The dentino-enamel junction is a broad transitional zone uniting dissimilar bioceramic composites

The dentino-enamel junction (DEJ) couples a hard, brittle, stiff layer of e namel to underlying flexible and resilient dentin, Prior microscopic images have shown an abrupt demarcation between enamel and dentin; however, new d ata on protein expression suggests a graded transition. In this study, Vick ers microindentations reveal a gradation in hardness with a wide transition al zone across the DEJ region. Therefore, the DEJ must be regarded as a bro ad transitional region between two interacting tissues, not as a discrete i nterface. This zone may reduce stress concentrations and act as an importan t toughening mechanism between mechanically and structurally dissimilar tis sues.