Polishing Methods' Influence on Color Stability and Roughness of 2 Provisional Prosthodontic Materials.

PURPOSE: To evaluate the roughness and color change of a conventional acrylic resin and a bis-acryl resin, submitted to different types of polishing and exposed to a staining solution. MATERIALS AND METHODS: One hundred specimens were manufactured from an autopolymerizing conventional acrylic resin (Duralay, shade 66) (n = 50) and a bis-acryl resin (Protemp 4, shade A3) (n = 50) according to the manufacturers' instructions. Specimens were subdivided into 10 groups (n = 10), according to the type of resin and polishing method, including no-polishing (control groups for acrylic resin [tungsten bur finishing] and bis-acryl resin [cotton and alcohol]), Enhance System, Edenta kit, Labordental kit, and sandpaper. The specimens were immersed in a staining solution (coffee at 60°C) for 7 days. Surface roughness was evaluated before the first immersion (baseline - Ra1) and after 7 days (Ra2). The color change (∆E) was determined after 24 hours (∆E1) and 7 days (∆E2), by CIE L* a* b* scale. Data were statistically analyzed with 3-way ANOVA for repeated measures test and Tukey test (α = 0.05). RESULTS: According to 3-way ANOVA test, material, polishing techniques, and polishing*material factors exhibited statistically significant influence (p < 0.0001) on the roughness, and, for color change, material, polishing techniques, time, polishing*material, and material*time factors were statistically significant (p < 0.0001). The polishing techniques successfully reduced the surface roughness of acrylic resin groups, when compared to control (p < 0.001), but for bis-acryl resin, results were not different from the control group (Enhance: p = 0.954, Edenta: p = 0.866, sandpaper: p = 0.366, Labordental: p = 0.945). Surface roughness was not affected by the immersion in staining solution for 7 days. Color change of acrylic resin groups after 24 hours and 7 days of immersion exhibited a clinically acceptable value (ΔE < 3.7) with the exception of the Enhance group, and all bis-acryl resin groups exhibited a clinically unacceptable color change value (ΔE > 3.7) independent of polishing technique and time interval (∆E1 and ∆E2). CONCLUSIONS: Roughness of both materials was similar when the polishing techniques studied were performed, although Ra values were superior to the clinically acceptable values (0.20 µm), and were not affected by the immersion protocol studied; however, when esthetics are critical, the selection of material type is more important than the surface treatment technique used, and bis-acryl resin was more susceptible to clinically unacceptable color change after immersion in a staining solution.

Effect of water storage on microshear bond strength of four dental adhesive systems to dentin

AIM: To evaluate the microshear bond strength of 4 dental adhesive systems after 1 year-water storage. MATERIAL AND METHODS: The sample consisted of 120 cylinders of composite, obtained from 24 bovine incisors, which were divided into four experimental groups: G1-Scotchbond Multi-Purpose, G2-Single Bond 2, G3-Clearfil SE Bond, G4-Adper Easy One and two storage times in distilled water: T0 - 24h and T1 - 1 year. A bivariate analysis was performed using the ANOVA and Tukey test (α=0.05). Results were evaluated inter-and intra-group in both times. RESULTS: After 24 hours, G1T0 (39.68A ± 11.55) showed higher bond strength (MPa) followed by G2T0 (22.71B ± 4.07), G3T0 (18.94BC ± 7.29) and G4T0 (13.30C ± 3.94). After 1 year of storage only G1T1 (33.95A ± 6.35) and G3T1 (13.59BC ± 2.63) maintained the bond strength values (p ≥ 0.05), while G2T1 (10.62C ± 4.32) and G4T1 (4.49D ± 2.49) presented a decrease in this values. CONCLUSION: The hydrophobic two-step adhesive systems maintained the bond strength after 1-year water storage.