How do Cavities Form?

What causes cavities to form in the mouth and ways to prevent them.


This post is going to explain a bit of the science behind cavities (also known as dental caries or tooth decay). It might seem a little dry, but try to hang in there and by the end you’ll have a much better understanding of how to care for your teeth.


Cavities result from acid damage to teeth. The enamel that covers teeth is the hardest substance in the body, but long-term exposure to acid can dissolve enamel. This acid can come from a number of places, but the most common source is the bacteria that live in the mouth.

There are many different types of bacteria that live in our mouths. This is completely normal, and while good oral hygiene habits will reduce the number of bacteria in the mouth, they can never be eliminated completely. Some of the bacteria that live in the mouth eat sugars and produce acid as waste. These sugars come from the foods we eat - this includes obvious sources of sugar like sweets and sodas, but also fruit juice, bread, pasta, and other starches.

Any time a person eats something that bacteria can break down and use to produce acid, the environment in the mouth becomes acidic. The mouth will usually stay like this for 20-30 minutes until the environment becomes neutral again. While the mouth is acidic, the outer layer of enamel is damaged on a microscopic level. When the mouth returns to a neutral environment, the outer layer is repaired by substances that are present in saliva. This process of damage and repair is normal and occurs in everybody’s mouth.

Cavities occur when the breakdown of teeth is out of balance with the repair of teeth. There are many factors involved in this process, but essentially it means that the mouth is spending too much time as an acidic environment. This can result from eating or drinking sugar-containing foods too frequently, and not cleaning the teeth adequately.


There are things you can do to tip the balance of the mouth’s environment toward the neutral side and away from the acidic side. Limiting the frequency of sugar intake is very important. If a person only eats three regular meals a day and drinks water, his or her mouth will be acidic for a much smaller time than a person who snacks constantly and drinks soda throughout the day.

Keeping the teeth clean is the other important part - brushing and flossing reduce the number of bacteria in the mouth that can produce acid, and toothpaste contains a mineral (fluoride) that helps the tooth repair process and strengthens teeth so acid causes less damage.

If you can tip the balance of your mouth’s environment the right direction, cavities can’t develop. The basic principles are the same, but every patient’s situation is unique. Talk to your dentist about what you can do to push things in your favor.