Abstract
The purpose of this study was to investigate the frequencies of fusion and missing of deciduous teeth, the frequency of the abnormalities of their successors, and the changes in mesio-distal and labio-lingual diameters of the crown of deciduous teeth.
One thousand and twenty-four children (506 boys and 518 girls), in Hellman's dental stages II A and II C, who had visited the Clinic of Tohoku University School of Dentistry, were investigated. The study models and oral photographs were used for examination.
The results were as follows.
The frequencies of fused teeth and missing teeth were 5.6 percent and 1.8percent, respectively. These frequencies were found higher in the mandible than in the maxilla. The number of fused teeth was 45 between the lower central and lateral incisors,17 between the lower lateral incisor and the canine, and 4between the upper central and lateral incisors. On the other hand, the number of missing teeth was 18 among the lower lateral incisors,2 among the upper lateral incisors, and 1 among the lower central incisors. There were neither fused teeth nor missing teeth among the deciduous molars tested.
In the case of the fused and missing deciduous anterior teeth, their successors also were found fused or missing with high frequency. Especially in the fusion of the lower deciduous lateral incisor with the canine and in the missing of the lower lateral incisor, the absence of their successors was found more frequently than in the fusion of lower deciduous central incisor with the lateral incisor.
The mesio-distal diameter of the crown of the fused teeth was larger compared with the larger one of the 2 corresponding teeth on the normal control side. The labio-lingual diameter of the crown of the fused teeth showed an intermediate value of the total diameter between the mesial tooth and distal tooth on the normal control side. When the lower lateral incisor was missing, the deciduous canine on the missing side was larger than the lateral incisor, and smaller than the canine on the normal control side. Therefore, the lateral incisor looks as if it is missing if a complete fusion occurs between the canine and the lateral incisor.
