Investigation of fracture strenght of implant abutments and crowns fabricated using different materials

Purpose: Esthetic implant abutments and crowns composed of ceramic and polymer based materials are increasingly employed in restorative dentistry; however, their mechanical durability under functional loading remains uncertain. This in vitro study aimed to evaluate the fracture resistance of implant supported restorations with various abutment crown material combinations, providing evidence based guidance for clinical decision making. Materials and Methods: To simulate a clinical edentulous premolar region in vitro, a total of 90 dental implants (4.1 mm diameter × 15 mm length) were embedded into autopolymerizing acrylic resin blocks. A Ti-base abutment was used for each specimen, and three different abutment materials; monolithic zirconia (5Y-TZP, DD CubeX2, Dental Direkt GmbH), lithium disilicate (IPS e.max CAD, Ivoclar Vivadent), and ceramic- reinforced polymer (breCAM.BioHPP, Bredent GmbH) were designed and fabricated using the CEREC SW CAD/CAM system. The fabricated abutments were bonded to the Ti-base components in accordance with the manufacturer's instructions. Each specimen was then rescanned for the digital design and fabrication of anatomically shaped right maxillary first premolar crowns. Three different monolithic CAD/CAM crown materials were used: 5Y-TZP zirconia (DD CubeX2), advanced lithium disilicate (CEREC Tessera, Dentsply Sirona), and hybrid nano-ceramic (GC Cerasmart, GC Corp.). Based on the combinations of the three abutment and three crown materials, nine experimental groups (n=10) were formed. All crowns were cemented onto the Ti-base abutments using a resin- based luting agent according to the recommended protocol. The samples were subjected to 5000 thermal cycles between two water baths at 5°C and 55°C, with each cycle consisting of 20 seconds in each bath and a 10-second transition time, totaling 60 seconds per cycle. After thermocycling, fracture strength testing was conducted using an Instron Universal Testing Machine (Model 3345). A compressive force was applied perpendicularly to the occlusal surface of each crown with a 6 mm diameter loading tip at a crosshead speed of 1 mm/min, and the fracture load (N) was recorded. The normality xv of the data distribution was assessed using the Kolmogorov-Smirnov and Shapiro-Wilk tests. The main and interaction effects of abutment and crown materials on fracture strength were statistically evaluated using two-way analysis of variance (ANOVA), and Tukey HSD post hoc test was applied for multiple comparisons among significant groups. Results: Statistical analysis revealed significant differences in fracture strenght among the tested groups (p < 0.05). The highest mean fracture strenght was recorded in the zirconia abutment and zirconia crown group (ZR-ZR: 1417 ± 285 N), which was significantly higher than all other combinations, except for the Emax-Zirconia group (EM-ZR: 1349 ± 3.). The EM-ZR group demonstrated significantly greater fracture strenght than the groups using Tessera crowns. There were no statistically significant differences among the groups using GC Cerasmart crowns, regardless of the abutment material, indicating consistent mechanical behavior across different abutments. In contrast, groups utilizing Tessera crowns exhibited generally lower fracture strenght. These findings highlight the superior mechanical performance of zirconia and e.max abutments compared to other materials, while Tessera crowns showed limited resistance under loading. Conclusions: This study demonstrated that the combination of abutment and crown materials has a significant impact on the fracture strenght of implant-supported restorations. The monolithic zirconia abutment and crown combination exhibited the highest fracture strength, while the lithium disilicate abutment combined with a monolithic zirconia crown also showed high mechanical performance. Hybrid nano- ceramic crowns provided consistent fracture strenght across all abutment types, indicating that their mechanical behavior is less affected by the supporting material. In contrast, combinations involving advanced lithium disilicate crowns generally showed lower fracture strength values. These findings suggest that monolithic zirconia and lithium disilicate abutments are more suitable choices in clinical scenarios where high mechanical durability is required. Keywords: Hybrid abutment, ti-base abutment, implant supported crown, CAD/CAM implant restoration, fractural strenght