Influence of material choice on the force delivery of bimaxillary tooth positioners on canine malpositions Der Einfluss der Materialwahl auf die Kraftabgabe von bimaxillären Zahnpositionern bei Fehlstellungen der Eckzähne

Abstract 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 posi-tioners are fabricated from various elastic, transparent materials. It was the aim of this study to evaluate the forces and moments pro-duced by current positioners on various upper canine malposi-tions.Material and methods. Seven positioners of different materi-als were tested on 11 upper canine malpositions: 0.25, 0.5, 1 mm supraposition; 0.25, 0.5, 1 mm infraposition; 5°, 10°, 20° mesioro-tation; 5° mesioinclination, 5° buccal root torque. We measured forces and moments in vitro after bite closure by 0.5 mm, and opening by 1 mm using a three-dimensional robotic device. All measurements were taken in a temperature-controlled environ-ment at 36 °C.Results. The forces and moments measured at the canine var-ied greatly among the different positioners, with the thermofor-med EVA positioner showing much greater forces and moments in almost all malpositions. At initial closure, we observed intrusive forces of 6–32 N for suprapositions, 0–11 N intrusive forces for in-frapositions, 0–20 Nmm for mesiorotations, 6–12 Nmm for mesio-inclinations, and -23 Nmm to 5 Nmm 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 cor-rective forces in all the malpositions tested. Clinically relevant cor-rectional forces or moments in conjunction with all supraposi-