Effect of internal hexagonal index on removal torque and tensile removal force of different Morse taper connection abutments.

STATEMENT OF PROBLEM: The maintenance of the mechanical stability of implant-abutment connections is relevant to the clinical success of implant-supported restorations. However, the reduction in the conical area of abutments with an internal hexagonal index may result in a biomechanical disadvantage in Morse taper connections.

PURPOSE: The purpose of this in vitro study was to evaluate the influence of an internal hexagonal index on the removal torque and tensile removal force of different Morse taper connection abutments submitted to thermomechanical cycling.

MATERIAL AND METHODS: Forty Morse taper implants with their respective abutments were divided into 4 groups (n=10): straight abutment without index (PRNI); straight abutment with index (PRI); angled abutment without index (PANI); and angled abutment with index (PAI). Each abutment received an insertion torque of 15 Ncm, and the removal torque was recorded before and after thermomechanical cycling (106 cycles, 2 Hz, load of 130 N). After cycling, the groups were submitted to tensile testing at 0.5 mm/min under a load of 500 N until displacement of the abutment. A paired t test was performed for the intragroup analysis of removal torque before and after cycling and 2-way ANOVA followed by the Tukey Honestly Significant Difference (HSD) test was used for intergroup comparison (α=.05).

RESULTS: Statistical analysis showed significant differences in intragroup removal torque values before compared with after thermomechanical cycling (P<.05). No statistically significant differences were found between the experimental groups in the removal torque of the prosthetic screw after cycling. The index factor (P=.028) was significant for tensile removal force.

CONCLUSIONS: The type of abutment did not significantly influence the removal torque or tensile removal force after cycling. However, the presence of the internal hexagonal index significantly reduced the force necessary to dislodge the abutment from the implant.