人の歯の過剰歯根について

抄録

Occurrence of supernumerary root was found in 4 cases among specimens of extracted human teeth as collected in the laboratory of Oral Anatomy, Kyushu Dental College. This report deals with some observations thereon and our view on this anomaly of tooth root. 1st case : Here an upper left 2nd molar had 4 separate roots, two in the buccal side and other two in the lingual side. These roots started to separate from each other at the cervical quarter of the full length ever widening toward apical direction. A variety of the-ories has been proposed as mechanism for such appearance of supernumerary roots. With the present case where the crown part was considerably large in size, there must have been great need to support the pressure of the crown effectively, and we presume that this led to development of the duplicate roots in the lingual side as reinforcement of supporting strength. 2nd case : This is an upper left 2nd molar with 5 roots. It was characteristic of this tooth that the crown had as many as 8 cusps or tubercles, that is, 4 normal cusps, each one of mesial and distal marginal tubercle, a paramolar tubercle and a central cusp. It is natural for this tooth that the crown should be large enough to accommodate such a large number of cusps or tubercles, and the root should be correspondingly reinforced by the supernumerary root to support the heavy load coming from the large crown. 3rd case : This case deals with 2 upper 1st premolars from both sides of the jaw with 3 roots. Both teeth showed very close resemblance in shape, and had 2 buccal and one lingual roots. Mechanism for the production of such anomaly may be somewhat different from that for the above two cases, because premolar with 3 roots is common in the species of anthropoid and moreover the human milk molar which is predecessor of the permanent premolar likewise has 3 roots. In view of these facts, we suggest that the present case represent a case of atavism of the tooth. 4th case : This is a case of lower right 2nd premolar with 2 roots. Although 2-rooted lower premolar is relatively frequent in its occurrence with respect to the 1st premolar, it is seldom encountered with the 2nd premolar. This case too is ascribed to atavism for the same reason with the above, despite the fact that the lower premolars in the anthropoid as well as in the human deciduous dentition have commonly 2 roots.