Influence of normal forces on the frictional behavior in tribological systems made of different bracket types and wire dimensions.

The aim of the present work was measuring the effect of varying normal forces on frictional forces applied to different bracket types in combination with archwires made of NiTi and stainless steel of variable cross section. The measurements were carried out in artificial saliva. Three-way ANOVA and Bonferroni post-hoc tests (alpha=0.05) were applied. Except for one subgroup the combination of normal force, bracket system and wire dimension had significant effect on friction (p<0.001) as friction increased with increasing normal forces. Only moderately tied ligatures or passive self-ligating brackets generate low friction forces. There was a statistically significant order (0.016"x0.022"<0.018"x0.025"<0.019"x0.025") for stainless steel wire material. Finite element modeling simulation showed the increasing effect of active clip force on friction especially for 0.025" wire profiles. If compared to NiTi wires, stainless steel archwires delivered higher friction. Combinations between wire-type and ligation should be chosen carefully for the intended treatment step.