Restorative materials

Date: 2015-10-07; view: 515.

Morphologic considerations

The crowns of the primary teeth are smaller but more bulbous than the corresponding permanent teeth, and the molars are bell-shaped, with a definite constriction in the cervical region. The characteristic sharp lingual occlusal angle of the facial surfaces results in the formation of a distinct faciogingival ridge that ends abruptly at the cemento-enamel junction. The sharp constriction at the neck of the primary molar necessitates special care in the formation of the gingival floor during class II cavity preparation. The buccal and lingual surfaces of the molars converging sharply occlusally, form a narrow occlusal surface or food table; this is especially true of the first primary molar. The pulpal outline of the primary teeth follows the dentoenamel junction more closely than that of the permanent teeth. The pulpal horns are longer and more pointed than the cusps would indicate. The dentin also has less bulk or thickness, and so the pulp is proportionately larger than that of the permanent teeth. The enamel of the primary teeth is thin but of uniform thickness. The enamel surface tends to be parallel to the dentinoenamel junction.

Silver amalgam.Silver amalgam has been used for restoring teeth for over 150 years and, despite the fact that it is not tooth coloured and that there have been repeated concerns about its safety (largely unfounded), it is still widely used. This is probably because it is relatively easy to use, is tolerant to operator error, and has yet to be improved as a material for economical restoring posterior teeth. Modern, non-gamma 2 alloy restorations have been shown to have extended lifetimes in permanent teeth when placed under good conditions, and have also been shown to be much less sensitive to poor handling than tooth-coloured materials. Despite these good properties, amalgam has two main disadvantages: it is not aesthetic and it contains mercury, a known poison.

Composite resin.Composite resins came on the market in the early 1970s and have been modified since then in an attempt to improve their properties. Current materials are still best applied to anterior teeth and small restorations in posterior teeth. The development of acid etching at the time that these materials were introduced has ensured that they have performed reasonably well in terms of marginal seal. They are sensitive to variations in technique and take longer to place than equivalent amalgam restorations. They must be placed in a dry field. The long-term success of composite resins is jeopardized by their instability in water. The best materials have maximum inorganic filler levels and low water absorption, but will deteriorate over time.

Before making decisions concerning the most appropriate restorative material in the treatment of children, the clinician should consider:

1. Moisture exclusion. Is it realistic for this patient?

2. Patient compliance. Will the patient sit still through the restoration?

3. The size of the cavity. Lesion extent determines operative duration.

4. Patient compliance after the procedure. Will he or she return for monitoring and review?

Glass ionomer.This group of materials tend to be more brittle than composites, but have the advantage of adherence to both enamel and dentine without etching. The coefficient of expansion of glass ionomer is very close to that of dentine and once set, these materials remain dimensionally stable in the mouth despite constantly changing moisture and temperature levels. Their biggest advantage over composites is that they are able to release fluoride over an extended period of time. Their lack of strength limits their use in the permanent dentition but they can be used in PRDs where there is no occlusal load and as an interim restoration while caries is brought under control. They are also the authors' choice of material for cementing stainless-steel crowns.

Resin-modified glass ionomer.These consist of a glass ionomer cement to which we added a resin system that will allow the material to set quickly using light or chemical catalysts (or both) while allowing the acid-base reaction of the glass ionomer to take place. Thus, the materials will set, albeit rather slowly, without the need for the resin system and the essential qualities of a glass ionomer cement should be retained.

Polyacid-modified composite resin (Compomer).In contrast, these materials have a much higher content of resin and the acid-base reaction of the glass ionomers does not take place. Therefore although they are easier to use (being premixed in capsules), there is some doubt as to the longer term benefits over conventional composite resins. However, recently published work has shown compomer to be as durable as amalgam after 3 years in approximal cavities in primary molars.