Dental Resins Linked to Mental Dysfunction

Laird Harrison

July 16, 2012

July 16, 2012 — Children with restorations made with bisphenol A-glycidyl methacrylate (bisGMA)-based composite resins may have more emotional and social problems than children with other types of restorations, according to results of a new study published online July 16 and in the August issue of Pediatrics.

Nancy N. Maserejian, ScD, an epidemiologist from the New England Research Institutes in Watertown, Massachusetts, and colleagues theorize bisphenol A (BPA) may leach from restorations and affect children's mental health.

Many commercial products contain this compound, and previous research has implicated it in neurological damage, particularly in children.

However, this retrospective analysis of a landmark trial does not definitively prove that children's health is affected by BPA from restorations, Dr. Maserejian told Medscape Medical News.

"The main message here is that we need more research," she said.

For now, her advice for dental professionals is simple: "Just keep doing what they have been doing."

The researchers are now undertaking a new study to find out whether children with bisGMA-based composite restorations in their mouths have elevated levels of BPA elsewhere in their bodies. Other studies have found such correlations.

That information is missing from the data Dr. Maserejian and colleagues used in their study, however. The researchers who collected the data were focused on potential risk from mercury in amalgam restorations, and as a consequence, they tested the children for exposure to mercury, but not to BPA.

2 types of resin compared with amalgam

Funded by the National Institutes of Health, the New England Children's Amalgam Trial measured neuropyschological and renal functioning in 534 children who were randomly assigned to receive either amalgam or composite resin restorations. The children were aged 6 to 10 years at baseline, and the study followed them for 5 years.

The study, along with the similarly designed Casa Pia Study of the Health Effects of Dental Amalgams in Children, showed no detrimental effects from dental amalgams. Publication of the twin trials in JAMA in 2006 has gone a long way toward addressing concerns about the safety of amalgam, but no study can definitively prove that a substance is harmless. And some critics of amalgam restorations argue that dentists should use composite resins on a "better-safe-than-sorry" principle. The current study calls into question what is truly safe.

The original report of the New England Children's Amalgam Trial noted that children with composite resin restorations had lower psychosocial scores than children with amalgam restorations, but the finding did not get much attention at the time.

In the current study, Dr. Maserejian and colleagues looked more closely to see exactly what type of restoration was associated with what type of risk.

The children in the study received 2 different types of composite resin restorations. In primary teeth the restorations were made with Dyract AP (Dentsply Caulk), and in permanent teeth the restorations were made with Z100 (3MESPE).

The main source monomers in Z100 are bisGMA and triethylene-glycol dimethacrylate.

The Dyract resin is composed of urethane dimethacrylate (UDMA) and carboxylic-acidmodified-dimethacrylate.

Psychosocial function data were available for 434 patients and were obtained from the self-reported Behavior Assessment System for Children (BASC-SR) and parent-reported Child Behavior Checklist (CBCL).

The researchers found no statistically significant association between the UDMA-based restorations and scores on these tests, but they did find that children with bisGMA restorations had higher scores for emotional symptoms and clinical maladjustment and lower scores for personal adjustment.

They noted stronger associations between composite resins on the occlusal surfaces of posterior teeth and BASC-SR psychosocial scores, and they suggested that these restorations were more likely to degrade as a result of chewing.

For every 10 posterior-occlusal surface-years, they found a reduction in the BASC-SR personal adjustment score of 2.2 points (P < .0001).

The effects were not huge. Fewer than 10% of the children had scores described as "at-risk" or "clinically significant." However, such scores were more common among children with greater composite exposure.

For example, 16.3% of children with 13 or more surface years of exposure to bisGMA had total problem behavior scores of concern compared with 6.3% of children with from 0.1 to 5.0 surface years.

The associations between bisGMA exposure and psychosocial scores were not as strong on the CBCL. In general, children improved less over time when they had more exposure to composite resins, but the trend was only statistically significant for activities competence — there was a 2.6-point difference between the highest tertile and those who were unexposed (P trend = .03).

If the study had only compared the 2 types of composite resin with each other, the difference might be attributed to the use of UDMA-based restorations on primary teeth and bisGMA on permanent teeth. For example, this distinction could suggest that more serious dental disease itself was causing the psychosocial effects, or vice versa, or that some third factor was responsible for both.

However, in the amalgam group, the researchers found no consistent associations between psychosocial scores and the amounts of the material used on primary or permanent teeth.

'Needs to be taken seriously.'

The study impressed Rodway Mackert, DMD, PhD, a professor of oral rehabilitation at Georgia Health Sciences University in Augusta, with an expertise in dental materials. "I think it's an important study," he told Medscape Medical News. "It's well controlled and it needs to be taken seriously." Dr. Mackert was not involved in the research.

He agreed that more research was needed, particularly on the release of BPA from bisGMA-based restorations.

For the time being, however, the research shows the fallacy of preferring one material over another based on theoretical risks, he said. "It's a good example of why we need a variety of materials," he noted. "It's certainly premature to talk about banning amalgam."

Composite resins have been used for restorations in the United States since the 1960s, but no one thought to test them for psychosocial effects until recently, he said. BPA and other xenoestrogens did not surface as a concern until the 1990s, he said.

If future studies bear out the risks suggested by this study, other materials could take the place of bisGMA materials. In addition to amalgam and UGMA-based materials, silorane-based materials are a possibility. Glass ionomers and gold can both can be used in some lesions.

Of course, any of these may pose risks that are not yet known. "They may not release xenoestrogens, but they may release something else," Dr. Mackert said. "But if you don't do anything, then that's a risk, too. So you have to base your decision on the current knowledge."

Dr. Maserejian and Dr. Mackert have disclosed no relevant financial relationships.

Pediatrics. 2012;130:1-11. Abstract

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