Friction in a hybrid system. An in vitro study

Aim. The aim of this study was to compare the frictional force generated by self-ligating and conventional brackets coupled with stainless steel wires when conventional elastomeric or stainless steel ligatures were applied. Method. Four types of brackets were selected for the study: one passive self-ligating bracket, two active selfligating brackets, and one conventional bracket. For each type of bracket one molar tube and two upper premolars were used in combination with three different wires (0.016x0.022, 0.017x0.025 and 0.019x0.025 inch). Testing was performed with an Instron machine. Each bracket/wire combination was tested with conventional elastomeric and stainless steel ligatures. Tests performed with self-ligating brackets were carried out also without conventional ligatures. ANOVA with Tukey's post hoc tests were used to compare the results for the different bracket/wire/ligature assemblies. Results. Active self-ligating bracket/0.017x0.025 inch or 0.019x0.025 inch/stainless steel ligature assemblies showed significantly higher values of frictional forces than conventional bracket for the same combinations. Passive self-ligating brackets showed significantly lower values of friction than conventional brackets for each wire/ligature assembly. Conclusions. The use of stainless steel ligatures applied on active self-ligating brackets produced significantly higher level of frictional force than in combination with conventional brackets for 0.017x0.025 inch and 0.019x0.025 inch wires