Chemical and physical properties of nickel-free brackets: An in vitro and ex vivo controlled clinical trial

Abstract

Objective:

To evaluate the chemical and dimensional changes of metallic and nickel-free metallic brackets in vitro and ex vivo, regarding oxidation, tie-wing deformation and surface roughness.

Design:

A split-mouth, in vitro and ex vivo controlled clinical trial.

Methods:

A total of 34 adult participants, aged 20–35 years, underwent conventional orthodontic treatment. The right upper central incisor carried the metallic bracket and the left upper central incisor carried the nickel-free metallic bracket. At the 120th day of treatment with a 0.018-inch steel alignment wire, the upper central incisor brackets were removed (ex vivo) and compared with unused brackets (in vitro), distributed into four groups (n = 34): group 1 = in vitro metallic brackets; group 2 = ex vivo metallic brackets; group 3 = in vitro nickel-free metallic brackets; and group 4 = ex vivo nickel-free metallic brackets. Analyses were performed using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) to assess slot dimensions and surface irregularity (roughness), respectively, and by energy dispersive spectroscopy (EDS) for oxidation. Analyses were performed with a significance level of 5%.

Results:

Evaluation of composition showed that ex vivo nickel-free and metallic brackets had higher percentages of oxygen (O) and carbon (C), lower percentages of niobium (Nb) and chromium (Cr) (P <0.05), and no significant difference in the percentage of iron (Fe) (P >0.05). Brackets showed no dimensional changes when comparing in vitro and ex vivo conditions. Ex vivo metallic brackets had increased roughness compared to in vitro metallic brackets.

Conclusions:

The oral environment promoted corrosion in both metallic and nickel-free brackets. Nickel-free brackets did not have rougher surfaces than metallic brackets, and there were no dimensional changes after use in participants.

Plain language summary

How nickel-free and metallic orthodontic brackets perform in the laboratory and after use

Why was this study done? Orthodontic brackets are small attachments that are stuck to teeth to help correct their position. Brackets can be made of metal, often containing nickel, which can set off allergic reactions in some people. Brackets without nickel have been made to reduce this risk. However, it was not clear whether their shape, surface or chemical make-up changes during use.

What did the researchers do? A total of 34 adults having orthodontic treatment had a normal metal placed on one of their top front teeth and a nickel-free metal bracket on the other one. After about 4 months, the brackets were removed and tested in the laboratory and compared with new brackets. Researchers used microscopes and chemical tests to look at changes in their shape, surface roughness and chemical make-up.

What did the researchers find? Both normal metal and nickel-free metal brackets had some changes in their chemical make-up after being in the mouth. Both types of bracket stayed the same shape and size. Nickel-free brackets stayed smooth. Normal metal brackets became slightly rougher. Nickel-free brackets did not release nickel ions into the mouth.

What do the findings mean? Nickel-free brackets are safe and strong They keep their shape and their surfaces stay smooth during early orthodontic treatment. They are a suitable option for patients, especially those with a nickel allergy. This research helps orthodontists choose brackets that are effective and safe for patients having orthodontic treatment with fixed metal braces.