What causes cavities?

Patients who come into our dental office and have several cavities, or have new cavities at each appointment are often at a loss as to why this is happening to them. Often they feel that it is inevitable or that they have “soft” teeth. Often they brush fairly well and do not understand that there are several factors that play a roll in whether or not you will experience decay. Your diet and the amount of saliva you have, are just as if not more important than how often you brush.

What causes decay? There are 4 factors that play into the decay process, in order to have decay all must be present.

  1. Bacteria
  2. Food (for the bacteria)
  3. Time
  4. A susceptible tooth


Cavity causing bacteria is found in plaque, and may also be free floating in the mouth. It is important to brush your teeth twice a day, taking care to do an excellent job before bed. It is important for us to rid our mouths of bacteria before bed because when we sleep we have less saliva. This means that anything that is on our teeth will remain there for the entire night. It is also now recommended that everyone use a mouth rinse. Our teeth only occupy 25% of our mouths, we need to clean our tongues, cheeks and palate as well, a rinse is the easiest way to do this. As for flossing, it is important to clean between your teeth, how you should do so (floss, waterpik, proxabrush etc) is dependant on what your mouth looks like. Not sure what to use, ask your hygienist.

A note on bacteria. Decayed teeth harbour bacteria, therefore in order to stop decay in the rest of the mouth, it is important to have the decay removed and the tooth fixed.


In this case we are talking about food for the bacteria. Bacteria take sugars and turn them into acids that decay teeth. While pure sugar like candy is the worst, any kind of starch can be bad. The worst kinds of foods are both high in sugar, and sticky and / or acidic. Sour Candy Keys are probably the absolute worst thing you could possibly do to your teeth. Starches like breads, crackers, and chips, are often overlooked because you might not think of them as “sticky”. However, they tend to form a mush that can get stuck in all the grooves of your teeth. We all know that soda is bad for our teeth, but juices can be bad too because they are high in sugar. This is not to say that you can never eat (or drink) these things, their intake however, needs to be limited. You should steer clear of sticky candies and soda altogether if cavities are an issue for you.

A note on food:Never ever send a baby to bed with anything in their bottle except water, preferably send them to bed with no bottle. The amount of sugar in milk or juice is enough to cause rampant decay.


Every time you eat or drink something acidic or sugary you are causing what is called an “Acid Attack” the pH in your mouth is lowered to one that is acidic enough to cause calcium and phosphate to be leached from your teeth. This causes your teeth to be susceptible to decay. It takes 20-30 minutes for your mouth to recover from an acid attack. It takes up to an hour for a plaque biofilm to return to neutral. So if you are sitting at your desk sipping on sugar laced coffee or soda all day, your mouth never gets a chance to recover. You will inevitably get demineralization and eventually decay. The same is true if you are snacking on chips, fishy crackers, cakes, candy etc…… As I said before this does not mean you can never consume these products, but they are best limited to meal times. If you must consume at other times, use a straw and rinse with water afterwards.

A note on demineralization.Demineralization is when the tooth starts to break down, your teeth will have white spots, often along the gum-line. This is not yet decay, but your tooth is not as strong in these areas and are more likely to become decayed.

Susceptible tooth


Some people are more susceptible to decay, this is thought to be because of the types and quantities of bacteria that are normally present in their mouth. There are also situations where the teeth are poorly developed, or have anatomical features that make them harbour bacteria. It is interesting to note that babies are not born with cavity causing bacteria, their bacteria are acquired, usually from parents or siblings, from sharing foods, spoons etc…. Being more susceptible to decay does not mean you are doomed to get it, you just have to try harder to prevent it.


As mentioned earlier acids leach minerals from the teeth, making them susceptible to decay. These acids can come from bacteria, or simply from acidic foods. This is why diet sodas are not good for your teeth, they leach calcium and phosphate from your teeth leaving them open for attack. Just add sugar. Acids from pop / citrus / gastric reflux / vomiting can also erode your teeth, leaving the enamel thin and more prone to decay or breakage.

A note about acid.Do not brush your teeth directly after drinking pop, gastric reflux or vomiting, your teeth have been softened by the acid and a toothbrush will cause damage to your teeth. Rinse with water or baking soda and water and wait an hour before brushing.


Saliva is probably the most important factor in protecting your teeth. Saliva provides the minerals needed to rebuild your teeth, cleans them and neutralizes the acids in your mouth. In a normal situation, after experiencing an acid attack the saliva will neutralize the acid and then provide the minerals needed to rebuild the teeth before any decay occurs. Without adequate saliva people experience rampant decay. If your mouth feels dry, your teeth sticky or it is hard to speak or swallow you probably have dry mouth. Seek advice right away, there are products available to combat a dry mouth. Whether you have dry mouth or not, drink lots of water.

Dental Work

Your tooth is never as strong as it is before it has had anything done to it. Any sort of restoration causes borders or nooks and crannies for plaque to cling to, increasing the chances of decay. Even though a crown covers the entire top of the tooth, you can still get decay on the part of the root that crown doesn’t cover, and this can go up into the crown. Bad dental work can cause all sorts of reservoirs and areas for decay to enter. This is why we cringe when you tell us you just had dental work done in Mexico or India, the standard of work in these countries is usually very low. Even if you’ve had excellent dental work done, you now have to take better care of your teeth. Research has shown that patients who have had one cavity are more likely to get another.

Now that we have discussed what causes decay, here is a quick summary of what you can do to prevent it.

  1. Brush twice a day with fluoridated toothpaste. It is important that the toothpaste has fluoride in it (even for babies), fluoride provides ions to help rebuild teeth after an acid attack.
  2. Use a daily mouth-rinse (if you’ve recently had decay use a daily rinse with 0.05% fluoride or a weekly rinse with 0.20% fluoride)
  3. Avoid frequent consumption of foods or drinks that are high in starch, acid or sugar
  4. Rinse with water or baking soda and water after an acid attack (soda, acid reflux, vomiting etc)
  5. Drink lots of water frequently
  6. If you have a dry mouth, seek treatment.
  7. Visit your dentist regularly and treat any decayed teeth

As a dental professional I often point out how oral health is related to overall health. It occurred to me as I was writing this, that in general foods that are bad for your teeth are bad for your body. Eat healthy whole foods, in healthy quantities and you will be doing both your teeth and your body a favour. Oh and drink lots of water.

Eryn Gakhal BSc, RDH

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