Measuring system for in vivo recording of force systems in orthodontic treatment - concept and analysis of accuracy

The aim of our developments is three-dimensional in vivo recording of those orthodontic force systems inducing tooth movements during treatment with f ixed appliances. The concept presented here is the first to permit the forc es and torques of these statically multiply undetermined systems to be reco rded in vivo. For this purpose the force systems transmitted to the teeth f rom the archwire are isolated from the respective tooth by means of divisib le special-design brackets and introduced into a 3D force-torque sensor via a gripping appliance. The sensor is fixed with a purpose-developed device relative to the patient's dental arch. The patient's head is positioned rel ative to the system by means of a bite fork as well as a forehead and chin support. Electrical measurement of the mechanical quantities is carried out by a six-axis force-torque sensor with semiconductor strain gauge elements , an electronical evaluator and a mobile measuring computer (PC). Extensive calibration of the sensor system has shown that the measuring uncertainty of the electrical measuring is less than 2%. Precise spatial fixing of brac ket slot and archwire in the therapeutic position is crucial to the measuri ng accuracy of the system, as even minimum displacements affect the force s ystem to be measured. Movements of the measuring system up to 0.04 mm resul t from a therapeutic force of 1.5 N. The results of extensive in vitro stud ies have already demonstrated that the system developed by us is suitable f or the specified in vivo measuring function. (C) 1999 Elsevier Science Ltd. All rights reserved.