Demonstration of Octacalcium Phosphate in Dental Calculus

Objective: The present study was designed to demonstrate ultrastructually the presence of octacalcium phosphate (OCP) in dental calculus and its rapid alteration of crystal lattice after having been exposed to the electron beam. Methods: Samples of dental calculus were obtained from the patients during scaling. The samples were dissected by using razor blade. They were fixed in 2% glutaraldehyde in 0.1M cacodylate buffered solution, followed by postfixation with 1% osmium tetroxide in the same solution. Subsequently, they were embedded in Araldite 502. Thin sections were obtained with an ultramicrotome equipped with a diamond knife, and then examined under a transmission electron microscope. Results: By electron microscopy, at the site near the calcification front, most of the bacteria usually were densely packed with fine crystals, which were predominant in the dental calculus. Large crystals seemed to be frequently present in the extracellular space between bacteria. A lattice interval of 16.7 angstrom, and the vulnerability to electron bombardment were confirmed within some large crystals. Furthermore, the lattice interval was quickly altered by the electron bombardment to about half of the above interval, i.e., 8.2 angstrom, which is compatible with that of the hydroxyapatite crystal. Conclusions: These findings strongly indicate that some apatitic crystals might be created by some conversion mechanism involving an OCP intermediate. Thus the apatitic crystals, which lack in their microstructure the central dark lines (CDLs), might be formed via a pathway involving OCP.