抄録
The ultrastructure of the attached bacterial plaque and the exposed acellular cementum due to periodontal disease was examined under the electron microscope. The author always compared the undecalcified ultrathin sections with the sections decalcified with PTA on the grids. 1) When the attached bacterial plaque was not calcified, no differences were found in density and crystal size between the surface layer and the inner layer of the cementum, but some inorganic crystals of the surface layer were more or less disarranged and some crystals of the cementum were left in the interbacterial matrix. On the decalcified sections, the surface layer of the cementum showed a narrow zone of reticular structures. 2) when the bacterial plaque was partly calcified from the side of exposed cementum, the surface layer was electron dense and composed of large crystals, the size of which was several times as large as those in the inner layer. The same large crystals as those in the surface layer were left in the interbacterial matrix. On the decalcified sections, the surface layer of exposed cementum showed a wide zone of reticular structures, and collagen matrix at that layer lost peculiar periodicity. This electron dense, hypermineralized zone of exposed cementum was considered probably to be related to the recrystallization phenomenon. 3) When the bacterial plaque was almost completely calcified, destructive changes of the cementum surface were of slight degree in general. The crystals of the surface layer of cementum were rather compact and some crystals were disarranged. A homogenous structure containing calcified bacteria was present over some cementum surface. On the decalcified sections, this structure was more clearly observed than that seen on the undecalcified sections. This structure was probably related to some extent with saliva and regarded as the acquired pellicle.
