The dentin–enamel junction—a natural, multilevel interface

Teeth contain two major calcified tissues, enamel and dentin, that are joined by an interface known as the dentin–enamel junction (DEJ). Enamel is the hard and brittle outer portion of the tooth that cuts and grinds food and dentin is composed of a tougher biological composite, that can absorb and distribute stresses. The DEJ is a complex and critical structure uniting these two dissimilar calcified tissues and acts to prevent the propagation of cracks from enamel into dentin. The DEJ has a three-level structure, 25–100 μm scallops with their convexities directed toward the dentin and concavities toward the enamel; 2–5 μm microscallops; and a smaller scale structure. Mechanical properties measurements, chemical differences and imaging have been used to determine the functional width of the DEJ. AFM based nanoindentation gave values of 11.8 μm, microRaman yielded a width of 7.0 μm, while the smaller probe used for AFM nanoscratching yielded 2.0 μm, and values from dynamic modulus mapping were less than 1 μm. The unique architecture of the DEJ may account for this variation based on enamel–dentin phase intermixing. The ultimate goal is to use the DEJ as a biomimetic model for other interfaces joining dissimilar materials.