Fluoride influences nickel-titanium orthodontic wires' surface texture and friction resistance

Abstract

Objectives: The aim of this study was to investigate the effects exerted by the acidulated fluoride gel on stainless steel and nickel-titanium (Ni-Ti) orthodontic wires.

Materials and methods: Sixty stainless steel and Ni-Ti orthodontic archwires were distributed into forty archwires used for in vitro study and twenty for in situ study. Fluoride was applied for 1 h in the in vitro experiment while it was applied for 5 min in the in situ experiment. The friction resistance of all wires with ceramic brackets before/after topical fluoride application was measured using a universal testing machine at 1 min intervals of moving wire. Moreover, surface properties of the tested wires before/after fluoride application and before/after friction test were examined by a scanning electron microscope (SEM). Dunnett's t-test was used to compare frictional resistance of as-received stainless steel wires and Ni-Ti wires to the wires treated by fluoride in vitro and in situ (P < 0.05). Two-way ANOVA was used to compare the effect of fluoride application and type of wire on friction resistance in vitro and in situ (P < 0.05).

Results: Ni-Ti wires recorded significantly high friction resistance after fluoride application when compared to stainless steel wires in vitro, P < 0.05. Fluoride application did not significantly affect the friction resistance of the tested wires in situ, P < 0.05. SEM observation revealed deterioration of the surface texture of the Ni-Ti wires after fluoride application in vitro and in situ.

Conclusions: The in vitro fluoride application caused an increase in friction resistance of Ni-Ti wires when compared to stainless steel wires. In vitro and in situ fluoride application caused deterioration in surface properties of Ni-Ti wires.

Keywords: Fluoride; friction resistance; orthodontics; prophylaxis; surfaces.

Figure 1

The archwire specimen is secured into the bracket slot

Figure 2

Summary for the experimental groups

Figure 3

The frictional resistance values of the tested wires to ceramic brackets in kg. Values are presented as mean ± standard deviation. Significant differences between the groups are marked with asterisks (P ≤ 0.05).

Figure 4

Scanning electron microscope pictures of tested wires before friction test. (a) As-received stainless steel wire showing smooth surface. (b) Stainless steel wire after in vitro fluoride application did not show significant defects. (c) Stainless steel wire after in situ fluoride application did not show significant defects. (d) As-received nickel-titanium wire. White arrows show areas of longitudinal cracks. (e) Nickel-titanium wires after in vitro fluoride application with major cracks marked with white arrows. (f) Nickel-titanium after in situ fluoride application. White arrows point to numerous areas of longitudinal defects

Figure 5

Scanning electron microscope pictures of tested wires after friction test. (a) As-received stainless steel wire showing smooth surface. Arrow points to line of wire draw. (b) Stainless steel wire after in vitro fluoride application. Arrows show line of wire draw. (c) Stainless steel after in situ fluoride application. Arrow shows line of wire draw. (d) As-received nickel-titanium wire. Arrow shows areas of longitudinal defects. (e) Nickel-titanium wires after in vitro fluoride application. Arrows show cracks. (f) Nickel-titanium after in situ fluoride application. Arrows point to longitudinal defects