Evaluation of the microhardness of materials used in the fabrication of provisional restorations for oral rehabilitation subjected to staining by colorants - an in vitro study

Abstract

Objective: To evaluate the influence of exposure to cola-based, green tea and coffee staining solutions on the Vickers microhardness of acrylic and bis-acrylic resins used in provisional restorations, aiming to understand possible changes related to their mechanical resistance. Methodology: Thirty-two specimens were fabricated, 16 made of bis-acrylic  resin and 16 of acrylic resin, divided into eight groups. Samples were pigmented with water, soluble coffee, cola beverage (Coca-Cola®) and green tea, and remained immersed for seven days with daily replacement of the solutions. After this period, specimens were stored in distilled water for 24 hours. Vickers microhardness was measured with a 100 g load for 15 seconds at three points per specimen, and the arithmetic means were used for statistical analysis. Results: Data were analyzed by ANOVA (p < 0.05). Green tea reduced the microhardness of the acrylic resin (p = 0.027). For the bis-acrylic resin, coffee, Coca-Cola® and green tea caused significant reductions (p < 0.001), with microhardness being lower for green tea compared to Coca-Cola® (p = 0.024). In the control group, the bis-acrylic resin exhibited higher microhardness than the acrylic resin (18.0 vs. 14.5; p = 0.001). Coffee did not affect the microhardness of the acrylic resin. Conclusion: There was a difference in microhardness between the resins, with the acrylic resin showing greater resistance to staining beverages compared with the bis-acrylic resin.