What Causes Cavities?

What Causes Cavities?

What Causes Cavities on Teeth
©Sebastian Kaulitzki/Shutterstock.com

If you’re like most people, you may believe that sugar causes cavities.  After all, candy is bad for our teeth, right?

Sugar doesn’t cause cavities.  In fact, this has been known for over 50 years!

In 1954, a man by the name of Frank Orland wanted to see if sugar caused cavities.  He conducted a pioneering research study, in which he raised 22 rats in a sterile environment.  From birth ’til death, these rats never had any contact with any germs.  He fed these rats lots of sugar throughout their entire life.

Guess how many of these rats that ate sugar every day ended up getting cavities?


None of the rats that were raised “germ-free” got any cavities even while they were eating all of the sugary foods that they wanted.  In contrast, 38 of the 39 rats that ate the same foods but were not raised “germ-free” ended up getting cavities.

Part of his conclusion states, “Findings indicated that twenty-two rats reared under germfree conditions remained entirely free of even microscopically demonstrable dental caries. Of thirty-nine conventional control rats, possessing the usual mixed microbial populations, thirty-eight developed various lesions when maintained on the same kind of dietary regime as the germfree animals. It is deduced from this evidence that dental caries in the rat is not possible in the absence of microorganisms.”

If you only looked at Dr. Orland’s study, you may be tempted to say that it must be bacteria, and not sugar, that causes cavities.

More recently, other studies have shown that it’s possible for rats with bacteria to not have any cavities if they are not fed sugar or fermentable carbohydrates.

These studies lead us to believe that bacteria and sugar must be present in order to get cavities.  But even these two elements don’t account for the whole picture.

For example, my wife never had a cavity in the first 25 years of her life.  Like most normal people, she ate sugar and had bacteria in her mouth.

So, what really causes cavities?  There are actually four components that, when present together, cause cavities:

What Causes Cavities?

In order to get cavities, you need to have four main ingredients:

1 – Sugar
2 – Bacteria
3 – A Susceptible Tooth
4 – Time

You can take a look at this relationship in the diagram below.  If you’re interested, you can then read about how you can use this information to prevent cavities.

4 Causes of Cavities & Tooth Decay


1 – Sugar

For simplicity’s sake, I labeled this category as sugar.  In reality, it could be called refined carbohydrates because anything that can be broken down into sugar inside of your mouth is able to feed the bacteria that contribute to causing cavities.

For example, potato chips are made of a simple starch that can be broken down into sugar by enzymes that are found in your saliva.  How often you eat sugar is more important than how much sugar you eat in one sitting.

To learn more, read What Happens In Your Mouth Every Time You Eat or Drink, What Fermentable Carbohydrates Are & How They Hurt Your Teeth, and 50 Names for Sugar that Food Makers Use to Trick You.

2 – Bacteria

Bacteria live inside all of our mouths (unless you’re one of the rats in Dr. Orland’s study!)  It’s really fascinating to me that there are millions of little creatures living inside of everyone’s mouth — this is what first got me interested in dentistry and was the subject of my first article here at Oral Answers, What Every Human Needs to Know About Plaque.

While you can’t completely rid your mouth of all the bacteria, you can destroy the homes they build on your teeth every time you brush and floss.  By regularly brushing and flossing, you can help win the fight against the bacteria in your mouth.

3 – A Susceptible Tooth

Many people who have had their share of cavities say that they have soft enamel or that  bad teeth run in their family.  While there’s no such thing as soft enamel, people can have enamel that may not have been formed correctly.  Also, bad teeth aren’t genetic, but some people’s teeth do have deeper pits and grooves than others.

These pits and grooves can be so deep that even a bristle on a toothbrush can’t reach down to clean them out.  In these cases, these people will almost always get cavities unless they have had sealants placed on these teeth when they were kids.

There are many other factors that influence how susceptible a tooth is to getting cavities.  I will only go over a few of the more common ones.

The first is the quality and amount of the dental enamel.  Pinkham’s Pediatric Dentistry text states that enamel hypoplasia (when not enough enamel forms), even at levels that are undetectable,  increases susceptibility to tooth decay.

Saliva also plays an important role in how susceptible a tooth is to decay.  The more saliva you have, the better.  To learn more about the role that saliva plays in your oral health, read How Saliva Protects Your Teeth and Six Main Causes of Dry Mouth/Xerostomia.

The last factor I will discuss that makes your tooth more susceptible to cavities is the wearing away of tooth structure.  This commonly occurs through the process of acid erosion, which can occur by drinking these nine teeth-dissolving drinks, however there are four ways that you can wear away your teeth.

4 – Time

Darius Rucker sang the following words Hootie & The Blowfish’s hit Time back in the 90’s

Time, Why you punish me? Like a wave crashing into the shore, you wash away my dreams.

Time can in fact wash away your dreams of having healthy teeth if you give the bacteria enough time on your teeth.  In fact, you can have all three elements above and not get cavities if you don’t give the bacteria time to eat away at your tooth.

Plaque eats sugar, which produces acid that slowly eats away at your susceptible teeth.  The key is to not give the bacteria enough time on your teeth.  You can do this by brushing and flossing regularly.

To learn more, read the article Try to Keep Your Teeth Below Freezing.


Cavities don’t just happen spontaneously.  You need four things to get cavities: sugar, bacteria, susceptible teeth, and time.

You can’t really control the bacteria unless you live in a sterile environment.  You also can’t control the genes that sculpted your teeth into their exact formation that might make them hard to clean. You can control how much sugar you eat, your oral hygiene, and how well you treat your teeth (don’t treat your teeth like tools!)

Do you have any questions, stories, comments, or concerns about what really causes cavities?  I’d love to hear them in the comments section below.  Thanks for reading!


  1. I read that babies are born without the oral bacteria that cause cavities, and that it is through other people (usually parents sharing food or blowing on food to cool it) that they end up with those bacteria in their mouths. Of course, I suppose there is really no way around that!

    • Hi Rachel – We did talk about this in our pediatric courses. Babies are born sterile and they do end up picking up all of the bacteria from their surroundings. Now that I have kids, I do think it’s nearly impossible to not share our bacteria with them!

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