Fluoride influences titanium orthodontic wires` surface texture and friction resistance

Objectives: Maintenance of good oral hygiene is an important component of successful orthodontic treatment. Fluoride is used extensively to prevent enamel demineralization around orthodontic brackets.  This study is investigating the effects exerted by the acidulated-fluoride gel on stainless-steel and two types of titanium orthodontic wires.

Methods: Sixty orthodontic wires Stainless-steel, TruChrome Resilient; Nickel-titanium, Orthonol Super-Elastic; Beta-titanium Bendaloy Nickel Free (RMO, Denver, USA; 0.019 x 0.025-inch, 4 cm length) were distributed into three groups.  Half number of wire specimens in each group was immersed in fluoride gel (Acidulated phosphate fluoride, Nupro APF, 1.23% NaF , Dentsply, USA) for 1 hour, while the remaining specimens served as control.  The wires were attached to ceramic brackets.  The frictional force generated by each wire-bracket assembly was observed on a universal testing machine at one minute intervals of moving wire.  All specimens were examined before/after the friction test before/after fluoride application by a scanning electron microscope.  T-test was used to compare the frictional resistance of each wire type before/after fluoride application p< 0.05.  Two way ANOVA and Tukey test were used to compare the effect of the wire type and fluoride application on the frictional resistance of the tested orthodontic wires to ceramic brackets p< 0.05.

Results: There were no significant differences between the frictional resistance of each wire type before/after fluoride application. The (as received) beta titanium wires showed significantly high friction resistance values when compared to the stainless steel wires p< 0.05, moreover, the stainless steel wires recorded significantly low friction resistance after fluoride application when compared to the titanium containing wires p< 0.05.  SEM observation revealed deterioration of the surface texture of the titanium wires after fluoride application.  

Conclusion:   Fluoride prophylactic application significantly affected the friction resistance and the surface texture of nickel titanium and beta titanium orthodontic arch wires.