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Resin Dental Sealants and Bisphenol A Oral Exposure 10-21-08
It acts like estrogen and is a growing concern because it leaches out in
minute quantities from baby bottles, the lining of cans and other food-related
packaging.
So would you paint it on your children's teeth?
Dental sealants and composites play a significant role in preventing tooth decay
and in maintaining dental health. Dental sealants are an important tool in
preventing dental caries by providing a protective barrier on the teeth,
particularly when used during a child's formative years. Dental composites are
mainly used to fabricate tooth colored fillings and veneers as well as in the
cementation of crowns. In addition to their functional and aesthetic properties,
composites provide an alternative to mercury amalgam.
In 1996, Nicolas Olea and coworkers at the University of Granada in Spain
reported detectable levels of bisphenol A (BPA) in the saliva of patients
treated with dental sealants, suggesting that children receiving this treatment
could be exposed to the chemical. These findings and the subsequent clinical
recommendations made by the authors, stimulated public concern about this dental
treatment. Subsequent studies, culminating with that of Eric Fung and coworkers,
indicate that while extremely low levels of BPA can be detected in the saliva of
individuals treated with selected dental resins in the hours immediately
following application, no BPA was detected in the blood stream.
A review of key studies on dental resins containing BPA-based materials reveals
that the highest reported acute oral exposure to BPA is more than 50,000 times
lower than levels shown to cause acute oral toxicity in animal studies. Although
repeated exposure to BPA from dental resins is not expected to occur, the
highest reported acute oral exposure is also below the maximum acceptable or
"reference" dose for BPA, which is set for repeated exposure over a lifetime.
Consequently, exposure to BPA from dental resins for both adults and children is
minimal and poses no known risk to human health.
For additional information, see the statement from the American Dental
Association and a summary of a study from the Journal of the American Dental
Association.
Background
Dental composites are complex mixtures of materials that generally consist of an
organic resin matrix, reinforcing inorganic filler and a silane-coupling agent,
which connects the filler and the resin matrix. Sometimes known as "white
filling" or "synthetic porcelain", composites are commonly used as a
tooth-colored restorative material, for example in the fabrication of fillings
and veneers, and the cementation of crowns. Composites without the filler and
coupling agent are commonly used as sealants, which effectively isolate pits and
fissures to help prevent caries in adults and children.
Composite resins are formulated from a mixture of monomers and are most commonly
based on bisphenol A glycidyl methacrylate, usually abbreviated as bis-GMA and
sometimes known as Bowen's monomer after it's inventor. Because of the new
treatment options made available, bis-GMA based composites are considered to be
one of the most significant innovations of modern dentistry.
In addition to bis-GMA, composite resins generally include other monomers to
modify the properties of the resin, for example bisphenol A dimethacrylate (bis-DMA),
ethylene glycol dimethacrylate (EGDMA) and triethylene glycol dimethacrylate (TEGDMA).
Although several key components of composite resins are derived from BPA, there
is no known use of BPA itself in composite resins.
Composites and sealants are provided and applied in the form of a paste or
viscous liquid, which is then cured or hardened after application by
polymerization of the resin with a UV or visible light treatment. In addition to
monomers and fillers, composites also may contain initiators, to promote
polymerization from light treatment, and stabilizers, to maximize storage of the
uncured resin and stability of the cured resin. (Soderholm and Mariotti, 1999;
Guertsen, 1998).
Dental Sealant Release
Is Bisphenol A Released from Dental Composites and Sealants?
Several researchers have studied whether BPA leaches from cured dental
composites or sealants. In 1996, Nicolas Olea and coworkers at the University of
Granada (Spain) and Tufts University in Boston, MA applied a commercially
available sealant to twelve molars each of eighteen men and women, using about
50 mg of sealant per person. Saliva samples were collected one hour prior to and
one hour after application. After treatment, all saliva samples were reported to
contain BPA in amounts ranging from 90 to 931 µg (3.3 to 30 ppm). (Olea et al,
1996)
In a similar study, Arenholt-Bindslev and coworkers applied two commercially
available sealants to four molars of four men per sealant. Saliva samples were
collected before and immediately after application, as well as one and
twenty-four hours after application. The only saliva samples reported to contain
BPA were those collected immediately after application of one of the sealants,
which was the same sealant studied by Olea. The level of BPA reported ranged
from 0.3 to 2.8 ppm, which is approximately 10 times lower than the amount of
BPA reported by Olea. No BPA was found in the saliva samples collected at one
and twenty-four hours after application of this sealant or in any of the saliva
samples collected after application of the other sealant, with a 0.1 ppm limit
of detection. (Arenholt-Bindslev et al, 1999)
In a third larger study, Fung and coworkers at the University of Nebraska
applied the same sealant studied by Olea and Arenholt-Bindslev to the teeth of
eighteen men and twenty-two women. Half of the subjects received 8 mg of sealant
applied to one tooth while the other half received 32 mg of sealant applied to
four teeth. Both saliva and blood samples were collected before application of
the sealant as well as at intervals of one, three and twenty-four hours, and
three and five days after application. Some, but not all, of the saliva samples
collected at one and three hours after application were found to contain BPA in
the range of 5.8 to 105.6 ppb. No BPA was found in saliva samples collected
after twenty-four hours or in any of the blood samples, in both cases with a
detection limit of 5 ppb. The maximum level of BPA detected was more than 250
times lower than the maximum amount reported by Olea. (Fung et al, 2000)
Based on the data reported in the three studies involving application of sealant
to teeth, it appears that low levels of BPA may be released from certain
sealants, although only during a short time period immediately after application
of the sealant. Further, no detectable levels of BPA have been found in blood
after application of a sealant that releases low levels of BPA into saliva.
Although a wide range of BPA levels have been reported in saliva, the validity
of the high levels reported by Olea has been questioned. The analytical method
used by Olea may not have been capable of distinguishing between BPA and TEGDMA,
which is known to be a predominant component released from dental sealants but
not reported at all by Olea. The maximum amount of BPA that could reasonably be
released from the dental sealant has been estimated to be less than the lowest
level reported by Olea. Consequently, TEGDMA may have been misidentified as BPA
in the Olea study (Atkinson et al, 2002). Additional complicating factors may
have been the excessively large amount of sealant applied per subject in the
Olea study, potentially resulting in incomplete polymerization and higher
leachability (Fung et al, 2000).
The validity of the lower levels of BPA reported by Fung and Arenholt-Bindslev
is supported by in vitro leachability studies on cured dental sealants.
Nathanson and coworkers at Boston University tested the leachability of seven
dental sealants that were cured in glass dishes. None of the seven sealants
showed detectable amounts of BPA after extracting with ethanol with a detection
limit of 0.0001 µg BPA/mg sealant (Nathanson et al, 1997). Similarly, Hamid and
Hume tested the leachability in water of seven dental sealants that were applied
to extracted teeth or stainless steel molds and cured. None of the seven
sealants showed detectable amounts of BPA (Hamid and Hume, 1997). In a later
study from Olea's laboratory, samples of composites and sealants polymerized in
glass dishes were extracted with water of varying pH for twenty-four hours. Low
levels of BPA (< 1 µg BPA/mg sealant) were reported for these materials (Pulgar
et al, 2000). Although these studies may not be fully predictive of sealant
leachability in vivo, since they do not consider potentially important factors
such as mastication or the effect of salivary enzymes, they do suggest that high
levels of BPA are not expected.
What is the Source of BPA in Dental Sealants?
Dental sealants typically contain monomers that are derived from BPA, such as
bis-GMA and bis-DMA, but there is no known use of BPA itself in dental sealants.
Since it is known that these monomers may leach from dental sealants, the
stability of the monomers has been studied under a variety of conditions,
including in saliva, to determine if they may hydrolyze to form BPA. Bis-GMA,
the base monomer for many composite resins, has been found to be stable to
various hydrolytic conditions (Schmalz et al, 1999). However, two researchers
have reported that bis-DMA is hydrolyzed to BPA, which likely accounts for the
BPA detected in extracts from certain sealants (Schmalz et al, 1999; Atkinson et
al, 2002).
Potential Exposure and Margin of Safety
The highest amount of BPA reported in saliva by Olea, 931 µg, forms the basis
for the calculation of potential exposure and margin of safety. This quantity
was reported in saliva after the application of one brand of dental sealant in
one individual in a single study. Further studies by other researchers have
reported much lower levels of BPA and have suggested that BPA may have been
misidentified in the Olea study due to interferences in the analytical method.
In addition, no detectable amounts of BPA were found in the blood, indicating
that while some BPA may leach into saliva, systemic exposure does not occur.
Assumptions:
1. 931 µg (0.931 mg) of BPA in saliva. This is a very conservative assumption
since it is the highest value found in the literature. This value is still the
highest even if one assumes that 100% of bis-DMA converts to BPA.
2. Average weight of a child is 25 kg (55 pounds).
3. Exposure subsides in the hours immediately following application. No BPA was
detected in samples after three hours.
Since exposure to BPA from dental sealants occurs only in a short time period
immediately after the sealant is applied, and dental sealants are applied only
very infrequently, safety is most appropriately evaluated as an acute exposure
event. In laboratory animals, BPA has been found to have very low acute oral
toxicity, with LD50 values greater than 2000 milligrams per kilogram of body
weight.
In comparison, the potential exposure to BPA from use of dental sealants on a
child of average weight, based on the assumptions above, is 0.037 milligrams per
kilogram of body weight. This exposure level is more than 50,000 times lower
than the LD50 values that have been reported for BPA. As noted, actual exposure
to BPA from dental sealants is most likely well below the highest reported
value, which further increases the margin of safety.
These assumptions also indicate that exposure to BPA is less than the maximum
acceptable or "reference" dose of 0.05 milligrams per kilogram of body weight
per day (US EPA, 1993). The EPA reference dose is set for a lifelong daily
intake of a substance and includes a considerable safety margin for sensitive
stages of life such as childhood. Although exposure to BPA from dental sealants
would not occur daily for a lifetime, this comparison further indicates that
even the worst-case exposure to BPA from dental sealants represents no harm.
The reference dose for BPA has recently been confirmed by a three-generation
study in rats (Tyl et al, 2002), which found no adverse effects on reproduction
from BPA at doses of 50 milligrams per kilogram body weight per day and lower.
The US EPA calculated the reference dose by dividing the
Lowest-Observed-Adverse-Effect-Level (LOAEL, 50 milligrams per kilogram body
weight per day) from an earlier chronic toxicity study by an uncertainty factor
of 1000. Applying that same uncertainty factor to the
No-Observed-Adverse-Effect-Level (NOAEL, 50 milligrams per kilogram body weight
per day) from the Tyl study confirms the safety of the reference dose, 0.05
milligrams BPA per kilogram body weight per day. Since the maximum estimate of
BPA exposure from dental sealants is less than the reference dose, human
exposure to BPA from dental sealants is minimal and poses no known health risk.
Conclusions
Small amounts of BPA may leach from dental sealants immediately after
application of the sealants to teeth. No BPA has been detected in blood samples,
indicating that there is no detectable systemic exposure to BPA from dental
sealants.
* The source of BPA that leaches from dental sealants is likely to be from
hydrolysis of bis-DMA, a common monomer used in dental resin formulations.
* When evaluated as an acute exposure event, the highest level of BPA reported
in saliva from dental sealants is more than 50,000 times lower than the LD50
values that have been reported for BPA.
* Although BPA exposure from dental sealants does not occur daily throughout a
lifetime, the highest level of BPA reported is also below the maximum acceptable
or "reference" dose for BPA of 0.05 mg/kg body weight/day.
* A recent three-generation study has confirmed the safety of the maximum
acceptable or "reference" dose for BPA of 0.05 mg/kg body weight/ day.
* Consequently, human exposure to BPA from dental resins is minimal and poses no
known health risk.
References
Atkinson, J. C., F. Diamond, F. Eichmiller, R. Selwitz, and G. Jones, 2002,
"Stability of bisphenol A, triethylene-glycol dimethyacrylate, and bisphenol A
dimethyacrylate in whole saliva", Dental Materials, vol. 18, pages 128-135.
Arenholt-Bindslev D., V. Breinholt, G. Schmalz, and A. Preiss, 1998,
"Time-related bisphenol A content and estrogenic activity in saliva samples
collected in relation to placement of dental fissures", Journal of Dental
Research, 77(B): 692 (abstract 481).
EPA (U.S. Environmental Protection Agency), Bisphenol A, CASRN 80-05-7, IRIS,
Integrated Risk Information System, on-line, 1993. Available on the Internet at
http://www.epa.gov/iriswebp/iris/subst/0356.htm.
Fung, E. Y. K., N. O. Ewoldsen, H. S. St. Germain Jr., D. B. Marx, C. Miaw, C.
Siew, H. Chou, S. E. Grunniger, and D. M. Meyer, 2000, "Pharmacookinetics of
Bisphenol A Released from a Dental Sealant", Journal of the American Dental
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Guertsen W., 1998, "Substances released from dental resin composites and glass
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Hamid A and W. R. Hume, 1997, "A study of component release from resin pit and
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Nathanson D., P. Lertpitayakun, M. Lamkin, M. Edalatpour, and L. Chou, 1997, "In
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Pulgar R., M. F. Olea-Serrano, A. Novillo-Fertrell, A. Rivas, P. Pazos, V.
Pedraza, J. Navajas, and N. Olea, 2000, "Determination of bisphenol A and
related aromatic compounds released from Bis-GMA-based composites and sealants
by highperformance liquid chromatography", Environmental Health Perspectives,
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Schmalz G., A. Preiss, and D. Arenholt-Bindslev, 1998, "Bisphenol A content of
resin monomers and degradation products", Journal of Dental Research, 77(B): 823
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Soderholm K., and A. Mariotti, 1999, "Bis-GMA Based Resins in Dentistry: Are
They Safe?", Journal of the American Dental Association, vol. 130, pages
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Tyl, R. W., C. B. Myers, M. C. Marr, B. F. Thomas, A. R. Keimowitz, D. R. Brine,
M. M. Veselica, P. A. Fail, T. Y. Chang, J. C. Seely, R. L. Joiner, J. H. Butala,
S. S. Dimond, S. Z. Cagen, R. N. Shiotsuka, G. D. Stropp, and J. M. Waechter,
2002, "Three-Generation Reproductive Toxicity Study of Dietary Bisphenol A in CD
Sprague-Dawley Rats," Toxicological Sciences, vol. 68, pages 121-146.