A B S T R A C TObjectives: The study evaluated the fracture resistance and fracture patterns of endodontically treated mandibular first molars restored with glass-fiber-reinforced direct composite restorations. Methods: In total, 60 extracted intact first molars were treated endodontically; a mesio-occluso-distal (MOD) cavity was prepared and specimens were then divided into six groups: sound teeth (G1), no restoration (G2), direct composite restoration (G3), fiber-post-supported direct composite restoration (G4), direct composite reinforced with horizontal mesio-distal glass-fibers (G5), and buccal-palatal glassfibers (G6). Specimens were subjected to 5000 thermocycles and 20,000 cycles of 45 oblique loading force at 1.3 Hz and 50 N; they were then loaded until fracture. The maximum fracture loads were recorded in Newtons (N) and data were analyzed with one-way ANOVA and post-hoc Tukey tests (p < 0.05). Fractured specimens were analyzed with a scanning electron microscope (SEM). Results: The mean static loads (in Newtons) were: G1, 831.83; G2, 282.86; G3, 364.18; G4, 502.93; G5, 499.26; and G6, 582.22. Fracture resistance did not differ among G4, G5, and G6, but was significantly higher than G3 (p = 0.001). All specimens fractured in a catastrophic way. In G6, glass fibers inducted a partial deflection of the fracture, although they were not able to stop crack propagation. Conclusions: For the direct restoration of endodontically treated molars, reinforcement of composite resins with glass-fibers or fiber posts can enhance fracture resistance. The SEM analysis showed a low ability of horizontal glass-fibers to deviate the fracture, but this effect was not sufficient to lead to more favorable fracture patterns above the cement-enamel junction (CEJ). Clinical significance: The fracture resistance of endodontically treated molars restored with direct composite restorations seems to be increased by reinforcement with fibers, even if it is insufficient to restore sound molar fracture resistance and cannot avoid vertical fractures.

The first null hypothesis has to be rejected since DC% and MH of the dual-cements tested were influenced by the curing time. The second null hypothesis is partially rejected since the bond strength was influenced by the curing time only for Rely-X Ultimate.

The purpose of this in vitro study was to evaluate the external marginal gap variation with a 3D quantitative method and the residual fracture resistance after cyclic fatigue in endodontically treated molars restored with overlays of different materials, with and without fiber posts-supported buildups. Forty-eight human maxillary molars were selected, endodontically treated, prepared with standardized MOD cavities and randomly allocated into 6 study groups considering the “core strategy” (build-up with composite resin; build-up with composite resin supported by a fiber post); and the “restorative material” of the indirect adhesive overlay (GrandioBlocks, Voco; Cerasmart, GC; CeltraDuo, Dentsply). All procedures were executed according with manufacturers guidelines. Micro-CT analysis prior and after cyclic fatigue were executed, followed by scanning electron microscope analysis and fracture resistance test. The Two-Way ANOVA analysis showed that interfacial gap progression was significantly influenced by the “core strategy” (p < 0.01) but not of “restorative material” (p = 0.59). Concerning fracture resistance, “restorative material” was statistically significant (p < 0.01), while “core strategy” (p = 0.63) and the interaction (p = 0.84) were not. In conclusion, the fiber post presence within the build-up promoted a lower interfacial gap opening after fatigue, evaluated through micro-CT scans. In terms of fracture resistance, teeth restored with Cerasmart and Celtra Duo were statistically similar, but superior to GrandioBlocks.

Clinical Relevance Using a material that optimizes marginal seal when using a margin elevation technique to manage deep class II cavities should enhance clinical outcomes.

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Objectives To evaluate three‐dimensional external gap progression after chewing simulation of high translucency zirconia (HTZ) and zirconia‐reinforced lithium silicate (ZLS) applied on endodontically treated teeth with different preparation designs. Materials and Method Endodontically treated molars were prepared with low‐retentive (adhesive overlay) and high‐retentive (full crown) designs above cementum‐enamel junction and restored with HTZ and ZLS. Micro‐computed tomography analysis was assessed before and after chewing simulation to evaluate three‐dimensionally the external gap progression. Results were statistically analyzed with two‐way ANOVA and post‐hoc Tukey test. Results High‐retentive preparation design had a significantly inferior gap progression compared to the overlay preparation (p < 0.01); ZLS exhibited a significant inferior gap progression compared to HTZ (p < 0.01). Conclusions High‐retentive preparations restored with ZLS seem to better perform in maintaining the sealing of the external margin after cyclic fatigue. Clinical significance The clinician should pay attention to the proper combination of preparation designs and ceramic material selection for an endodontically treated molar restoration. HTZ seems to perform worse than lithium silicate in terms of marginal sealing, still showing lacks in resistance to cyclic fatigue when adhesive preparations are performed.

The aim of the present study was to evaluate the fatigue to cyclic and static resistance of indirect restorations with different preparation designs made either of lithium disilicate (LS) or polymer-infiltrated ceramic network (PICN). Eighty-four (n = 84) molars were chosen, endodontically treated, and prepared with standardized MOD cavities. The molars were randomly divided into 6 study groups (n = 14) taking into account the “preparation design’’ (occlusal veneer with 1.2 mm occlusal thickness; overlay with 1.6 mm occlusal thickness; adhesive crown with 2 mm occlusal thickness) and the “CAD/CAM material’’ (E-max CAD, Ivoclar vivadent; Vita Enamic, Vita). A fatigue test was conducted with a chewing simulator set at 50 N for 1,500,000 cycles. Fracture resistance was assessed using a universal testing machine with a 6 mm diameter steel sphere applied to the specimens at a constant speed of 1 mm/min. A SEM analysis before the fracture test was performed to visually analyze the tooth-restoration margins. A statistical analysis was performed with a two-way ANOVA and a post-hoc pairwise comparison was performed using the Tukey test. The two-way ANOVA test showed that both the preparation design factor (p = 0.0429) and the CAD/CAM material factor (p = 0.0002) had a significant influence on the fracture resistance of the adhesive indirect restorations. The interaction between the two variables did not show any significance (p = 0.8218). The occlusal veneer had a lower fracture resistance than the adhesive crown (p = 0.042) but not lower than the overlay preparation (p = 0.095). LS was more resistant than PICN (p = 0.002). In conclusion, in the case of endodontically treated teeth, overlay preparation seems to be a valid alternative to the traditional full crown preparation, while occlusal veneers should be avoided in restoring non-vital molars with a high loss of residual tooth structure. LS material is more resistant compared to PICN.

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