ABSTRACT
BACKGROUND: Clinical ligation of traditional brackets by stainless steel ligature wires has greater randomness among doctors, and previous studies have mainly concerned on brackets and wires. There are less studies on the differential frictional force due to tight or loose ligation, and moreover, how to define tight ligation or loose ligation is rarely reported. OBJECTIVE: To compare the frictional force of different archwires in multiple brackets with various ligations. METHODS: A plaster model with moderate crowded malocclusion was randomly selected, and copied by 3D digital scanning technologies and Objet30 OrthoDesk3D printing technologies. Then, the models were bonded with Damon Clear brackets, Damon 3MX brackets, 3M traditional MBT brackets and Habit monocrystal brackets. Frictional forces of different brackets on models combined with two types of low frictional NiTi archwires which were 0.30 mm (0.012 inch) and 0.36 mm (0.014 inch) were measured by microcomputer servo dynamometer. Traditional brackets were ligatured by tight ligation and loose ligation, respectively. RESULTS AND CONCLUSION: (1) When low-friction NiTi archwires of 0.30 mm were used, significant differences in the frictional force were found between different brackets with various ligations except for Damon Clear bracket versus 3M bracket with loose ligation as well as Damon Clear bracket versus Damon 3MX bracket (P ＜ 0.05). (2) When low-friction NiTi archwires of 0.36 mm were used, similarity in the frictional force was found between 3M bracket with loose ligation, Damon Clear bracket and Damon 3MX bracket, while there were no significant differences between 3M bracket with loose ligation and Damon 3MX, between 3M bracket with tight ligation and Habit bracket with loose ligation, as well as between Damon Clear bracket and 3M bracket with loose ligation (P ＞ 0.05). Comparing two kinds of archwires, the friction force showed no statistical difference between Damon Clear bracket and 3M bracket with loose and tight ligation (P ＞ 0.05), but a statistical difference was found between Damon 3MX bracket and Habit bracket (P ＜ 0.001), whatever two conventional brackets with tight ligation or loose ligation. To conclude, conventional MBT bracket with loose ligation can reduce frictional force as similar as self-ligating bracket in the alignment phase, and the reduction in the friction force is impacted by archwire size and bracket material.