The dynamic frictional resistance between orthodontic brackets and arch wires

Limited published research on friction deals mainly with conventional stainless steel brackets and arch wires. However, the clinician can choose from a range of modern materials in determining arch wire and bracket combinations. This study quantifies the dynamic frictional force of sliding between different modern orthodontic brackets and arch wires. From the multitude of factors involved in the frictional process, the following were selected for investigation: arch wire material, bracket material, bracket-to-arch wire angulation, and lubrication (artificial saliva). The frictional force involved in sliding a ligated arch wire through a bracket slot was measured with a universal materials testing machine. A four-way analysis of variance was used to assess the results. Of the four factors investigated, all were found to have a significant influence on friction. Polycarbonate brackets showed the highest friction and stainless steel brackets the lowest. Friction increased with bracket-to-arch wire angulation. Lubrication significantly reduced friction. A range of 0.9 to 6.8 N frictional force was recorded. The actual force values recorded were most useful for comparing the relative influence of the factors tested on friction, rather than as a quantitative assessment of friction in vivo. The forces observed suggest that friction may be a significant influence on the amount of applied force required to move a tooth in the mouth. Hence, arch wire and bracket selection may be an important consideration when posterior anchorage is critical.