A very rare case, a median incisor fusion, was seen both in primary and permanent dentitions of a 5-year-old Japanese girl, who visited the Pedodontic Clinic of Tsurumi University Dental Hospital. These median incisors appeared in the primary as well as in the permanent dentition and were extracted for esthetic reasons and subjected to morphological and histological examinations.
The etiology of the median incisor fusion is also discussed. The following findings were obtained:
1) Morphologically, both median incisors showed no traces of fusion and their appearance was more like that of a single normal tooth, except that they were mesiodistally symmetrical and the mesiodistal width of the primary median incisor was larger than that of the Japanese average of upper primary central incisor.
2) Histologically, there was no evidence of fusion between upper right and left incisors. Their structure was more like that of a single normal tooth.
3) Embryologically, it is reasonable to consider that it originated from a single germ rather than from two germs fused completely. The possibility of a relationship between the median incisor fusion and her nasal disease was also pointed out.