Comparison of Screw Loosening and Fracture Resistance in Different Hybrid Abutment Crown Restorations After Thermomechanical Aging.

PURPOSE: To investigate the screw loosening and fracture resistance of different hybrid abutment crown restorations after thermomechanical aging.

MATERIALS AND

METHODS

Restorations were produced from zirconia, lithium disilicate, and hybrid ceramics with a CAD/CAM system (n = 10). Restorations and titanium bases (Ti-bases) were cemented, and the abutment screws were torqued to 30 Ncm. They were retorqued after 10 minutes, and then the removal torque values (RTVs) were measured. After 250,000 and 500,000 cycles of thermomechanical aging were completed, the RTVs were measured again, and removal torque loss (RTL) ratios were calculated. The specimens were subjected to a fracture resistance test after 750,000 cycles of thermomechanical aging, and the load at failure was recorded as the fracture resistance (N). The results were statistically analyzed (α = .05).

RESULTS

Aging was effective on the RTVs and RTL ratios (P < .001). The highest RTV was observed before aging; however, the RTVs significantly decreased and RTL ratios significantly increased after aging (P < .05). The fracture resistance values significantly differed among the ceramic materials. All lithium disilicate and hybrid ceramic specimens showed restoration fracture and most of the zirconia specimens showed Ti-base-related failure.

CONCLUSIONS

Hybrid abutment crowns made of zirconia, lithium disilicate, and hybrid ceramics can withstand the average occlusal forces in the molar region; however, the ceramic type may affect the failure type. Retightening of the abutment screws after 10 minutes following the first tightening and annually may be beneficial to prevent the adverse effects of screw loosening on the integrity of the implant-abutment connection.