Measurements of trueness and precision of various dental torque wrenches: An in vitro study

Implant-supported restorations depend on the precise application of torque to prosthetic screws. Deviations from the intended torque-whether insufficient, leading to screw loosening and micromovement, or excessive, risking screw fracture-can compromise the longevity of the restoration. Despite the widespread clinical use of torque-limiting wrenches, the relative accuracy and consistency of friction-style versus spring-style devices remains unclear.

The purpose of this in vitro study was to evaluate and compare the trueness and precision of tightening forces generated by friction-style and spring-style dental torque wrenches to determine which type more reliably achieved the manufacturer-recommended torque values.

Twenty new torque wrenches from 4 manufacturers- MIS Implant Technologies (spring-style), Institut Straumann AG (spring-style), Alpha-Bio Tec (friction-style), and Surcam Dental Pro. (friction-style)-were evaluated. Using a calibrated torque meter, a single operator applied a standardized, horizontal force to each wrench. For each device, 20 measurements were recorded at an initial session (M1) and repeated 2 days later (M2), yielding 800 total measurements. Trueness was assessed by calculating the difference between the preset torque and the measured value, while precision was quantified by the standard deviation of repeated measurements. Statistical analysis was performed using 2-way ANOVA with post hoc Tukey tests (α=.05).

Overall, deviations in trueness ranged from -0.7 to 3.8 Ncm, and precision values ranged from 0.2 to 1.5 Ncm. Notably, spring-style wrenches (MIS and Straumann) exhibited significant differences in trueness between M1 and M2-indicating greater variability-with deviations reaching up to 4.5 Ncm, whereas friction-style wrenches (Alpha-Bio and Surcam) consistently demonstrated lower deviations (up to 2.5 Ncm) and better precision.

The study demonstrated that friction-style torque wrenches exhibited better trueness and precision than spring-style devices. These findings suggest that friction-style devices may reduce the risk of prosthetic screw damage or loosening.