In vitro comparison of the mechanical behaviour of archwires after computer-assisted and conventional bracket positioning protocols

Introduction > The mechanical properties of orthodontic archwires can be defined using experimental setups incorporating brackets that provide conditions closer to those encountered in vivo. We aimed to compare a methodology based on computer-aided design with the gold standard protocol, performed when brackets are engaged to a full-size archwire to test the behaviour of wires in this condition. Methods > Three models simulating a dental arch with an orthodontic fixed appliance (0.018-inch aesthetic conventional brackets) were designed. The brackets were positioned with a stainless steel full-size wire on the first two models, with different interbracket distances. The setup 3, based on a computer-assisted design, allowed individualized placement of each bracket. Mean forces recorded and standard deviation were compared for a 0.016 x 0.022-inch copper-nickel titanium wire deflected until 2 mm. Results > The interbracket distances do not cause a statistical difference in the average maximum force recorded (12.6 N and 11.4 N; P = 0.081) whereas the behaviour of the wires is affected. With setup 3, the recorded efforts (mean value: 8 N) are statistically lower than with setup 1 and 2 respectively (P = 0.018; P = 0.012). Conclusion > An individualization of the housings by CAD-CAM dedicated to each bracket optimizes their placement. In our test conditions, the mechanical behaviour of the wires is more influenced by the positioning methods of the brackets than by the value of the interbracket distance. In perspective, our innovative methodology can be extended to other types of brackets.