Vibration Effects on Stick-Slip at the Bracket-Wire Interface

Objectives: Friction associated with stick-slip behavior at the bracket-wire interface is likely to affect rates of orthodontic tooth movement. To date, no reported data describe characteristics of intraoral archwire vibration and whether or not vibration differentially affects stick-slip behavior at the bracket-wire interface of self-ligating compared to conventional brackets. Our objective was to evaluate bracket-archwire stick-slip behavior as a function of ligation method and archwire vibration.

Methods: According to IRB oversight, in vivo archwire vibrations were measured using a piezoresistive accelerometer on 2 separate days in 6 individuals during biting on raw carrots. From in vivo data, mean±1 SD frequency and amplitude of vibrations were identified for use in bench-top friction testing apparati.  Active and passive orthodontic bracket ligation methods were compared for differences in stick-slip behavior for 9 vibration scenarios, where each testing apparatus had a nickel titanium spring which created a 1500 cN-mm moment.  As retraction forces were applied, the amount of time (ln, s) for each bracket configuration to move along a stainless steel wire was recorded in 90 trials. ANOVA and Ryan-Einot-Gabriel-Welsh F Post hoc tests were used to investigate effects.

Results: Intra-oral wire vibration frequencies (mean 98±41, range 45 – 208 Hz) and amplitudes (mean 151±39, range 84-240 mV) were used to define the bench-top test scenarios. Testing apparati subjected to medium (150mV) and high (190mV) amplitude vibrations had significantly less friction, 4.81±2.08 and 4.67±2.00, respectively, than those subjected to low (110mV) amplitudes, 5.80±1.39 (p=0.04).  There were no significant differences between passive and active ligation methods (p=0.100) and no significant effects of frequency of vibrations (p=0.317) on bracket-archwire frictional resistance.

Conclusions: Amplitude of archwire vibration significantly affected stick-slip behavior regardless of method of ligation. Funded in part by the Rinehart Memorial Foundation, UMKC School of Dentistry.