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Unfortunately that can lead to other problems. Last year 272,000 adults had decayed teeth removed; poor oral health has also been linked with other poor health outcomes we might not expect, including diabetes, heart disease, respiratory disease, gastrointestinal and pancreatic cancers and arthritis. There's a theory this is due to the inflammation caused by unhealthy gums creating chronic inflammation in the body. We know many diseases are linked to chronic inflammation.
So what can we do, apart from regular dental check-ups, to keep our teeth, and our kids', as healthy as possible?
Obviously what we eat and drink plays a major part. A basic healthy diet featuring lots of vegetables and fruit is a good start.
Sugar, of course, is tooth decay's best friend. The more sugar we eat and drink, the more likely we are to suffer from caries. Sugar is food for bacteria in the mouth, which creates an acidic environment that then creates decay.
Most of us know lollies, cakes, icecream and sugary drinks are bad for our teeth. But there are some sneaky sugars we might not be so aware of that can do equal damage.
Bach says "health food" trends can hide damaging sugar. She reported talking to parents who say they never give their children sugary treats, only home baking sweetened with dates, honey or maple syrup. These, though, are no different to white sugar in terms of how they behave in our mouths. And lots of so-called "natural" bars and balls are full of clingy, sticky dried fruit that act much the same.
What and how we drink makes a difference. Plain, still water and plain, unflavoured milk should be our drinks of choice, dentists say. That goes for kids, too. Milk contains proteins that are protective for teeth, which is good. There's a caveat, though: it's not a good idea to give toddlers bottles of milk (or worse, juice), at bedtime, say. That's because the prolonged sucking on a bottle means the natural sugars in the milk cling to the teeth, creating food for bacteria and an acidic environment in the mouth.
The growing popularity of non-dairy milks such as almond milk and soy milk can have consequences, too. These are often sweetened with added sugar – again, more damaging than regular milk. And they don't contain the protective proteins that cow's milk has.
The idea of how we consume any sugary foods or drinks is important. Katie Bach emphasises it's not necessarily the amount of sugar we have (though less is definitely better) but the frequency and timing. Constantly sucking on a juice bottle, or grazing on sweet treats, is worse than eating or drinking it all at once. Grazing means the teeth are constantly being bathed in sugar; the mouth doesn't get the chance to return to a neutral state. If you're going to have a sweet drink, have it with a meal rather than on its own.
While water is great, the increasingly popular sparkling water might not be the best thing to drink constantly. Sparkling water contains carbonic acid (created when carbon dioxide is added) which makes it slightly acidic, and so potentially bad for tooth enamel. It's a whole lot better than a sugary drink, though.
If you're a fan of sparkling water, try mixing it up with plain to keep your teeth healthy. The same goes for sugar-free carbonated drinks. And trendy kombucha can be acidic, too. If you're a big fan of the "booch", follow it with tap water to rinse the mouth.
Lastly – and this shouldn't need saying, but here it is – dentists in New Zealand, in consensus with dentists worldwide, strongly recommend fluoridated water. If you've got it coming out of your tap, enjoy, and leave the bottled water on the shelf.
Niki Bezzant is a food and nutrition writer and speaker. Follow Niki on social media @nikibezzant.