Dr. Dana Boyd Barr and colleagues’ March JADA article, "Exposure to Bisphenol A From Bis-glycidyl Dimethacrylate–based Dental Sealants," (JADA 2006;137[3]:353–62) reaffirmed results from previous studies showing potential for low-level transient exposures from one particular sealant product. Several of the background statements in this article, however, could erroneously lead one to conclude that the potential for exposure is much greater.
The opening statement that bisphenol A (BPA) "is a common ingredient in restorative resin-based composites and sealants used in dentistry" is incorrect. There is no BPA used as an ingredient in the manufacture of any resin-based dental product. The Schmalz and colleagues1 reference was cited to support this statement. But these investigators did not analyze any dental products. Rather, they looked at a series of commercially available monomers. That study determined that BPA was not found in bisphenol A glycidyl dimethacrylate (bis-GMA), the most common monomer used in dental products, but that BPA could be derived from the breakdown of another monomer, bisphenol A dimethacrylate (bis-DMA). Bis-DMA has been confirmed to be the source of BPA in the Delton Light Cure (LC) Opaque pit-and-fissure sealant (Dentsply/ Ash, York, Pa.) product reported by Barr and colleagues, and by several prior studies cited in this article.2–5
The references cited for the statement that "unpolymerized BPA can leach from the dental composite or sealant"6–12 did not carry out any BPA measurements on dental resins. The authors cite several references to "BPA exposures resulting from the placement of dental sealants or composites."2–5 It is important to point out that three of these studies2–4 reported BPA from the same Delton LC sealant, and the fourth5 detected only trace amounts of BPA after placement of composites.
Another referenced statement by the authors states that "about one-third of the BPA produced in the United States is used in epoxy resins, including dental sealants."13 It should be made clear that dental sealants are not epoxy resins, and BPA is not used in the manufacture of dental sealants. The Web site referenced, "www.bisphenol-a.org", does not identify any dental product as being manufactured from or using BPA. It does address the release of BPA from dental sealants in its "Frequently Asked Questions,"13 as follows:
Several studies have reported that trace levels of bisphenol A (BPA) may be released from certain dental sealants, but only during a short time period immediately after application of the sealant. In addition, the highest level of BPA exposure reported from dental sealants is more than 50,000 times lower than levels shown to cause toxicity in animal studies. Based on these findings, human exposure to BPA from dental sealants is minimal and poses no known health risk.
It is a common misconception that BPA is used in dental composites and sealants, is present as carry-over from the synthesis of the common dental monomer bis-GMA, or is produced by the breakdown of bis-GMA used in dental products. BPA has not been shown to be used in the formulation of any dental composite or sealant. The synthesis of bis-GMA can be done by using two different pathways. The first includes the reaction of BPA with glycidyl methacrylate to form bis-GMA. The second pathway is the reaction of diglycidyl ether of BPA with methacrylic acid, which does not use BPA as a starting material.
This second pathway is used for the manufacture of all dental bis-GMA, and is the reason why studies have not identified significant quantities of BPA in dental composites. Great care is taken in synthesis of dental monomers to assure that BPA is not present. The Schmalz and colleagues1 study that the authors referenced demonstrated that BPA could not be derived by the hydrolytic breakdown of bis-GMA. This study did confirm, however, that both hydrolysis and salivary esterase conversion of bis-DMA resulted in rapid production of BPA. The Delton LC product that was used in the study is known to contain bis-DMA as a diluent monomer.
We commend the authors of this article for using highly sensitive analytical techniques and including urinary analysis in assessing the kinetics of BPA release and clearance. They have confirmed that the release of BPA from Delton LC sealant is low-level and short-lived. We need to be diligent, however, in accurately identifying this as a reaction unique to this product, and not one that is pervasive in resin-based dental materials in general.
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