The Effect of Torque Application Technique on Screw Preload of Implant-Supported Prostheses

To examine the effect of different torque application techniques (torqued, retorqued once, and retorqued twice) on the removal torque of implant-supported fixed complete dental prostheses.

Four Nobel Biocare implants (4.3 × 13 + 3; 13-mm thread height + 3-mm collar height) were stabilized temporarily inside four holes made in an acrylic mandibular master model. A metal framework was constructed, casted, and finished using a standardized technique. A passively fitting framework was achieved by removing the implants from the acrylic master model and hand-screwing them to the metal framework. Then, the whole assembly was restabilized in the acrylic master model. The torque experiment consisted of three protocols: (1) torquing screws to 35 Ncm a single time; (2) torquing the screws to 35 Ncm and then immediately retorquing the same screws to the same value; and (3) torquing the same screws to 35 Ncm three consecutive times. Removal torque was recorded for each implant using a digital torque meter.

The highest torque value was recorded for the retorqued-once application technique (29.5 ± 1.5 Ncm); next was the torqued technique (27.9 ± 0.7 Ncm); and, last was the retorqued-twice technique (27.2 ± 1.6 Ncm). The Games-Howell post hoc test showed that the retorqued-once application technique resulted in significantly higher torque values than the torqued and retorqued-twice torque application techniques (P ≤ .05).

Retightening abutment screws once after the initial torquing could enhance the removal torque of the screw. Care must be taken when retorquing the screws more than once, as this may inversely affect the removal torque.