Screw stability of CAD-CAM titanium and zirconia abutments on different implants: An in vitro study.

BACKGROUND Limited information is available regarding the removal torque values (RTVs) of screws of different abutment materials when used with different implants. PURPOSE To evaluate the effect of implant type and abutment material (zirconia; Zir and titanium; Ti) on the RTVs of abutment screws after cyclic loading. MATERIALS AND METHODS Internal conical connection implants (CC, OsseoSpeed TX) and modified internal conical connection implants (MCC, OsseoSpeed EV) (n = 10) were clamped in resin dies. Zir and Ti (N = 20) custom abutments were tightened to implants (20 Ncm for CC and 25 Ncm for MCC) as specified by their manufacturers. The abutments were cyclically loaded by using a sequentially increased loading protocol; 2-million cycles under 100 N, 3-million cycles under 200 N, and 2-million cycles under 300 N loads with 2 Hz. After 7 million cycles, RTVs (Ncm) were measured by using a torque gauge. The data were analyzed with ANOVA by using the restricted maximum likelihood estimation method. Tukey-Kramer adjustment was used for any significant interaction of implant-abutment pairs (α = 0.05). RESULTS Two CC implants, 1 with Ti and 1 with Zir abutment, fractured during cyclic loading (under 300 N loads within the 6th and 7th million cycles) and discarded for statistical analysis. Only implant type had a significant effect on RTVs (p