[Frequency of the developmental disturbances of tooth structure]

In permanent and deciduous dentitions, the frequency of congenitally missing teeth, supernumerary teeth, conical teeth, fused teeth, germinate teeth, abnormal tubercles (basal ridge of incisor or canine, central cusps of molars, Carabelli's cusp, protostylid, and para-molar tubercles), and enamel hypoplasia (white spots, pigmentation, and enamel defects) were surveyed. Furthermore, mesio-distal and bucco-lingual dimensions of the crowns were measured and the relationship between developmental disturbances of dental hard tissue and tooth size was examined. For the deciduous dentition, the frequency of children with congenitally missing teeth, conical teeth and fused teeth was 7.2%, 1.1% and 5.3%, respectively. Enamel hypoplasia appears with the following frequency; white spots (16.0%), pigmentation (6.4%), and enamel defects (5.2%). Mesio-distal widths of the upper canine and lower lateral incisors of the children with congenitally missing teeth was significantly smaller than the standard values. For the permanent dentition, congenitally missing teeth, conical teeth and fused teeth were detected in 5.7%, 3.0%, and 0.5% of the children, respectively. The frequency of children with basal ridge, central cusps, Carabelli's cusp, protostylid, and para-molar tubercles was respectively, 1.1%, 2.6%, 7.1%, 0.3% and 1.3%. Children with central cusps or Carabelli's cusp tended to have larger crowns, while children with congenitally missing teeth or conical teeth tended to have smaller teeth. As for enamel hypoplasia, white spots were detected in 24.9% of the children, and pigmentation was in 8.1%, and enamel defects were in 9.2%. These results indicate that abnormality of tooth number and tooth morphology correlate with the tooth size and this tendency is more striking in permanent dentition than in deciduous dentition.