Passivity, torque stability, and fracture resistance in screw-retained and dual-retained metal-ceramic implant-supported restorations: an in vitro study, part II.

BACKGROUND

This study aimed to compare the passivity, screw torque stability, and fracture resistance between dual- and screw-retained implant restorations, before and after thermomechanical loading.

METHODS

Twenty metal-ceramic restorations were divided into two groups (n = 10 each). Group 1 (G1) featured dual-retained restorations on prefabricated titanium abutments, while Group 2 (G2) had screw-retained restorations on UCLA chromium-cobalt cast-to abutments. Passivity, adjustment ease, and torque loss were compared, along with fracture resistance and mode, post-fabrication and after thermomechanical loading (500 thermal and 500,000 mechanical loading cycles). Independent t-tests and Mann-Whitney U tests were used to compare passivity characteristics and fracture resistance, while torque losses were analyzed using a generalized estimating equations (GEE) model with LSD post-hoc test (α = 0.05).

RESULTS

G1 required significantly less adjustment time and frequency (P < .001) and exhibited a lower torque angle (higher passivity) (P = .001) compared to G2. In G1, the screw torque loss (%) measured 24.02 ± 3.01 before and 36.51 ± 4.28 after loading compared to the initial torque and 16.17 ± 3.67 after loading compared to the detorque value. In G2, these values were 24.76 ± 3.45, 39.9 ± 2.55, and 20.1 ± 3.96, respectively. While the rate of torque loss did not differ significantly before loading, it was significantly higher in G2 after loading (P < .05). Fracture resistance was significantly higher in G1 (P < .05). Both groups exhibited a mixed type of failure mode.

CONCLUSIONS

Dual-retained metal-ceramic restorations outperformed screw-retained counterparts, demonstrating improved passivity, lower screw torque loss percentages, and higher fracture resistance.

CLINICAL TRIAL NUMBER: Not applicable.