Bisphenol A (BPA): in our environment, food and dental restorations.

For more than a year, we have seen increased news coverage concerning our exposure to Bisphenol A (BPA) from plastics in our environments. An ABC News report on August 5, 2007, warned the public of the potential dangers of the "toxic" chemical BPA leaching into foods and beverages from the plastic lining of cans and plastic bottles, respectively. The report further suggested that baby bottles containing BPA not be used, as the chemical could leach into the baby's formula and therefore contaminate it. (1) BPA is also found in various pit-and-fissure dental sealants as well as some composite restorations.

On September 16, 2008, an NBC World News report again warned the public of new evidence regarding the safety of BPA and concerns that the United States Food and Drug Administration (FDA) is not responding to the advice of their scientific advisors. (2)

The National Toxicology Program (NTP), United States Department of Health and Human Services (HHS), and the Center for the Evaluation of Risks to Human Reproduction (CERHR) conducted an evaluation of the potential for BPA to cause adverse effects on reproduction and development in humans. The CERHR Expert Panel on BPA completed its evaluation in August 2007, concluding that NTP had concern for the effects on the brain, behavior and prostate gland in fetuses, infants and children at current levels of human exposure to BPA. Additionally, they reported minimal concern for effects on the mammary gland in female fetuses, infants and children; and on early onset of puberty in female children, at current levels of human exposure to BPA. (3)

On April 18, 2008, the Minister of Health and the Minister of the Environment of Canada announced that the government was taking action to protect the health of Canadians and the environment from BPA by initiating a 60-day public comment period on whether to ban the importation, sale and advertising of polycarbonate baby bottles, which contain BPA. (4) The government has labeled this chemical "toxic," is also proposing alternatives to BPA in can linings, and will consider setting stringent migration targets for BPA in infant formula cans. Environment Canada, a governmental department, is taking early action to protect the environment from the harmful effects of BPA by finding ways to stop its release into the environment and by taking measures to ensure its safe use and disposal. (5)

For health care providers, parents and concerned consumers, the recent media coverage regarding the possible toxicity of plastics used in dental restorations, as well as the plastics that contain our foods and beverages, is alarming. We need to protect ourselves and the next generations from the possible neurological and developmental effects of this chemical.

Bisphenol A

BPA is an industrial chemical used to make polycarbonate plastic and epoxy resins from which food and beverage containers and dental materials are made. (6) Commercial production began in the late 1950s in the United States and Europe, and today it is one of the highest-volume chemicals produced worldwide. (6) BPA has become controversial because it is thought to be an endocrine-disrupting chemical that mimics the hormone estrogen, and thus could induce hormonal responses. Because BPA acts like the body's own hormone, it is thought that long-term exposure can lead to physiological changes and have toxic effects on the body. (7)

The major source of human exposure to BPA in the general population is likely through consumption of contaminated foods and beverages that have contacted epoxy or polycarbonate resins. (8) Certain plastic containers with the recycling code (7) inside the triangle of chasing arrows contain polycarbonate. Polycarbonate is a code seven (7) plastic; however, the majority of code (7) plastics are not polycarbonate. To be certain, one can check to see if the plastic is identified by its name or acronym (PC for polycarbonate) somewhere on the product or package, or contact the manufacturer. (5) Only hard, clear plastic bottles are made from polycarbonate. BPA is not found in softer, more flexible products such as single serving water bottles. Plastic recycling codes 1-6 do not use BPA in their manufacturing process. As a general rule, if you can squeeze the plastic bottle, it is not made from polycarbonate plastic and does not contain BPA. (5)

We are exposed to this chemical on a daily basis, in and outside our homes. Our environmental exposure coupled with exposure from food and beverages is distressingly high. About 100 tons of BPA are released into the atmosphere each year by plastic manufacturers during production, resulting in air, water and land contamination. (9) BPA is used in the synthesis of many plastics and is found in countless household items, but the ones of most concern are plastic bottles, plastic-lined food cans and microwave ovenware. Because heat and contact with acidic or basic foods can accelerate the leaching of the BPA into the food we consume, we are at increased risk for daily exposure. (7) According to the Centers for Disease Control and Prevention (CDC), BPA was found in the urine of 93 percent of the 2,517 Americans tested during its National Health and Nutrition Examination Survey (NHANES) conducted in 2003-2004. The test results indicated females having significantly higher levels than males, with children having the highest levels, followed by teens and adults. (10)

A 2008 article published in the Journal of the American Medical Association reported the results of a cross-sectional study that analyzed BPA concentrations and health status in the United States. The data used in this cross-sectional study was from the above referenced NHANES study. The researchers reported higher urinary concentrations of BPA associated with an increased prevalence of cardiovascular disease, diabetes and abnormal liver enzymes. The study further postulates that these findings add to the evidence suggesting adverse effects of low-dose BPA in animals. The researchers are calling for follow-up studies to confirm these findings and to provide evidence on whether the associations are causal. (11)

Review of the Literature

Over the years, there have been approximately 176 studies conducted that reported on the effects of low doses of BPA to experimental animals. Of these studies, 149 reported significant and in many cases clearly adverse effects, and 27 published studies reported no evidence of harm. (6) According to Frederick vom Saal, PhD, professor of biology at the University of Missouri-Columbia, the 27 studies reporting no harm used a very specific type of large rat that is not as sensitive to estrogenic chemicals and requires high doses to show responses. He also indicated that this strain of rat demonstrates insensitivity to any estrogenic chemical, not just BPA. It should also be noted that of the 27 studies showing no harm, 13 were conducted and funded by chemical corporations. (6)

Maffini et al. reported that because BPA is an estrogen mimic and endocrine disruptor, perinatal exposure results in alterations of the mammary glands and male and female genital tracts. (9) The researchers hypothesized that these effects may lead to altered fertility, altered lactation and earlier onset/higher incidence of breast, testicular and prostate cancers.

American Chemistry Council

The American Chemistry Council reported on July 23, 2008, that the European Food Safety Authority (EFSA) reaffirmed the safety of BPA in common consumer products such as baby bottles, water bottles and food containers; this is based on the EFSA's review of new scientific data. They concluded that BPA is not harmful to children or adults at very low levels of exposure and use of consumer products. (12)

The American Chemistry Council represents the leading companies that produce the plastics in question and would like people to believe that low-dose exposure to BPA is not harmful. According to Sharon Kneiss, vice president of products divisions at the American Chemistry Council, all of the polycarbonate plastics to which consumers are exposed have passed stringent FDA standards and pose no hazard. (13) She further stated that the numbers located on the bottom of plastic containers are used to identify the resin used in the bottle for recycling purposes only and are not meant to provide any other information concerning the plastic. (13) However, the majority of research studies and researchers disagree and are concerned about the health hazards resulting from exposure. (6-9)

Dental Restorations

Although there have been numerous studies conducted reporting the effects of BPA, few have been conducted on the release from dental resin materials. In 1996, Olea and colleagues reported alarmingly high levels of BPA in the saliva of subjects one hour after the placement of dental sealants. (14) Subsequent studies reported values up to 250 times less and concluded that in the Olea study, another component of the sealant was identified mistakenly as BPA. (15) A study conducted by Fung et al. reported BPA levels in blood and saliva samples from each subject one hour before each sealant was placed. (15) Additional levels were reported at three hours, one day, three days and five days after sealant placement. BPA was detected in some saliva specimens collected at one and three hours, but not detected beyond three hours after sealant placement or in any of the blood specimens. Confirming the Fung et al. study, (15) Arenholt-Bindslev and colleagues (16) reported minute amounts of BPA, also significantly lower than previously reported studies, immediately after placement; and no detectable amount at one hour and at 24 hours after placement. BPA was not detected immediately after placement of Visio-Seal fissure sealant. (16) Fung et al. concluded that BPA released orally from dental sealants may not be absorbable systemically or may be present in non-detectable amounts. (15)

In a recent study, researchers detected BPA in saliva and urine samples in all baseline (pretreatment) samples. It was concluded that these levels resulted from environmental exposure, as the participants had no pretreatment composite restorations or sealants, and the concentrations of urinary BPA in the study participants were similar to those found in the general U.S., Japanese and Korean population. (17) This study by Joskow and colleagues also reported varying saliva and urine levels of BPA according to product brand. (17) Delton LC (DENTSPLY Professional) demonstrated higher levels of BPA than Helioseal F (Ivoclar Vivadent, Inc.). However, one hour after placement, BPA levels were close to pretreatment levels due to active stimulation and elimination of saliva immediately after sealant placement. The researchers suggest that BPA exposures can be effectively reduced by rubbing the sealant surface and removing the resultant stimulated saliva after sealant placement. (17) While this study reported that BPA was completely eliminated from the body 24 to 34 hours after low-dose exposure, which confirms the results of the Fung et al. (15) and Arenholt-Bindslev and colleagues' (16) studies, the researchers acknowledged limitations in this study, including a small sample size. (17)

American Dental Association Position and Statements

According to the latest published position statement (May 2008) from the American Dental Association (ADA), consumers are not at risk from BPA exposure through the use of dental materials. This statement is based on the latest peer-reviewed evidence. (18,19) The statement also avowed that concerns about potential BPA exposure from dental composites or sealants is unwarranted at this time because dental materials pose significantly lower exposure than other sources. ADA refers to the HHS for recommendations on issues that affect the health of Americans and to FDA for recommendations on product safety. HHS considers population exposure to BPA from dental sealants low and infrequent. FDA also believes that the FDA-regulated products on the market that contain BPA are safe. However, ADA states that they are "interested in and support BPA research because some dental sealants, and to a lesser extent dental composite resin filling materials, may contribute to low-level BPA exposure." (18)

Conclusion

Every day, we are exposed to a vast variety of environmental chemicals. Research has shown a wide range of adverse effects caused by exposure to low-dose estrogenic chemicals in laboratory animals and as a result have speculated about the implications for human health. Researchers conclude that there is reason to have concerns regarding the safety of estrogen-like chemicals and are advocates for further research.

It is essential for regulatory agencies to assess the potential hazards posed to humans from low-dose exposure to BPA and establish stringent food safety standards for our protection to ensure that all products on the market are safe for children and adults. The National Institute of Dental and Craniofacial Research is currently conducting clinical trials assessing the levels of BPA in urine and saliva following placement of composite restorations. (20)

In the meantime, we can take steps at home to reduce our exposure to BPA. Glass baby bottles or BPA-free bottles can be used. Select plastics that do not contain polycarbonate, and do not use plastics in the microwave, expose them to harsh chemicals, or wash them in the hot water cycle of a dishwasher.

Since dental hygienists place dental sealants, patients may pose questions and concerns regarding their safety. Concerned parents should be assured that pit-and-fissure sealants are safe and provide significant benefits in the prevention of dental caries. In practice, dental hygienists can select to use the following pit-and-fissure sealants that do not contain BPA: Embrace (Pulpdent Corp.), Clear Check SLP (Shofu Dental Corp.), Ultra Seal XT Plus (UltraDent Products. Inc.) and Clinpro (3M ESPE). As suggested by Joskow et al., if the sealant does contain BPA, exposures can be effectively reduced by rubbing the sealant surface immediately after placement and also removing the resultant stimulated saliva. (17)

Update

As of March 6, 2009, Playtex Products Inc., Gerber, Evenflo co., Avent America Inc., Dr. Brown and Disney First Years will no longer market polycarbonate baby bottles in the United States.

Source: Kay J. 6 firms stop sales of hard-plastic baby bottles. San Francisco Chronicle, March 6, 2009.

Maura Y. Ordovensky, RDH, BS

What most excites me most about the upcoming ADHA meeting is the opportunity to be with so many other dental hygienists from around the country. It will be an incredible thing to see. I can't wait to be a part of a multiple day event geared strictly toward bettering the practice and profession of dental hygiene.

[ILLUSTRATION OMITTED]

References

(1.) Chemical threat in plastics. August 5, 2007. Available at http:// www.bisphenolAfree.org. Accessed May 7, 2008.

(2.) NBC Mixed messages over plastic chemical safety. NBC's Robert Bazell explains the controversy over bisphenol A. Available at http://www.msnbc. msn.com/id/26723119/. Accessed Dec. 5, 2008.

(3.) National Toxicology Program U.S. Department of Health and Human Services Center for the Evaluation of Risks to Human Reproduction. NTP-CERHR monograph on the potential human reproductive and developmental effects of bisphenol A. September 2008. NIH Publication no. 08-5994. Available at http:// cerhr.niehs.nih.gov/chemicals/bisphenol/bisphenol.pdf. Accessed Oct. 6, 2008.

(4.) Government of Canada. Consumer information safety of plastic containers commonly found in the home. Available at http://www.chemicalsubstanceschimiques. gc.ca/challenge-defi/bisphenol- a_e.html. Accessed Oct. 14, 2008.

(5.) Government of Canada. Questions and answers for action on bisphenol A under the chemicals management plan. June 13, 2008. Available at: http:// www.chemicalsubstanceschimiques.gc.ca/faq/bisphenol_a_qa-qr_e.html. Accessed Oct. 14, 2008.

(6.) vom Saal, F. Bisphenol A. October 2006. Available at http://endocrinedisruptors. missouri.edu/pdfarticles/Bisphenol A References.doc. Accessed May 9, 2008.

(7.) vom Saal F, Hughes C. An extensive new literature concerning low-dose effects of bisphenol A shows the need for a new risk assessment. Available at http://www.ehponline.org/members/2005/7713/7713.html. Accessed Oct. 7, 2008.

(8.) Le HH, Carlson EM, Chua JP, Belcher SM. Bisphenol A is released from polycarbonate drinking bottles and mimics the neurotoxic actions of estrogen in developing cerebellar neurons. Toxicology Letters 2008; 176 (2): 149-56.

(9.) Maffini MV, Rubin BS, Sonnenschein C, Sotto AM. Endocrine disruptors and reproductive health: the case of bisphenol A. Mol Cell Endocrinol 2006; 254-255: 179-86.

(10.) Centers for Disease Control and Prevention. National report on human exposure to environmental chemicals. Available at http://www.cdc.gov/exposurereport/pdf/factsheet_bisphenol.pdf. Accessed May 7, 2008.

(11.) Lang IA, Galloway TS, Scarlett A et al. Association of urinary bisphenol A concentration with medical disorders and laboratory abnormalities in adults. J Am Med Assoc 2008; 300 (11): 1303-10.

(12.) American Chemistry Council. European food and safety authority reaffirms science and safety of bisphenol A. Jul. 23, 2008. Available at: http://www. americanchemistry.com/s acc/sec_news_article.asp?SID= 1&DID=7795&CID= 206&VID=142&RTID=0&CIDQS=&Taxonomy=&specialSearch=. Accessed Oct. 14, 2008.

(13.) Kneiss S. Statement customer teleconference, Apr. 22, 2008. Available at http://www.factsonplastic.com/?gclid =CL_ugIX21JMCFQ4yGgodyVICgw. Accessed May 7, 2008.

(14.) Olea N, Pulgar R, Perez P et al. Estrogenicity of resin-based composites and sealants used in dentistry. Environmental Health Perspectives 1996; 104 (3): 298-305.

(15.) Fung EY, Ewoldsen NO, St. Germain HA et al. Pharmacokinetics of bisphenol A released from a dental sealant. J Am Dent Assoc 2000; 131 (1):51-8.

(16.) Arenholt-Bindslev D, Breinholt V, Preiss A, Schimalz G. A time-related bisphenol A content and estrogenic activity in saliva samples collected in relation to placement of fissure sealants (abstract 481). J Dent Res 1998; 77: 692.

(17.) Joskow R, Boyd Barr D, Barr JR et al. Exposure to bisphenol A from bis-glycidyl dimethacrylate-based dental sealants. J Am Dent Assoc 2006; 137 (3): 353-62.

(18.) American Dental Association. Bisphenol A and dental sealants, composite dental fillings. ADA Position and Statements. Available at http://www.ada.org/ prof/resources/positions/statements/bisphenola.asp. Accessed Oct. 6, 2008.

(19.) American Dental Association. Evidence indicates dental materials not a bisphenol A exposure risk. Available at http://www.ada.org/prof/resources/ pubs/adanews/adanewsarticle.asp?articleid=3035. Accessed Oct. 12, 2008.

(20.) National Institute of Dental and Craniofacial Research (NIDCR). Levels of bisphenol A in urine and saliva following placement of composite restorations. Available at http://clinicaltrials.gov/ct2/show/NCT00339339?spons= %22National+Institute+of+Dental+and+Craniofacial+Research+%28NIDCR% 29%22&rank=44. Accessed Dec. 5, 2008.

Rita Krajac-Salva MA, RDH, CDA is an assistant professor in the Allied Dental Education Program in the School of Health-Related Professions at the University of Medicine and Dentistry of New Jersey.