In‑Vitro Comparison of Screw Loosening, Fracture Strength and Failure Mode of Implant‑Supported Hybrid‑Abutment Crowns and Screwmentable Crowns Manufactured with Different Materials

Abstract

Background: Hybrid‑abutment crowns and screwmentable crowns offer a fusion of the benefits from both screw and cement‑retained  restorations, potentially enhancing the overall performance of the restoration. 

Aim: This study aimed to evaluate the screw loosening  and fracture strength of hybrid-abutment crowns and screwmentable crowns made with two different materials. 

Methods: Forty single- crown were made on titanium implants and divided into four groups (n = 10) [SM-Ti: Screwmentable titanium-porcelain crowns on stock  titanium abutment; SM-Zr: Screwmentable zirconia-porcelain crowns on stock zirconia abutment; AC-Ti: Titanium-porcelain abutment  crowns; AC-Zr: Zirconia-porcelain abutment crowns.] Specimens were torqued with 30 NCm and thermocycled between 5℃ and 55℃ in  20‑second cycles for 5000 cycles. Removal torque values (RTV) were measured. Following the RTV measurement, the screws were  changed with fresh screws and torqued again. Afterwards, specimens were loaded to fracture and fracture strengths were recorded,  failure modes were examined. Statistical Analysis Used: Analysis of variance and Bonferroni test was performed.

Results: The AC-Ti group  displayed the highest mean torque loss (%20.09 ± 6.49) and the SM-Ti group displayed the lowest (%9.59 ± 8.84). Only the difference  between AC‑Ti and SM‑Ti groups was found statistically significant, there are no significant differences between other groups. The fracture strengths are 385.84 ± 27.68 N, 313.18 ± 39.97 N, 272.69 ± 35.03 N, and 156.71 ± 19.83 N for AC-Ti, AC-Zr, SM-Ti, and SM-Zr groups,  respectively and all differences were found to be statistically significant. Failures occurred as deformation in titanium components,  whereas fractures were observed in zirconia components. 

Conclusion: Screw loosening was observed only in the AC-Ti group. No  significant difference was observed among the torque loss values in the remaining groups. Titanium and zirconia materials do not exert  any influence on screw loosening after thermal aging for hybrid-abutment crowns. Moreover, when assessing fracture strength, hybrid- abutment crowns exhibit superior strength and durability compared to screwmentable crowns.