Structural events in the caries process in enamel, cementum, and dentin.

The structural events observed in enamel, cementum, and dentin during the caries process have been reviewed. In incipient enamel lesions, the prevailing concept of an almost intact surface layer has been seriously challenged by SEM and TEM observations demonstrating structural pathways (such as enlarged prism junctions or sheaths) from the enamel surface to the sub-surface lesion. The destruction in this latter location consisted of (1) enlarged prism junctions, (2) diffuse mineral destruction in the prism cores, and (3) destruction of the interprismatic substance. In root caries, the destruction of cementum started along junctions between calcified layers of extrinsic (Sharpey) and intrinsic collagen fibers as well as along incremental lines. Invasion of Gram-positive micro-organisms followed these enlarged junctions. Dentin caries was similar in coronal and root caries. It consisted of sclerosis of the lumens of the dentinal tubules, followed by an important gradient of demineralization of intertubular dentin and destruction of occluded tubular lumens and peritubular dentin. Bacterial penetration occurred initially in the dentinal tubules and was followed by bacterial invasion and destruction of the intertubular dentin. Various phenomena of crystalline remineralization were described in enamel and dentin. Whereas in enamel and dentin caries, an important gradient of demineralization was observed before bacterial invasion, a simultaneous destruction of the mineral and organic components seemed to occur in cementum.