Influence of shoulder coverage difference of abutment on stress distribution and screw stability in tissue-level...

Tissue-level internal connection implants are widely used, but the difference in abutment screw stability because of the shoulder coverage formed by the contact between the shoulder of the implant collar and the abutment remains unclear.

The purpose of this finite element analysis (FEA) and in vitro study was to investigate stress distribution and abutment screw stability as per the difference in shoulder coverage of the abutment in tissue-level internal connection implants.

Abutments were designed in 3 groups as per the shoulder coverage of the implant collar, yielding complete coverage (complete group), half coverage (half group), no coverage (no group) groups. In the FEA, a tightening torque of 30.0 Ncm was applied to the abutment screw, a force of 250 N was applied to the crown at a 30-degree angle, and the von Mises stresses and the stress distribution patterns were evaluated. In the in vitro study, the groups were tested (n=12). A total of 200 000 cyclic loads were applied at 250 N, 14 Hz, and at a 30-degree angle. Removal torque values and scanning electron microscopy (SEM) images were assessed. Removal torque values were analyzed by ANOVA and paired t tests.

The maximum von Mises stress of the abutment screw was the lowest in the complete group, slightly higher in the half group, and highest in the no group. High stresses were concentrated in 1 location in the implant abutment connection area of the no group. The removal torque values after loading were significantly lower in the no group than in the complete group (P=.047). The SEM images revealed concentrated structural loss and wear in 1 location of the no group.

FEA and in vitro studies confirmed that the shoulder coverage of the abutment in the tissue-level internal connection implant helped improve screw stability. Cyclic loading reduced the removal torque of the abutment screw.