Preparation of dental enamel for use in intraoral cariogenicity experiments

Dental enamel of human or bovine origin finds use in human intraoral cariogenicity testing. Such material must be sterile, and this is commonly achieved using ethylene oxide. The choice of this gas as a means of sterilization in cariogenicity work was vindicated when it failed in experiments to produce significant changes in the hardness of bovine enamel specimens. The gas is, however, shortly to become unavailable on environmental grounds. Alternatives investigated include autoclaving and gamma irradiation. Autoclaving produced significant softening of bovine enamel, the changes in microhardness recorded being similar to those produced by some experimental cariogenic substrates. Gamma irradiation caused no significant changes in enamel hardness. Recent in vitro work has, however, shown that enamel may gain resistance to artificial caries attack, and exhibit decreased acid solubility, following exposure to ionizing radiations. The results of experiments in which the test enamel was sterilized by this means may therefore lack comparability with experiments using an alternative sterilization method. However, with this qualification, gamma irradiation appears the most appropriate replacement for ethylene oxide.