Detection of mature collagen in human dental enamel

Mature dental enamel is the most mineralized of all mammalian tissues and considered to be free of collagen. Hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) are two nonreducible cross-links of mature collagen. Hydroxyproline (Hyp) is an amino acid that is believed to be indicative of the presence of collagen. We set out to assess the concentrations of Hyp, HP, and LP in dental enamel and dentin (control) to clarify whether there was minor collagen content in dental enamel. We studied 17.53 g of enamel and 22.12 g of dentin gained from 120 extracted human teeth. Enamel and dentin (control) were separated with a diamond dental drill under microscopic control by wasting a margin of enamel (Ca. 2 mm) at the dentin-enamel border. Collagen alpha-chains were analyzed by Sodium dodecylsulfate-polyacrylamide gel (SDS-PAGE) after decalcification and collagen extraction. Concentrations of HP and LP where measured by using high-performance liquid chromatography (HPLC). Hyp was analyzed by a spectrophotometric method. The pooled probe of enamel contained 0.23 mug/g of Hyp. This concentration was 49 times lower than that in dentin. Concentrations of HP and LP in enamel were 0.07 nmol/g and 0.02 nmol/g, respectively being 605.57 (HP) and 251.50 (LP) times lower in enamel as compared to dentin. Collagen type I was found in enamel; collagen types I and V were found in dentin samples. In reports of many studies and textbooks, collagen is considered to be completely absorbed in the course of the mineralization and maturation of dental enamel. We show that this is not the case. However, the concentration of collagen in enamel was considerably lower as compared to that in dentin.