Effects of Ethanol on the Surface and Bulk Properties of a Microwave-Processed PMMA Denture Base Resin Rˆ omulo Rocha Regis, DDS, Nat´ ercia Carreira Soriani, DDS, Alessandra Miranda Azevedo, DDS, MSc, Cl ´ audia Helena Silva-Lovato, DDS, PhD, Helena Freitas Oliveira Paranhos, DDS, PhD, & Raphael Freitas de Souza, DDS, PhD Department of Dental Materials and Prosthodontics, School of Dentistry of Ribeir ˜ ao Preto, S˜ ao Paulo, Brazil Keywords Acrylic resins; denture bases; ethanol; surface properties; mechanical stress. Correspondence Raphael Freitas de Souza, Department of Dental Materials and Prosthodontics, University of S ˜ ao Paulo, Ribeir ˜ ao Preto Dental School, Av. do Caf ´ e s/n Bairro Monte Alegre Ribeir ˜ ao Preto S ˜ ao Paulo 14040-904, Brazil. E-mail: raphael@forp.usp.br. Previously presented at the 2007 meeting of the Brazilian Division of the IADR. Accepted August 19, 2008 doi: 10.1111/j.1532-849X.2009.00475.x Abstract Purpose: This study evaluated the effect of different concentrations of ethanol on hardness, roughness, flexural strength, and color stability of a denture base material using a microwave-processed acrylic resin as a model system. Materials and Methods: Sixty circular (14 × 4 mm) and 60 rectangular microwave- polymerized acrylic resin specimens (65 × 10 × 3 mm 3 ) were employed in this study. The sample was divided into six groups according to the ethanol concentrations used in the immersion solution, as follows: 0% (water), 4.5%, 10%, 19%, 42%, and 100%. The specimens remained immersed for 30 days at 37 ◦ C. The hardness test was performed by a hardness tester equipped with a Vickers diamond penetrator, and a surface roughness tester was used to measure the surface roughness of the specimens. Flexural strength testing was carried out on a universal testing machine. Color alterations (E) were measured by a portable spectrophotometer after 12 and 30 days. Variables were analyzed by ANOVA/Tukey’s test (α = 0.05). Results: For the range of ethanol-water solutions for immersion (water only, 4.5%, 10%, 19.5%, 42%, and 100%), the following results were obtained for hardness (13.9 ± 2.0, 12.1 ± 0.7, 12.9 ± 0.9, 11.2 ± 1.5, 5.7 ± 0.3, 2.7 ± 0.5 VHN), roughness (0.13 ± 0.01, 0.15 ± 0.07, 0.13 ± 0.05, 0.13 ± 0.02, 0.23 ± 0.05, 0.41 ± 0.19 μm), flexural strength (90 ± 12, 103 ± 18, 107 ± 16, 90 ± 25, 86 ± 22, 8 ± 2 MPa), and color (0.8 ± 0.6, 0.8 ± 0.3, 0.7 ± 0.4, 0.9 ± 0.3, 1.3 ± 0.3, 3.9 ± 1.5 E) after 30 days. Conclusions: The findings of this study showed that the ethanol concentrations of tested drinks affect the physical properties of the investigated acrylic resin. An obvious plasticizing effect was found, which could lead to a lower in vivo durability associated with alcohol consumption. Acrylic resins are widely used for denture fabrication. 1 A draw- back of these materials is that their esthetic, physical, and me- chanical properties change rapidly over time in the oral envi- ronment. Typical changes are due to sorption, which depends upon liquid absorption and adsorption. 2 Furthermore, it is well known that foods and drinks contain solvents that can chemi- cally soften polymeric dental materials. 3 Ethanol and water are two solvents with deleterious effects for dental materials. Akova et al 4 stated that beverages can soften, degrade, and age dental composites for interim prosthe- ses. The hardness of provisional materials is notably lowered after immersion in food-simulating liquids containing ethanol. 5 Ethanol also enhances the plasticization of the crack tip in poly(methyl methacrylate) (PMMA) 6 and causes irreversible dental composite degradation by penetrating the matrix and expanding the space between polymer chains. 7 Water, on the other hand, is a complex solvent because of its possible strong interaction with the polymer, due to its polarity and ability to form hydrogen bonds. Thus, there is a tendency for it to cluster and cause plasticization of the material matrix. 8 A high percentage of elderly people consume ethanol- containing beverages. 9 Ethanol is present in several drinks and has been shown to soften the denture base PMMA. 10 The me- chanical behavior of PMMA can be affected by the presence of ethanol according to the following mechanisms: 11 first, it presents a long-term dissolution on the surface of unloaded resin; second, a stress crazing effect is expected at points of high stress concentration. In general, there are scarce reports of the effect of ethylic solutions simulating food contents on denture base mate- rials, mostly restricted to mechanical properties. Regard- ing other properties, it has been described that alcoholic Journal of Prosthodontics 18 (2009) 489–495 c  2009 by The American College of Prosthodontists 489