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Dental amalgam

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An amalgam is an alloy of mercury with another metal. Most metals are soluble in mercury, but some (such as iron) are not. Amalgam also may be a solution of metal-like ion complexes, such as ammonium. Amalgams are commonly used in dental fillings.

Modern use as a dental restorationEdit

Amalgam is an "excellent and versatile restorative material"[1] 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 than other direct restorative materials, such as composite;[2] on average, most amalgam restorations serve for 10 to 12 years, whereas resin-based composites serve for about half that time.[3] However, because of recent improvements in composite material science and a better understanding of the technique-sensitivity of placement, the length of composite survival has increased substantially.[4]

The cost benefit analysis of the use of amalgam is often compared to that of resin-based composites because it would be the latter material that would generally be used as an alternative should the amalgam analysis prove unfavorable. There are many reasons why amalgam enjoys greater overall longevity than that of resin-based composites. Among these reasons are that composites are technique sensitive and require "extreme care"[5] and "considerably greater number of exacting steps"[6] in their proper placement. On the other hand, amalgam is "tolerant to a wide range of clinical placement conditions and moderately tolerant to the presence of moisture during placement.[7]

Another important issue is the environment at the tooth-restoration margin. Whereas the elemental composition of amalgam serves as a bacteriostatic agent, TEGMA, the basic constituents in many resin-based composites, actually "encourages the growth of microorganisms."[8] Because of this, recurrent marginal decay underneath resin-based composites "requires almost immediate removal, whereas those underneath amalgam restorations progress much more slowly."[9]

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.[10] Polymerization shrinkage, the shrinkage that occurs during the composite curing process, has been implicated as the primary reason for postoperative marginal leakage.[11][12]

It is for these reasons and more that amalgam has been substantiated as 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 teeth[13][14] and composites in permanent teeth.[15][16] Compomers were seven times as likly to require replacement and composites were seven times as likely to require repair.[17]

There are circumstances in which composite serves better than amalgam; when amalgam is not indicated, or 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,[18] as well as in "enamel sites beyond the height of contour."[19]

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."[20]

Dental amalgam controversyEdit

Main article: Dental amalgam controversy

Dental amalgam is a source of low-level exposure to mercury, and concerns have been raised about whether this poses a health hazard. Despite considerable investigation, no scientific evidence links it as a cause of clinically significant toxic effects, except for the rare local hypersensitivity reaction. The American Dental Association Council on Scientific Affairs concluded that both amalgam and composite materials are safe and effective for tooth restoration,[21] and The National Institutes of Health has stated that amalgam fillings pose no personal health risk, and that replacement by non-amalgam fillings is not indicated.[22] Recent random clinical trials have also established that amalgams are safe, finding no evidence of neurological harm or deleterious renal effects associated with their use in children after examining a period of 5–7 years following treatment.[23][24] However, these studies did not address longer-term effects.[25] The preparation of amalgam could pose a potential health hazard to dental workers who work with mercury compounds in relatively high concentrations. Because mercury is a regulated waste in some countries, its disposal can be costly.

See alsoEdit


ReferencesEdit

  1. Berry TG, Summit JD, Chung AKH, Osborne JW. Amalgam and the new millennium. JADA 1998;129:1547-1556.
  2. Allan DN. A longitudinal study of dental restorations. Br Dent J 1977;143:87-9.
  3. Moffa JP. Comparative performance of amalgam and composite resin restorations and criteria for their use. In: Quality evaluation of dental restorations; criteria for placement and replacement. Proceedings of the International Symposium on Criteria for Placement and Replacement of Dental Restorations, Lake Buena Vista, FL., Oct. 19-21, 1987. Carol Stream, Illinois.: Quintessence; 1989:125-38.
  4. Leinfelder KF. Do restorations made of amalgam outlast those made of resin-based composite? JADA 2000;131:1186-1187.
  5. Christensen, GJ. Longevity of posterior tooth dental restorations. JADA 2005;136:201-203.
  6. Leinfelder KF. Do restorations made of amalgam outlast those made of resin-based composites? JADA 2000;131:1186-1187.
  7. Soncini JA, Maserejian NN. The longevity of amalgam versus compomer/composite restorations in posterior primary and permanent teeth. JADA 2007;138:763-772.
  8. Leinfelder, KF. Do restorations made of amalgam outlast those made of resin-based composite? JADA 2000;131:1186-1187.
  9. Leinfelder KF. Do restorations made of amalgam outlast those made of resin-based composite? JADA 2000;131:1186-1187.
  10. Bernardo M, Martin MD, Lerouz BG. Survival and reasons for failure of amalgam versus resin-based composites posterior restorations placed in a randomized clinical trial. JADA 2007;138:775-783.
  11. Burgess JO, Walker R, Davidson JM. Posterior resin-based composite: review of the literature. Pediatr Dent 2002;24(5):465-479.
  12. Estefan D, Agosta C. Eliminating microleakage from the composite resin system. Gen Dent 2003;51)6):506-509.
  13. Forss H, Widstrom E. The post-amalgam era: a selection of materials and their longevity in the primary and young permanent dentition. Int J Paediatr Dent 2003;13(3):158-164.
  14. Soncini JA, Maserejian NN. The longevity of amalgam versus compomer/composite restorations in posterior primary and permanent teeth. JADA 2007;138:763-772.
  15. Qvist V, Thylstrup A. Restorative treatment patterns and longevity of amalgam restorations in Denmark. Acta Odontol Scand 1986;44(6):343-349.
  16. Soncini JA, Maserejian NN. The longevity of amalgam versus compomer/composites restorations in posterior primary and permanent teeth. JADA 2007;138:763-772.
  17. Soncini JA, Maserejian NN. The longevity of amalgam versus compomer/composites restorations in posterior primary and permanent teeth. JADA 2007;138:763-772.
  18. Fuks AB. The use of amalgam in pediatric patients. Pediatr Dent 2002;24(5):448-455.
  19. Newman SM. Amalgam alternatives: what can compete? JADA 1991;122(8):67-71.
  20. [1]
  21. ADA Countil on Scientific Affairs. Direct and indirect restorative materials. JADA 2003;134(4):463-472.
  22. Clifton JC 2nd (2007). Mercury exposure and public health. Pediatr Clin North Am 54 (2): 237–69, viii.
  23. (2006). Neurobehavioral effects of dental amalgam in children: a randomized clinical trial.. JAMA. URL accessed on 2006-12-23.
  24. (2006). Neuropsychological and renal effects of dental amalgam in children: a randomized clinical trial.. JAMA.
  25. (2006). Mercury in Dental Amalgam—A Neurotoxic Risk?. JAMA.

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