The effect of fluoride gel on tensile properties, surface morphology and chemical composition of two types of orthodontic wires (an in-vitro study)

OBJECTIVE: Stainless steel and nickel-titanium wires are commonly used in fixed orthodontic appliances. Orthodontists often prescribe fluoride gel to avoid demineralization of teeth. This study investigated the effect of acidulated phosphate fluoride gel on the tensile properties, surface morphology and surface chemical composition of stainless steel and nickel-titanium wires. METHODS: Forty samples of stainless steel and nickel-titanium wires were examined, twenty for each type. Each wire type was divided into four subgroups. The first subgroup was not immersed in fluoride gel and considered as control, while the other three subgroups were immersed in 10 mL of fluoride gel for different periods of time. Then, the wires were removed from the gel, rinsed in a distilled water and left to dry. The ultimate tensile force of each wire was measured using a tensile testing machine. Scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to examine the control and 24 h immersed subgroups. RESULTS: One-way analysis of variance ANOVA showed that there were no significant differences in the ultimate tensile forces between control and fluoride-treated subgroups (P = 0.172 for SS wires and P = 0.672 for NiTi wires). However, changes in the surface morphology and elemental composition of wires were shown by the SEM and EDX. CONCLUSIONS: Although immersion of stainless steel and nickel-titanium wires in the fluoride gel did not affect their tensile properties, however, surface deterioration was evident. So, further investigations are recommended to study the effect of these changes on the oral health of patients.