CHARACTERIZATION OF THE ENAMEL ULTRASTRUCTURE AND MINERAL-CONTENT IN HYPOPLASTIC AMELOGENESIS IMPERFECTA

Amelogenesis imperfecta (Al) comprises a diverse group of hereditary enamel disorders that are characterized by hypoplastic and in some cases hypomineralized defects. The specific biochemical abnormalities remain unknown for all Al types, making histologic and chemical analyses of affected dentitions essential for resolving the etiology of Al. The purpose of this investigation was to characterize the ultrastructure and mineral content of smooth hypoplastic Al enamel. The Al enamel showed no evidence of surface pitting and was uniformly reduced in thickness by approximately 60% compared with control enamel. Imbibition studies indicated that the Al enamel was generally porous. The first 30-mu-m of Al enamel adjacent to the dentinoenamel junction was translucent with poorly formed prisms. Abnormal prism structure was seen throughout the Al enamel. Amorphous, presumably organic material that may have been retained enamel protein was also seen. Although the crystallite widths were similar in both Al and normal enamel, the Al teeth showed areas where the crystallite order and continuity appeared disrupted. The mean mineral content was similar for all variables measured except sodium, which was significantly lower in the Al teeth. The calcium concentration was very low in the Al enamel directly adjacent to the dentinoenamel junction and showed a steeper concentration gradient moving from the dentin to the surface compared with control teeth. It may be concluded that the ameloblasts in smooth hypoplastic Al produce a tissue of reduced thickness, which is excessively porous and displays alterations in its ultrastructural organization.