BPA Leaching Into Urine, Saliva From Dental Composites?

Laird Harrison

December 10, 2012

Bisphenol A (BPA), a potentially toxic compound, gets into patients' saliva and urine when composite resin restorations are placed on their teeth, a new study shows.

In an article published in the December issue of the Journal of the American Dental Association, Albert Kingman, PhD, chief biostatistician, Center for Clinical Research, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland, and colleagues found that on average, patients had 43% more BPA in their urine 30 hours after a restoration was placed than they did before getting the restoration.

However, the researchers note that they could not draw any conclusions about the safety of composite resin, which is the most widely used filling material in the United States, if not the world.

''Our study design does not enable us to determine the meaning of these increases,'' Dr. Kingman told Medscape Medical News in an email. ''Our study findings suggest a larger and longer clinical study is merited.''

BPA is a common ingredient in epoxy resins and polycarbonate plastics used to make drinking bottles, food containers, adhesives, flame retardants, water pipes, and other dental materials.

The compound mimics estrogen activity, and studies in animals have shown that it can disrupt endocrine function. In addition, some epidemiological studies have shown that people with greater exposure to the compound are more likely to suffer illness.

One study showed that children who had composite resin restorations scored lower on social and emotional tests than children who had amalgam restorations.

Damning Evidence

However, that study did not measure concentrations of the compound in the children's bodies. The current study provides one more piece of damning evidence against the compound, although not enough to close the case.

For this study, Dr. Kingman and colleagues collected saliva and urine from 172 people receiving composite resin restorations.

Dental sealants and resin-based composite restorations are formulated from a mixture of compounds based most commonly on BPA–glycidyl methacrylate (bis-GMA). In addition to bis-GMA, resin-based composites can include BPA-dimethacrylate (bis-DMA), ethylene glycol dimethacrylate, urethane dimethacrylate, and triethylene glycol dimethacrylate.

In their assays of the patients' urine and saliva, the researchers measured the concentrations of BPA alone, BPA and bis(2,3-hydroxyphenyl) ether, triethylene glycol dimethacrylate, BPA diglycidyl ether, bis-DMA, and bis-GMA both before and after placing restorations.

They found some variations depending on the age and sex of the participants, but in general, 2 broad findings emerged: The concentrations in the saliva of most of the compounds were elevated an hour after the restorations were placed, and the concentrations were particularly high when dentists did not use a rubber dam.

However, by the end of 8 hours, the saliva concentrations of all the compounds had dropped back to baseline, regardless of whether a rubber dam was used.

The researchers also found significant increases in urinary concentration of various compounds after placing the restorations, although the levels in urine did not rise right after the restorations were placed. In fact, levels in urine actually declined in the first hour before rising again over the course of the next 30 hours.

The researchers speculate that the patients may have drunk water in that interval, resulting in lower concentrations of the compounds in their urine, but this was only a hypothesis for a phenomenon that remains "unexplained."

All the compounds in urine returned to baseline levels after 30 hours except for BPA, which remained elevated at 2.38 ng/mL, up from 1.67 ng/mL of urine before the restorations were placed. The difference was statistically significant (P < .0005).

The use of a rubber dam did not appear to affect urine concentrations of any of the compounds. Whether the restorations were placed on posterior or anterior teeth also did not seem to make much difference.

The authors speculate that compounds continue to leach from the restorations after they are placed, which would explain why the use of a rubber dam did not affect the levels of compounds detected in urine.

Results Not Definitive

Nancy Masserejian, ScD, a coauthor of the study on psychosocial scores of children with composite resin restorations and epidemiologist from the New England Research Institutes in Watertown, Massachusetts, told Medscape Medical News the current study was useful but not definitive.

"Although this study does add some more information, it doesn't add enough to have clinicians change their practice," she said.

Not all composite resin restorations contain BPA — some are made with urethane dimethacrylate and carboxylic-acid modified-dimethacrylate, and there are also other materials not made from composite resins, such as amalgam, silorane-based materials, glass ionomer, and gold

"It's an option to use another type material," said Dr. Masserejian. "You have to weigh the concerns about BPA against the cost, availability, and technique required."

Analytical chemistry support for the study described in this article was provided by the National Institute of Environmental Health Sciences under contract with Midwest Research Institute. The authors and Dr. Masserejian have disclosed no relevant financial relationships.

JADA. 2012;143:1292-1302. Full text