Effect of Repeated Microwave Disinfection on Surface Hardness and Dimensional Accuracy of Two Type IV Dental Stones

Abstract

There is controversial evidence in relation to the effect of microwave on mechanical properties of stone casts. The present study was designed to evaluate the effect of repeated microwave disinfection on surface hardness and dimensional accuracy of two dental stone. Materials and methods:In this in vitro study, 48 cylindrical stone samples were prepared using two products of type IV stone to assess surface hardness and 48 impression were taken from a model with prepared abutments for long-span bridges and poured by these stones to prepare stone samples to assess the dimensional accuracy. The evaluation of surface hardness and dimensional measurement of the samples were carried out sequencely by a microhardness tester and a digital caliper after the stone samples were exposed to 7 consecutive rounds of 900 watts(W) microwave irradiation for five minutes each time after cooling. Data were analyzed by t-test and ANOVA. Results: The mean surface hardness values of case and control samples in Ernst Hinrichs stone type were 52.17, and 39.81, respectively. For the Dentona stone, mean surface hardness values of case and control samples were 44.53 and 42.89, respectively. According to t-test results, a Dentona stone samples did not show a significant difference in surface hardness after irradiations (P = 0.212), while a statistically significant increase in surface hardness was observed for Ernst Hinrichs samples following irradiations (P = 0.000).With regards to dimensional accuracy, there were no significant differences between case and control samples(P > 0.05). Conclusion: According to the obtained results, multiple disinfections of the stone casts by microwave do not negatively affect their surface hardness and dimensional accuracy