One of the most common questions that we encounter on a day to day basis in our Preventive Dentistry program is usually related to why our patients develop cavities.   Often we hear something along the line “I have really soft teeth” or “My parents both had horrible teeth so I must be destined to have horrible teeth.”  Although genetics does play a factor in development of tooth decay, it can be argued that it is not the primary driving force. 

To develop a cavity all three of the following must be present.

  1. Teeth.  Without a tooth you cannot develop decay.
  2. Bacteria. Bacteria in our mouths are the principle source for acid production. This acid is what causes the teeth to demineralize and initiate the decay process.
  3. Sugar. Sugars, both complex and refined, will provide fuel for the bacteria in our mouths to live and thrive. Without sugar as an energy source the bacteria cannot produce acid. Simple sugars such as high fructose corn syrup that we find in most soda pops and energy drinks are the ones that are most easily metabolized and are a ready source for energy for the bacteria.

I would like to elaborate a little on how the dynamics between these three essentials for tooth decay operate. 



Most people see teeth and imagine teeth as being something that is hard. Rock solid. Teeth are very different from its organic counterparts rocks and wood. On a chemical level enamel is a crystalline structure that has a space in the center for a calcium ion. This is a very strong bond but acid can break this bond and cause the calcium ion to separate from the crystal substructure. Calcium can be lost and replenished in that space. Sources for replenishment include calcium in our saliva along with the foods that we eat. Fortunately we have another ion that can bond into that same space but with a stronger bond and that is what is commonly known as fluoride. Fluoride can be delivered in the form of rinses and pastes and can also be ingested as a supplement or in our water.  

Balanced vs Unbalanced Ion Exchange 

Everybody loses calcium out of their teeth. It’s a fluid relationship that is constantly changing. People that don’t develop cavities are considered to have a balanced exchange of ions. People who develop cavities have an unbalanced exchange of ions and lose more than they put back in. This is what causes the deterioration of the teeth.

Enamel and dentin are similar in structure but dentin is much less dense and decay can spread through dentin much more easily than enamel.  If decay is present only in the enamel layer it can often times be reversed. If it enters the dentin layer of the tooth the only way it can be fixed is by restoring it with a filling.


Most of the bacteria in our mouths are considered to be safe bacteria. Approximately 60 percent of oral bacteria is safe whereas the other 40 percent can be considered pathogenic or decay causing.  We eliminate bacteria off the surfaces of our teeth with diligent brushing and flossing between the teeth. If neither of these surfaces are cleaned then the bacteria will continue to colonize on these surfaces. Over a period of months if the bacteria colonies are not removed the plaque film becomes much more complex and the bacteria develops into even more aggressive strains that can cause more damage both from a decay perspective and a periodontal (gum disease) perspective.  This is why debriding of plaque off of all tooth surfaces is essential.


This is where it gets complex and this is also where the greatest misunderstandings about the development of tooth decay occurs.  Bad bacteria in your mouth metabolize or digest the simple sugars like those found in pop, candy, chocolate, energy drinks, flavored coffee drinks and gum. These are just some examples but simple sugars are found in so many of our food products that are available today. This acid production is what causes the teeth to lose minerals. The acid breaks the calcium ion bond in the tooth. 

Frequency vs Quantity

If someone was to drink a 20 oz Mountain Dew in a period of 20 minutes vs someone who drank the same quantity over a period of four or five hours the affect on the teeth would be remarkably different.  Natural salivary flow will typically wash away mouth acids approximately 20 minutes after eating or drinking has subsided. With the first person they would only have acid in their mouths for a period of 40 minutes. The second individual would have acid in their mouths for over four or five hours. That means an acid attack that is 6-8 times longer but with the same amount of sugar. Bacteria do not require a large amount of sugar to exist. A mouthful of pop is plenty of energy to keep them going.

What does this mean in a practical sense?  If you don’t take breaks between meals and constantly introduce high risk food and drink into your mouth throughout the day then the acidity levels in your mouth stay consistently high. If you do this long enough then you would basically be causing acid erosion of your teeth.   Your teeth need breaks from these acid attacks to replenish and recharge the calcium ions. They never have that opportunity so they start to break down. 

The Stephan Curve is explained in the charts below.  The safe zone is when pH is above 5.5.






Bacteria living and born in acid.

Over a period of months the balance of bacteria in your mouth shifts. Good bacteria do not like acid. The acid kills them off. What ends up happening is a proliferation of pathogenic bacteria. So now instead of 40 percent bad bacteria we end up with 80 or 90 percent bad bacteria. This causes EVEN MORE acid production with similar amounts of sugar intake. That would explain why someone would develop cavities at a much higher rate than the next individual.  Subsequently the bacteria that are born in acid are even stronger and more destructive.

So what do you do now?

Understanding the process is the only way to make change.  Other than oral hygiene habits and the use of fluoride to replenish teeth the main change usually has to come with dietary change.  The bacteria flora NEEDS TO CHANGE.  Until that happens the destructive process will continue.

Depending on your caries risk assessment any or all of the following will be necessary.

  1. The use of antibiotics like Doxycycline or Peridex (chlorhexidine), to kill off bad bacteria.
  2. The use of high fluoride toothpastes (Prevident) and Calcium Phosphate toothpastes (ClinPro 5000) can help address the remineralization of the teeth and slowing down of the decay process.
  3. In office fluoride treatments to remineralize affected teeth.
  4. Nutritional counseling to alter the diet to minimize the ingestion of foods high in sugar content  with special focus on frequency of intake.
  5. The use of Xylitol gum has been shown to reduce cavity rates by stimulating salivary flow and decreasing bacteria levels in the mouth.

Your dental hygienist will evaluate you and prescribe a treatment plan that will restore your oral health.