Comparison of the frictional characteristics of aesthetic orthodontic brackets measured using a modified <em>in vitro</em> technique

Objective: The coefficients of friction (COFs) of aesthetic ceramic and stainless steel brackets used in conjunction with stainless steel archwires were investigated using a modified linear tribometer and special computer software, and the effects of the bracket slot size (0.018 inches [in] or 0.022 in) and materials (ceramic or metal) on the COF were determined. Methods: Four types of ceramic (one with a stainless steel slot) and one conventional stainless steel bracket were tested with two types of archwire sizes: a 0.017 × 0.025-in wire in the 0.018-in slots and a 0.019 × 0.025-in wire in the 0.022-in slot brackets. For pairwise comparisons between the 0.018-in and 0.022-in slot sizes in the same bracket, an independent sample t-test was used. One-way and two-way analysis of variance (ANOVA) and Tukey’s <em>post-hoc</em> test at the 95% confidence level (α = 0.05) were also used for statistical analyses. Results: There were significant differences between the 0.022-in and 0.018-in slot sizes for the same brand of bracket. ANOVA also showed that both slot size and bracket slot material had significant effects on COF values (<em>p</em> &lt; 0.001). The ceramic bracket with a 0.022-in stainless steel slot showed the lowest mean COF (μ = 0.18), followed by the conventional stainless steel bracket with a 0.022-in slot (μ = 0.21). The monocrystalline alumina ceramic bracket with a 0.018-in slot had the highest COF (μ = 0.85). Conclusions: Brackets with stainless steel slots exhibit lower COFs than ceramic slot brackets. All brackets show lower COFs as the slot size increases. [Korean J Orthod 2015;45(1):29-37]