Preventing metal allergies caused by orthodontic appliances ― New orthodontic wire developed by Tohoku University

A research group led by Assistant Professor Arata Ito of the Department of Oral Health Enhancement, Tohoku University Hospital, and Associate Professor Hideki Kitaura and Professor Itaru Mizoguchi of the Division of Orthodontics and Dentofacial Orthopedics, Graduate School of Dentistry, Tohoku University, has found that using an ion plating method to coat orthodontic wires with titanium nitride (TiN), a ceramic with excellent biocompatibility, can suppress metals from leaching out of orthodontic wires. Furthermore, they succeeded in experimentally demonstrating that TiN does not flake off even after being brushed 20,000 times with a toothbrush, which is thought to be the main cause of coatings flaking off.

Patients with metal allergies often react to nickel (Ni), which may then interfere with orthodontic treatments because orthodontic wires containing Ni cannot be used. The research group began this research on wire surface coatings to find a way to keep Ni ions from leaching from the surface of a wire. Although the research group looked at a variety of coating methods and materials, they found that using an ion plating method to apply the TiN coating to stainless steel orthodontic wires suppressed the amount of Ni and chromium (Cr) ions that leached out of the wires when they were immersed in strong acids. The coating also has excellent biocompatibility because it uses Ti as a raw material.

The effects of daily tooth brushing and clinical wire bending adjustments were also examined as possible causes for coating detachment. No coating peeling was observed even after brushing the wire 20,000 times with toothbrushes and then analyzing it with electron microscopy and energy-dispersive spectroscopy. However, metal leaching was observed as the bending angle of the wire increased, which indicated the need for further improvements.

According to Kitaura, "Going forward, we plan to use mice that are allergic to metal to examine whether allergic symptoms can be suppressed when the coated wires are in contact with the mice. In the future, we hope to be able to take the coated wires that we developed and clinically apply them to patients with metal allergies."

■ Ion plating method: One of the methods for coating metals. In this method, Ti and other metals are vaporized by an electron beam, are positively charged via plasma, and then a coating film is formed on the negatively charged metal through electrical attraction.

Journal Information
Publication: Applied Sciences
Title: Analysis of coating loss from coated stainless steel orthodontic wire
DOI: 10.3390/app12199497