Enamel protein in smooth hypoplastic amelogenesis imperfecta

Amelogenesis imperfecta (AI) remains a poorly understood group of hereditary enamel defects characterized by a wide array of clinical presentations. Although numerous reports have described the histological features of AI, knowledge concerning the biochemical composition of the affected enamel remains minimal. The purpose of this investigation was to examine the protein of smooth hypoplastic AI enamel. Exfoliated primary teeth were obtained from an individual with smooth hypoplastic AI together with exfoliated teeth from normal healthy individuals for controls. Enamel was dissected from the AI and control teeth to determine protein content and amino acid profile. The analyses showed that the hypoplastic AI teeth contained 2% protein, compared with 0.3% in normal primary enamel. The protein content of the hypoplastic AI enamel was similar to that reported for the late maturation stage of normal primary enamel. The amino acid profiles of both normal and AI enamel were similar although there appeared to be increased amounts of glycine in the AI enamel. Hypoplastic AI enamel showed an amino acid profile similar to normal mature primary enamel in contrast to hypomaturation AI that exhibits an amelogenin-like character. The amount of retained protein also was different from that reported for hypomaturation AI enamel which contains approximately 5% protein compared with the 2% seen in hypoplastic AI enamel. This study emphasizes the potential usefulness of protein characterization in delineating different AI types and illustrates how this information may lead to an understanding of the developmental defects responsible for producing abnormal enamel.