The Effect of PTFE Coating and PTFE Tape Wrapping Abutment Screw After Cyclic Loading: An In Vitro Study.

Abstract

Objective: This study aimed to compare the effect of PTFE tape wrapping and PTFE-coated titanium alloy screws on the removal torque after cyclic loading and on preload values under repetitive tightening.

Methods: A total of 60 titanium abutment screws were allocated to three surface-treatment groups (n = 20 each): untreated (Control), PTFE tape-wrapped (Wrap), and PTFE-coated (Coat). Within each group, 10 specimens underwent cyclic loading, whereas 10 were assigned to preload evaluation. Cyclic loading followed ISO 14801:2016. Screws were tightened to 30 N·cm, retightened after 10 min, and subjected to 300 000 cycles at 200 N using a fatigue testing machine (DYNA-MESS Prüfsysteme GmbH, Aachen, Germany). Removal torque was measured with a digital torque gauge (BTGE50CN, Tohnichi, Japan). For preload assessment, each specimen completed 10 tightening-loosening cycles at the same torque during which tensile force was recorded using a customized device. One representative screw per group was analyzed by SEM and micro-CT before and after loading to evaluate surface and structural changes.

Results: After cyclic loading, the removal torque did not differ significantly between the Control group (17.58 ± 1.85 N·cm) and the Wrap group (17.50 ± 1.77 N·cm), whereas the Coat group demonstrated significantly lower removal torque (14.71 ± 2.35 N·cm; p < 0.05). In the preload test, preload progressively decreased in the Control (-3.13 N per cycle) and Coat groups (-0.51 N per cycle), while the Wrap group showed a consistent increase with repeated tightening (+8.22 N per cycle). SEM revealed surface wear and partial loss of PTFE material after loading, particularly in the coated specimens. Micro-CT analysis showed no detectable differences in internal adaptation among groups before or after cyclic loading.

Conclusions: PTFE tape wrapping increased preload during repeated tightening but did not improve removal torque after cyclic loading compared with those of untreated screws. Although PTFE-coated screws produced the highest initial preload, they were associated with reduced removal torque after loading. SEM analysis confirmed coating deterioration, whereas internal fit remained comparable across groups.