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BIOMATERIALS

Treatment with quality

A method developed at Unesp guarantees more efficient dental implants

A novel process for the treatment of the surface of titanium metal that serves as raw material for dental implants took on important innovations at the Chemical Institute (IQ) of the State of São Paulo University (Unesp) on the campus of the town of Araraquara. A new technique, kept as a secret as it is in the process of being patented, guarantees a better integration between the implant and the bone. It will provide more quality in the products of the manufacturers of pins that sustain the implanted tooth.

Under the coordination of professor Antônio Carlos Guastaldi, the research that began four years ago, is keeping an eye on the development of the use of titanium as a biomaterial. For professor Guastaldi, a biomaterial is defined as any substance or combination of substances that are not drugs or medicines, and are of natural or synthetic origin. They are used for any period of time as part or a complete system in substitution of tissues, organs or functions of the body. So that coexistence does not unleash adverse or uncontrolled reactions in the biological systems, the foreign material in the body must be biocompatible.

Titanium has already been used as a biomaterial in orthopedics replacing bones for at least twenty years. To improve the knowledge of this material in the area of odontology, professor Guastaldi took as a stepping stone the research project financed by FAPESP the Study of the Mechanical and Corrosive Properties of Titanium and of its Applied Alloys as a Biomaterial plus the collaboration of several masters and doctorate projects. The research starts out from the main characteristic of titanium, that it is a material very reactive in the presence of oxygen and consequently capable of self-oxidizing quickly.

With this reaction the metal creates an oxide coating on the surface, with a high thermodynamically stability that makes further chemical reactions difficult. Even though, titanium is used successfully as a biomaterial. The challenge of the researchers of Unesp-Araraquara is to develop a process that allows the alteration of the characteristics of the oxide coating. The objective is to have a more adequate response from the implants and prosthesis to the essential requirements for good use as a biomaterial i.e. to be biocompatible and biofunctional, to have bioadhesion and a compatible price with the Brazilian reality.

Synthetic bonding
“Our concern is to promote a change on the surface of the titanium turning it into an appropriate support, with a specific area for the placement of hydroxyapatite, a synthetic material that is similar to the inorganic part of the bone and bonds the implant to the bone, a phenomenon that is denominated Bone integration.”, explains professor Guastaldi. “Our research has been focusing on a path that is completely different from what is done elsewhere in the world.”, he states, further adding that the secret of the technique is in promoting subtle mutations on the surface of the titanium.

Even the most modern solutions have limitations. “To the naked eye, the dental implants look perfect.”, says professor Guastaldi. “However, when submitted to electronic systems of analysis, such as the electronic sweep microscope with an amplification from 35 to 10,000 times, they spot imperfections on the surface of the materials used that could endanger the so much desired bone integration. “One of the consequences is the opening of millimetric cracks in the implanted parts. In these cracks the substances that exist in saliva spur the growth of a bacterial plaque, responsible for the corrosion induced by micro organisms, thus putting the performance of the implanted biomaterial at risk. To be able to face such challenge, it is necessary to understand the basic chemistry and the chemistry of materials. With these concerns and necessities, professor Guastaldi huddled a team, called the Biomaterials Group, which includes chemists, dentists, pharmaceutics materials engineers and mathematicians.

A pioneer study
The first study of titanium within the Biomaterial Group was by the chemist Ivan Ramires with his doctorate thesis a Study of the Mechanics of Corrosion Employing Spectroscopy of Electrochemical Impedance of Biomaterials: Titanium and Metal Alloys Based on Titanium and had a grant from FAPESP. With the help of the mathematician Jorge Capela, he looked into the mechanisms of corrosion and the types of films that formed on the surface of the material when they are in contact with means that simulate the harshness of the saliva.

The chemist Luci Cristina de Oliveira studies in his doctorate thesis the Modification of the Surface of Titanium and of the Alloy Ti-6Al-4V for Dental Implants also with a grant from FAPESP, the modification of the surface of the materials, with the later incorporation of calcium phosphate that can create the hydroxyapatite, responsible for bone integration.

Plasma technique
Another chemist, Anselmo Colombo de Alencar, in 1998 began his doctorate with the theme a Study of the Modifications on the surface of c.p. TI – Commercially Pure Titanium and of the Alloy Ti-6Al-4V Used as Biomaterials Using Deposition by Plasma Spray, with a scholarship from the National Council of Scientific and Technological Development (CNPq in the Portuguese acronym). He used the technique of plasma spray that is one of the ways used for the covering of metallic implants with ionized gases through thermal effusion.

In this technique, the powder of the metal that you want to deposit on the material to be treated is sprinkled together with a cloud of plasma ( the fourth state of a material) with a high temperature pistol and pushed by the argon gas, which is inert. This way the metallic powder is targeted and fused onto the surface of the titanium. The result is an increase in the durability of the coating and an improvement of biocompatibility.

The problem, in all of the cases, is the instability or the short lifespan of the process of adhesion of the deposits of metal. “With this”, he explains, “the parts of the implant and the deposits present different mechanical properties and consequently work with modules of elasticity that are different, or that is to say, instead of acting in harmonious movement, they react in an antagonistic manner during the movements of chewing, prompting implant to fail .”

Business interest
The team of professor Guastaldi hopes to complete the tests of the new titanium implants during this semester. “It could take a little longer, but we are going to take all precautions so that the discovery has a practical application in a quick way.”, he says. Professor Guastaldi tells that the Brazilian company Conexão Sistemas de Prótese, a manufacturer of material for dental implants, is interacting with the Biomaterial Group and has a strong interest in the results commented by the researchers.

After having the method completely tested and the patent registered in Brazil and in other countries, a process that will have the support of FAPESP, the researchers of Unesp will negotiate the passing on of the technology to the company Conexão. The company has a strong interest in manufacturing parts for implants that provide greater safety and quality. If all runs well, new dental pins will be in the odontology market in 2002.

The project
A Study of the Mechanical Properties and Corrosion of Titanium and its Alloys Applied as Biomaterial; Modality Aid to research project; Coordinator Professor Antônio Carlos Guastaldi -Chemical Institute of Unesp-Araraquara; Investment R$ 13,173.27 and US$ 34,475.00

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