Screw Loosening with Interchangeable Abutments in Internally Connected Implants After Cyclic Loading

Purpose: The purpose of this study was to observe and compare any loosening of screws attaching several interchangeable abutments to internally connected implants after cyclic loading. Materials and Methods: Four different abutment groups mated with Straumann single-stage transmucosal implants (n = 7 each group) were assessed: Straumann solid abutment, Restore COC abutment, Neoplant solid abutment, and AVANA solid abutment. Each implant was fixed rigidly in a special holding jig. Abutments were tightened to 35 Ncm with a torque controller. A cyclic load of 150 N at a 30-degree angle to the long axis was applied to the implants for 1 million cycles. Prior to loading, Periotest values (PTVs) were measured. After cyclic loading, PTVs were measured and removal torque values (RTVs) of abutments were measured with a digital torque gauge. Results: No mechanical failures were noted for the Straumann solid abutment or the Restore COC abutment. Six Neoplant abutment screws fractured (86%), and four implants fractured (57%) in the group restored with AVANA solid abutments. The RTVs of the Straumann solid abutment were significantly higher than those of the other abutments. The final mean PTV of the Straumann solid abutment was significantly lower than the final mean PTVs of the other abutments. The final mean PTV (4.76 ± 5.58) was significantly higher than the initial mean PTV (-4.29 ± 0.47). Conclusions: Although different abutments are interchangeable with each other, they possess different chemical compositions and physical characteristics. The use of an abutment and implant manufactured by the same company is recommended to prevent the loosening of the abutment screw. Keywords: abutment, cyclic loading, implant-abutment interface, internally connected implant, removal torque, screw loosening