Dental Watch Home Page

The Clinical and Legal Mythology of Anti-Amalgam

Michael J. Wahl, D.D.S.


Myth #4: Amalgams cannot be bonded to teeth.

Fact #4: Amalgam can be bonded to teeth, often yielding higher
bond strengths than are obtained by resin composites.

In 1996, Freedman stated, "Composites are bonded to dentin and enamel, recreating the monobloc of the original undecayed tooth. Amalgam simply fills a cavity, and may act as a wedge during mastication." He stated further that "teeth are prepared more conservatively for composite restorations. The preparation for amalgams requires extensions for retention and prevention, implying the loss of healthy tooth structure."[1] Vasserman stated that amalgam "has forced us to extend cavity preparations to accommodate the material rather than have the materials accommodate the preparation." [2] Simonsen stated that amalgam should "move over" because of "the ability to carry out far more conservative cavity preparations with the bonded, and better, alternative materials, be they resin composite or resin-modified glass-ionomer materials." [3] In criticizing the use of amalgam, Erickson stated, "There still is a heavy anti-bonded-restorations voice out there." [4]

All these authors state or imply that amalgam is not or cannot be bonded to teeth. But amalgam bonding is now routinely used by many if not most dentists who place amalgam restorations. Although most studies have shown bond strengths of amalgam to dentin to be less than those of composite to dentin, some studies have shown amalgam-to-dentin bond strengths of 27 [5,6] and even 33 MPa [7], higher than the 23 to 25 MPa normally reported for composite-to-dentin bonding [8]. A 1999 study of various dentin adhesives indicated that mean bond strengths were significantly greater for amalgam than for composites [9]. The highest bond strength was 33.0 MPa for amalgam to dentin but only 26.4 MPa for resin composite to dentin.


Myth #5: Because of recent advances in materials and techniques,
most studies of composites are outdated; most studies of amalgams are not.

Fact #5: Improvements in amalgam restorative materials
and techniques in recent years have been at least as dramatic
as those of resin composite restoration materials.

Many anti-amalgamists assert that resin composite materials and techniques have improved in the last few years, rendering any past studies of composites irrelevant, but amalgam materials and techniques have also improved. High-copper amalgams have much better properties than do conventional amalgams, including better corrosion resistance, higher early strength, and better performance, were not widely available until after 1975 [10]. Tooth preparation techniques for amalgam restorations have changed from sharp to rounded line angles [11]. Caries-indicating dyes, fluoride-releasing cavity liners, adhesive bonding materials, and smaller preparations are some recent advances in the placement of amalgam restorations.


Myth #6: Resin composites are superior to amalgam because composites can be repaired.

Fact #6: Like resin composites, amalgam restorations can often be repaired.

A feature of resin composite restorations is that they can be repaired simply by bonding new composite to the old composite, usually after placement of additional retention with undercuts in the old restoration or in the preparation. Amalgam can be repaired also; even without bonding, it is often possible to repair the restoration simply by placing undercuts in the remaining old restoration before adding new amalgam [12]. It is now also possible to bond fresh amalgam to old amalgam [13].


Myth #7: Amalgam is 100 years old; composite is much newer and therefore better.

Fact #7: Like radiography and gold restorations, amalgam's
longevity is testament to its safety and efficacy.

Dickerson [14] called it "a crimethat the most common restoration today is the same as it was 100 years ago. Where is the progress in our profession? What other industry has not had a significant advancement in materials used in the last 100 years?" Although amalgam has been in use for over 100 years, there have been dramatic improvements in amalgam materials and techniques, especially in the last 25 years. The modern amalgam materials and techniques bear little resemblance those of 100 years ago. Aspirin, the automobile, the electric light bulb, the telephone, the flush toilet, and central heating are each in common use and are more than 100 years old. In dentistry, radiography, nitrous oxide, gold restorations, and rubber dams are more than 100 years old, and are still commonly used today. Even the history of resin composite can be traced to the discovery of acrylic acid over 150 years ago and to the discovery of methacrylate esters and their polymers over 100 years ago [15].

The quality of a material or technique should not be judged solely on its age, but rather on its clinical and scientific performance. The fact that dental amalgam has been used for more than 100 years is not in and of itself a negative; it simply means there has been more time to study it.


References

  1. Freedman G. Fifth-generation bonding systems: predictable posterior composite restorations. Dent Today 1996;15(11):68-75.
  2. Vasserman A. It's time to bury our amalgamators! Dent Econ 2000;90(3):16,171.
  3. Simonsen RJ. Move over amalgam ­ at last. Quintessence Int 1995;26:157.
  4. Erickson RH. Controversy continues. [Letter.] Dent Econ 1998;88(7):16-7.
  5. Summitt JB, Miller B, Buikema DJ, Chan DCN. Shear bond strength of Amalgambond Plus cold and at room temperature. J Dent Res 1998;77(Spec Issue A):274 [abstract 1345].
  6. Miller B, Chan DCN, Cardenas HL, Summitt JB. Powder additive affect on shear bond strengths of bonded amalgam. J Dent Res 1998;77 (Spec Issue):274 [Abstract 1346].
  7. Evans DB, Neme AL, Kohn DH. Bondstrength of amalgam and composite adhesive systems. J Dent Res 1997;76 (Spec Issue):67 [Abstract 432].
  8. Swift EJ, Bayne SC. Shear bond strength of a new one-bottle dentin adhesive. Am J Dent 1997;10:184-8.
  9. Evans DB, Neme A-ML. Shear bond strength of composite resin and amalgam adhesive systems to dentin. Am J Dent 1999;12:19-25.
  10. Dunne SM, Gainsford ID, Wilson NHF. Current materials and techniques for direct restorations in posterior teeth. Part 1: silver amalgam. Int Dent J 1997;47:123-6.
  11. van Noort R. Dental Amalgams. In: van Noort R. Introduction to Dental Materials. Mosby:St. Louis;1994:75-88.
  12. Cowan RD. Amalgam repair--a clinical technique. J Prosthet Dent 1983;49:49-51.
  13. Jessup JP, Vandewalle KS, Hermesch CB, Buikema DJ. Effects of surface treatment on amalgam repair. Oper Dent 1998;23:15-20.
  14. Dickerson WG. Why is esthetic dentistry grouped with the outlaws? Dent Econ 1998;88(12):42-46,105.
  15. Bowen RL, Barton JA, Mullineaux AL. Composite restorative materials. National Bureau of Standards Special Publication 354. Dental Materials Research. Proceedings of the 50th Anniversary Symposium, Held Oct. 6-8, 1969, Gaithersburg, Md. (Issued June 1972.)


Dr. Wahl practices dentistry in Wilmington, Delaware. This article was originally published in Quintessence International 32:525-535, 2001 and is reproduced here with the kind permission of Quintessence Publishing Co. The author also thanks Drs. J. Rodway Mackert, Ivar A. Mjör, and Fred Eichmiller for reading the manuscript and offering several helpful suggestions.


Part 1: Intro ||| 1 ||| 2 ||| 3 ||| 4, 5, 6, 7 ||| 8, 9 ||| 10, Conclusion
Part 2: Intro ||| 1 ||| 2 ||| 3 ||| 4 ||| 5 ||| 6 ||| 7 ||| 8 ||| 9 ||| 10, Conclusion

Dental Watch Home Page

This page was posted on November 1, 2002.