Unusual Case Report: Ectopic Canines, Resorption and Hypodontia in Monozygotic Twins

Ectopic maxillary permanent canines occur in 1–3% of the population, over two-thirds of which are impacted palatally.^1–3 Despite the frequency of ectopic canines, they are often missed in routine dental examinations and, as a result, are often not referred until permanent and irreversible resorption has occurred. Although there is no single cause known, two common theories for maxillary canine impaction include the guidance theory and the genetic theory.⁴ A polygenic, multifactorial genetic pattern of inheritance of palatally displaced canines was suggested by Peck and Peck.⁵ Similarly, hypodontia is thought to have a multifactorial origin and incidence varies from 2.6% to 11.3% of the population.⁶ After the wisdom teeth, it most frequently affects the second premolars and lateral incisors. Interestingly, the relationship between ectopic canines and hypodontia has been investigated in several studies, particularly detailing the relationship between ectopic canines and agenesis of lateral incisors based on the guidance theory. There are fewer studies that detail a relationship between palatally ectopic canines and agenesis of the second premolars.^7–9 Furthermore, resorption of incisors adjacent to ectopic canines may be commonly expected sequelae. This report demonstrates the similar presentation of such resorption, but also idiopathic resorption of the lateral incisors on the contralateral side. A genetic link for internal and external root resorption has been suggested in the literature to be the result of genetic polymorphism of the interleukin (IL-1) mutation.^10,11 This report of monozygotic twin boys who attended the orthodontic department with palatally ectopic canines, agenesis of one of more second premolars and root resorption of both adjacent and contralateral teeth may, therefore, add to the evidence suggesting a genetic susceptibility for root resorption.