Biomedical Engineering Reference
In-Depth Information
4.1 Dental applications
The existing dental materials are mainly based on amalgam, resin composites or glass
ionomers. Amalgam, originating from the Tang dynasty in China, was introduced in the
early 19
th
century as the first commercial dental material. It is anchored in the tooth cavity
by undercuts in the bottom of the cavity to provide mechanical retention of the metal.
Although it has excellent mechanical characteristics it is falling out of favor in most dental
markets because of health and environmental concerns. One exception is the US in which
amalgam still has a redlatively large market share.
The second generation material is the resin composites, first introduced in the late 1950s.
These are attached to the tooth using powerful bonding agents that glue them to the tooth
structure. After technical problems over several decades, these materials today have
developed to a level where they work quite well and provide excellent aesthetic results.
Despite the improvements, resin composites have some drawbacks related to shrinkage,
extra bonding, irritant components, a risk of post-operative sensitivity, and technique
sensitivity in that they require dry field treatment in the inherently moist oral cavity. The
key problem, due to shrinkage or possible degradation of the material and the bonding, is
the margin between the filler material and tooth, which often fails over time leading to
invasion of bacteria and secondary caries. Secondary caries is a leading cause of restorative
failure and one of the biggest challenges in dentistry today. As a significant number of
dental restorations today are replacement of old, failed tooth fillings, it is clear that tackling
this problem is a major market need (Mjör, 2000). Secondary caries occurs not only after
filling procedures but also following other restorative procedures such as the cementation of
crowns and bridges.
Glass ionomers were first introduced in 1972 and today are an established category for
certain restorations and cementations. Their main weakness is the relatively low strength
and low resistance to abrasion and wear. Various developments have tried to address this,
and in the early 1990s resin-modified ionomers were introduced. They have significantly
higher flexural and tensile strength and lower modulus of elasticity and are therefore more
fracture-resistant. However, in addition to the problems of resin composites highlighted
above, wear resistance and strength properties are still inferior to those of the resin
composites.
The nature of the mechanisms utilized by Ca-aluminate materials (especially Mechanism 1
above) when integrating and adhering to tooth tissue and other materials makes these
materials compatible with a range of other dental materials, including resin composite,
metal, porcelain, zirconia, glass ionomers and gutta-percha. This expands the range of
indications for Ca-aluminate based products from not only those involving tooth tissue, e.g.
cavity restorations, but also to a range of other indications that involve both tooth tissue and
other dental materials. Examples include dental cementation, base and liner and core build-
up and endodontic sealer /filler materials, which involve contact with materials such as
porcelain, oxides and polymers and metals, and coatings on dental implants such as
titanium or zirconia-based materials.
The use of the Ca-alumiante materials may be a first step towards a paradigm shift for
dental applications. The features are summarized below.
Nanostructural integration
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Reduced risk of secondary caries and restoration failure
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Excellent biocompatibility
