Thermal-cycling, simulated brushing, and beverages induced color changes and roughness of CAD/CAM poly (methyl methacrylate) denture resins

Abstract

The aim of the present study was to evaluate and compare the effect of thermal-cycling, mechanical brushing and beverage storage on the colour changes and surface roughness of conventional heat-polymerized and CAD/CAM PMMA used to fabricate complete dentures. A total of 100 specimens measuring 10 mm in diameter and 3 mm in thickness were fabricated from conventional PMMA resin (Heat-cured, Major. Base.20, Moncalieri, Italy) and CAD/CAM blocks (Opera system, Principauté de Monaco, French). The specimens were subjected to a combined surface treatment involving thermo-cycling, mechanical brushing, and immersed in either artificial saliva (AS), coffee, tea, Coca-Cola, or lemon juice. Colour differences (ΔE) and surface roughness (Ra) was determined using a spectrophotometer and non-contact profilometer, respectively. The data were analyzed using IBM SPSS v.20 (α = 0.05). Factorial ANOVA showed that independent factors, namely material, beverages, and the interaction between independent factors, significantly influenced ΔE (F = 76.862; p < 0.001) and surface roughness (F = 71.685; p < 0.001). The overall highest and lowest colour differences was obtained for CAD/CAM PMMA (ΔE = 1.93 ± 1.29) and conventional PMMA (ΔE = 1.41 ± 1.39) resins, respectively (p = 0.061). Conventional PMMA (1.22 ± 0.20) demonstrated significantly increased roughness compared to CAD/CAM PMMA (0.91 ± 0.17) (p < 0.001). Pearson correlation showed a low degree of correlation, which was non-significant for both the PMMA (r = 0.015; p = 0.917) and C-PMMA materials (r = 0.097; p = 0.505). CAD/CAM milled PMMA resins demonstrated greater colour change and lower surface roughness compared to conventional heat-polymerized PMMA resins. Specimens in tea and coffee demonstrated maximum colour changes and were perceivable by the human eye. On the contrary, specimens immersed in low pH acidic beverages namely Coca-Cola and lemon juice demonstrated maximum surface roughness.