小臼歯における歯髄腔および硬組織の増齢的変化

抄録

It is well known that the diametrical size of the enamel, dentin, cement layers and the pulp cavity of the human teeth change with aging. But, only a limited number of quantitative study on this issue have so far been made. In this study, a total of 325 human premolars were cross-sectionally cut into ten sections with the purpose of examining the age changes of the pulp cavity and the hard tissues. All premolars were classified into four age groups, 10-19, 20-39, 40-49 and over 50. Especially, the upper premolars were further classified into following three types according to the morphology of the root. A : a single root with a single canal. B : a single root with double canals. C : double roots with double canals. The age change of diametrical size of each hard tissue and pulp cavity was examined both mesio-distally and buccolingually, and relative change was examined. As a result, following observations were obtained. 1. The diametrical size of enamel layers decreased both mesio-distally and buccolingually with aging, especially in age groups over 40, the decrease was evident. This tendency was most apparent in upper first premolars. In direction, mesio-distal decrease was more apparent in general, but the reverse tendency was observed in lower premolars aged over 40 years. 2. The diametrical size of dentin layers increased with aging. This phenomenon was observed in almost everywhere except for crown portion, and it was most evident in upper first premolars. Among upper first premolars, type A showed this tendency most apparently. These changes were most active in age groups 10-39. In direction, there was no significant relative change between the mesio-distal and bucco-lingual size of dentin layers. 3. The diametrical size of cement layers increased with aging. This phenomenon was more apparent in the first premolars than the second premolars both in the upper and the lower side. The increasing ratio at the middle and at the apical portion of a root seemed to be the same. The increasing ratio in premolars with a single canal seemed to be higher than that in premolars with double canals. This tendency was most apparent in the age groups 10-39. In direction, there was no significant relative change between the mesio-distal and bucco-lingual sizes of cement layers. 4. The diametrical size of pulp cavity decreased with aging. This tendency was most apparent in premolars with a single root canal, and in age groups 10-39. In direction, there was no significant relative change of the diametrical size of pulp cavities in upper premolars. In lower premolars, however, the mesio-distal decreasing ratio was higher at cervical portion. On the contrary, the bucco-lingual decreasing ratio was higher at the middle and the apical portion of the root.