Dental Watch Home Page
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." Vasserman stated that amalgam "has forced us to extend cavity preparations to accommodate the material rather than have the materials accommodate the preparation."  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."  In criticizing the use of amalgam, Erickson stated, "There still is a heavy anti-bonded-restorations voice out there." 
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 , higher than the 23 to 25 MPa normally reported for composite-to-dentin bonding . A 1999 study of various dentin adhesives indicated that mean bond strengths were significantly greater for amalgam than for composites . The highest bond strength was 33.0 MPa for amalgam to dentin but only 26.4 MPa for resin composite to dentin.
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 . Tooth preparation techniques for amalgam restorations have changed from sharp to rounded line angles . Caries-indicating dyes, fluoride-releasing cavity liners, adhesive bonding materials, and smaller preparations are some recent advances in the placement of amalgam restorations.
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 . It is now also possible to bond fresh amalgam to old amalgam .
Dickerson  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 .
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.
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.