The effect of mechanical loading cycles on different abutment types in implants with tapered internal connection

Aim The purpose of this in vitro study was to evaluate the influence of the application of cyclic mechanical load on  torque loss and on the seating installation of internal tapered abutments.

Materials and methods Forty tapered implants and 40 abutments were used and divided into four groups (n=10): Group 1 (Titamax CM) and Group 2 (Strong SW Morse) received one-piece abutments; Group 3 (Titamax CM) and Group 4 (Strong SW Morse) received two-piece abutments. Tightening torque and reverse torque were applied, after 5 minutes, on all abutments. After that, tightening torque was applied to all the abutments, and were mechanically loaded and uninstalled. The two-piece abutments of Group 3 and Group 4 were divided in two subgroups (Subgroup 3a and Subgroup 4a: traction test required to remove the implant - pull out). The specimens were submitted to fatigue tests consisting of 1.200.000 cycles at a frequency of 2 Hz, dynamic compressive load of 50 N, and an angle of 30°. Data were analyzed through the normal distribution (Shapiro-Wilk, p> 0.05), followed by parametric statistical tests.

Results After mechanical loading torque loss was higher in Group 4 (over 70% loss), followed by Group 1, Group 2 and Group 3 (over 50% loss). Group 1 and Group 2 presented no statistical difference. Subgroup 3a presented higher traction strength seating in post removal after mechanical loading (67.91 N), while Subgroup 4a presented only 1.92 N, it may present greater loosening of abutments.

Conclusions The mechanical load significantly reduced the removal torque of the four groups of abutments tested, in addition to increasing frictional lock installation to the abutments of  Subgroup 3a in the pull out test.