Tooth decay: how it forms and how to actually prevent it

In short: decay does not appear from one day to the next. It is a slow process in which the bacteria in your mouth turn sugar into acid, and that acid gradually dissolves the tooth’s enamel. The good news: once you understand how it works, preventing it is fairly straightforward. We explain it step by step below.

What exactly is a cavity?

A cavity is a hole in the tooth, but that hole is the end of a story that begins much earlier. Millions of bacteria live in your mouth; that is normal. The problem comes when they gather in a sticky layer on the tooth (plaque) and you feed them sugar.

Those bacteria turn the sugar into acid. And that acid attacks the enamel, slowly dissolving its minerals. At first you cannot see anything; then a whitish spot appears; and if it carries on, the hole forms. At that point we are talking about a fully fledged cavity.

How does a cavity form, step by step?

Let us tell it as a sequence, because it makes more sense that way:

1. Plaque builds up. If you do not brush well, a sticky layer is left on the tooth, especially between the teeth and along the gum.
2. You eat sugar. Not just sweets: bread, biscuits, fizzy drinks, juices… all of it feeds the bacteria.
3. The bacteria produce acid. Every time you eat, there is an “acid attack” that lasts a while.
4. The enamel demineralises. The tooth loses minerals. If you give it a break and some fluoride, it recovers; if the attack is constant, it does not have time to.
5. The hole forms. When more mineral is lost than is recovered, the enamel gives way and the cavity appears.

The key to steps 3 and 4 is frequency. Having something sweet once is not the same as nibbling ten times a day: each snack restarts the acid attack and the tooth never rests.

Why do some people get more cavities than others?

Because several factors come into play, not just sugar:

• How often you eat, more than how much.
• The quality of your brushing and whether you use floss or interdental brushes.
• Saliva, which neutralises acid naturally (certain medications reduce it).
• Fluoride, which helps remineralise the enamel.
• The shape of your teeth: back teeth with deep grooves trap more plaque.

How do you genuinely prevent decay?

Here is what really works, no miracles:

• Brush twice a day with fluoride toothpaste. Fluoride is your best ally: it repairs enamel in its early stages. The night-time brush is the most important.
• Clean between your teeth. The brush does not reach the sides; that is where most cavities form. Floss or an interdental brush, every day.
• Manage your snacking. Reduce the number of times you have something sweet rather than the amount. Sweet things at the end of a meal are better than sipping all afternoon.
• Regular check-ups. A small cavity does not hurt and is not visible to the naked eye. At a check-up it is caught early, when fixing it is simple.
• Professional cleaning. Plaque that hardens (tartar) can no longer be removed by brushing. A dental cleaning removes it and leaves your mouth in good shape.

And if the cavity has already formed?

If there is already a hole, it does not fix itself or with more brushing: the damaged area has to be cleaned out and rebuilt with a filling. The sooner the better, because if the decay advances and reaches the nerve, treatment becomes more complicated and we move into the territory of root canal treatment. In little ones, prevention also has very effective tools of its own, which we discuss in paediatric dentistry.

This guide is for information only and does not replace a consultation or a professional diagnosis. If a spot or some discomfort is worrying you, the best thing is to have it assessed in person.

If it has been a while since your last check-up or you have doubts about a particular tooth, at our dental clinic in Bilbao we will take a calm look. Write to us from the contact page and we will see how your mouth is doing.