ASSESSMENT OF THREE ORTHODONTIC ARCH WIRES FOR CORROSION RESISTANCE IN ARTIFICIAL SALIVA AND FLUORIDE ENVIRONMENTS -AN IN VITRO STUDY.
BRIEF RESUME OF THE INTENDED STUDY:
NEED FOR THE STUDY:
Corrosion is the gradual destruction of materials by chemical reaction with its environment. The oral cavity itself is corrosive in nature, due to the presence of chloride ion concentration in it. Dental gels and resins which contain fluoride, used regularly will prevent dental caries.
The orthodontic metal wire has progressed from nickel-chromium-iron, stainless steel alloy to nickel-titanium alloy. The poor corrosion resistance of the orthodontic arch wires affects the effectiveness and prolongs the orthodontic treatment and may also give rise to toxic and allergic reactions due to nickel release. A protection layer of nickel oxide and titanium oxide forms on nickel titanium and titanium surface’s respectively when they come in contact with aqueous nature. This passivation layer prevents further diffusion of oxygen and results in corrosion resistance. If this layer is disrupted the wires becomes corroded.
Therefore the aim of this study is to compare the corrosion resistance of three arch wires in artificial saliva and fluoride environment.
REVIEW OF THE LITERATURE:
A study1was conducted toassess the influence of fluoride concentration on the corrosion behavior of nickel titanium and to compare the corrosion resistance of Nickel-Titanium (NiTi) with that of beta titanium alloy with and without addition of fluoride. They were done through electro-chemical impendence spectroscopy and anodic polarization in sodium chloride (NaCl 0.15 M). Galvanic corrosion between NiTi and beta titanium were investigated, samples were subjected to scanning electron microscopy. Nickel titanium suffer localized corrosion, while beta titanium remained passive. When lesser concentration of sodium fluoride added to sodium chloride solution, nickel titanium presented with localized corrosion. When the concentration of sodium fluoride increased the alloy presented generalized corrosion.
A study2 of hypothesis test done, to see that different nickel-titanium arch wires may have dissimilar corrosion resistance in fluoride oral environment. Linear polarization test, a fast electrochemical technique, was used to evaluate the corrosion resistance. Two way analysis of variance was used to analyze with the factor of arch wire manufacture and sodium fluoride concentration. They were analyzed using scanning electron microscope, atomic force microscopy and x-ray photoelectron spectroscopy. The surface topography did not correspond to the difference in corrosion resistance of the nickel titanium arch wires. The nickel titanium arch wires severely corroded and showed similar corrosion resistance in 0.5% sodium fluoride containing environment .Different nickel titanium arch wires had dissimilar corrosion resistance in acidic fluoride containing artificial saliva, which did not correspond to the variation in the surface topography of the arch wires.
The purpose of this study3 was to investigate the different manufactures using the fast electrochemical technique. The linear polarization test was used to evaluate the corrosion resistance, in terms of polarization resistance (Rp). One way ‘Analysis of Variance’ was used to analyze the Rp with the wire manufacturer as the variable factor. Electron spectroscopy for chemical analysis was used to see the chemical structure of the passive film on the nickel titanium wires. Atomic force microscopy was used to analyze the three dimensional surface topography and roughness (Ra). The statistical difference seen in Rp (P<.001) in different manufacturers of nickel titanium wires.
The purpose of the study4 was to determine if there is a significant difference in the corrosive potential of stainless steel, nickel titanium, nitride-coated nickel titanium, epoxy-coated nickel titanium and titanium orthodontic wires. At least two specimen of each wire were subjected to potentiostatic anodic dissolution in 0.9% NaCl solution with neutral ph. at room temperature. They used wenking MP95 potentiostat and an electrochemical cell, the break down potential of each wire was noted. Scanning electron microscope photograph were taken and surface changes were evaluated. The break down potentials of stainless steel , two nickel titanium wires, nitride-coated nickel titanium, epoxy-coated nickel titanium, and titanium were400mV, 300mV, 750mV, 1800mV, and >2000mV,respectively.scanning electron microscope photographs showed some nickel titanium, stainless steel wires were susceptible to pitting and localized corrosion .stainless steel corrode readily. The nitride coating did not affect the corrosion of the alloy, but epoxy coating decreased corrosion.
The study5 was done to see the effect of fluoride prophylactic agents on the loading and unloading mechanical properties and surface quality of beta titanium and stainless steel orthodontic wires. Rectangular beta titanium and stainless steel were immersed in either an acidulated fluoride agent, a neutral fluoride agent, or distilled water (control) for 1.5 hours at 370C.their loading and unloading elastic modulus and yield strength of the wires were measured. A one way analysis of variance and Dunnett’s post hoc, alpha=.05were used to analyze the mechanical testing data. Scanning electron microscopy was used to evaluate the wire topography. Their properties were decreased, and corrosive changes in surface topography were also observed.
OBJECTIVES OF THE STUDY:
To assess the influence of fluoride concentration on corrosion behavior of stainless steel, nickel titanium, and beta titanium.
The arch wire of each will be immersed in artificial saliva for 1 to 2 hour which acts as control group and different concentration of sodium fluoride is added to artificial saliva with ph. being maintained using diluted Hydrochloric acid (HCl) in a three cell electrode assembly.
After one hour of immersion, the potentiostatic reactions and scanning electron microscopy images are taken of orthodontic wires that are been tested.
PLAN FOR DATA ANALYSIS:
The statistical tests used is :
The data will be analyzed using “Analysis of Variance” to study the effect of corrosion on different wires.