US Dentists' Amalgam Use Surprises Researchers

Laird Harrison

June 17, 2011

June 17, 2011 ( UPDATED June 24, 2011 ) — Despite improvements in resin-based composite technology, US dentists are placing more amalgam restorations than composites, and amalgam is still emphasized by US dental schools, according to the results of 2 studies published in the June issue of the Journal of the American Dental Association.

"I thought that most people were using composite," researcher Sonia K. Makhija, DDS, MPH, an assistant professor of dentistry at the University of Alabama at Birmingham, told Medscape Medical News. "It was surprising that so many people are using amalgam."

Dr. Makhija and colleagues in the Dental Practice-Based Research Network, a collaboration of practicing dentists who participate in research, analyzed reports from 182 US dentists on 5599 restorations of carious lesions in posterior teeth.

Overall, the dentists used amalgam for 3028 of these restorations, and composite in 2571 others. (The researchers collected no data on the 930 restorations these dentists made out of gold, glass ionomer, or anything else other than composite and amalgam.)

Although the dentists were not a statistical sample, previous studies have suggested that they are generally representative of what dentists are doing in the United States, Dr. Makhija said.

In the second study, researchers from universities in England, Wales, and Ireland and from the Georgia Health Sciences University in Augusta, surveyed 67 dental schools in the United States and Canada about how they teach students to restore posterior teeth.

At the 49 schools that responded, almost half the restorations placed in 2009 and 2010 were resin-based composites. Although this was a 30% increase from a similar survey done 5 years earlier, the study authors wrote that US and Canadian schools "lag" schools in Britain and Ireland, where composite gets more attention.

Not only is composite prettier, it is less invasive because it does not require as much cavity preparation, and in recent studies it has proved at least as durable, the authors write. "These tooth-friendly features of resin-based composites make them preferable to amalgam, which has provided an invaluable service but which, we believe, now should be considered outdated for use in operative dentistry."

They called for new national guidelines that would emphasize the superiority of composite.

However, Dr. Makhija said such guidelines are premature. "I think we don't have enough data yet," she said. "You can find longevity studies on both that are good." The Dental Practice-Based Network is following up on the 5599 restorations participants placed to see how they fare in coming years.

Glass Ionomer: Pros vs Cons

Offering another perspective, Douglas A. Young, DDS, EdD, MBA, associate professor of dental practice at the University of the Pacific, San Francisco, California, told Medscape Medical News that dentists should not limit themselves to amalgam and composite. "Conventional glass ionomer cement [GIC] has certain advantages when viewed as a chemical treatment for caries lesions," he said. "It has the ability to seal, remineralize, and prevent future caries lesion formation." Restorations should not be chosen solely on the basis of retention and other physical properties, he said.

Conventional GIC forms a chemical bond to dentin and enamel via ionic exchange that takes place between the fluoride and strontium (or calcium in some products) in the glass ionomer and the calcium and phosphate in the tooth. This has been described in the literature as "internal remineralization," which occurs underneath GIC. In contrast, composite forms a micromechanical bond via a polymerization reaction. With GIC, there are no double bonds to break, so it should provide a long-lasting chemical seal, said Dr. Young.

When it is used under a composite, a sealed GIC can often remain in place when it is time to replace a "leaky" composite restoration, and the composite layer can often be removed with no anesthesia, he said. "I use GIC on dentin and cementum, and also for sealants and small restorations, when occlusion allows."

Dr. Young said that in his experience, when used under these conditions with proper placement, GIC is just as durable as composite resin.

Dr. Young also said that clinicians in the United States are currently using GIC more often on the facial and lingual of root surfaces than they were in the past, and he wondered why some clinicians are still opposed to using it on the mesial and distal surfaces of a deep box. "After all, it's still on the root, just around the line angle from the facial or lingual surface, where there is no enamel to micromechanically bond to," he said.

So what are dental schools teaching? In the survey, 44 of the 49 schools said they taught the total etch technique for cavities in the outer third of the dentin, whereas the other 5 taught the glass ionomer cement approach only.

For cavities in the middle third of the dentin, 24 schools taught the total etch approach, and 24 the glass ionomer approach, whereas 1 taught calcium hydroxide and glass ionomer. For those restorations in the inner third of the dentin, 6 schools taught total etch and 30 glass ionomer, with 24 schools teaching calcium hydroxide and glass ionomer.

However, dental schools teachings are only one factor in what dentists practice, Dr. Makhija found. Surprisingly, older dentists were more likely to place composite restorations, even though they were more likely to have attended dental school when this approach was less emphasized (P = .02)

Dentists who graduated in the past 5 years placed amalgam on 61% of the lesions they treated. One explanation may be that younger dentists are more likely to be in large group practices where they work on salary, rather than fee-for-service, said Dr. Makhija. The type of material might be dictated by managers of the group practice. In large group practices (4 dentists or more), 79% of the restorations were amalgam (P < .001). "It's quicker, it's easier and it's cheaper to use amalgam," Dr. Makhija said.

Dr. Makhija, Dr. Young, and the authors of the dental school survey have disclosed no relevant financial relationships.

J Am Dent Assoc. 2011;142;612-620. Abstract

J Am Dent Assoc. 2011;142;622-632. Full text

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