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Background/purpose: Recently, an effective core build-up system for teeth with flared root canals is needed. This research aimed to evaluate the effect of foundation restorations using a composite resin core with a fiber post reinforced with a zirconia tube for the surface strain at the cervical area and the fracture load of teeth with flared root canals. Materials and methods: Bovine teeth were shaped to mimic human premolars with flared root canals and restored using three types of composite resin foundation restorations with each materials described below: a fiber post (FC), a zirconia tube (ZC), a fiber post and zirconia tube (ZFC). Each specimen was restored with a zirconia crown. The surface strains of the specimens at the cervical area and fracture loads were analyzed using a one-way analysis of variance (ANOVA), followed by Tukey's honest significant difference test. Results: The surface strains of Groups ZFC and ZC were significantly lower than that of Group FC in the buccal root. The fracture strengths of Groups ZFC and ZC were significantly higher than that of Group FC. The strength of Group ZFC was significantly higher than that of Group ZC. Conclusion: The use of a composite resin core with a zirconia tube for the simulated premolar with flared root canals reduced surface strain at the cervical area and provided higher fracture strength compared to using a composite resin core with a fiber post. And the zirconia tubes provided even higher fracture strength when used with a fiber post.
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Background/purpose: 4-methacryloyloxyethyl trimellitate anhydride/methyl methacrylate-tri-n-butyl borane (4-META/MMA-TBB) resin is used for indirect restorations. We aimed to evaluate effects of immersion in 4-META/MMA-TBB-activated liquid on the bond strength of root canal dentin. Materials and methods: We used freshly extracted single-rooted human teeth. After decoronation, each root was vertically sectioned into halves; their dentin walls were polished and flattened. The control group underwent dentin treatment with Green Activator. The immersion group was treated with Green Activator and Teeth Primer and immersed in 4-META/MMA-TBB-activated liquid. After bonding the resin blocks with Super-Bond, microtensile bond strength (µTBS) tests were performed (n = 6), and fracture surfaces were analyzed. Before surface treatment, dentin was immersed in a sodium fluorescein solution for 3 h, and resin blocks were bonded with Super-Bond with rhodamine B as in the bond strength test. The bonded cross section was observed using confocal laser scanning microscopy (CLSM). Results: µTBS was significantly higher in the immersion group than in the control group (61.5 [51.3-66.7] vs. 33.0 [20.4-57.8] MPa; P < 0.05). Fracture mode analysis showed that, compared with the control group, the immersion group had a significantly lower rate of adhesive failure at the dentin interface and a significantly higher rate of cohesive failure in Super-Bond (P < 0.01). CLSM showed a water droplet-like accumulation of fluorescein dye above the hybrid layer in the control group, not in the immersion group. Conclusion: Immersion in a 4-META/MMA-TBB-activated liquid inhibited water exudation from the root canal dentin and improved the bond strength.
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Background/purpose: Retainer debonding of resin-bonded fixed dental prostheses (RBFDPs) is one of the major reasons for their lower survival rates than fixed dental prostheses (FDPs) with full-coverage crowns. Recent advances in milling technology have enabled the fabrication of RBFDPs with complex retainers (D-shaped designs). This study aimed to assess the marginal fit and retention force of zirconia RBFDPs with inlay-, L-, and D-shaped designs to clarify their clinical applications. Materials and methods: Three abutment teeth models without maxillary second premolars were created using inlay-, L-, and D-shaped retainer designs. The zirconia RBFDPs were designed and fabricated according to the manufacturer's instructions (n = 10). The marginal gap was measured using the silicone replica technique. Zirconia frameworks were bonded to the abutment teeth using resin cement. Tensile test was conducted after thermal cycling and dynamic loading tests. The loads during debonding or fracture were recorded. The failure pattern was analyzed by observing the fracture surface using a scanning electron microscope. Results: D-shaped RBFDPs showed a significantly larger marginal gap than inlay- and L-shaped RBFDPs (P < 0.05). However, the mean marginal values were clinically acceptable (<120 µm). The D-shaped model exhibited the highest tensile strength in the tensile tests. The inlay-shaped and most of the D-shaped RBFDPs experienced debonding with cohesive failure, whereas the L-shaped RBFDPs showed fractures near the connector. Conclusion: The D-shaped retainer design was superior to the inlay- and L-shaped designs with respect to the inhibition of retainer debonding. However, the marginal fitness needs to be improved.