The impact of abutment type on abutment screw removal torque value after experimental aging.

Purpose: To evaluate the changes in abutment screw removal torque value (RTV) of anatomic, original hybrid, and non-original hybrid abutments after simulated clinical use.

Materials and methods: Ninety-three implant-abutment-crown specimens were divided into groups according to abutment types (n = 31): anatomic (stock) (A), original hybrid (OH), and non-original hybrid (NOH). After the initial abutment screw tightening, the specimens were subjected to five screw tightening (insertion/removal) cycles, or to 5000 thermal cycles with 500,000 chewing cycles combined with one or five screw tightening cycles. RTV measurements and surface analysis using scanning electron microscope were performed before and after aging. The impact of abutment types and aging treatments on RTV was determined using two-way repeated measures ANOVA, data were described with mean ± SD and range, whereas the differences were significant at p < 0.05.

Results: A significant interaction was found between abutment types and screw tightening cycles only (p = 0.036) or combined with thermomechanical aging (p < 0.001) on RTV. RTV was lower in NOH than in A and OH groups after screw tightening and thermomechanical aging (p < 0.05). Before aging, the NOH abutment screw was slightly more damaged than OH and A abutment screws. After aging, screw damage was more pronounced on the surfaces of hybrid abutments, and more evident in the NOH group.

Conclusions: The abutment screw RTV of anatomic, original hybrid, and non-original hybrid abutments become significantly lower after abutments undergo screw tightening and/or thermomechanical aging cycles, with higher RTV loss in hybrid abutments, especially non-original ones.