Hypodontia in human twins and families

Abstract

The incidence of hypodontia was studied in 369 pairs of twins ranging in age from 5 years to 18 years. The condition was present in forty-two (5.7 per cent) of the 738 persons investigated. The incidence was 6.1 per cent for females and 5.3 per cent for males. The tooth most frequently missing was the mandibular second premolor (55.7 per cent). The mandibular central incisor (15.2 per cent) was the second most frequently absent tooth, and the maxillary lateral incisor (13.9 per cent) ranked third. A comparison of the frequencies of concordance and discordance for missing teeth between monozygotic and dizygotic twin pairs resulted in a chi-square value of 0.82 (df = 1), indicating no significant difference between concordance for hypodontia in the two types of twins. The families of forty-four children known to have hypodontia were studied. The forty-four propositi had a total of 109 siblings 5 years of age or older. Fourteen of these 109 children (12.8 per cent) were found to be missing teeth. This percentage of siblings missing teeth was not significantly higher than would be expected to occur by chance in a random sample of 109 children (chi-square = 1.52, df = 1). The incidence of hypodontia was found to be equally frequent in siblings, regardless of birth order. No association was found between maternal health during pregnancy, maternal age at birth of the child, or early childhood diseases and the incidence of hypodontia. There was a tendency for those children with a very low birth weight (5 pounds 8 ounces or less, or premature children) to show a greater incidence of hypodontia. Also, children with hypodontia, especially those missing two or more teeth, showed a higher incidence of premature births when compared with children without hypodontia.