Fracture resistance of soft tissue level implants after cyclic loading and external modification

Statement of problem: The exposure of the implant collar in the esthetic zone is a challenging complication of implant dentistry. The preparation of the exposed implant collar to create room for restorative material may decrease the strength of the abutment/implant assembly. Purpose: The purpose of this in vitro study was to evaluate the effect on the failure load of preparing a 0.5-mm chamfer finish line on an implant collar at various apical depths. Material and methods: Thirty solid abutments and 30 implants were screwed into a customized metal mold at a 30-degree angle to the vertical axis. An intact group (IN) (control) (n=10) had no preparation, experimental group P1 had a 0.5-mm chamfer margin placed 1 mm apical to the implant/abutment interface, and experimental group P2 had the margin placed 2 mm apical. The specimens were subjected to a fatigue loading of 200 N for 1 000 000 cycles. Unfractured specimens were then loaded until failure. Mean fracture load (MFL) values were compared with 1-way ANOVA, and the Tukey test was used to identify differences among groups (α=.05). Results: One specimen from both the IN and P1 groups and 2 specimens from the P2 group failed after fatigue loading. Significant differences in the MFL values were found between the IN group (3825) and P1 group (2944), P<.001 and between the IN group and the P2 group (2553), P<.001. Conclusions: The mean load required to fracture the abutment/implant assembly decreased significantly after various amounts of implant collar preparation.