Bioceramics

Bioceramics are ceramic materials specially developed for use as medical and dental implants. They are usually used to replace hard tissue in the body like bone and teeth.

Common bioceramics are alumina, zirconia and a form of calcium phosphate known as hydroxyapatite.

Bioactive and bioinert

Bioactive ceramics interact with the body so that tissue bonding and eventual incorporation into the body occurs after a time. Calcium phosphate-based bioceramics are bioactive.

Bioinert ceramics do not interact with the body’s environment apart from causing an initial ‘fibrous tissue’ reaction, which coats the ceramic. Alumina and zirconia-based ceramics are classed as bioinert.

Raw materials

Alumina (Al₂O₃) is a white powder. When shaped, compressed and heated to a high temperature (sintering), the ceramic that results has high density, high strength, excellent corrosion resistance, good biocompatibility and high wear resistance. In addition, it can be machined, ground and polished to a high-quality product.

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Hip replacement components

In hip replacement operations, the ball and socket joint is surgically removed. Some of the artificial replacement parts such as the femoral head are made of the bioceramic known as alumina.

Zirconia (ZrO₂) is also a white powder. Like alumina, it can be compressed and sintered into a very strong ceramic. Unlike alumina, its wear-resistance properties are not as good. By adding yttrium oxide and small amounts of magnesium oxide, a better-wearing bioceramic called Y-TZP can be made.

Calcium phosphate or hydroxyapatite – Ca₁₀(PO₄)₆(OH)₂ – is the principal component of natural bone in the body. Ceramics made from synthetic calcium phosphate can also be used in medical applications. The problem is that these ceramics are not as strong as alumina or zirconia ceramics.

Bioceramic bones and teeth

Alumina bioceramics are used as replacement parts in hip and knee operations. The inertness of the ceramic, its high wear resistance and its excellent biocompatibility make it the ceramic of choice.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Hip joint

Wear and tear on the ball and socket joint of the hip can result in pain, discomfort and restricted movement. A hip replacement operation may be needed.

The high load-bearing properties of alumina also makes it an ideal ceramic for dental implants.

Zirconia bioceramics do not have the high wear resistance of alumina bioceramics and are not as widely used in hip joint applications. However, their fracture toughness and bending strength give them additional qualities.

Calcium phosphate ceramics can bond to bone and promote bone growth at their surfaces. A popular use of these ceramics is as coatings on dental and orthopaedic implants. For example, titanium tooth root pegs coated with hydroxyapatite (a form of calcium phosphate) give a longer lasting implant than pegs that have been glued or cemented in place. The hydroxyapatite binds chemically with living bone because it is a bioactive ceramic.

Find out more about the minerals found in human teeth and bones that give them their hardness and strength.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Tooth decay

Once the dentin under the tooth enamel is exposed, tooth decay can set in. Over time, the decay can progress, resulting in significant pain and people becoming more self-conscious about their smiles.

Bovine hydroxyapatite

Often as a result of injuries sustained in road crash accidents, bone reconstruction operations are needed. A novel method involving the use of bovine hydroxyapatite has been successfully tested in sheep and dogs.

Spongy bone material from cow bones is cut out and subjected to chemical and physical processes that remove all of the fat and protein. The remaining material is then heated to 1,000°C. After this heating process, what remains is an open 3D mineral shell of hydroxyapatite.

Small cubes of this material can be grafted into the damaged living bone site. Over a period of time, new bone develops and grows in and around the implant. Eventually, successful repair of the damaged bone is achieved.

Although not yet tested on humans, the indications are that, in the future, this method of bone repair could be used, but only in non load-bearing settings.