Effect of sterilisation methods on the structural integrity of artificial enamel caries for intra-oral cariogenicity tests.

Enamel blocks bearing artificial caries are used in intra-oral appliances for cariogenicity tests. These blocks are often sterilised to prevent the possibility of cross-infection via this route. This study therefore aimed to determine the effect of sterilisation methods on the structural integrity of artificial enamel caries used for intra-oral cariogenicity tests. Four experimental groups were devised. Ten bovine incisors were used in each group. Artificial caries was produced in each tooth which was subsequently cut into two halves. One half of each tooth was reserved as control while the other was sterilised. The four groups were subjected to respective sterilisation methods: gamma irradiation (approximately equal to 25 KGy), steam autoclaving (121 degrees C for 15 min), sodium hypochlorite (12% w/v for 24 h) and povidone-iodine (7.5% w/v for 24 h). The control and sterilised specimens in each group were examined for microbial growth after incubation in nutrient broth for up to 7 days at 37 degrees C under aerobic and anaerobic conditions. Mineral loss and lesion depth were quantified from microradiographs of sections from control and sterilised specimens using transverse microradiography. Data were analysed statistically by paired Student's t-test. Microbial growth was observed only in control specimens. Gamma irradiation and NaOCL caused cream discolouration and bleaching of the enamel surface, respectively. Autoclaving, sodium hypochlorite and povidone-iodine resulted in further demineralisation of the lesions. The four sterilisation methods were all effective sterilants for artificial caries. However, gamma irradiation appears the most acceptable method considering the more adverse effects of the other methods with regards to cariogenicity tests.