Ales Bezrouk1, Libor Balsky2, Martin Smutny3, Iva Selke Krulichova4, Jiri Zahora4, Josef Hanus5, Torstein R Meling6. 1. Assistant professor, Department of Medical Biophysics, Charles University, Prague, Faculty of Medicine, Hradec Kralove, Czech Republic. Electronic address: bezrouka@lfhk.cuni.cz. 2. Private practice, Hradec Kralove, Czech Republic. 3. Postgraduate student, Department of Medical Biophysics, Charles University, Prague, Faculty of Medicine, Hradec Kralove, Czech Republic. 4. Assistant professor, Department of Medical Biophysics, Charles University, Prague, Faculty of Medicine, Hradec Kralove, Czech Republic. 5. Associate professor and chair, Department of Medical Biophysics, Charles University, Prague, Faculty of Medicine, Hradec Kralove, Czech Republic. 6. Head, Department of Neurosurgery, National Hospital, Oslo, Norway.
Abstract
INTRODUCTION: The aim was to study nickel-titanium closed-coil springs in a clinically relevant test setting with respect to the accuracy of the "preactivation" for nickel-titanium closed-coil springs application and whether it is possible to keep activation forces constant during the whole time of treatment. METHODS: We tested 10 types of springs from 5 manufacturers under clinically relevant conditions, allowing us to study the interactions between load and temperature over time. Hystereses were compared using t tests. RESULTS: Springs with a large mechanical hysteresis also showed a large thermal hysteresis. After heating shock, these springs showed intensive force spikes and persistent high loads. Some springs showed negligible thermal and mechanical hysteresis. Such springs never showed any clinically significant persistent high loads. CONCLUSIONS: Springs with a large hysteresis were unable to keep activation forces constant during the whole time of treatment even after any preactivation, and they might cause persistently high loads and possibly overloading. Only springs with minor hysteresis, low temperature dependence of force, and a clinically useful plateau have the following clinical advantages: reduced chair time, optimal rates of tooth movement, reproducible clinical results, and conservation of anchorage.
INTRODUCTION: The aim was to study nickel-titanium closed-coil springs in a clinically relevant test setting with respect to the accuracy of the "preactivation" for nickel-titanium closed-coil springs application and whether it is possible to keep activation forces constant during the whole time of treatment. METHODS: We tested 10 types of springs from 5 manufacturers under clinically relevant conditions, allowing us to study the interactions between load and temperature over time. Hystereses were compared using t tests. RESULTS: Springs with a large mechanical hysteresis also showed a large thermal hysteresis. After heating shock, these springs showed intensive force spikes and persistent high loads. Some springs showed negligible thermal and mechanical hysteresis. Such springs never showed any clinically significant persistent high loads. CONCLUSIONS: Springs with a large hysteresis were unable to keep activation forces constant during the whole time of treatment even after any preactivation, and they might cause persistently high loads and possibly overloading. Only springs with minor hysteresis, low temperature dependence of force, and a clinically useful plateau have the following clinical advantages: reduced chair time, optimal rates of tooth movement, reproducible clinical results, and conservation of anchorage.