Glass ceramic material is effective for treatment of dentin hypersensitivity

Biosilicate is also being tested in ocular implants and artificial middle ear ossicles.

By Elton Alisson

Agência FAPESP – Researchers at the University of São Paulo’s Dentistry School in Ribeirão Preto, São Paulo State, Brazil, are testing a glass-ceramic material for use in the treatment of dentin hypersensitivity. This condition, which manifests as acute pain in response to hot or cold drinks and food, arises from exposed dentin surfaces due to receding gums. Dentin is the tissue that forms the bulk of a tooth.

The material was developed by researchers at the Vitreous Materials Laboratory (LaMaV), part of the Federal University of São Carlos’s Materials Engineering Department (DEMa-UFSCar), São Paulo State, Brazil. It is also being tested in ocular implants and artificial middle ear bones, among other applications, at the Center for Research, Teaching, and Innovation in Glass (CeRTEV), one of the Research, Innovation and Dissemination Centers (RIDCs) funded by FAPESP.

“The material, which we call biosilicate, is obtained by controlled crystallization of a special glass using heat treatment. The technique enables us to produce a glass ceramic material with significant advantages over conventional glass,” said Edgar Dutra Zanotto, who heads CeRTEV and is a professor at DEMa-UFSCar.

According to Zanotto, one of the key features of this material is its bioactivity. On coming into contact with bodily fluids, such as saliva or blood plasma, biosilicate undergoes reactions that lead to surface coating with hydroxycarbonate apatite (HCA), a compound chemically similar to the mineral phase of bone. As a result, the bioactive glass ceramic material bonds with bones, teeth and even cartilage. “There are dozens of possible applications for biosilicate. So far, we’ve clinically tested only a few in medicine and dentistry,” Zanotto told Agência FAPESP.

Dentin hypersensitivity

To treat dentin hypersensitivity, the researchers applied biosilicate powder in the form of micrometric particles of sufficient size to fill cavities in dentin tubules.

When in contact with saliva, the material undergoes reactions that lead to the formation of HCA on its surface. The HCA coating occludes the dentin tubules, preventing the fluid within these microchannels from being stimulated by cold or hot drinks or food to cause sensitivity.

“Clinical trials have already been performed in humans to evaluate the effectiveness of this glass ceramic material for the treatment of dentin hypersensitivity,” Zanotto said.

In one of the clinical trials, conducted by researchers at the University of São Paulo’s Dentistry School in Ribeirão Preto, 142 patients were divided into groups submitted to different types of treatment.

The results showed that pain levels in the group of patients treated with biosilicate dispersed in a distilled water solution fell more than in patients treated with commercially available desensitizing toothpaste.

“The study suggested micronized particles of biosilicate can provide an immediate, effective and lasting response for patients who suffer from dentin hypersensitivity,” Zanotto said.

Artificial bone

The researchers at LaMaV are developing biosilicate-based artificial human middle ear ossicles, such as hammer, anvil and stirrup bones.

The middle ear prostheses are approximately 10 mm long and 1-2 mm thick. They are implanted in patients with hearing loss due to problems in these bones caused by infection or disease.

One of the key advantages of these biosilicate bones over implants based on other materials, according to Zanotto, is that besides being bioactive they are machinable, such that their size can be adjusted to a patient’s middle ear cavity during surgery.

“Each person’s cavity is a different size,” he said. “The surgeon can machine the biosilicate implant during the operation in order to make sure it fits properly into the patient’s ear.”

The prostheses were evaluated in a clinical trial by researchers at the University of São Paulo’s Dentistry School in Ribeirão Preto, involving 29 patients with hearing loss due to middle ear dysfunction.

Audiometric tests were performed three months after total or partial replacement of ossicles with biosilicate implants. The results showed that the prostheses were efficient. Twenty-four of the 29 patients recovered their hearing. The other five presented with problems that were not due to the implants.

“The percentage of patients whose hearing recovered is spectacular, indicating that these artificial implants are effective substitutes for middle ear ossicles, not only thanks to their biochemical and mechanical properties but also because they’re machinable,” Zanotto said.

Orbital implants

One of the most recent applications of biosilicate explored by researchers at LaMaV is in ocular implants (“glass eyes”).

Because biosilicate is bioactive, the ocular implants produced by the researchers using glass ceramics can bond with the tissue around a patient’s eyes. As a result, they accompany the motion of the patient’s healthy eye. “Conventional glass eyes are static,” Zanotto said. “They remain motionless when the undamaged eye moves.” According to Zanotto, polymer-based ocular implants that can also move are already on the market but cost as much as US$1,200.

“The idea of developing glass ceramic ocular prostheses is to obtain a product with a better biological response and at the same time to reduce the cost,” he said. The orbital implants are being evaluated in a clinical trial by researchers at the Ophthalmology Department of São Paulo State University’s Botucatu Medical School (FMB-UNESP), involving some 30 patients who have lost an eye to severe trauma.

According to a preliminary report produced by the surgical team responsible for the clinical trial, so far, none of the patients has presented with post-operative complications or signs of inflammation, dehiscence (breaking open of a surgical incision along the suture) or implant extrusion more than six months after surgery. Laboratory tests and CT scans also showed no alterations in the vital organs of the patients who completed the trial, and the implants have not suffered migration, abscess formation or inflammation of the surrounding tissue.

“The development of bioactive materials for medical applications is growing worldwide,” Zanotto said. “In our case, we have a collaborative network with more than 50 researchers at several institutions in areas such as biology, physical therapy, medicine and dentistry.”

The team’s biosilicate applications have resulted in several patents, some of which have been licensed to companies, including a patent for the use of biosilicate powder to treat dentin hypersensitivity.

“The idea is to develop these technologies and transfer them to spinoffs or established firms so that they come to market quickly and affordably,” Zanotto said.