Effect of two microwave disinfection protocols on adaptation of poly (methyl methacrylate) denture bases

A few protocols of microwave irradiation have been proposed for disinfection of dental prostheses, but their effect on dimensional alteration still is unknown. This study evaluated the effect of 2 protocols of microwave disinfection on adaptation of resin denture bases polymerised by conventional hot water bath or by microwave energy.

Thirty-six resin bases were obtained from stone casts duplicated from a metallic master model of an edentulous maxilla and polymerised by either conventional hot water bath or microwave energy. Experimental disinfection treatments were: 1) control (no disinfection); 2) protocol 1 (690 W/6 min); 3) protocol 2 (345 W/6 min). Disinfection procedures were performed 3 times (T1, T2, T3) with a 7-day interval. Adaptation was measured by weighing a vinyl polysiloxane film reproducing the gap between resin base and master model. Data were analysed by ANOVA for repeated measures and Bonferroni test (a=0.05).

In T1 and T2, all groups polymerised by microwave energy had higher mean values than the groups polymerised by conventional technique. In T3, denture resin bases polymerised by microwave energy had increased poor adaptation when submitted to microwave disinfection at 690 W for 6 min. No significant changes were found for bases submitted to microwave disinfection at 345 W for 6 min (P>0.05).

Adaptation of denture bases varied as a function of polymerisation technique and protocol of microwave disinfection (power and time) over time. Microwave disinfection at 690 W for 6 min proved harmful to denture bases after repeated disinfection procedures.