Everything you ever wanted to know about cavities including how to avoid them!

Let’s start our discussion with a simple human molar. The molar faces a unique set of challenges compared to the other teeth (premolars, canines, and incisors), but it will serve as an adequate model for demonstrating the decay process. Here is a drawing of the tooth:

Lower right first molar

This tooth will never get a cavity as is. In fact, let’s put the tooth on a coffee table and see what happens:

Human molar sitting on a coffee table

This tooth can sit on this coffee table for millennia. In fact, the coffee table will probably break down and disintegrate, and the tooth will still be perfectly fine. So that raises an interesting point. A tooth outside of the mouth will never get a cavity. So what is it about being inside a mouth that makes it so easy for a tooth to decay? Let’s place our molar in a more natural environment:

Molar in a natural environment

Ok, so now the tooth is getting a little crowded. There are teeth on either side, there is a tongue to contend with, there are gums surrounding the tooth. It’s not pictured, but there is also saliva constantly washing over the tooth.

Guess what? This tooth will STILL never get a cavity as is. In fact there are some protections in place that prevent that from occurring. The tongue, for one, constantly moves, gently polishing the surface of the tooth with its irregular surface. The gums and bone cover all but the strongest part of the tooth (the enamel). The saliva that washes over the tooth has some AMAZING properties as well, including:

So how do teeth get cavities?

If there are so many protections in place naturally, why do teeth still get cavities? It all starts with your diet.

Illustration showing the source of decay, strep mutans

Although this guy kind of looks like an amoeba, it is actually streptococcus mutans bacteria. He is our typical “Bad Guy Bacteria”, and he loves to eat the remnants of all the sugary foods that YOU eat, and turn them into “byproducts” as you can see by the illustration.

Now, if everything went according to plan, this guy might get to digest a little bit of sugar, produce a little bit of acid, but at the end of the day, your saliva would help wash down remaining particles of food and buffer the acid, and maybe you could naturally clean the teeth with the tongue a bit, and that would be the end of this bacteria’s fun.

Unfortunately, this bad guy bacteria has some tricks up his sleeve. For one, he doesn’t just eat the sugar. He actually uses it to build a house. So he turns sugar into a big elaborate framework that no longer simply “washes away” with saliva. It sticks to the teeth. Now, he has a place to live, he has plenty to eat, and the house he lives in continues to collect more and more sugar as time goes on. Only when he is allowed to “set up shop” long term (read: at least 4 months), can he really do some damage.

So what if I never eat sugar or starch or anything that this guy digests?

ANSWER: you will never get cavities. END OF STORY.

Now some people ask, can I substitute DIET soda for regular soda? NO, and here’s why. When this bad guy bacteria is building his house out of sugar, he decorates the inside of his house to make it more comfortable to live in. What does he decorate it with? Acid. Now, I’m not sure what it says about this guy that he decorates his house with his own “byproducts”, but hey, he likes it and it makes him more productive. When you drink diet soda, or lemonade, or any other acidic drink, you are simply giving him a better place to live, where he can raise a family and invite all his friends. So diet sodas just don’t cut it as a healthy alternative for your teeth.

What happened to all the other natural protections against cavities?

Well, the answer is that they still work PRETTY WELL. For the most part, the teeth will naturally cleanse themselves of this bad bacteria. But these natural protections take time. Saliva can’t buffer acid instantaneously. The tongue cleanses the teeth, but it doesn’t naturally reach certain areas. The digestive enzymes in the saliva break down the bacteria’s home, but again, it takes time. If we give these processes time to work, they will work, which is why I always recommend that patients LIMIT THE FREQUENCY OF SUGARY FOODS AND DRINKS.

If we can’t limit the frequency of sugary foods and drinks, there are a few areas where our natural defenses break down, and next we will go over where those areas are.

DANGER ZONE #1, in between the teeth

Illustration showing the contact area between two teeth

Here, we zoomed in on our molar. We’ve drawn the tooth next to it as semi-transparent so that you can see the anatomy around our molar. The GREEN area is a depiction of where the two teeth touch each other. Because the teeth are curved, they only touch in this one spot. Now, normally, this tight contact between the two adjacent teeth naturally prevents food from getting stuck in between the teeth, but sugary liquids and other small particles still tend to get in there. The next illustration shows this “danger zone”:

Illustration showing where food boluses get stuck, causing interproximal caries

This is a danger zone because it tends to provide a nice safe area for the bad guy bacteria to set up shop. So this is a very common place for him to stay long-term.

Long-term dumping of acid onto a tooth will dissolve the minerals in the tooth, eventually leading to a cavity, or hole. Often times people will have a cavity in this area of their tooth and never know it. Even dentists can miss it if they don’t take proper x-rays.

Remember it takes at least 4 months for a cavity to even start, so when a tooth “suddenly breaks,” keep in mind that there was probably something going on that you didn’t know about under the surface and that it had been occurring for quite a while. An important takeaway is that:

Cavities are caused by poor LONG-TERM habits, not one-time or infrequent insults to the tooth

THE LESSON HERE, as it is for all of the “danger zones” of a tooth, is that:

  1. Reduction of the frequency of sugars and starches in the diet is most important thing, and
  2. Regular cleaning of the area is the second most important thing

Get used to this lesson, because we will be repeating it multiple times on this page and throughout our website.

In this case, to clean this danger zone, you probably already guessed, but FLOSS is our friend.

DANGER ZONE #2, the groovy part, baby!

Illustration of the occlusal surface of a lower right first molar

Here is a depiction of the top of our tooth. If other dentists are looking at this, don’t judge me, I drew this from memory!

This intricate series of pits and grooves and fissures and valleys is a brillant mechanical solution to grinding, mashing, and in general crushing large chunks of food into smaller chunks of food. We won’t go into here what the function of each main or secondary groove is, but the fact is they all have some function.

UNFORTUNATELY, it looks like we also found a perfect place for our bad guy bacteria to live, which is right in the deepest areas of these pits and valleys.

We also have another challenge, which is that this particular tooth COMES IN AT AGE 6. I’ve met quite a few six-year-olds in my practice, but I’ve never seen one who had the foresight at that age to really CARE about preventative oral hygiene. So this is where our lessons come into play. Once again:

  1. Reduction of the frequency of sugars and starches in the diet is most important thing, and
  2. Regular cleaning of the area is the second most important thing
How do you clean the grooves of a molar?

ANSWER: It is not easy. The tooth brush bristles often don’t reach down into the depths of a pit or fissure in a molar. In the past, dentists took this challenge and said “No problemo!” and often just cut out the groove, turning it into a large channel, and smoothed out the whole thing by packing in a large filling. As barbaric as it sounds, it actually works pretty well. Consequently, some of you may have teeth that look like this:

Molar with an amalgam occlusal filling

…which is not the end of the world, but hopefully nowadays a more conservative approach would be a minimal or no-preparation method, simply filling in the deep grooves with a thin and light resin-based sealant, like so:

Sketch of a molar with a conservative sealant

Now, we’ve eliminated an area where those bad guy bacteria can set up shop LONG-TERM.

DANGER ZONE #3, along the gumline

Illustration showing the area along the gum line where plaque accumulates

This is somewhat of a cross-section image, showing the tooth from the side, and showing how the gum meets the tooth in a round-ish shape. I’ve colored in blue the area where our bacteria would most likely set up shop long term, releasing his by-products on your tooth and dissolving your precious enamel. As a dentist, I often see cavities in these areas, but between the two, it is much more likely to have a cavity on the “Cheek Side” versus the “Tongue Side.” This follows what we talked about before, and is a testament to our natural defenses against cavities. This is also why, as a parent, you should mostly focus on brushing the outward facing sides of your children’s teeth (if you have to choose - some children may go along with the program more easily than others…), because the tongue will naturally clean the inside surfaces of the teeth.

In this case, although we are showing a molar, it is extremely common for front teeth to get this particular brand of cavity, especially among young males, who are constantly consuming Gatorade, energy drinks, sodas, etc.

So what are the lessons to learn here?

  1. Reduction of the frequency of sugars and starches in the diet is most important thing, and
  2. Regular cleaning of the area is the second most important thing

This type of cavity is why dentists always tell you to “brush along the gums”. Now, you don’t need to brush the gums themselves, that would be like saying you have to brush the skin on your face to keep it clean. But you do have to get that corner between the gum and the tooth to be effective.


In the case of front teeth, we can MITIGATE the effects of sugary drinks by using a straw, and only letting the sugar touch the inside of the teeth (where we have our trusty “tongue defense”).


After probably boring you to death, we’ve actually only scratched the surface of this topic. Here are a couple things to consider:

That said, as a dentist I’ve seen the full gamut of possibilities. Even people who believe they were “dealt a bad hand” can have great oral health if they have the right knowledge and willpower to change damaging habits.