Bisphenol A

Bisphenol A (BPA) is a chemical first synthesized more than 100 years ago; it is frequently used for the production of polycarbonate plastics and epoxy resins.^{1, 2} BPA can bind to estrogen receptors with weaker affinity than estradiol, and even so may affect estrogen-responsive tissue and cells.^{2, 3} Studies suggest numerous health disorders associated with high BPA levels, typically associated with industrial exposure.^{4, 5}

There is still scarce evidence on the effects of long-term, low-dose exposure to BPA in human health.⁵ Sources of low-dose BPA include canned food, meat products, plastic bottles, thermal papers (receipts), personal care products and dental restorative composites.^6-8 Diet is the main source of BPA exposure in most countries.⁹

Acceptable exposure limits are specified by national or regional regulatory agencies, such as the U.S. Environmental Protection Agency (EPA) and European Food Safety Authority.  In the U.S., a consortium was created to address research gaps and interpret relevant data, the Bisphenol A Toxicity (CLARITY-BPA) core study, which is a research program between the National Institute of Environmental Health Sciences (NIEHS) and the National Center for Toxicological Research (NCTR) of the U.S. Food and Drug Administration (FDA). Initial results in rats suggested that differences between BPA treatment groups (below 25,000 μg per kg body weight per day) and the control group were not dose responsive and did not demonstrate a clear pattern of consistent responses, suggesting that potential adverse effects of low-dose BPA exposure are uncertain.¹⁰

Specifically relevant to dentistry, significant increase in urinary BPA levels has been observed in pediatric patients two days after treatment, which declined to baseline levels after 4 weeks.¹¹ Three trials have compared potential outcomes of BPA exposure between children with amalgam restorations to children with resin composite restorations.  The first was a randomized, controlled trial that examined behavioral parameters and did not find differences between the two groups.¹²  A second trial found no statistically significant differences in body mass index, percentage body fat, or height.¹³ The third trial monitored psychological problems, and found no relationship with the type of dental restorations children had, except for an association between psychological problems and having more than 13 surfaces of resin restorations.¹⁴

BPA is widely used in the production of polycarbonate plastics, polyacrylate resins, and epoxy resins. Although BPA is not used in the manufacture of dental materials, it is used in the synthesis of monomers common to dental resins, such as Bis-GMA, Bis-EMA, Bis-DMA, and BADGE (please see abbreviation list at the end). Residual BPA may remain from the synthesis process of these monomers and thus trace amounts may be present as a contaminant in dental resins.^15,16 Bis-DMA is a monomer occasionally used, in small amounts, to decrease viscosity of dental sealants. It is the only monomer that when exposed to salivary esterase may break down to form BPA. 

It is the trace amounts of residual BPA, which may leach out of the freshly polymerized resin that contributes to a small, transient (Figure 1) increase in BPA levels seen in saliva and urine following procedures involving resin-based dental materials.^17-19 Wear of the soft, underpolymerized surface layer of unpolished composite restorations is likely the reason for the clinical observation that the majority of BPA released in saliva occurs within 24-48 hours post-placement.^{11, 18, 19} Inadequate curing and exposing resin-based materials to saliva may further exacerbate BPA exposure.

Maximizing the degree of conversion of resin-based materials likely helps minimize unreacted monomer leaching and potential BPA exposure, which can be achieved by: ^{19, 20}

• Reading and following manufacturers’ instructions;
• Ensuring proper curing light function (i.e. proper emission spectra and light intensity);
• Reducing the distance between light curing tip and restoration surface;
• Applying glycerin gel for the polymerization of the last resin layer.
  
  

Placement of resin based dental sealants can result in small, transient increase in BPA detected in children’s saliva and urine (Figure 1).^{17, 19} The magnitude of the change, which typically resolves within 24-48 hours after dental sealant placement, is dependent on the number of teeth treated with sealant and/or resin composite.¹¹ The main source of BPA is believed to be the outer layer of sealants and resin composites that does not polymerize in the presence of oxygen.¹⁷ Washing the unpolymerized resin layer away, and/or asking patients to rinse their mouths, may minimize potentially free BPA leaching following sealant placement.¹⁷

Research indicates that there is a transient increase in the amount of BPA measured following placement of composite resin restorations (Figure 1).¹⁹ Longer follow-up studies showed salivary or urinary BPA levels back to pre-treatment levels after 2-4 weeks following dental procedures involving sealant or composite restorations.^{11, 18, 21} Leaching of unreacted monomers is linked to polymerization condition and poor degree of conversion of resin composites.^{17, 18}

Resin-based orthodontic adhesives¹⁷ used to bond brackets to teeth surfaces are also composed of BPA derivatives, such as Bis-GMA and Bis-EMA. Temporary increase of BPA content in saliva has been observed after bracket bonding (Figure 1),¹⁸ likely due to the presence of an oxygen-inhibited layer after light-curing of the orthodontic adhesive, which is exposed to saliva. Asking patients to rinse their mouths immediately after bonding of orthodontic devices helps minimize ingestion.²

Figure 1. Range of BPA detection in urine by different sources of exposure.^{7, 17-19, 22, 23}

Following are examples of strategies to help minimize dental patient BPA exposure:^{2, 15, 17-20, 24}

• Rubber dam isolation for placement of composite restorations and dental sealants;
• Complete restorative material curing to maximize the material’s monomer-to-polymer conversion and minimize potential BPA release; 
• Use mild abrasive, or pumice on cotton applicator or prophylaxis cup to help reduce the possibility of unpolymerized BPA remaining on the surface;
• Wash sealant surface with an air-water syringe with suction to remove fluids and debris; 
• Have patients rinse with water after curing is complete for all resin-based restorations, dental sealant application and orthodontic bonding.

1. Wazir U, Mokbel K. Bisphenol A: A Concise Review of Literature and a Discussion of Health and Regulatory Implications. In Vivo 2019;33(5):1421-23.
2. Fleisch AF, Sheffield PE, Chinn C, Edelstein BL, Landrigan PJ. Bisphenol A and related compounds in dental materials. Pediatrics 2010;126(4):760-8.
3. Welshons WV, Nagel SC, vom Saal FS. Large effects from small exposures. III. Endocrine mechanisms mediating effects of bisphenol A at levels of human exposure. Endocrinology 2006;147(6 Suppl):S56-69.
4. Ribeiro E, Ladeira C, Viegas S. Occupational Exposure to Bisphenol A (BPA): A Reality That Still Needs to Be Unveiled. Toxics 2017;5(3).
5. Vandenberg LN, Colborn T, Hayes TB, et al. Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses. Endocr Rev 2012;33(3):378-455.
6. Biedermann S, Tschudin P, Grob K. Transfer of bisphenol A from thermal printer paper to the skin. Anal Bioanal Chem 2010;398(1):571-6.
7. Fisher M, Arbuckle TE, MacPherson S, et al. Phthalate and BPA Exposure in Women and Newborns through Personal Care Product Use and Food Packaging. Environ Sci Technol 2019;53(18):10813-26.
8. Berge TLL, Lygre GB, Lie SA, Lindh CH, Bjorkman L. Bisphenol A in human saliva and urine before and after treatment with dental polymer-based restorative materials. Eur J Oral Sci 2019;127(5):435-44.
9. EFSA CEF Panel (EFSA Panel on Food Contact Materials, Enzymes, Flavourings and Processing Aids). Scientific Opinion on the risks to public health related to the presence of bisphenol A (BPA) in foodstuffs: Executive summary. EFSA Journal 2015;13(1):3978.
10. National Toxicology Program U.S. Department of Health and Human Services. NTP Research Report on the CLARITY-BPA Core Study: A Perinatal and Chronic Extended-Dose-Range Study of Bisphenol A in Rats: National Toxicology Program; 2018.
11. McKinney CM, Leroux BG, Seminario AL, et al. A Prospective Cohort Study of Bisphenol A Exposure from Dental Treatment. J Dent Res 2020:22034520934725.
12. DeRouen TA, Martin MD, Leroux BG, et al. Neurobehavioral effects of dental amalgam in children: a randomized clinical trial. JAMA 2006;295(15):1784-92.
13. Maserejian NN, Hauser R, Tavares M, et al. Dental composites and amalgam and physical development in children. J Dent Res 2012;91(11):1019-25.
14. Maserejian NN, Trachtenberg FL, Hauser R, et al. Dental composite restorations and psychosocial function in children. Pediatrics 2012;130(2):e328-38.
15. Azarpazhooh A, Main PA. Is there a risk of harm or toxicity in the placement of pit and fissure sealant materials? A systematic review. J Can Dent Assoc 2008;74(2):179-83.
16. Soderholm KJ, Mariotti A. BIS-GMA--based resins in dentistry: are they safe? J Am Dent Assoc 1999;130(2):201-9.
17. Kloukos D, Pandis N, Eliades T. In vivo bisphenol-a release from dental pit and fissure sealants: a systematic review. J Dent 2013;41(8):659-67.
18. Marzouk T, Sathyanarayana S, Kim AS, Seminario AL, McKinney CM. A Systematic Review of Exposure to Bisphenol A from Dental Treatment. JDR Clin Trans Res 2019;4(2):106-15.
19. Paula AB, Toste D, Marinho A, et al. Once Resin Composites and Dental Sealants Release Bisphenol-A, How Might This Affect Our Clinical Management?-A Systematic Review. Int J Environ Res Public Health 2019;16(9).
20. Deviot M, Lachaise I, Hogg C, et al. Bisphenol A release from an orthodontic resin composite: A GC/MS and LC/MS study. Dent Mater 2018;34(2):341-54.
21. Lofroth M, Ghasemimehr M, Falk A, Vult von Steyern P. Bisphenol A in dental materials - existence, leakage and biological effects. Heliyon 2019;5(5):e01711.
22. Carwile JL, Ye X, Zhou X, Calafat AM, Michels KB. Canned soup consumption and urinary bisphenol A: a randomized crossover trial. JAMA 2011;306(20):2218-20.
23. Rudel RA, Gray JM, Engel CL, et al. Food packaging and bisphenol A and bis(2-ethyhexyl) phthalate exposure: findings from a dietary intervention. Environ Health Perspect 2011;119(7):914-20.
24. Colombo S, Beretta M, Ferrazzano GF, Paglia L. Dental Sealants Part 4: Bisphenol A: What dentists should know. Eur J Paediatr Dent 2018;19(4):333-34.
    
    

ADA Oral Health Topics: Dental Sealants

ADA Professional Product Reviews (PPRs):

• Bisphenol A Released from Resin Based Sealants: Lab Report, Expert Panel, and Caries Corner (August 2016)
• An ADA Laboratory Evaluation: Bisphenol A Released from Resin-Based Dental Sealants (May 2015)
• Determination of Bisphenol A Released from Resin-Based Dental Composite Restoratives (July 2014)
  
  

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