Microwave-cured acrylic resins and silicone-gypsum moulding technique

This study evaluated the residual monomer (RM), Knoop hardness (KHN) and transverse strength (TS) of two microwave-cured acrylic resins (Acron MC(R) (A), GC Dent. Ind. Corp., Tokyo, Japan and Onda Cryl (O), AO Classico Ltda, São Paulo, Brazil) when processed with an all-type III gypsum moulding technique (G) or a silicone-gypsum moulding technique (S). One hundred and forty four specimens were fabricated and equally distributed into four groups (AG, AS, OG and OS). The TS tests were conducted after 48 h of water storage, and KHN values were obtained after 24, 48, 72 h and 30 days. The RM was determined every 24 or 48 h over a period of 288 h. The acrylic resins were prepared and processed according to the manufacturer's directions. Both AS and OS showed the highest means (P < 0.05) for RM (microg cm-2) only after 24 h (AS = 56.84 +/- 27.39/AG = 7.51 +/- 5.75/OS = 3.59 +/- 1.60/OG = 1.02 +/- 0.3), 48 h (AS = 28.99 +/- 9.35/AG = 2.65 +/- 2.17/OS = 2.37 +/- 0.84/OG = 0.68 +/- 0.49) and 72 h (AS = 15.98 +/- 9.01/AG = 1.40 +/- 0.57/OS = 1.87 +/- 0.52/OG = 0.75 +/- 0.44). Both AS and OS showed the highest means (P < 0.02) for KH after 24 h (AS = 18.69 +/- 2.3/AG = 17.79 +/- 0.7/OS = 18.41 +/- 1.0/OG = 16.04 +/- 0.6). After 48 h the mean values for OS and OG differed significantly (P < 0.03) (OS = 18.67 +/- 0.8/OG = 16.75 +/- 0.8). No differences of KHN were found among the groups during the storage periods. The TS values for A and O were not affected by either G or S (P > 0.05). Silicone-gypsum mould technique affected the RM and KHN of the resins in the first 2 and 5 days of analysis, respectively. The type of mould did not affect TS, and the acrylic resins differed from each other for all properties regardless of the type of mould.