Clinical ligation forces and intraoral friction during sliding on a stainless steel archwire

The efficiency of tooth movement associated with some orthodontic mechanics can be compromised by friction between archwire and bracket. This study examined the effects of bracket ligation forces (F_{N Ligation}) and mastication on friction when sliding a bracket along an archwire. Preliminary data from 5 orthodontists and 5 orthodontic residents characterized average tight and loose stainless steel F_{N Ligation}. These values were reproduced by a calibrated operator in a custom device used to estimate changes in the measurement of ex vivo and intraoral frictional forces, represented by μ_a, the apparent coefficient of static friction. Ten subjects chewed gum with the device in place to determine whether vibration eliminated friction when compared to ex vivo measurements. Nested analysis of variance and Tukey HSD tests determined the effects of ligation type and environmental variables. No significant differences (P > .01) were found between ex vivo and intraoral μ_a values for tight and loose stainless steel ligation. Intraoral μ_a values for elastic ligation were significantly greater than ex vivo μ_a values (P ≤ .001). The results suggested that vibration introduced by mastication did not eliminate friction when sliding a bracket along an archwire. In addition, there was considerable intraoperator variation in F_{N Ligation}, although ligation techniques were well controlled. Variations in clinical ligation forces are likely to be equal or greater than these experimental data. These variations could affect treatment efficiency.