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The Relationship Between Presence and Absence of Third Molars Hypodontia of other Teeth

Third molar agenesis is the most common form of hypodontia, occurring in 5-25% of the population (Banks, Angles Orthodont 4:223, 1934; Grahnen, Odont Rev 7:Suppl. 3, 1956; Garn and Lewis, Angles Orthodont 32:14, 1962). It has been repeatedly suggested that when one or more third molars are missing there is an increase in frequency of hypodontia of other teeth (Garn, Lewis and Vicinus, J Dent Res 41:717, 1962; Keene, Angles Orthodont 35:289, 1965). In the present communication we are reporting a survey of 7,886 Canadian individuals, in whom there was no association between congenitally missing third molars and agenesis of other tooth types. Intraoral radiographs and dental and medical histories of a series of 7,886 patients, registered at the Faculty of Dentistry, The University of British Columbia, Vancouver, were examined for presence or congenital absence of third molars and other teeth. From this sample, patients 20 years and older were selected. Only 653 cases were useful in the present study, the remainder being discarded because of youth, supernumerary teeth, impaction, history of early extraction, incomplete history regarding the status of missing teeth, and systemic illness during early childhood. Data collected were analyzed using the Student-t test method, for frequency, anatomical location, sex distribution and tooth type.