Teeth, hypomineralisation, fluoride and fissure sealants. What do we know so far?

19 Apr

“The Kitchen is your lab and food is your best medicine!”

~ Dr Nina

Structure of the tooth:

Tooth consists of several anatomical parts:

1. Crown: visible part of the tooth and consist of enamel and dentin. Enamel is the outmost layer of a tooth. It is the hardest tissue in the body and helps to protect teeth from bacteria and to withstand the pressure from chewing. Dentin is a layer of mineralised tissue just below the enamel. It protects teeth from heat and cold.

2. Root: is the unseen portion of the tooth that extends into the bone and holds tooth in place. It is made up of several parts: root canal, cementum, periodontal ligament, nerves and blood vessels and jawbone.

3. Neck: is the area where the crown joins the root. It has three main parts: gums (gingiva), pulp (innermost portion of the tooth, made of blood vessels and nerve tissue) and pulp cavity.

Hypomineralisation: is a condition that affects the enamel, making it more prone to the caries and decay. With up to 20% of the UK population having some form of hypomineralisation. Dental enamel is the hardest tissue comprising 98% mineral and 2% organic matrix (collagen) and water.

Two types of hypomineralisation are distinguished:

- Molar Incisor Hypomineralisation (MIH) – affects first permanent molars and incisors. The enamel is softer than normal, making these teeth more vulnerable.

- Primary Teeth Hypomineralisation – affects “milk” teeth.

The exact aetiology of MIH is unknown, however, number of external factors during tooth development, either during the pregnancy or in the first two years of life is considered: coughs, colds, antibiotic used during pregnancy, sever childhood illness, high fevers, exposure to environmental pollutants. Hypomineralised teeth exhibit chalky white or yellow patches and increased sensitivity. Child is suffering from sensitivity, toothache and potentially rapid decay.

Dental enamel consists of the approximately 90% of inorganic hydroxyapatite (crystalline calcium and phosphate) Ca10(PO4)6(OH)2. Researchers believe that when some hydroxyl (OH-) groups are replaced with fluoride (F-) ion, it makes enamel stronger and less likely to develop caries. This replacement will create a compound called fluorohydroxyapatite Ca10(PO4)6(OH)(2-x)Fx. This process occurs readily even at low fluoride concentrations. The maximum stability was shown at 50% substitution of (OH-) groups with (F-). When large amount (>135mg/L) of fluoride introduced to the oral cavity (fluoridated varnishes, toothpastes etc.), calcium can form a calcium-fluoride (CaF2)-like deposits on enamel, which can be detrimental to enamel integrity by reducing the available calcium ions required for remineralisation. On the other hand, fluoride has known for its toxic properties which can cause enamel malformation called dental fluorosis.

Both hydroxyapatite and fluorohydroxyapatite are essentially the same structure (fluoride structure is slightly stronger), which is very compact and the least soluble in aqueous solution, therefore great for enamels.

Our saliva is neutral aqueous solution (pH~7) and some ions from the surface of the dental enamel can go into the solution. On the other hand, saliva contains calcium, phosphate and hydroxyl ions that can offset the loss of ions from the enamel. This process is constant. Calcium and phosphate can also be received thought the blood vessels located in the pulp. This process is extremely important in maintaining structural integrity of the dentin and enamel. Magnesium is also essential in this process as it helps the body to absorb calcium and vitamin D.

When kids consume a lot of sugar it is metabolised into lactic acid by Streptococcus mutans. This lactic acid will be neutralised by salivary bicarbonate, lowering the salivary pH. This is turn will lower levels of phosphate and hydroxyl ions below the levels needed to sustain mineralisation and remineralisation of teeth. The stability of the enamel mineral depends on the several parameters: keeping total calcium and phosphate concentration constant and making sure that saliva is not too acidic (normally should be neutral). The pH at which fluoridated enamel will start to demineralise is lower (more acidic) than the pH at which non-fluoridated hydroxyapatite will start to demineralise.

Most common therapeutic interventions:

- Empowering good oral hygiene

- Use of Tooth Mousse (concentrated paste containing calcium and phosphate)

- Use of fluoride varnishes

- Use of different fissure sealants.

Fluoride plays an important role in maintaining the structure and physiological function of bones and teeth. Although, we are highly recommended to take fluoride supplementation daily, the Recommended Daily Intake is not set in the United Kingdom. However, the National Institutes of Health (USA) recommends that adults take 4mg of fluoride daily. Children between 9- and 13-years old take 2mg daily and between 14- and 18- years old take 3mg daily. The principal sources of fluoride are fluoride containing dental products (toothpaste, varnish, mouthwash) and fluoridated water. The concentration of fluoride in fluoridated water depends on the geographic locations and normally vary between 0.5 and 1.0mg/L (higher in USA and 1.5mg/L is recommended by WHO). Fluoridated toothpastes contain between 1000 and 1500ppm fluoride (about 0.4-0.72mg of fluoride in a pea-size portion). Fluoride mouth rinses contain between 230 and 900ppm (230 to 900mg/L), whereas dental fluoride varnish contains up to 22,600ppm (22,600mg/L) of fluoride. Dentists apply 25ml of fluoride varnish per child before 6 years old (correspondence to 565mg of fluoride) and 4ml per child above 6 years old (correspondence to 90.4mg of fluoride) twice per year.

Almost all food contains at least trace amounts fluoride depending on soil they are grown in, water they are made from or live in, pesticides used for farming and cookware used for cooking. Highest fluoride containing are canned salmon and sardines, raisins, shrimps. Vegetables and nuts are usually low in fluoride.

Is fluoride safe?

Long-term ingestion or inhalation of fluoride in high concentrations can lead to dental or skeletal fluorosis. Enamel fluorosis may occur even by drinking fluoridated water, depending on total intake, and considered to be acceptable side effect of community level fluoride-based caries prevention programme. According to WHO the global prevalence of dental fluorosis is not known, however, according to the Centres for Disease Control and Prevention (CDC) around 41% of American children aged 12-15 exhibit fluorosis to some degree. Dental fluorosis is irreversible.

It has been shown that fluoride may inhibit protein synthesis, promote production of reactive oxygen species (ROS) and alter cellular metabolism. Excessive fluoride intake can induce toxic effects by binding with calcium and interfering with the digestive enzymes and glucose conversion into energy (ATP). Ingested fluoride reacts with gastric acid to produce hydrofluoric acid in stomach leading to abdominal pain, excessive saliva, nausea and vomiting. Seizures and muscle spasms may also occur.

Low-to-moderate fluoride from drinking water is also known to penetrate blood-brain barrier and may directly impair brain function leading to neurodevelopmental issues and low IQ in children. Animal studies have shown that excess amount of fluoride can negatively impact reproductive and immune systems. Pathological changes have been observed in liver, kidney, lungs, heart, brain, thyroids leading to the following conditions: risk of fractures, bone cancer, diabetes, high blood pressure, immune system dysfunction, insomnia, iodine deficiency and thyroid dysfunction, lower fertility rates, osteoarthritis, increased risk of heart attack etc. Fluoride is shown to cause significant increase in total plasma lipids and associated with the increased BMI and odds of overweight/obesity in school-age children especially girls.

Fissure sealants.

Fissure sealants are plastic coatings that are painted on to the grooves of the back teeth (molars and premolars). The sealants suppose to form a protective layer that keeps bacteria and food from getting stuck in the grooves in the teeth and may cause decay.

The fissure sealants can be classified by their main ingredients into two main groups. However, different combinations of these materials also exist.

1. Resin-based sealants are the most commonly used fissure sealants. They typically contain the following components:

- Urethane dimethacrylate (UDMA) – a monomer that contributes to the sealant’s adhesive properties.

- Bisphenol A-glycidyl methacrylate (bis-GMA) – a monomer that enhances bonding and durability.

- Light-cure initiator system:

o Camphorquinone – a photoinitiator that activates the curing process when exposed to light.

o Tertiary amine – an accelerator tat helps initiate the polymerization reaction.

o Iodonium salt – enhances the curing process.

2. Glass ionomer sealants are alternative to resin-based sealants, however, less durable. They typically contain the following:

- Fluoroaluminosilicate glass powder – provides strength and stability.

- Water-based polymeric acid solution – acts as the matrix for the glass particles.

NHS usually uses resin-based fissure sealants as part of dental care. They are applied to the permanent molars of all children as early as possible after eruption. Teeth are cleaned, prepared with special solution and dried before application. The blue light is used to set sealants hard (polymerize it). They usually last for many years, but need to be checked regularly making sure that seal is intact, and no decay has appeared underneath it.

There is clear evidence that using resin-based sealants creates a physical barrier that protects teeth from caries. But disadvantages should also be considered. The resin-based materials can shrink and result in microleakages, allowing saliva and bacteria to penetrate the barrier and grow underneath the sealant, voiding its protective properties. To avoid even worse damage the teeth and sealants need to be checked regularly to facilitate timely treatments.

Additionally, research has shown that not all monomers are converted into polymers during the polymerization process. Unconverted monomers can be released into the oral cavity from the sealants’ surface or due to leakage through the sealant during its lifetime. Therefore, both UDMA and bis-GMA resins has been studied for its potential toxic properties.

Our oral cavity plays a crucial role in immune response due to its contact exposure to foreign substances. High amount of specialised immune cells can be found there. Macrophages, which are ubiquitous in oral tissues, serve as the first line of defence against invading microbial pathogens and unfamiliar chemicals. Research has shown that UDMA induces cytotoxicity in macrophages leading to both apoptosis (programmed cell death) and necrosis (unplanned cell death). UDMA has shown to cause genotoxicity (DNA damage) implicating cell health and to disrupt mitochondrial functions affecting essential energy production and potentially overall health.

Bis-GMA contains bisphenol A (BPA), which is a xenoestrogen (endocrine disruptor). It is known to impair the development, health and functionality of the reproductive system. Although, according to the American Dental Association (ADA) patients should not worry about the potential exposure to the BPA from fissure sealants. This claim was never supported by any actual data. The research has, however, shown that BPA was detected in small amounts in the saliva of patients’ for up to three hours after the application of resin-based sealing material.

Some dentists see the advantage of using glass ionomer cement (GIC) for their fluoride-releasing properties and in simplicity of the application process (could be apply to the wet teeth and no light required for polymerisation). However, they need to be reapplied every 3-12 months.

It is thought that glass ionomers can remineralise dental hard tissue, such as enamel, as a result of fluoride release into the oral cavity. After 28 days, enamel adjacent to GIC contains 1,181.03 ppm more fluoride than after use of resin-based sealants. Additionally, calcium and phosphate ions can be also release into the tooth structure. Although these materials are highly affective in protecting the teeth, they can affect the surrounding tissues as they come into contact with or interact with body tissues and fluids. Therefore, biological compatibility should be considered when deciding whether use them or not. Given that both components of glass ionomers (glass powder and acid solution) consist of several chemicals, the toxicity of them needs to be discussed. Researchers have shown that the GICs which release the most fluoride have the highest cytotoxicity.

Patients should also consider that GIC contains a lot of additional potentially toxic chemicals such as methyl methacrylate (can cause skin irritation and allergic reactions, potentially cancerogenic), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, methacryloyloxydecyl dihydrogen phosphate, 2,6-di-tert-butyl-p-cresol (suspected of damaging fertility, may cause respiratory irritation) and many other.

Conclusion:

The UDMA and bis-GMA containing materials should be used cautiously. Application of proper polymerization techniques is crucial to minimize residual monomer release and associated toxicity. Additionally, a surface of the dental sealant needs to be treated properly. The easiest way is to make sure the patient gargles with tepid water for at least 30 seconds and spits it out.

Parents need to be properly informed about the potential toxic effects of these material. As fissure sealants are part of mandatory preventative dental treatments across the world (including UK) for every child, the safety of this materials needs to be accurately evaluated.

Alternative, more holistic options are available and I am happy to discuss them with you if you are interested.

References:

1. https://doi.org/10.1186/s12903-024-04005-2

2. https://doi.org/10.1007/s10266-022-00758-w

3. https://doi.org/10.3390/polym12061398

4. www.dentaly.org/en/babies-children/fissure-sealant/

5. https://www.cda-adc.ca/jcda/vol-74/issue-2/179.pdf

6. https://doi.org/10.3390/dj6020018

7. https://doi.org/10.1016/j.chroma.2018.09.039

8. https://www.aapd.org/globalassets/media/policies_guidelines/g_sealants-re.pdf

9. https://doi.org/10.12659/msm.939065

10. https://doi.org/10.1016/j.ecoenv.2019.109558