Impacto de pinos pré-fabricados, anatômicos, fresados em CAD/CAM e universais adaptáveis na resistência de união e microdureza de um cimento resinoso autoadesivo e na resistência à fratura em raízes dentárias enfraquecidas

Abstract

The aim of this study was to evaluate the influence of different glass fiber-based intraradicular retainer systems (prefabricated, anatomical, CAD/CAM milled, and universal 2-piece fiber posts) on the bond strength (BS), microhardness (MH), and

fracture resistance (FR) of teeth with weakened roots. One hundred permanent single- rooted teeth were selected, where 30 teeth had their crowns removed immediately

after the cementoenamel junction (CEJ), and the other 70 teeth had their crowns removed 2 mm above the CEJ, with their roots endodontically treated. The 30 teeth sectioned at the CEJ were selected for experiment 1, and the 70 teeth sectioned 2 mm above the CEJ were selected for experiment 2. In experiment 1, standardized canal preparation was performed, and the roots were divided into 3 groups (n=10) according to the use of different restorative techniques: Control - prefabricated glass fiber post (PFP), CAD/CAM milled glass fiber post (MFP), and universal 2-piece glass fiber post (UFP). After post cementation, six specimens (slices) were obtained for the 10 roots of each group, distributed as follows: coronal third (two slices), middle third (two slices), and apical third (two slices). Fiber posts were cemented using self-adhesive resin cement (RelyX U200/ Solventum). The first slice of each third was selected for the BS test, and the second slice was selected for the Vickers MH test. The obtained BS (MPa) and MH (VHN) data were subjected to 2-factor ANOVA (restorative techniques vs. root region) and Tukey's test (α=0.05). In experiment 2, standardized canal preparation was performed, and the roots were divided into 7 groups (n=10) according to the use of different restorative techniques: PFP (control), anatomical (AFP), MFP and UFP; and different weakened protocols: no weakened (NW), moderate weakened (MW), and severe weakened (SW). Standard preparations for metal-free crowns, milling of indirect crowns, and cementation of crowns were performed for the 10 roots of each group. Subsequently, all roots were evaluated for FR under compression. The obtained FR data were subjected to 2-factor ANOVA (restorative technique vs. weakening

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protocol) and Tukey's test (α=0.05), and Student's t-test for independent samples to compare the experimental groups to the control group. For the BS test, the cervical third presented the highest BS values, while the apical third presented the lowest values (p < 0.001). Among the fiber posts, the MFP and UFP groups showed statistically higher BS values compared to the PFP group (p < 0.001), with no statistical significance between them (p > 0.05). For the MH test, the cervical third presented the highest VHN values, while the apical third presented the lowest values (p < 0.001). Regarding the fiber posts, PFP and UFP showed the highest VHN values, with no difference between UFP and MFP and between PFP and UFP (p < 0.05), only PFP and MFP were statistically different (p < 0.001). For the FR test, 2-factor ANOVA demonstrated that the MW group obtained the highest FR values, showing a statistical difference compared to the SW group (p < 0.05). MFP and UFP presented similar FR values (p > 0.05), being superior to the AFP group (p < 0.001). Student's t-test showed that the MW-MFP group obtained higher FR values than the SW-PFP group (control group) (p = 0.002). The other experimental groups showed no difference when compared to the control group (p > 0.05). It can be concluded that milled glass fiber posts and universal 2-piece fiber posts represent a viable alternative for restoring weakened roots.