The occurrence of hypodontia in patients with cleft lip and/or palate.

The frequency of hypodontia (but for the third molar) was studied in a series of 600 patients with cleft lip and/or palate. The series was subdivided into three groups according to the type of facial cleft. As compared to the general normal population the occurrence of hypodontia was markedly increased in patients with clefts. The highest percentage of hypodontia was recorded in patients with cleft lip and palate, the lowest frequency was present in cleft lip only. In cleft lip and in cleft lip and palate girls were affected significantly more frequently than boys. The occurrence of hypodontia in the lower and in the upper jaw differed according to the type of cleft. The upper jaw was affected more often in cleft lip and in cleft lip and palate, the mandible was involved more frequently in isolated cleft palate. The dental bud of the upper lateral incisor was affected most commonly in cleft lip and in cleft lip and palate, while the second lower premolar was most frequently absent in isolated cleft palate.