The present study was to investigate the incidence of deciduous fused teeth in Japanese and to compare this with Caucasians, excluding congenitally missing teeth, peg-shaped and supernumerary teeth. Four thousand four hundred and twenty-two 3-6 year old children were investigated in Sasebo-City, Nagasaki Prefecture,2245 boys and 2177 girls.
One hundred twenty-four boys and girls (66 boys; 58 girls) were found to have 138 fused teeth. Fourteen children (0.32%) had bilateral fused teeth in their right and left mandibles. The frequency of the fused teeth in deciduous dentition in Japanese was 2.80%. On the other hand, according to Duncan and Helpin (Oral Surg. Oral Med. Oral Pathol.64: 82-87,1987), the frequency of fused teeth in Caucasians is about 0.5% and that of bilateral fused teeth 0.02%. An application of the chi-square test shows the differences are satistically highly significant (P<0.005). The difference between the sexes and left and right sides is not significant (P>0.05).
Fused teeth occurred ca.6 times more frequently in Japanese than in Caucasians. Bilateral fused teeth in the primary dentition occurred 16 times more frequently in Japanese than in Caucasians.
McKusick pointed out that the inheritance of deciduous fused teeth is of a Mendelian autosomal dominant trait pattern. However, the present authors have collected many cases that reject the autosomal dominant trait pattern. Therefore we support the theory that the inheritance of fused incisors is an autosomal recessive trait rather than an autosomal dominant trait. Further reports will be published.