Scanning electron microscopy of type I collagen at the dentin-enamel junction of human teeth

The dentin-enamel junction constitutes a unique boundary between two highly mineralized tissues with very different matrix composition and physical properties. The nature of the boundary between the ectoderm-derived enamel and mesoderm-derived dentin is not known. This study was undertaken to identify the presence, type, and distribution of collagen at the dentin-enamel junction as an initial step in understanding its structural-functional role in dental occlusion. Sections of human teeth were demineralized with 0.1 M neutral EDTA and examined by high-resolution field-emission scanning electron microscopy at low accelerating voltage. Enamel and dentin were observed to be linked by many parallel 80-120-nm diameter fibrils, which were inserted directly into the enamel mineral and also merged with the interwoven fibrillar network of the dentin matrix. Immunogold labeling for collagen was visualized by secondary electron imaging and backscatter electron imaging at low accelerating voltage. The collagen fibrils at the junctional zone as well as in the dentin matrix were identified as Type I collagen. Collagenase digestion led to loss of the fibrillar structures and prevented immunogold labeling with antibody specific to Type I collagen. Consequently, the dentin-enamel junction can be regarded as a fibril-reinforced bond which is mineralized to a moderate degree.