171 human premolars which had been extracted for orthodontic purposes were divided into two groups. The first group, consisting of sixty specimens, were coated with nail varnish leaving a “window” at the enamel-cementum junction on the mesial or distal approximal surface, and placed in acidified gel pH 4.5 (Silverstone 1966), for periods of 1, 2, and 4 weeks. After exposure to the acidified gel, the specimens were sectioned longitudinally without embedding through the middle part of the “window” and examined. The second group of 111 specimens were first sectioned longitudinally in a mesiodistal plane and classified into three types on the basis of the morphology of their enamel-cementum junction. In Type I the enamel and cementum did not meet leaving a narrow region of exposed dentin; in Type II the enamel and cementum just met; and in Type III the cementum overlapped the enamel. From these sections ten examples of each type were selected. After this they were coated as before with nail varnish leaving a narrow “window” on the tooth surface with the enamel-cementum junction exposed. The sectioned specimens were then placed in acidified gel for a total of 168 hours and examined serially after 5, 10, 15, 20, 30, 40, 50, 60, 80, 100, and 168 hours. The lesions of these specimens were examinined by transmitted and polaraized light microscopy, contact microradiography, SEM, and XMA.
Results: In both groups the artificial caries-like lesion of the root surface could be divided into 6 layers from surface to bottom. In light microscopy, the first layer was a slightly translucent zone which had on an intensely opaque surface and bottom, and that corresponded to acellular cementum, the second layer was a very translucent zone, the third layer was a slightly opaque zone, the fourth layer was a slightly translucent zone, the fifth layer was a very opaque zone, and the sixth layer was a very translucent zone.
In microradiography the first layer was a considerably demineralized zone which had a very opaque surface and bottom, the second layer was an intensely demineralized zone, the third layer was a slightly remineralized zone, the fourth layer was a demineralized zone, the fifth layer was a considerably mineralized zone, and the sixth layer was an intensely mineralized zone.
Although the remineralization of the surface of the first layer became unclear as the demineralization process progressed, the remineralization on the tooth crown side and on the root apex side, where the initial demineralization was expanding, could be clearly observed.
The lesion in acellular cementum progressed along the Sharpy fibers, enlarging the portion which enclosed the Sharpy fibers. Although the lesion in the dentin progressed along the dentinal tubules, it did not progress along the incremental lines. On the tooth crown side the lesion also progressed along the enamel-dentin junction.
In the Type I enamel-dentin-cementum lesions the dentin which was exposed became demineralized and the profile on the tooth crown side was deep and rounded. On the other hand in the Type III specimens with cementum overlapping the enamel, the lesion in the dentin was shallow with a sharp profile.
It is concluded that the structure, progression, and expansion of artificial tooth root surface caries-like lesions are dependent on the chemicophysical phenomenon by demineralization and the natural histological structure of this site.
It is believed that the findings of this study will be useful for a better understanding of the progression of natural tooth root surface caries lesions.
抄録全体を表示