Comparação das propriedades mecânicas e superficiais de diferentes resinas acrílicas utilizadas na confecção de placas estabilizadoras

Abstract

Introduction: Currently, different types of acrylic resins have been used for the fabrication of occlusal splints. These resins may be processed using different manufacturing techniques, which may result in differences in their physicomechanical properties. Objective: To compare the surface roughness, hardness, flexural strength, and failure patterns of different acrylic resins used for the fabrication of occlusal splints processed by distinct manufacturing techniques: chemically activated acrylic resin (CAAR), heat-activated acrylic resin (HAAR), 3D-printed resin (PR), and milled resin (MR). Methods: Fifteen bar-shaped specimens (65 × 10 × 2.5 mm; ISO 20795- 1) were fabricated for each experimental group. Specimens from the HAAR (Artigos Odontológicos Clássico Ltda.) and CAAR (Artigos Odontológicos Clássico Ltda.) groups were produced using flask molds according to their respective conventional polymerization protocols. For the MR (SmileFind Dental) and PR (Smart Print) groups, the specimens were initially designed as STL files using CAD technology with MillBox 2023 (CIMsystem, Italy) and CHITUBOX Dental version 1.2 (CBD-Tech/Chitu Systems, China), respectively, and subsequently manufactured according to the corresponding CAM technology for each group. After fabrication, all specimens were polished with 600-, 1200-, and 2000-grit silicon carbide abrasive papers using a mechanical polishing machine, followed by ultrasonic cleaning in isopropyl alcohol for 5 minutes and storage in distilled water at 37 °C for 48 hours. Surface roughness (Ra) was measured using a contact profilometer (0.25 mm cutoff; 0.5 mm/s; n = 15), flexural strength was determined by a three-point bending test (100 kgf; 5 mm/min; n = 12), and Knoop hardness was evaluated using a microhardness tester (n = 3; three indentations per specimen spaced 16 mm apart; 10 s; 50 g). Failure patterns were analyzed using a stereomicroscope at 12× magnification. Quantitative data were analyzed by one-way analysis of variance (ANOVA) followed by Tukey's post hoc test (α = 0.05). Results: The printed resin exhibited significantly lower surface roughness (CAAR: 0.17 ± 0.06 µm; HAAR: 0.14 ± 0.06 µm; MR: 0.14 ± 0.08 µm; PR: 0.11 ± 0.03 µm; p = 0.006) and higher flexural strength (CAAR: 125.10 ± 19.20 MPa; HAAR: 126.43 ± 21.41 MPa; MR: 150.58 ± 16.73 MPa; PR: 161.84 ± 13.89 MPa; p < 0.001) than the other groups, which did not differ significantly from one another for these properties. Knoop hardness was significantly higher for the heat-activated acrylic resin (CAAR: 15.47 ± 1.04 HK; HAAR: 18.62 ± 2.03 HK; MR: 18.50 ± 1.60 HK; PR: 17.62 ± 0.73 HK; p < 0.001) compared with the other groups, which also showed no significant differences among themselves. Failure pattern analysis demonstrated that all fractures, regardless of the group, originated from the tensile stress region; however, the PR group exhibited a more well-defined and clearly demarcated fracture pattern than the other groups. Conclusion: The choice of material and processing technique directly influences the final quality of occlusal splints. Milled acrylic resins appear to be the most suitable option when superior mechanical and surface performance is desired.