Fighting decay

Media item: article

Date published: 12 March 2015

Subject: dental caries and its prevention

This page records the media item. The original article is the property of its publisher and is not reproduced here.

What tooth decay actually is

Decay — dental caries — is not a hole that appears. It is a continuous chemical process that runs in both directions, every day, in every mouth.

Bacteria in dental plaque metabolise fermentable carbohydrate and produce acid. When the pH at the tooth surface falls below roughly 5.5 for enamel (and around 6.2 for the softer root dentine), calcium and phosphate dissolve out of the tooth. That is demineralisation.

The World Health Organization describes the same sequence in one sentence: caries ‘results when plaque forms on the surface of a tooth and converts the free sugars … contained in foods and beverages into acids that destroy the tooth over time’, and it names three things that let that happen — ‘a continued high intake of free sugars, inadequate exposure to fluoride and a lack of removal of plaque by toothbrushing’.

Between those acid episodes, saliva buffers the pH back up and returns calcium and phosphate — and, if fluoride is present, forms fluorapatite, which is more acid-resistant than the original mineral. That is remineralisation.

A cavity forms only when demineralisation outweighs remineralisation, repeatedly, over months. Caries is a balance, not an event.

This single idea explains almost everything useful about prevention.

The consequence people find most surprising

Frequency of sugar matters more than quantity.

Each exposure to fermentable carbohydrate produces an acid episode lasting roughly 20 to 40 minutes. A can of soft drink consumed in five minutes is one acid episode. The same can sipped across three hours is a near-continuous one.

The Australian Dental Association's policy on diet and caries does not rank these against each other, but it does put frequency on the same footing as amount: ‘the form, frequency, timing and total amount of sugar intake are significant in the initiation of the caries process’, with ‘special emphasis’ on ‘snacking on sugary-beverages and/or sugar-rich foods that have limited nutritional value’. The same policy singles out ‘sipping drinks, other than water, during interrupted sleep’ as a habit to discourage.

So:

• Six sweetened coffees across a working day is worse for your teeth than a dessert after dinner, even if the dessert contains more sugar.
• Grazing is worse than eating. Constant snacking never lets pH recover.
• Sipping is the worst pattern of all — sports drinks, juice, cordial, sweetened tea, and the water bottle with squash in it.
• A sugary item at the end of a meal does less damage than the same item alone between meals, because the meal has already stimulated saliva flow. How diet drives cavities is set out separately.

On total amount, the WHO's position is specific: limiting free sugars to less than 10% of total energy intake — and ideally to less than 5% — ‘minimizes the risk of dental caries throughout the life course’, and free sugar consumption is ‘the most common risk factor for dental caries’.

Early decay can reverse. Cavities cannot.

This is the other consequence, and it changes what a good dentist does.

A white-spot lesion — demineralised but intact enamel — can remineralise. It does not need a filling. It needs fluoride, plaque control and a change in the frequency of acid exposure, and then monitoring.

Once the surface breaks down into a cavity, it cannot heal. Enamel has no cells and no blood supply. From that point the only options are restoration or extraction, and every restoration is temporary — each replacement removes more tooth than the last, which is why the first filling in a tooth begins a cycle rather than ending a problem.

‘Watch and monitor’ is a legitimate clinical decision, not neglect, and a practitioner who fills every early lesion on sight is not being thorough. Ask which lesions are cavitated and which are being watched.

What actually works, ranked by evidence

Fluoride toothpaste, twice a day

This is the single most effective thing an individual can do, and the evidence for it is among the strongest in preventive medicine. The ADA's own list of ‘main oral hygiene strategies’ begins with it: ‘brushing for two minutes twice a day; using an age-appropriate fluoride toothpaste; clean between teeth once a day using floss or interdental brushes; and visit a dental professional for regular check-ups and professional cleaning.’

The detail that matters and is almost never explained: spit, don't rinse. Rinsing with water after brushing washes away the fluoride that would otherwise sit on the teeth working for another hour or two. Spit out the excess and leave it.

Concentration matters. Standard adult toothpaste contains around 1000–1500 ppm fluoride — the concentration the WHO names when it describes toothbrushing as caries prevention. High-fluoride toothpaste (5000 ppm) is available on prescription or through a dental practice for people at high risk — dry mouth, high decay rate, exposed root surfaces, orthodontic appliances — and it is significantly more effective for them.

Children need less. A smear for under-threes and a pea-sized amount for three- to six-year-olds, supervised, with the child encouraged to spit. Excess swallowing during tooth development causes fluorosis — white or brown mottling that is cosmetic, permanent, and entirely preventable. The NHMRC's explanation of the timing is worth knowing: fluorosis arises only while teeth are still developing inside the jawbone, ‘usually from birth to six or eight years of age’, and it is why the public health message is to ‘use only a small pea-sized amount’ and to ‘encourage children not to swallow toothpaste’.

Water fluoridation

The most cost-effective population-level measure available, and one of the most studied public health interventions anywhere. Melbourne's water supply is fluoridated. The benefit accrues without anyone doing anything, which is precisely why it works and why it disproportionately helps people who see a dentist least.

The NHMRC's 2017 Public Statement on water fluoridation and human health recommends community water fluoridation ‘as a safe, effective and ethical way to help reduce tooth decay’, within a range of 0.6 to 1.1 mg/L, and states that ‘the existing body of evidence consistently shows that water fluoridation safely and effectively reduces tooth decay across the population at the current Australian levels’. On the size of the effect, NHMRC's review found water fluoridation reduces tooth decay by 26 to 44% in children and adolescents, and by about 27% in adults.

Interdental cleaning

A toothbrush does not reach between teeth, and interproximal surfaces are where a large share of adult decay starts — unseen, and often not visible until it is well into dentine.

Interdental brushes have better evidence than floss where the spaces are large enough to admit them. Floss remains appropriate for tight contacts. It is worth saying that the ADA itself does not rank them: its main-strategies list reads ‘clean between teeth once a day using floss or interdental brushes’, and its list of proven aids names ‘interdental aids including floss & interdental brushes’ as one item. The best one is the one actually used daily; a perfect technique performed twice a year is worth nothing.

Fissure sealants

The deep grooves on the biting surfaces of molars are narrower than a toothbrush bristle. Sealing them is well-evidenced, particularly on newly erupted permanent molars in children at elevated risk. They need checking, because a partially lost sealant can trap what it was meant to exclude.

Saliva

Saliva is the body's own defence and it is easy to forget until it is gone. Dry mouth dramatically increases decay risk, and the most common cause is medication — antidepressants, antihistamines, antihypertensives, diuretics. Also radiotherapy to the head and neck, and Sjögren's syndrome.

If your mouth is dry: sugar-free gum stimulates flow (and xylitol-containing gum has some direct evidence), high-fluoride toothpaste helps, saliva substitutes help, and recall intervals should be shorter. Sugar-free chewing gum appears on the ADA's list of proven aids to oral hygiene, alongside the toothbrush, fluoridated toothpaste, interdental aids and mouthrinse. Do not stop a medication over this — raise it with the prescriber.

The things with weaker evidence than their marketing

• Mouthwash is not a substitute for mechanical cleaning. The ADA's position is precise and often misreported in both directions: mouthrinse is a proven aid to oral hygiene, but it is not among the main strategies — an aid alongside brushing, interdental cleaning and regular professional care, not a replacement for any of them. Australian Prescriber puts it as ‘an adjunct to, not a substitute for, regular brushing and flossing’. A fluoride rinse used at a different time of day from brushing can help high-risk patients; the strongest evidence for fluoride mouthrinse is narrower than that, though — a Cochrane review found that supervised regular use by children and adolescents, mostly in school programmes, is associated with a large reduction in decay in permanent teeth, with the reviewers ‘moderately certain of the size of the effect’ and the effect in unsupervised settings ‘less clear’. An alcohol-based cosmetic rinse mostly changes breath.
• ‘Sugar-free’ is not the same as ‘tooth-friendly.’ Diet soft drinks and sparkling water with citric or phosphoric acid erode enamel directly, without any bacteria involved. Erosion and caries are different processes with the same endpoint.
• Natural sugars are still sugars. The WHO's definition of free sugars settles this: ‘all sugars added to foods and beverages by the manufacturer, cook or consumer, plus sugars naturally present in honey, syrups and fruit juices’. Honey, agave, fruit juice and dried fruit are all fermentable carbohydrate. Dried fruit is worse than most because it is sticky and retentive — as are several other foods worth avoiding.
• Charcoal and ‘whitening’ abrasives remove enamel, which is the thing protecting you.

Who is actually at risk

Caries is not evenly distributed, and risk is largely predictable:

• Anyone with a dry mouth, from any cause
• Anyone with exposed root surfaces — root dentine dissolves at a higher pH than enamel, so older adults with gum recession are at high risk even if they have never had a cavity
• Orthodontic patients, because brackets create plaque traps
• People who graze or sip, regardless of total sugar intake
• Children whose habits were set early — bottles at bedtime and sweetened drinks in sippy cups produce a recognised pattern of early childhood caries
• Anyone who has had a lot of decay before. Past caries experience is the strongest single predictor of future caries.

The children's end of this is measurable. The ADA's Children and Young People Oral Health Tracker records that nearly 11 — 10.8 — in every 1,000 children aged 5 to 9 are hospitalised for potentially preventable problems due to dental conditions, rising to 14.3 per 1,000 for Indigenous children, and that only 56% of children visit the dentist before age 5.

Recall interval should follow risk. Six months is a convention, not evidence. Some people are safe at twelve or eighteen months; others need three.

The uncomfortable one

Decay is painless until it is not. By the time a tooth aches, the process has usually reached the pulp, and the choice has narrowed from ‘a filling’ to ‘root canal treatment or extraction’. Pain is a late signal in dentistry, not an early one — which is the entire argument for examination and radiographs at an interval matched to your risk, rather than attendance when something hurts.

Common questions

Melbourne's water is fluoridated. Do I still need fluoride toothpaste?

Yes. The NHMRC treats them as parts of one package rather than alternatives: ‘Along with a combination of healthy diet, good oral hygiene, appropriate use of fluoridated toothpaste and regular dental check-ups, water fluoridation is an effective public health measure to prevent tooth decay.’ The 26 to 44% reduction in children and about 27% in adults quoted above is the benefit of fluoridated water in a population already using toothpaste — not instead of it.

The corollary is worth checking in your own house, because several ordinary things remove the water half of that package:

• Filters. NHMRC states that ‘Distillers and filtering systems containing ion exchange resins, activated aluminium or reverse-osmosis membranes have been shown to be effective and will remove most of the fluoride from water’, and adds the position plainly: ‘it is not necessary or desirable to remove the fluoride’. A simple carbon jug filter is a different thing from a reverse-osmosis unit under the sink, and it is worth knowing which you have.
• Bottled water. ‘In most cases, the answer is no’ — though NHMRC notes some products contain naturally occurring fluoride, and that Australian food regulations permit adding it within 0.6 to 1 mg/L, so the label is the place to look.
• Rainwater tanks. ‘Rainwater collected in domestic tanks will not contain fluoride’, and NHMRC does not recommend fluoridating tank water because ‘it can be difficult to maintain the correct concentration’. It suggests people relying on tank water ‘seek advice concerning fluoride requirements’ from a dental practitioner or the ADA.

If you drink filtered, bottled or tank water almost exclusively, say so at your next examination. It changes your risk category, and it is the kind of thing nobody thinks to mention.

Is fluoride actually safe? I keep seeing claims about IQ and cancer.

The NHMRC reviewed this and its 2017 statement is specific about which claims the evidence rules out and which it merely fails to support — a distinction worth holding onto, because the two get conflated in both directions.

Where it found reliable evidence of no association: community water fluoridation as practised in Australia ‘is not associated with cancer, Down syndrome, cognitive dysfunction, lowered intelligence or hip fracture’. On cancer specifically it goes further: ‘There is no association between community water fluoridation and any form of cancer, including osteosarcoma and Ewing sarcoma (types of bone cancer).’

Where it found no reliable evidence of an association, a longer list: ‘chronic kidney disease, kidney stones, hardening of the arteries (atherosclerosis), high blood pressure, low birth weight, all-cause mortality, musculoskeletal pain, osteoporosis, skeletal fluorosis, thyroid problems or other self-reported ailments such as gastric discomfort, headache, and insomnia’.

And then the honest part, in NHMRC's own words: ‘The term “no reliable evidence” is used by NHMRC when there is a lack of confidence that the evidence reviewed is relevant to Australia or valid to accept any association’ — affected by ‘the small numbers of studies, the study designs, the low quality of the studies and the lack of control for possible confounding factors’. That is not the same as proof of absence, and NHMRC does not pretend it is. Two things follow: the Australian dose matters (0.6 to 1.1 mg/L, not the much higher natural concentrations behind some overseas studies), and a study from elsewhere is not automatically about the water here.

My child has white marks on their front teeth. Is that fluorosis, and is it my fault?

Possibly, possibly not, and probably not your fault either way — but it is worth having looked at, because the two common causes are managed differently.

On fluorosis, the Australian picture is more reassuring than the internet suggests. NHMRC records that dental fluorosis ‘has declined over the time period during which the extent of community water fluoridation has expanded’, and attributes that decline to ‘reduced exposure to fluoride from other sources such as toothpaste, which is now available in low fluoride toothpastes for children’. On severity: ‘in most cases it is classified as very mild or mild’, and ‘Mild to very mild dental fluorosis does not affect the function of the teeth, is not of aesthetic concern to those who have it and is associated with a protective benefit against tooth decay in adult teeth.’ Moderate fluorosis ‘is very uncommon and severe dental fluorosis is rare in Australia’, and the small amount that exists ‘is not statistically different between fluoridated and non-fluoridated areas’.

The other common cause looks different. Fluorosis tends to present as ‘white lines or areas on the surface’ of the teeth. Molar incisor hypomineralisation produces creamy-white, yellow or brown patches that are sharply demarcated from the enamel around them, and it is a developmental defect that is not caused by anything a parent did — it is covered on Molar Power and in My child has chalky teeth. The distinction matters because hypomineralised enamel is soft, sensitive and decay-prone, and needs active management; mild fluorosis needs nothing.

What you can do about the toothpaste half is simple and specific: ‘use only a small pea-sized amount’ and ‘encourage children not to swallow toothpaste’. Kids' teeth cleaning tips.

I am pregnant, or making up formula. Is fluoridated water a problem?

No, on both counts, and NHMRC addresses each directly.

On pregnancy and breastfeeding: ‘It is safe for the unborn child and infant when pregnant and breast feeding mothers drink water fluoridated at Australian levels.’ It adds a detail that answers the obvious follow-up — ‘Breast milk naturally contains about 5–10 μg (micrograms) of fluoride per litre of milk’, and ‘The level of fluoride in breast milk remains steady when a nursing mother drinks fluoridated water.’ So the fluoride does not concentrate in the milk.

On formula: ‘Infant formula products sold in Australia are safe to feed to infants when made up with fluoridated drinking water.’ NHMRC restates its general feeding advice alongside that — exclusive breastfeeding until around six months where possible, and formula as the alternative until 12 months for infants not breastfed or only partly breastfed.

The dental risks that actually matter in the first two years are elsewhere: a bottle in bed with anything but water, and sweetened drinks in a sippy cup. Pregnancy and oral health covers the rest.

At my first visit I was told I need a clean and four fillings. How do I check that?

By asking for the findings rather than the plan, and by knowing that variation between practitioners is documented rather than imagined. A submission to the Senate inquiry into private health insurance and out-of-pocket costs, published by the Parliament of Australia, puts it this way: ‘It is well known that private patients can go to multiple dentists and receive conflicting diagnoses and widely varying quotes for unpredictable dental fees.’ That is a submitter's argument, not a regulator's finding — but it describes something most people eventually experience.

Three questions get you most of the way:

• ‘Which of these lesions are cavitated, and which are being watched?’ Given that early demineralisation can remineralise and a cavity cannot, that distinction is the whole decision. A plan that fills everything visible has skipped it.
• ‘Can I see the radiographs and the chart?’ You are entitled to your records, and a lesion into dentine looks different from a shadow.
• ‘What happens if we do the urgent part now and review the rest in six months?’ Sequencing is a legitimate answer far more often than it is offered.

There is a regulatory backstop, and it exists precisely for this. Section 133 of the National Law prohibits advertising that ‘directly or indirectly’ encourages ‘the indiscriminate or unnecessary use of regulated health services’, and AHPRA's guidelines explain why: doing so ‘can lead the public to buy or use a regulated health service they do not need and is not clinically indicated or provides no therapeutic benefit’, and ‘any health intervention involves inherent risks’. If a treatment plan arrives with urgency language attached rather than findings, that is the thing to slow down over. Second Opinions and Corrective Dentistry and Understanding Your Treatment.

Related reading

• Tooth Fillings and Children's Dentistry
• How do I prevent dental decay? and what can I do to strengthen my teeth?
• Caring for your teeth: 8 steps to dental health
• Dental Myth Busters
• Dental Cleans and Hygienists and General Dentistry
• More coverage in Our Media

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