Abstract
The aim of this study was to explore whether changes in the salivary pH influence mechanical properties, surface roughness, and ion release from NiTi archwires with various surface coatings, and discuss the clinical significance of the findings. The uncoated, rhodium-coated, and nitrified NiTi wires were immersed into artificial saliva of different pH values (4.8, 5.1, 5.5, and 6.6). Released nickel and titanium ions were measured with inductively coupled plasma-optical emission spectroscopy at the end of 28 days. Atomic force microscopy was used to measure the arithmetic average surface roughness Ra, the root-mean-square roughness Rq, and the maximum height of the asperities RZ. The nanoindentation hardness (HIT) and Young’s modulus (EIT) measurements were performed. The change in the pH of artificial saliva is inversely proportional to the release of titanium from both coated and uncoated wires, and the release of nickel from uncoated wires. The surface roughness parameters of both coated and uncoated wires are unaffected by the change in the pH of artificial saliva. The change in the pH of saliva has minor influence on the hardness and Young’s modulus of elasticity of both coated and uncoated wires. The concentration of released metal ions measured was below the recommended upper limit for daily intake; nevertheless, hypersensitivity effects cannot be excluded, even at lower concentrations and at low pH.
Highlights
The design of fixed orthodontic appliances can be complex, enabling plaque formation and accumulation [1], resulting in increases in the incidence and severity of the white spot lesions associated with orthodontic treatment [2]
The amounts of Ni- and Ti-ions for two wires were compared to the acceptable daily intake (ADI), which is the amount of a given substance in food or drinking water that can be ingested daily over a lifetime without posing a significant health risk [13]
The results showed that the most sensitive groups may react with systemic contact dermatitis at normal daily nickel exposure from drinking water, or food of 0.22–0.35 mg nickel in 1% of those individuals
Summary
The design of fixed orthodontic appliances can be complex, enabling plaque formation and accumulation [1], resulting in increases in the incidence and severity of the white spot lesions associated with orthodontic treatment [2]. The plaque pH remains low (4.8 or lower) for as long as the biofilm is undisturbed. Saliva flow and pH vary during the day, and, in patients with an increased number of S. mutans bacteria, periods of lowered pH of saliva happen more often because of the bacterial acid production [3]. In such patients, the periods of lowered pH are longer, i.e., in between meals and during sleep [4]. Most often, the pH of saliva fluctuates in the range from the low dental plaque to a near-neutral pH. The focus of this study will be on the changes caused by saliva in the pH range from 4.8 to 6.6
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