The mineral and protein content of enamel in amelogenesis imperfecta

The purpose of this investigation was to characterize the enamel composition of teeth affected with the hereditary enamel disorders known as amelogenesis imperfecta. Teeth from 10 individuals representing all 3 major AI types (hypocalcified, n = 3; hypomaturation, n = 3; hypoplastic, n = 4) and 10 normal teeth were studied. Half of each tooth was used for histological and biochemical studies. The enamel protein content was estimated by amino acid analysis. The enamel mineral content (volume %) was determined from the calcium and/or phosphorus content. Calcium was measured using atomic absorption and phosphorus was determined colorimetrically. The mean enamel mineral content was reduced for all hypomaturation and hypocalcified AI teeth while hypoplastic AI enamel varied from normal to reduced compared with normal enamel. The enamel protein content was increased in all but one AI case (7 cases were examined for protein) compared with the normal enamel. The mineral and protein content in AI enamel showed a significant inverse relationship (R = -0.939, P = 0.001). This study shows that all three of the major AI groups can have subtypes associated with substantial decreases in the enamel mineral content, although hypomineralization appears most severe in the hypomaturation and hypocalcified AI types. The decreased mineral content was associated with an increased protein content in AI enamel. These findings provide further evidence that altered enamel mineralization in AI teeth likely involves abnormal post-secretory processing of the enamel proteins.