The Safety of Sealants

The recent news about potential harm coming from bisphenol-A (BPA), particularly in baby bottles and children’s “sippy-cups,” has led to the examination of other products that use this polymerization process, including dental pit and fissure sealants. Up-to-date information is necessary in order for dental health care professionals to best answer patients’ concerns if and when questions arise concerning the safety of sealants.

Dental pit and fissure sealants have long been recognized as effective in preventing early, noncavitated caries in children. The sealant material provides a barrier preventing microorganisms and food particles from collecting in pits and fissures.¹ Two types of sealant materials and placement techniques are available— resin-based sealants and glass inonomer cements. In dentistry, BPA is used in some dental composite resins and pit and fissure sealants. BPA appears as an impurity in some resins and it’s possible that some residual monomers can leach out of the cured resin.² A transient amount of BPA may be detected in saliva immediately after placement as a result of salivary enzymes on bisphenol-dimthacrylate, a component of some sealant materials.³

WHAT IS BPA?

BPA is an organic compound that contains two phenol groups and is a building block to several important polymers and polymer additives.⁴ BPA is controversial because it mimics estrogen and may induce hormonal responses.⁵ Studies show that BPA has the potential to bind to the estrogen receptor, activate estrogen-response elements, and stimulate the growth of estrogen-sensitive cells.⁶

In 2007, a consensus statement by 38 experts on BPA concluded that the average levels found in people are above those that cause harm to animals in laboratory experiments.^2,3 A panel convened by the United States National Institutes of Health determined that there was some concern about BPA’s effects on fetal and infant brain development and behavior.⁷ A 2008 draft report by the United States National Toxicology Program (NTP) agreed with the panel, concluding that “there is some concern for neural and behavioral effects in fetuses, infants, and children at current human exposures,” and that there is “some concern for bisphenol A exposure in these populations based on effects in the prostate gland, mammary gland, and an earlier age for puberty in females.” NTP also concluded that there is negligible concern that “exposure of pregnant women to bisphenol A will result in fetal or neonatal mortality, birth defects, or reduced birth weight and growth in their offspring” or that it causes adverse effects in exposed adults.⁸

In April 2008, the Canadian government concluded that the chemical may pose some risk to infants and proposed classifying the chemical as “toxic to human health and the environment.”⁹ BPA can leach from the plastic lining of canned foods¹⁰ and, to a lesser degree, polycarbonate plastics that are cleaned with harsh detergents or used to contain acidic or high-temperature liquids. Studies by the Centers for Disease Control and Prevention found BPA in the urine of 95% of adults sampled in 1988-1994¹¹ and in 93% of children and adults tested in 2003-04.¹²

On April 18, 2008, Health Canada announced that it will ban the import, sale, and advertising of polycarbonate baby bottles containing BPA due to safety concerns. Around the same time, Wal-Mart announced that it was immediately ceasing sales in all its Canadian stores of food containers, water and baby bottles, sippy cups, and pacifiers containing BPA, and that it would phase out baby bottles made with it in American stores by early 2009.¹³

IS THERE A RISK?

Recent concern over the potentially harmful effects released from BPA has led to a re-evaluation of the literature examining whether pit and fissure sealant placement causes harm to patients.¹⁴ The results of studies from 11 articles about the toxicity of dental sealants found no significant level of BPA.

None of the dental sealants that carry the American Dental Association (ADA) Seal in 2007 released detectable BPA. In a recent position and statement paper, the ADA states that there is no cause for concern about potential exposure to BPA from composites or sealants at this time, but the ADA “supports additional research into how much BPA people are actually exposed to and at what levels of exposure health effects start to occur.”¹⁵

The overall findings from the reviews conclude that “BPA released orally from a dental sealant may not be absorbed or may be present in nondetectable amounts in systemic circulation.”¹⁵ Government regulatory agencies in Europe, Japan, and the United States have concluded that human exposure to BPA from normal contact with food that is in contact with polycarbonate plastic is very low and poses no known health risk to human health.

Dental providers can avoid the potential for BPA toxicity from dental sealants by treating the surface layer of the sealant immediately after placement to reduce the possibility of unpolymerized BPA remaining on the tooth by:

1. Using a mild abrasive, such as pumice, either on a cotton applicator or with a prophy cup.
2. Having older children and adolescents gargle with tepid water for 30 seconds.
3. Washing the surface of the sealant for 30 seconds with an air-water syringe while suctioning fluids and debris from a child’s mouth.¹⁴

The ADA position paper states that “BPA is widely used in the manufacture of some types of plastics, primarily for consumer products. Concerns have been raised about the safety of such widespread use of BPA in consumer products, because laboratory testing has suggested that it may affect reproduction and development by mimicking the effects of the female hormone estrogen. To date, these effects observed in laboratory animals have not been observed in humans. Humans are exposed to BPA through its use by the food industry in the manufacture of epoxy resins that coat cans and polycarbonate bottles that hold foods and beverages. It is also used in the manufacture of some children’s toys, plastic tableware, and infant bottles. BPA is also released to the environment in industrial and household wastes. Although BPA is not an ingredient in any dental product, there is some evidence that some dental sealants and to a lesser extent composites may contribute to low-level BPA exposure, probably through the action of salivary enzymes on a minor ingredient.”

On November 26, 2007, the United States Department of Health and Human Services (HHS) announced the availability of the Bisphenol A Expert Panel Report on the reproductive and developmental effects of BPA. The report states that, “Dental sealant exposure to bisphenol A occurs primarily with use of dental sealants bisphenol A dimethylacylate. This exposure is considered an acute and infrequent event with little relevance to estimating general population exposures.”⁷

The ADA sees no cause for concern at this time regarding potential BPA exposure from composites or sealants. Exposure from these dental materials is significantly lower and occurs infrequently when compared to all other sources of exposure. The presence of a substance in the environment or in human blood or urine samples does not mean that that substance is necessarily causing harm. Whether or not a substance is harmful to human health typically depends on the amount that people are exposed to. Virtually any substance can have a harmful effect at high doses—even water and vitamins. Nevertheless, the ADA supports additional research into how much BPA people are actually exposed to and at what levels of exposure health effects start to occur.¹⁵

REFERENCES

1. National Institutes of Health Consensus Development conference statement. Dental sealants in the prevention of tooth decay. J Dent Educ. 1984;48:126-131.
2. Arenholt-Bindslev D, Breinholt V, Preiss A, Schmalz G. Time-related bisphenol-A content and estrogenic activity in saliva samples collected in relation to placement of fissure sealants. Clin Oral Investig. 1999;3:120-125.
3. Volkel W, Colnot T, Csanady GA, Filser JG, Dekant W. Metabolism and kinetics of bisphenol-A in humans at low doses following oral administration. Chem Res Toxicol. 2002;15:1281-1287.
4. Fiege H, Voges HW, Hamamoto T, et al. Phenol derivatives. In: Ullmann’s Encyclopedia of Industrial Chemistry. Hoboken, NJ: Wiley-VCH; 2002.
5. 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. Toxicol Lett. 2008;176:149–156.
6. Atkinson JC, Diamond F, Eichmiller F, Selwitz R, Jones G. Stability of bisphenol-A, triethylene-glycol dimethacrylate, and bisphenol A dimethacrylate in whole saliva. Dent Mater. 2002;18:128-135.
7. Center for the Evaluation of Risks to Human Reproduction. NTP-CERHR Expert Panel Report on the Reproductive and Developmental Toxicity of Bisphenol A. Available at: http://cerhr.niehs.nih.gov/chemicals/bisphenol/BPAFinalEPVF112607.pdf. Accessed June 23, 2008.
8. National Institute of Environmental Health Sciences. Since You Asked—Bisphenol A. Available at: www.niehs.nih.gov/news/media/questions/sya-bpa.cfm. Accessed June 18, 2008.
9. Government of Canada Takes Action on Another Chemical of Concern: Bisphenol A, Chemical Substances. Available at: www.chemicalsubstanceschimiques.gc.ca/challenge-defi/bisphenol-a_e.html. Accessed June 19, 2008.
10. Environmental Protection Agency. Bisphenol A. Available at: www.epa.gov/iris/subst/0356.htm. Accessed June 19, 2008.
11. Calafat AM, Kuklenyik Z, Reidy JA, Caudill SP, Ekong J, Needham LL. Urinary concentrations of bisphenol A and 4-nonylphenol in a human reference population. Environ Health Perspect. 2005;113:391–395.
12. Calafat AM, Ye X, Wong LY, Reidy JA, Needham LL. Exposure of the U.S. population to bisphenol A and 4-tertiary-octylphenol: 2003-2004. Environ Health Perspect. 2008;116:39–44.
13. Austen I. Bottle maker to stop using plastic linked to health concerns. The New York Times. Available at: www.nytimes.com/2008/04/18/business/18plastic.html. Accessed June 19, 2008.
14. Azarpazhooh A, Main PA. Is there a risk of harm or toxixity in the placement of pit and fissure sealant materials? A systematic review. J Can Dent Assoc. 2008;74:179-183.
15. American Dental Association. ADA Positions & Statements: Bisphenol A and dental sealants, composite dental fillings. Available at: www.ada.org/prof/resources/positions/statements/bisphenola.asp. Accessed June 19, 2008.

From Dimensions of Dental Hygiene. July;6(7): 36-37.