What is tooth decay?

Most of us know that too much sugar is bad for our teeth, but why? Looks like bacteria are to blame.
25 April 2017

Interview with 

Dr Chris Vernazza, Newcastle University


Tooth Decay


You might not think of the mouth as being part of the gut, but the long, hollow tube that is the digestive system starts here. Food, drink (and, rumour has it, the occasional spider) go in and digestion begins, powered by your saliva and your teeth that turn big chunks of food into bite-sized morsels that are easier to swallow. But, as many people have been made all too painfully aware, our teeth can decay and according to the most recent Children's Dental Health Survey, almost 50% of 15 year olds have evidence of tooth decay. But why, and what can we do about it? Kat Arney speaks to Chris Vernazza, paediatric dentist and co-author of the survey...

Chris - We need a few different ingredients for tooth decay to actually happen and, maybe, the principle one of those is the bacteria that live in your mouth. The mouth’s home to billions of bacteria and all sorts of different species as well. We think there are about 500 to 700 different species, but it’s when these all get out of balance with each other that actually the decay starts.

Kat - What is the decay? How do the bacteria make our teeth break down? What goes on there?

Chris - The bacteria, if you like, feed on sugar, which is what people will commonly recognise as the major ingredient of decay. And as they feed on that sugar they metabolise it and produce acid as a waste product and excret that out of their cells. It’s the acid that’s actually attacking the hard bits of the teeth (the enamel) that leads to them dissolving away and creating holes in the teeth.

Kat - So it’s the acid created by the bugs that breaks down the structure of our teeth. You’ve said that it’s the sugar that the bugs are feeding on that’s doing this so is that presumably just things like sweets - where does this sugar come from?

Chris - We’re really interested in what we call free sugars and that would classically be things like sweets, cakes, puddings. They’re the very obvious ones that people think about and, increasingly people are also thinking about drinks as well. Sugary drinks have been much featured in the news of late as a major problem for obesity, but are also a major problem for tooth decay.

But there are other forms of free sugars that are more hidden away and so that might be things like honey, which people might think of as quite healthy but, actually, is very bad for teeth. Dried fruits, because they’ve dried the sugar that’s naturally bound up in the cells and isn’t really available for bacteria to make decay from actually begins to get released, so dried fruits are particularly bad. And fruit juice is as well and can be quite problematic because, again, the fruits been blitzed and the sugar’s been released from the cells.

Kat - But these are all things that are meant to be super healthy for us.

Chris - Yeah, absolutely. And that’s a bit of a problem for us because often people will turn to those as a healthy alternative but, actually, they’re damaging the teeth quite badly.

Kat - So what should we do? Because I’d be the first to admit that I do love sweeties but I also like fruit and I like fruit juices, and dried fruit, and honey, and things like that. What should I do, should I just stop eating them; that would make my life miserable? How do I protect my teeth?

Chris - In an ideal world we would like everyone to stop eating them but that’s probably not a reasonable way of doing things. So, as well as the amount of sugar that you eat, the really important thing is how often you eat them. Every time you eat some sugar, the bacteria produces acid for about half an hour afterwards. The saliva actually brings the acidic environment back to a normal environment, so it takes about half an hour for that to happen. So you can imagine, if you're having a sugary intake every half hour, your teeth are constantly under attack. Whereas, if you reduce the number of intakes, then there’s going to be a safe period between each where your teeth can begin to remineralise and grow back again, if you like.

Kat - So, that would argue for just eating your sweets or sweet stuff at once, or only a few points during the day rather than constantly dipping into your pockets and snacking?

Chris - Absolutely! One of the common things we advise our patients is if they can have sweet things with their meals then we know that the teeth are only going to be attacked at meal times, and sticking to non-sugary things between meals.

Kat - What about things like tooth brushing, because we’re all brought up to brush our teeth in the morning and at night and do things like flossing, and all that sort of thing? What should we be doing there?

Chris - As I’ve said, the decay happens when the bacteria get out of balance. There are lots of naturally living bacteria in the mouth and the bacteria grow in these communities that we call plaque - the furry stuff that sticks to your teeth. As the plaque gets more and more mature, the bacteria begin to select out themselves as the ones that are going to cause more decay. So, if we can disrupt that plaque by removing it, then that will be very beneficial in preventing decay, which is why brushing is so important, and flossing to get between the teeth.

Our recommendations are to brush twice a day with a fluoride-containing toothpaste. The fluoride's really good at preventing decay, both because it stops the bacteria producing as much acid but it also means the teeth become harder and less susceptible to the acid. So, brushing twice a day with a fluoride toothpaste is the key there.

Kat - Very briefly, we’ve mentioned this report that shows that almost 50% of 15 year olds have tooth decay which, obviously, is not great and later in life they could be losing their teeth. But is there a trend here - are the nation’s teeth getting better are are we just descending into horrible teeth forever?

Chris - No. Things have actually got quite considerably better over the last forty years, and a lot of that has been driven by the addition of fluoride toothpaste. So, if we look at the 15 year olds when we first did the survey in 1973, 97% of 15 year olds had some kind of cavity, which was a shocking figure, and that’s gone down to 42% in 2013.

So we have some big improvements, but I think the fact that we’re still sitting just below half of 15 year olds with some kind of cavities, or having had experience of them is really quick shocking when it’s a completely preventable disease.


definition of tooth decay

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