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 enamel to underlying flexible and resilient dentin. Prior microscopic images have shown an abrupt demarcation between enamel and dentin; however, new data on protein expression suggests a graded transition. In this study, Vickers microindentations reveal a gradation in hardness with a wide transitional zone across the DEJ region. Therefore, the DEJ must be regarded as a broad transitional region between two interacting tissues, not as a discrete interface. This zone may reduce stress concentrations and act as an important toughening mechanism between mechanically and structurally dissimilar tissues.