Fracture Strength of Implant-Supported Hybrid Abutment Crowns: An In Vitro Study of Ceramic and Polymer-Based Materials in the Premolar Region

<b>Background/Objectives</b>: Ceramic and polymer-based abutments and crowns are increasingly used for esthetic implant restorations, but their mechanical reliability under functional loading remains unclear. This study aimed to evaluate the fracture strength of implant-supported restorations with different abutment-crown material combinations. <b>Methods</b>: Ninety titanium implants (4.1 × 15 mm; BEGO, Germany) were restored with nine combinations of CAD/CAM-fabricated abutment and crown materials (zirconia, lithium disilicate, and ceramic-reinforced polymer; crowns of zirconia, advanced lithium disilicate, and hybrid nanoceramic; <i>n</i> = 10 per group). Ti-base abutments were bonded and cemented following material-specific surface treatments and thermocycled 5000 times (5-55 °C). Fracture tests were performed under static vertical loading at 1 mm/min in a universal testing machine. Data were analyzed using two-way ANOVA and Tukey HSD (α = 0.05). <b>Results</b>: Fracture resistance differed significantly among groups (<i>p</i> < 0.001). The highest mean strength was obtained for zirconia abutment-zirconia crown restorations (1417 N), followed by lithium-disilicate abutment-zirconia crown (1349 N), whereas BioHPP abutment-Tessera crown showed the lowest (823 N). Hybrid composite (Cerasmart) crowns exhibited stable performance across abutments, while Tessera crowns showed lower resistance. BioHPP abutments produced only crown-level fractures (<i>p</i> = 0.004), indicating a more reparable failure mode. <b>Conclusions</b>: Zirconia-based combinations showed the highest fracture resistance and are suitable for posterior use. Clinicians should balance strength with esthetics when considering translucent materials like advanced lithium disilicate or hybrid ceramics. Long-term clinical studies are needed to confirm these results and guide material selection.