Effect of Viewing Angle While Tightening on Torque Values in Beam-Type Torque Wrenches

Background/Objectives: Controlled tightening force of implant prosthetic screws is achieved using dental torque wrenches. Beam-type wrenches are prone to a parallax error, where different viewing angles can unintentionally alter the applied force, potentially leading to screw loosening and fracture. The objective of this study was to determine the effect of different viewing angles of the operator relative to the wrench's reading scale and the actual force applied on the prosthetic screw. Methods: Two types of beam torque wrenches (Institut Straumann AG, Switzerland; MIS Implant Technologies, Israel) were used. Five wrenches for each group were connected to a torque meter mounted on a custom 3D printed apparatus, allowing torque read at different viewing angles. Each wrench was tightened according to manufacturer recommendations at angles ranging between ±60 degrees from center position. A camera mounted on a tripod provided magnification and consistency in recordings. For each measurement, a comparison was made between intended tightening force and actual force exerted on the torque meter. Data were analyzed to determine the effect on clinical settings. Results: Both wrenches exhibited a parallax effect with its resulting impact on force delivery by the wrench. When the operator was positioned at a negative angle relative to the wrench, while applying tightening force, the actual force delivered by the wrench was amplified. The greater the angle, the greater the force amplification was. The opposite effect took place when the wrench was viewed from a positive angle relative to the operator. Force alteration reached up to 8.72 Ncm, which can account for as much as 25% from intended force. This effect was notable and statistically significant for both types of wrenches. Conclusions: The tested beam-type torque wrenches present an inherent potential deficiency in which oblique viewing angles lead to either amplification or attenuation of the actual force that is applied. This phenomenon might be associated with a variety of prosthetic failures. Operators are recommended to adopt a viewing strategy that minimizes undesired outcomes.