction more frequently in skeletal Class III patients. These findings are hypothesis-generating, not proof of a universal Class III association.

• The stronger and more reproducible association is: impacted/displaced maxillary canine ↔ anomalous maxillary lateral incisor. Peg-shaped lateral incisors and tooth agenesis occur significantly more often in patients with impacted maxillary canines than in controls.

• This supports two complementary explanations:

  • Genetic/developmental-field theory: lateral-incisor microdontia, peg laterals, and lateral-incisor agenesis may be variable expressions of an underlying developmental disturbance; canine displacement/impaction can cluster with these anomalies.