Color Changes of Self-Polymerizing Acrylic Resin in Various Soaking Environments

Objectives: Acrylic resins are self-polymerized composite resins highly used in provisional crowns and removable dentures that change color over time. This research aimed to evaluate four factors that affect staining, including roughness, temperature, solutions and time.
Methods: The PMMA specimen was prepared by mixing powder and liquid (supplied by UNIFAST^TM Trad, GC, Tokyo, Japan) with the proportion of 4:3 and manually stirring for 15 second. Then instantly fill it into the mold (6.6*6.6*3.6 mm³) and apply a flat glass board on the mold until it fully dried. Totally 90 specimens (N=5) were randomly divided into three surface roughness (abrasive paper: P150, P240, P600), three different solutions (water, coffee, and mouthwash), two different temperatures (37°C and 4°C), and three different soaking time (5, 7, and 12 day continuously). CIELAB coordinates (L*a*b) were measured before and after the soaking process to calculate the deviations, and the surface roughness of specimen was measured before soaking experiment.
Results: The results show that all four factors (surface roughness, soaking solution, soaking time, and soaking temperature) hold a significant effect in ΔL (P<0.05). Soaking solutions and roughness significantly affect Δa (P<0.05). Soaking solutions and temperature hold a significant effect in Δb (P<0.05).
Conclusions: The conclusion was that all four factors (roughness, temperature, solutions and time) affect the color change of acrylic resins, especially since the different solutions would affect the main color change (ΔL, Δa, Δb).