Objective: Since their introduction in 1945, tooth positioners have been used to treat a range of malpositions. Although the original appliance was made of natural rubber, today's tooth positioners are fabricated from various elastic, transparent materials. It was the aim of this study to evaluate the forces and moments produced by current positioners on various upper canine malpositions. Material and methods: Seven positioners of different materials were tested on 11 upper canine malpositions: 0.25, 0.5, 1mm supraposition; 0.25, 0.5, 1mm infraposition; 5°, 10°, 20° mesiorotation; 5° mesioinclination, 5° buccal root torque. We measured forces and moments in vitro after bite closure by 0.5mm, and opening by 1mm using a three-dimensional robotic device. All measurements were taken in a temperature-controlled environment at 36°C. Results: The forces and moments measured at the canine varied greatly among the different positioners, with the thermoformed EVA positioner showing much greater forces and moments in almost all malpositions. At initial closure, we observed intrusive forces of 6-32N for suprapositions, 0-11N intrusive forces for infrapositions, 0-20Nmm for mesiorotations, 6-12Nmm for mesioinclinations, and − 23Nmm to 5Nmm for buccal root torque. All positioners were most effective on suprapositioned teeth. Very low or negligible correctional forces and moments in conjunction with all infrapositions and 5° with rotation were noted. Labial root torque led to unpredictable moments. Conclusion: Positioner material plays a major role in delivering forces to the teeth. However, tooth positioners did not induce corrective forces in all the malpositions tested. Clinically relevant correctional forces or moments in conjunction with all suprapositions, rotations of 10° and 20° as well as mesial tipping of the canine were observe
