Tooth-coloured materials

This chapter is concerned with the essential classification of the materials used to repair teeth and restore their function. As far as direct restoratives are concerned, we follow the classification on Mount et al. [1] and consider that the two basic types of modem tooth-coloured materials are the composite resins and the glass-ionomer cements. They are fundamentally different, and though hybrids have been attempted, combining their advantages is not feasible for sound scientific reasons. 

The alternative tooth-coloured material, the glass-ionomer cement, has also been widely studied, especially in terms of its bioactivity. This arises from its ability to exchange ions with its surroundings when placed in the mouth. Typical conventional glass-ionomers have been shown to release sodium, silicon and phosphorus under neutral conditions, and also calcium and aluminium under acidic conditions [48]. The non-metals are assumed to be released as sihcate, Si03 ", and phosphate, PO/, respectively. In addition, they release fluoride [49], a process that is capable of continuing for several years [50]. 

Lloyd, C. H. Mitchell, L. (1984). The fracture toughness of tooth coloured restorative materials. Journal of Oral Rehabilitation, 11, 257-72. 

Qvist, V. (1975). Pulp reactions in human teeth to tooth coloured filling materials. Scandinavian Journal of Dental Research, 83, 54-66. 

As we have seen, in the classification of tooth-coloured dental restorative materials, the composite resins represent one of the major types [1,6], The other major type is the glass-ionomer cement. 

Clinical aspects of the tooth-coloured restorative materials... 

Glass polyalkenoate cement has a unique combination of properties. It adheres to tooth material and base metals. It releases fluoride over a long period and is a cariostat. In addition it is translucent and so can be colour-matched to enamel. New clinical techniques have been devised to exploit the unique characteristics of the material. 

A restorative material can be used for the aesthetic restoration of the front (anterior) teeth only if it is as translucent as tooth enamel. This is because colour matching depends on translucency as well as hue and chroma. 

For certain AB cements, used in dentistry, optical properties are important for their overall acceptability as materials. The two particular properties of interest have been colour and translucency, both of which need to match natural tooth material as closely as possible if good aesthetics are to be developed (Wilson McLean, 1988). Of the AB cements currently used in dentistry, the glass-ionomer cement has the best aesthetics, since it has a... 

Evaluation of these optical properties may be done by simple observation this approach is useful clinically (Knibbs, Plant Pearson, 1986), since acceptability of the colour match to the surrounding tooth material can be readily seen without the need for instrumental measurement. On the other hand, for quantitative evaluation of optical properties, some kind of instrumental measurement is necessary, and the property usually evaluated is opacity. 

Colour and opacity have been foimd to be connected for glass-ionomer cements (Crisp et al., 1979 Asmussen, 1983), with darker shades giving increased opacity. However, this is merely a consequence of the underlying physical relationships, and is not thought to be a clinical problem (Wilson McLean, 1988), mainly because the stained tooth material for which the darker shades are necessary for colour match is itself of reduced translucency. 

Live and dead lice (about 3 mm long and greyish-white or brown in colour) and yellowish cast exoskeleton shells can be seen by combing the hair with a fine-tooth comb over a sheet of white paper, after shampooing and towelling dry. Lice faecal material (black specks) may be found on pillows and collars. 

Dental silicate cements were used as aesthetic repair materials for anterior teeth [7]. Though they lacked the ability to adhere to the tooth, they did have a reasonable match for the appearance of the natural tooth, both in terms of colour and translucency. Nonetheless, they were not entirely satisfactory in clinical service and in particular were susceptible to acid erosion and staining in the mouth [7]. 

Filler loadings are low by comparison with some of the better conventional composites available, and this means that there is a relatively large volumetric shrinkage on polymerization [1]. However, to an extent swelling due to moisture uptake offsets this. Despite this moisture uptake, aesthetics of these materials are reasonable though they are now generally recommended for use in children s dentistry, and are available in a variety of colours (pink, blue, green) so that aesthetics in the sense of a close visual appearance to the natural tooth is less of a concern [38]. 

Composite materials are widely used in dentistry, mainly for tooth repair, but also for bonding orthodontic brackets. The range of components that can be used is restricted by a number of considerations, including the need to match the appearance (colour and translucency) of the natural tooth, and the need to restrict the substances used to those which are non-toxic. It is also important to use materials having appropriate mechanical properties. Current materials are described in this chapter, with information on their clinical applications and performance. Some information is also included on recent developments in these materials and these may affect their clinical use in the future. 

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