Effect of Titanium Base Abutment Height and Restorative Material on Torque Maintenance of Hybrid Abutment Restorations with Offset Implant Placement.

Abstract

Purpose: To evaluate the effect of titanium base height on torque loss of monolithic zirconia, lithium disilicate, and polymer-infiltrated ceramic hybrid abutment restorations for an offset placed implant.

Materials and methods: A total of 42 hybrid abutment restorations supported by offset implant placement (4.2-mm diameter, 10-mm length) were divided into six groups: short titanium base and zirconia (SZ), long titanium base and zirconia (LZ), short titanium base and lithium disilicate (SE), long titanium base and lithium disilicate (LE), short titanium base and polymer-infiltrated ceramic (SP), and long titanium base and polymer-infiltrated ceramic (LP). An adhesive resin cement was used to bond the restoration to the titanium base. The restoration was secured with a titanium screw, tightened to 30 Ncm using a calibrated torque meter device. The specimens were exposed to thermocycling (5,000 cycles at 5°C to 55°C), then cyclic loading (120,000 cycles, 50 N, 1.6 Hz), where the load was placed vertically in the mesial fossa of the restoration. The loosening torque value of the abutment screw was measured by the torque meter device, and then the torque loss and its percentage were calculated. Two-way and one-way ANOVA and post hoc Tukey tests were used for statistical data analysis (α = .05).

Results: Two-way ANOVA showed significant differences in loosening torque, torque loss, and percentage of torque loss across the restorative material (P < .001), with no significant difference across the height of the titanium base (P = .213) and no significant interaction (P = .845) between the restorative material and titanium base height. Regarding the restoration type, one-way ANOVA showed a significant difference (F ratio = 15.95, P < .001) in torque loss between groups. The mean torque loss was significantly higher for monolithic zirconia than for lithium disilicate (P = .039) and polymer-infiltrated ceramic (P < .001). A significant difference (P = .013) was also found between the lithium disilicate and polymer-infiltrated ceramic.

Conclusions: The restorative material had a major effect on the torque maintenance in hybrid abutment restorations supported by offset implant placement, while the titanium base abutment height had no influence on torque maintenance. Compared to lithium disilicate and polymer-infiltrated ceramic materials, monolithic zirconia induced higher torque loss when used as a hybrid abutment restoration.