Re: AMALGAM

Modern use as a dental restoration

Amalgam is an "excellent and versatile restorative material"and is used in dentistry for a number of reasons. It is inexpensive and relatively easy to use and manipulate during placement; it remains soft for a short time so it can be packed to fill any irregular volume, and then forms a hard compound. Amalgam possesses greater longevity when compared to other direct restorative materials, such as composite.However, this difference has decreased with continual development of composite resins.

Amalgam is typically compared to resin-based composites because many applications are similar and many physical properties and costs are comparable.
Longevity

Amalgam is "tolerant to a wide range of clinical placement conditions and moderately tolerant to the presence of moisture during placement.[20] In contrast, the techniques for composite resin placement are more sensitive to many factors and require "extreme care"and "considerably greater number of exacting steps".

Mercury has properties of a bacteriostatic agent whereas TEGMA (constituting some older resin-based composites) "encourages the growth of microorganisms.".This leads to increased decay underneath older resin-based composites while those underneath mercury restorations progress much more slowly."

Recurrent marginal decay is a very important factor in restoration failure, but more so in composite restorations. In the Casa Pia study in Portugal (1986–1989), 1,748 posterior restorations were placed and 177 (10.1%) of them failed during the course of the study. Recurrent marginal decay was the main reason for failure in both amalgam and composite restorations, accounting for 66% (32/48) and 88% (113/129), respectively.Polymerization shrinkage, the shrinkage that occurs during the composite curing process, has been implicated as the primary reason for postoperative marginal leakage.

These are some of the reasons why amalgam has remained a superior restorative material over resin-base composites. The New England Children’s Amalgam Trial (NECAT), a randomized controlled trial, yielded results "consistent with previous reports suggesting that the longevity of amalgam is higher than that of resin-based compomer in primary teethand composites in permanent teeth.Compomers were seven times as likely to require replacement and composites were seven times as likely to require repair

There are circumstances in which composite serves better than amalgam. For example, when a more conservative preparation would be beneficial, composite is the recommended restorative material. These situations would include small occlusal restorations, in which amalgam would require the removal of more sound tooth structure,as well as in "enamel sites beyond the height of contour."For cosmetic purposes, composite is preferred when a restoration is required on an immediately visible portion of a tooth.

Removal and replacement of amalgam restorations has traditionally been considered when "ditching" is present on the edges of the restoration. Ditching is "a deficiency of amalgam along the margin, preventing the margin of the cavity preparation from being flush… An area of ditching is also commonly referred to as a submarginal area and it requires removing tooth structure or replacing the amalgam to correct the situation."