Effect of microwave irradiation on properties of an acrylic resin

OBJECTIVE: The aim of this study was to evaluate the flerural strength and hardness of an autopolimerizing acrylic resin for provisional fixed prosthodontics, after microwave irradiation. METHODS: Forty-eigth rectangular specimens (64mm x 10mm x 3,3mm) were manufactured in acrylic resin (Duralay, Reliance Dental Mfg. Co., Worth, II, EUA) and divided in four groups (n=12), according to the heat-treatment: G1- no heat-treatment (negative control); G2- microwave irradiation, 3min/500W; G3- microwave irradiation, 5min/500W; G4- water-bath 90min/74 °C and 30min/100°C (positive control). Specimens were measured using a 3-point bending test. Vickers' hardness was also evaluated. Data were analyzed using 1-way analysis of variance (alpha=.05). RESULTS: The mean values(MPa) and SDs were: G1: 63,5±12,2; G2: 62,7±6,4; G3: 63,0±6,1; G4: 56,8±8,3 (no significant difference, P=0,21). Vickers' hardness values(VHN) and SDs were: Gl: 11,1±0,6; G2: 11,2±0,6; G3: 11,8±0,7; G4: 14,0±0,8 (significant difference, P<0,01). For hardness, Gl, G2 e G3 were similar, however G4 was different (Tukey HSD test, P<0,01). CONCLUSIONS: The microwave irradiation didn't modified the tested mechanical properties in Duralay acrylic resin. However, greater hardness was obtained with water-bath.