Effect of Different Simulated Microwave Disinfection Cycles on Hardness, Roughness and Gloss of Acrylic Resins

Objectives: This study evaluated the effect of microwave disinfection on hardness, roughness and gloss of acrylic resins for denture base. Materials and Methods: Samples (20 mm in diameter and 2 mm in height) were prepared using QC-20, Onda Cryl, Classico, Vipi Cril Plus, Vipi Wave, and Vipi Characterized acrylic resins according to manufacturers' recommendations. After polymerization procedures, the samples were bench cooled, deflasked and conventionally finished and polished. The samples were immersed in glass vessel containing 150 mL of water and subjected to disinfection cycles at 7, 14, 21 and 30 days. Four disinfections of 650 W/1 min was performed in each cycle using microwave oven. The samples were water stored at 37°C between each cycle. Average of three readings for each sample was considered as values of roughness (Ra, µm), Knoop hardness number (50 kgf/10 s), and gloss (GU – 60 degrees). The samples were analyzed at baseline, and after disinfection cycles. Data were submitted to two-way ANOVA for repeated measures considering the factors disinfection and acrylic resin, and followed by Tukey's test (5%). Results: Roughness ranged from 0.295 to 0.842 µm, Knoop hardness from 20.69 to 25.24 KHN, and gloss from 65.52 to 2.74 GU. Conclusions: Roughness, Knoop hardness and gloss values of different acrylic resins for denture base were differentelly influenced after subjected to disinfection cycles at 7, 14, 21 and 30 days. Clinical Relevance: Factors as hardness, roughness, and gloss are essential to avoid the formation of biofilm in prostheses; therefore, the smoother is the denture base, the easier is the cleaning and comfort for the patients, whatever the disinfection method used.