Characterization of the organic matrix of mature human tooth enamel: Structure, macromolecular composition and effect of radiotherapy

Mature human tooth enamel contains a small amount of organic matrix locally concentrated within its innermost region, which is tougher and more crack resistant than the outer bulk phase. Although the enamel organic matrix is regarded to contribute to these properties, its structure and macromolecular composition remain largely unknown. To characterize these unknowns, the hypotheses tested were, "The organic matrix of mature human tooth enamel is comprised of a well-organized network of proteins; that the epithelial-derived organic matrix of mature human tooth enamel contains type VII and type IV collagen; and that radiotherapy affects the ultrastructure and type VII and type IV collagen components of the organic matrix of mature human tooth enamel." To achieve these goals, three aims were addressed: 1) To characterize the distribution and ultrastructure of the organic matrix of mature human tooth enamel using multiple techniques; 2) To identify and localize macromolecular components of the organic matrix of mature human tooth enamel; and 3) To characterize the ultrastructure and collagenous components of the organic matrix of mature human tooth enamel subsequent to in vitro and in vivo radiotherapy. Results of these studies were as follows. First, the organic matrix of mature human tooth enamel was distributed within enamel's inner region in proportion to the thickness of the anatomical enamel layer; and was composed of a meshwork of integrated protein fibrils reflective of the rod/interrod and aprismatic morphology of the surrounding inorganic phase. Second, the enamel organic matrix, for the first time, was shown to contain type VII collagen and collagen IV; each of which exhibit a unique distribution pattern relative to the DEJ. Third, though the enamel organic matrix was not directly affected by simulated in vitro radiotherapy, enamel-matrix type IV collagen was affected in teeth exposed to in vivo radiotherapy. Further testing of teeth exposed to in vivo radiotherapy is required. We hypothesize that the results of these studies will help define the unique material properties of inner enamel, and further the identification and characterization of other macromolecular components of the enamel organic matrix at the DEJ.