Modelling of Cr and Ni ions release during orthodontic treatment: in vitro and in vivo methods

Evaluation of the release of nickel and titanium under orthodontic treatment

The metal alloys used in dentistry are made mainly of nickel (Ni), titanium (Ti), and other elements such as molybdenum (Mo), zirconium (Zr), iron (Fe), tin (Sn), chrome (Cr), carbon (C), copper (Cu) and niobium (Nb) which can release metal ions in unstable environments. The aim of this work was determine the salivary pH before and during orthodontic treatment; evaluate the release of metal ions, mainly Ni and Ti, in urine and saliva using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES); and evaluate the corrosion using Scanning Electronic Microscopy (SEM). In this study, we selected 35 individuals under orthodontic treatment, from whom saliva and urine samples were collected in 3 stages: (a) basal, (b) at 3 and (c) 6 months after the placement of the fixed appliances. SEM analyzed the Ni-Ti (0.016″) and stainless steel (SS) (0.016 × 0.022″) archs after 1 month of being in contact with the oral cavity. Statistical analysis was performed with Stata using the ANOVA model of repeated measures with a p < 0.05. A statistically significant difference in the concentration of Ni in saliva were found between 3 and 6 months of intervention and Ti in urine was found 3 and 6 months.

The effect of electro-thermal treatment of stainless steel arch wire on mechanical properties and cell proliferation

Background

Electric resistance heat treatment may be performed on orthodontic arch wires, but it remains unclear whether this procedure reliably provides better mechanical properties or whether an austenite phase transition affords less cytotoxicity and less arch wire width change.

Methods

Stainless steel (SS) arch wires of 0.017 × 0.025 and 0.019 × 0.025 inches in size were heat-treated using a spot welder for eight seconds at power settings of 2, 4, 6 and 8. The surface morphology, coefficient of friction (COF), flexural modulus, cytotoxicity, austenitic content, colour change and arch width of the samples were subsequently analysed.

Results

The COF, flexural modulus and austenitic content of the orthodontic SS arch wires increased after heat treatment. SS wires appearing brownish-yellow and blue exhibited higher flexural moduli. The heat treatment of the SS wires did not significantly increase arch wire width or cause cytotoxicity.

Conclusions

Electric resistance heat treatment of SS arch wires is a feasible method to improve the flexural modulus without widening the arch wire and increasing cytotoxicity. The colour of the wire helps determine the heating status, and the maximum flexural modulus of the wires is obtained when the colour changes to brownish-yellow.

In vitro and in vivo evidence of the cytotoxic and genotoxic effects of metal ions released by orthodontic appliances: A review

Intraoral fixed orthodontic appliances are frequently used in the clinical practice of dentistry. They are made from alloys containing different metals at various percentages. The use of these appliances leads to the long-term exposure of patients to these materials, and the potential toxic effects of this exposure raises concerns about patient safety. Thus, the biocompatibility (corrosion behaviour and toxicity) of these materials has to be evaluated prior to clinical use. In the present report, the most recent studies in the scientific literature examining metal ion release from orthodontic appliances and the toxic effects of these ions have been reviewed with a special focus on cytotoxicity and genotoxicity. Previous studies suggest that a case-by-case safety evaluation is required to take into account the increasing variability of materials, their composition and the manufacturing processes. Moreover, in vivo toxicity studies in regard to metal release, cytotoxicity and genotoxicity are still scarce. Therefore, in vitro and in vivo monitoring studies are needed to establish cause-effect relationships between metal ion release and biomarkers of cytotoxicity and genotoxicity. Further investigations could be performed to elucidate the toxic mechanisms involved in the observed effects with a special emphasis on oxidative damage.