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 f or cariogenicity tests. These blocks are often sterilised to prevent the po ssibility of cross-infection via this route. This study therefore aimed to determine the effect of sterilisation methods on the structural integrity o f artificial enamel caries used for intra-oral cariogenicity tests. Four experimental groups were devised. Ten bovine incisors were used in eac h group. Artificial caries was produced in each tooth which was subsequentl y 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 ste rilisation methods: gamma irradiation (congruent to 25 KGy), steam autoclav ing (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 i n each group were examined for microbial growth after incubation in nutrien t broth for up to 7 days at 37 degrees C under aerobic and anaerobic condit ions. Mineral loss and lesion depth were quantified from microradiographs o f sections from control and sterilised specimens using transverse microradi ography. 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 irradia tion appears the most acceptable method considering the more adverse effect s of the other methods with regards to cariogenicity tests. (C) 1999 Elsevi er Science Ltd. All rights reserved.