Annotation The Relationship Between Presence and Absence of Third Molars Hypodontia of Other Teeth RAVINDRA M. SHAH and MARCIA A. BOYD Faculty of Dentistry, The University of British Columbia, Vancouver, B.C. V6T TWS J Dent Res 58(1):544, January 1979 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. Received for publication February 28, 1978. Accepted for publication, June 30, 1978.

The results are summarized in the Table. Of the total of 483 individuals who had all four third molars present, 121 (25%) showed hypodontia of other teeth. The total number of missing teeth was 241, with females showing a higher incidence than males. One can also deduce from the Table that of the 152 individuals lacking one or more third molar teeth, 18 (12%) showed additional hypodontia. The absolute number of missing teeth for all others was 43, with males showing a higher incidence than females. The most commonly missing teeth in both groups were maxillary lateral incisors and mandibular second premolars, which together accounted for more than 80 percent. Our observations clearly indicate that congenitally missing third molars are not associated with an increased incidence of hypodontia of other tooth types. In fact, they show that the frequency of other missing teeth is higher when 3M are present. These results are contrary to the observations of Garn, Lewis and Vicinus (J Dent Res 41:717, 1962) and Garn and Lewis (Angles Orthodont 32:14, 1962), who noted a 13-fold increase in the incidence of other missing teeth when one or more third molars were congenitally absent. Thus the hypothesis of Garn, Lewis and Vicinus (J Dent Res 41:717, 1962), that third molar agenesis is not an isolated anomaly, is also not supported by our observations.

INCIDENCE OF HYPODONTIA OF OTHER TEETH WHEN THIRD MOLARS ARE PRESENT OR CONGENITALLY ABSENT No. of individuals

No. of No. of No. of individuals Total no. of individuals individuals Total no. of with third with hypodontia other missing with third with hypodontia other missing molar present of other teeth teeth molar agenesis of other teeth teeth Statistics Male 267 55 98 70 8 26 t = 4.58 Female 216 Total483

66

143

82

10

17

121

241

152

18

43

p < .0001 t= 7.47 p < .0001 t= 8.51 p < .0001

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The relationship between presence and absence of third molars hypodontia of other teeth.

Annotation The Relationship Between Presence and Absence of Third Molars Hypodontia of Other Teeth RAVINDRA M. SHAH and MARCIA A. BOYD Faculty of Dent...
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