Influence of pH Level and Type of Archwire on the Time Bound Release of Nickel Ions from Orthodontic Appliances - An In Vitro Study

Abstract

BACKGROUND Orthodontic metallic appliances in the oral cavity are constantly in contact with biological fluids or tissues thereby releasing particulate masses. They can be common causes of contact allergies and should be considered as a critical issue in determining properties of biomaterials. Nickel ions in various forms and compounds have been known to cause carcinogenic, mutagenic, cytotoxic and allergenic reactions. Pattern of metal ions released from different stainless steel orthodontic appliances in vitro could provide valuable information to consider their application in clinical scenarios. The purpose of the present study was to evaluate metal ions released under different ph levels, immersion period time and using different archwire orthodontic appliances. METHODS Orthodontic appliances were constructed consisting of five brackets from central incisor to the second premolar, a buccal tube welded molar band and an archwire that were used as samples. Total of twelve appliances were constructed; using stainless steel, Ni - Ti, and Thermal Ni - Ti wires (N = 4 each). Half of these samples were immersed in artificial saliva at pH 3.5 and the other half were immersed in artificial saliva at pH 6.75. The samples were stored in an incubator at a temperature of 37 degrees Celsius. Saliva samples from these bottles were collected at the end of 1, 7, 14 and 28 days and subjected to spectrophotometric analysis for estimation of nickel content. RESULTS Nickel release was maximum during the first week of immersion from orthodontic appliances comprising of Ni - Ti wires compared to Stainless steel and thermal Ni - Ti. A gradual decline in the nickel release was observed in the subsequent weeks. Ion release was increased by 30 times in the acidic pH medium, as compared to neutral pH conditions. CONCLUSIONS There is a definite release of nickel ions from orthodontic appliances when exposed to oral environment; however, the amounts are much lower than the daily dietary intake and don’t pose risk of toxicity. Care should be taken in patients with nickel hypersensitivity and wires such as beta - titanium or epoxy coated wires can be substituted. As there is an increase in ion release under acidic conditions the patients need to maintain hygienic oral environment thereby limiting corrosion of appliances. KEY WORDS NitiAlloy, Archwires, pH, Hypersensitivity