Resistência à fratura de raízes fragilizadas reabilitadas com pinos de fibra de vidro reembasados ou fresados

Abstract

The aim of the present study was to compare the fracture resistance of weakened roots restored with CAD/CAM milled GFPs to the prefabricated ones, relined with two different resins. For this experimental in vitro laboratory study, seventy bovine incisors were endodontically treated and divided into seven groups (n=10), according to the weakening protocol (medium: 1mm of remaining dentin around the root canal; or highly: 0.5mm of remaining dentin) and the post anatomization technique. The control group was non-weakened, and the GFP was directly luted. In groups MW-Z350 and HW-Z350, medium weakened (MW) or highly weakened (HW) roots were restored with a GFP relined with conventional nanoparticle composite resin. In MW-Bulk fill and HW-Bulk fill groups, MW or HW roots were restored with a GFP relined with Bulk fill resin. In MW-M and HW-M groups, MW or HW roots were restored with a milled GFP. After thermomechanical cycling (88 N, 3.8 Hz, 1,200,000 cycles, thermal equilibrium between 5°C and 45°C), the roots were submitted to compression in a universal testing machine until fracture. The failure mode was analyzed under a stereomicroscope (7.5x), and the frequencies were compared by the chi-square test. The groups were compared by two-factor ANOVA, Tukey's post hoc, and T-test at a 5% significance level. The mean value of fracture resistance (kgf) was 47.5for the control group. In the groups with medium weakening protocol, the values were 65.5in the MW-Bulk fill group, 63.4in the MW-Z350 group, and 56.4in the MW-M group. In the highly weakened groups, 72.7in the HW-Bulk fill group, 65.7in the HW-Z350 group, and 16.8in the HW-M group. The HW-M group obtained the lowest values, showing a significant difference compared to all groups (p < 0.001), and the highest value was HW-Bulk fill, with a significant difference compared to MW-M (p = 0.037) and HW-M (p < 0.001). Compared to control, MW-Bulk fill, MW-Z350, HW-Bulk fill, and HW-Z350 showed higher fracture resistance values; HW-M, lower value, and MW-M no difference. In the control group, the frequency of repairable fractures was 100%, and in the groups with moderate and highly weakening the frequency was 87% and 63%, respectively. It was concluded that the highly weakened roots rehabilitated with milled GFP showed lower fracture resistance values than control group and the relined ones. However, the failure pattern in all groups was predominantly repairable. The remaining tooth structure was determinant for dental survival since teeth with high weakened samples showed a higher frequency of catastrophic failures.