Load Fatigue Performance Evaluation on Two Internal Tapered Abutment–Implant Connection Implants Under Different Screw Tightening Torques
This study evaluates the load fatigue performance of different abutment–implant connection implant types—retaining-screw (RS) and taper integrated screwed-in (TIS) types under 3 applied torque levels based on the screw elastic limit. Three torque levels—the recommended torque (25 Ncm), 10% less, and 10% more than the ratio of recommended torque to screw elastic limits of different implants were applied to the implants to perform static and dynamic testing according to the ISO 14801 method. Removal torque loss was calculated for each group after the endurance limitation was reached (passed 5 × 106 cycles) in the fatigue test. The static fracture resistance results showed that the fracture resistance in the TIS-type implant significantly increased (P < .05) when the abutment screw was inserted tightly. The dynamic testing results showed that the endurance limitations for the RS-type implant were 229 N, 197 N, and 224 N and those for the TIS-type implant were 322 N, 364 N, and 376 N when the screw insertion torques were applied from low to high. The corresponding significant (P < .05) removal torque losses for the TIS-type implant were 13.2%, 5.3%, and 2.6% but no significant difference was found for the RS-type implant. This study concluded that the static fracture resistance and dynamic endurance limitation of the TIS-type implant (1-piece solid abutment) increased when torque was applied more tightly on the screw. Less torque loss was also found when increasing the screw insertion torque.
(a) Structural diagrams of retained screw (RS)- and taper integrated screwed-in (TIS)-type implants. Left: RS-type implant with 2-piece abutment transfixed by a screw; right: TIS-type implant with 1-piece solid abutment. (b) Cross-section of the static/fatigue test setup according to the ISO14801 method.
(a) Schematic diagram of the maximum insertion torque strength measurement for the abutment screw. (b) Static/fatigue test equipment and the local test setup diagrams according to the ISO14801 method.
Static fracture resistance results for retained screw- and taper integrated screwed-in–type implants. The “star” symbol shows that statistical analysis presented significant differences (P < .05) between different groups. RS indicates retaining screw; RSrtr, ratio of the manufacturer's recommended torque (25 Ncm) to the average maximum strength of the insertion torque of RS connection type implants; TIS, taper integrated screwed-in; TISrtr, ratio of the manufacturer's recommended torque (25 Ncm) to the average maximum strength of the insertion torque of TIS connection type implants.
Endurance limitations obtained from dynamic testing load-cycle diagrams of (a) retained screw-type implant and (b) taper integrated screwed-in–type implant.
Polished cross-sections of embedded failed specimens of the different implant–abutment connection types. The red circles show that a fracture on the first thread junction of the screw and large deformation on the implant neck were the 2 major failure modes after static testing. (a) Retained screw-type implant and (b) taper integrated screwed-in–type implant.
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