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Archaeologists have long appreciated the importance of materials to the development of man and classified time periods according to the dominant materials in use. Thus we have the stone age, iron age etc. In today's world we use such a diversity of materials for such a diversity of applications, that the importance of materials is rarely appreciated. Today we use materials in the form of polymers, metal ceramics and glasses for applications as far apart as heat resistant tiles on the space shuttle to integrated circuits in your home computer.
Material Scientists use a combination of physics, chemistry and maths to design new materials and optimise the performance of existing ones. This article will look at new materials for filling teeth. Most people are susceptible to dental decay where bacteria in the mouth produce acid which destroy teeth. These decayed teeth have to be repaired and to do this successfully a dentist requires a suitable material. In Ireland most dentists will carry out the repair by filling the tooth with an amalgam, which consists of a mixture of silver particles and liquid mercury. The mercury dissolves the silver particles and forms a solid alloy or amalgam. Whilst the amalgam filling is very strong and wear resistant it has many drawbacks. In particular it does not stick to the tooth and this means the dentist has to make a large under cut cavity to keep the filling in place (Figure 1). Whilst amalgams can be keyed in place successfully the filling leaks and bacteria and oral fluids can seep down between the filling and tooth causing subsequent tooth decay. Amalgams also suffer from conducting heat too well which results in many people with fillings experiencing pain when hot or cold foods are taken into the mouth.
The new generation of filling materials being developed at the University of Limerick are based on the reaction between a polymeric acid and a basic glass to give a polymeric salt and water (Figure 2). These new filling materials can bond chemically to tooth material so less tooth material has to be cut away by the dentist, which conserves the healthy tooth (Figure 3).
In addition these new fillings release fluoride ions, which are swapped for hydroxyl groups in the mineral phase of the tooth and make it much less soluble in the acids produced by bacteria. Whilst the glass-ionomer cements have many advantages and are used at present for filling front teeth they lack the toughness and wear resistance of the amalgams.
At the University of Limerick we are studying how cracks propagate in Glass-ionomer cements and designing new versions with improved toughness and wear resistance for a new generation of dental fillings.
Dr. Robert Hill is a lecturer in Materials Science at UL. His primary interest is in Biomedical Materials.