PURPOSE: . This study evaluated the fracture resistance of premolar screwretained implant-supported hybrid abutment crowns (HACs) fabricated from different monolithic restorative materials following artificial aging. MATERIALS AND METHODS: . Forty-four titanium implant analogs were restored with HACs fabricated from four materials: 5 mol% yttria-partially stabilized monolithic zirconia (ST), strength-gradient multilayered zirconia (YM), lithium disilicate ceramic (LD), and resin composite containing dispersed nanoparticles (CM) (n = 11 per group). All specimens were subjected to thermocycling (10,000 cycles) and mechanical loading (1.2 million cycles) to simulate 5 years of clinical service.Fracture resistance was evaluated under compressive loading, and failure modes were analyzed using optical microscopy and scanning electron microscopy.Statistical analysis was performed using the Kruskal-Wallis and Steel-Dwass tests (α = 0.05). RESULTS: . Significant differences were found among all groups (P = 0.00033-0.0022). The YM group exhibited the highest median fracture resistance (2.06 kN, IQR: 2.00 – 2.60 kN), followed by ST (1.74 kN, IQR: 1.69 – 1.80 kN), LD (1.29 kN, IQR: 1.14 – 1.41 kN), and CM (0.87 kN, IQR: 0.79 – 0.92 kN). All specimens survived the artificial aging protocols. Distinct fracture patterns were observed depending on the restorative material, with zirconia-based groups showing more favorable resistance than resin composite. CONCLUSION . All tested HACs exhibited fracture resistance values exceeding maximum bite forces, supporting their clinical applicability. Strength-gradient multilayered zirconia demonstrated superior reliability after simulated 5-year aging, emphasizing its structural advantage and broader safety margin compared with other restorative materials.

PURPOSE: In this study, the shear bond strengths (SBS) of luting cements to fixed superstructure metal surfaces under various seating forces were investigated. MATERIALS AND METHODS: Seven different cements [Polycarboxylate (PCC), Glass-Ionomer (GIC), Zinc phospahate (ZPC), Self-adhesive resin (RXU), Resin (C&B), and Temporary cements ((RXT) and (TCS))] were bonded to a total number of 224 square blocks (5×5×3 mm) made of one pure metal [Titanium (CP Ti) and two metal alloys [Gold-Platinum (Au-Pt) and Cobalt-Chrome (Co-Cr)] under 10 N and 50 N seating forces. SBS values were determined and data were analyzed with 3-way ANOVA. Pairwise comparisons and interactions among groups were analyzed with Tukey's simultaneous confidence intervals. RESULTS: Overall mean scores indicated that Co-Cr showed the highest SBS values (1.96±0.4) (P < .00), while Au-Pt showed the lowest among all metals tested (1.57±0.4) (P < .00). Except for PCC/CP Ti, RXU/CP Ti, and GIC/Au-Pt factor level combinations (P < .00), the cements tested under 10 N seating force showed no significantly higher SBS values when compared to the values of those tested under 50 N seating force (P>.05). The PCC cement showed the highest mean SBS score (3.59±0.07) among all cements tested (P < .00), while the resin-based temporary luting cement RXT showed the lowest (0.39±0.07) (P < .00). CONCLUSION: Polycarboxylate cement provides reliable bonding performance to metal surfaces. Resin-based temporary luting cements can be used when retrievability is needed. GIC is not suitable for permanent cementation of fixed dental prostheses consisting of CP Ti or Au-Pt substructures.
Alloys ; Cementation ; Dental Prosthesis ; Metals ; Polycarboxylate Cement ; Zinc