Abstract
This study evaluated the effect of six screw-tightening sequences and two tightening methods on the screw preload in implant-supported superstructures. The preload was measured using strain gauges following the screw tightening of a metal framework connected to four implants. The experiment included six sequences ([1] 1-2-3-4, [2]4-2-3-1, [3]4-3-1-2, [4]1-4-2-3, [5]2-3-4-1, and [6]3-2-4-1), two methods (one-step, three-step), and five replications. Significant differences were found between tightening sequences and methods.. In the three-step method, a higher total preload was found in sequences 2 (312 +/- 85 N), 3 (246 +/- 54 N), and 4 (310 +/- 96 N). In the one-step method, a higher total preload was found in sequences 1 (286 +/- 94 N), 5 (764 +/- 142 N), and 6 (350 +/- 69 N). It is concluded that the highest total screw preload was achieved when anterior implants of the superstructure were first tightened in one step, followed by posterior implants.