We had a roentgenological study of the supernumerary teeth in the incisal regions of upper jaws, based on an examination of 1789 school children from the age of 8 to 13 years in the Department of Oral Diagnosis of ABCC at Hiroshima in the year of 1951. The subjects consist of 870 boys and 919 girlds, who were selected at random among the pupils of the grammer schools in the same city, The results were summerized briefly as follows:
1) Among the pupils examined, the fifty-three cases of supernumerary teeth were found in the incisal regions of upper jaws ; those occuring between the first and second incisors were only in the two cases, and the others were all found mesially to the first ones. (so-called “Mesiodens”)
2) The occurence of the supernumerary teeth in the incisal regions of upper jaws were distributed forty-three cases (4.96 %, 0.73 %) in males and ten (1.09 %, 0.33 %) in females ; the difference in both sexes was highly significant statistically.
3) Among sixty-one teeth found in the fifty-three cases, fifteetn ones had been erupted, but forty-six, including thirty-eight inverted teeth, were unerupted: They were found unilaterally in the forty-five cases and bilaterally in the eight cases.
4) Median diastema and other maleruptions of the permanent incisors due to the erupted or unerupted supernumerary teeth were evidenced in the twenty-eight cases.
5) The slight enlargement of tooth sac was observed on the roentgenograms of the four unerupted supernumerary teeth of our series, and one of them showed cyst formation evidently on the coronal portion of the embedded tooth.
6) The supernumerary teeth were of rudimentary form ; most cases (75.4 %) showed peg in shape and the others were turbinated.
7) Regarding the incipience of the supernumerary teeth by observing comparative state of its development with that of the permanent first incisors, the development of the supernumerary teeth were ahead of the first incisors in the thirteeth cases, a contemporary in the four cases and the retarded only in the one case among the nineteen cases, in which the root formation could be compared.
In addition, we believed that our materials regarding the shape and size of the supernumerary teeth, its position in the dental arch and the comparative state of its development with that of the permanent teeth could offer the important data on discussing the occurrence of the supernumerary teeth.
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