Dental sealants

Are there any side effects to having children's back teeth covered with a thin layer of silicone, which is supposed to prevent painful decay? M S, Norwich, Norfolk.....

Once we invented plastic tooth coloured fillings, dentists came up with a way to prevent tooth decay in children. The dentist places a thin layer of this filling over the chewing surfaces of the back molars.

The idea is that by sealing off the chewing surfaces of the molars during the years when a child's teeth are most vulnerable to decay usually the teenage years the child will be able to reach adulthood with a full set of healthy teeth.

Dentists target the back molars because they're the teeth that have deep pits and grooves for chewing. Food and bacteria in the mouth can get trapped in these grooves, and when bacteria or plaque in the mouth turns the sugar in food into acid, this acid can eat a cavity in the tooth. Typically, a sealant lasts two to five years, when it can be "resoled", so to speak.

Many dentists are so bullish about dental sealants that they recommend that children get their teeth sealed as soon as they appear. The National Institutes of Health in America recommends that the first permanent molars, often called the six year molars, get sealed as soon as they arrive when a child is aged 5 to 7, and then the back molars, the 12 year molars, get sealed as soon as they appear, when a child is between 11 and 14.

The NIH also says to consider the premolars and bicuspids, the other grooved teeth right in front of the molars, potential candidates for sealing. It recommends that teenagers and young adults consider getting sealants, even if their molar teeth don't have decay or fillings, and that mums have sealants placed on baby teeth that is deeply pitted and grooved.

Thankfully, the British Society of Paediatric Dentistry is a bit more cautious, suggesting that children be evaluated and fissure sealants only be recommended after a thorough clinical examination of the child and his teeth, taking into account medical history, illnesses, diet and any past history of dental decay. All vulnerable pits and fissures should be considered for fissure sealing regardless of the time that they have been in the mouth, says the society, only if the child has: special needs, has a medical problem, has learning difficulties, or comes from a disadvantaged social background.

The society recommends that any child with extensive decay in his primary teeth should have all permanent molars sealed as soon as they come through. Children whose baby teeth are free of cavities don't have to have their first permanent molars routinely sealed but should have the teeth reviewed at regular intervals.

The cautious line taken by the BSPD may reflect the uncertainty surrounding bisphenol-A diglycidylether methacrylate (or bis-GMA, as it is known for short), the resin used for white resin based composite restorative materials, or white "composite" fillings, and dental sealants. The concern centres around whether composite fillings, like many plastics, are oestrogen mimicks, or xenoestrogens, which leach out and upset the balance of a child's hormones.

A recent study at the University of Granada in Spain determined that dental sealants do in fact leak an oestrogen like substance.

In the Spanish study, samples of saliva from 18 subjects treated with 50 mg of a bis-GMA based sealant applied on their molars were collected one hour before and one hour after treatment. Bisphenol-A was identified only in saliva collected after treatment.

The study group, headed by Nicolas Olea at the School of Medicine based at Granada University, then attempted to determine whether bis-GMA has oestrogenic activity in a culture medium of human target breast cancer cells.

In the lab test, they discovered that the resin increased cell yields, progesterone receptor expression and secretion in the cells that is, they helped the cells grow, as oestrogen itself would. The study concluded: "The use of bis-GMA based resins in dentistry, and particularly the use of sealants in children, appears to contribute to human exposure to xenoestrogens" (Environ Health Perspect, 1996; 104: 298-305).

One of the reasons for this leakage is that these sealants are polymerised (ie, cured) in the mouth. Furthermore, the mouth's saliva and constant chewing causes these sealants to degrade over time, increasing the possibility that the xenoestrogens "leak".

What this means in terms of your child's health is anyone's guess. However, you should know that bisphenol-A given off in industrial processes is toxic to fish and invertegrates at concentrations of 1.1-10mg/litre of water (Environ Tox Chem, 1988; 7: 19-26). It's also been found to be toxic to the foetus if given during the development of organs and has also been shown to significantly reduce sperm weight and motility in animals (Dutch Expert Committee on Occupational Standards, the Netherlands Committee of the Health Council of the Netherlands, 1995).

In humans, we have evidence that seven components of composites, including bisphenol-A, have been found to be toxic in the 10-100 umol/l concentration (J Dent Res, 1991; 70: 1450-55).

London dentist and WDDTY panel member Robert Hempleman says that the level of harm may depend upon which type of sealant is used. The clear variety, called "unfilled" sealants, are purely made from plastic resin and so would be the most toxic. Filled sealants, the more usual variety, are bulked out with particles of quartz crystals and other substances, and so have less of the potentially dangerous resin.

Sealants also contain a small amount of fluoride which would dripfeed into the body.

Besides the unknown hormonal dangers of sealants, there's a practical concern. Rochdale dentist John Roberts, secretary of the International Academy of Oral Medicine and Toxicology, says that teeth are often sealed at the first signs of decay which is brown staining in the grooves of the teeth. Oftentimes dentists will seal away the top of the tooth without checking underneath, where there might be an enormous hole in the tooth. This happens increasingly with the use of fluoride, which makes the outside of the tooth brittle, but doesn't do anything to strengthen the inside of the tooth, where decay is more likely to occur. In this instance, dental sealants mask the problem, allowing the decay to carry on unnoticed.

Choosing whether to seal your child's teeth depends on carefully considering whether the child is at risk of developing decay. If the tooth does decay he would have to have a composite filling, and so be exposed to the plastic resins, anyway (mercury amalgam as a filling is not a option either dentist would ever recommend see WDDTY's Dental Handbook).

If your child does have teeth that appear likely to decay, only have those teeth sealed off and only for the shortest posssible time, to avoid long exposure.

Both Hempleman and Roberts do not routinely seal teeth on children with healthy molars. Both favour regular examinations and would recommend sealing at the first sign of brown staining and only on those teeth at risk.

John Roberts uses a technique of sandblasting a tooth with brown staining using aluminum oxide in order to confirm that he is not sealing a tooth with decay underneath. This technique, which doesn't cause stress cracks like drilling, which will ultimately weaken a tooth, also creates a better surface on which to place a sealant, he says.

Alternatively, as the BSPD recommends, your child can have x-rays to see if there is any decay lurking underneath, although you should make sure your child wears a lead shield to prevent his reproductive organs and gonads from being exposed to x-rays. This is best only done if absolutely necessary as children are more susceptible to the dangers of radiation.

If your child does have x-rays, make sure to tell the dentist you want the copies saved and request that you take them with you if you change dentists for any reason to avoid having them needlessly repeated.

If there is decay, Roberts uses a liquid acid called Carisol, which eats away decay and so avoids the need to drill. His favoured filling uses a gas ionomer glass and silicant product, which sticks well to teeth, avoiding the need for resin glues. Over that he places a thin layer of composite. Robert Hemplemen uses a Biogun, which creates a stream of negative ions in the mouth, killing bacteria up to three months afterward before he places a sealant.

Both dentists recommend that a good nutritious diet and good oral hygiene are the best ways to prevent molars from getting cavities. Make sure that your child is having a nutrient dense diet with whole foods and fresh fruits and vegetables, and limit his sweets.

John Roberts recommends that children brush twice a day, at night and before breakfast. If you brush after a meal, you brush away the protective saliva and leave your teeth defenceless against the more acidic pH in your mouth produced during eating. If you do wish to brush after eating, he says, wait until a half hour afterward.