Cavities Explained

                                            Cavities Explained
                                         
                                             By Dr. Jeff Shnall



“You have a cavity.”  The four words none of us wants to hear when we go to the dentist.  But what is a cavity?  What causes them? How do you prevent them?

While all of us have been told since we were little kids that cavities are caused by sugar bugs and we will get cavities if we eat too much candy,  there is far more to it.

I hate having to tell my  patients they have a cavity or worse, cavities.  No one likes being the bearer of bad news and even I can understand that there are many things you would rather be doing than having a cavity filled.

  I do have some patients who never seem to get a cavity while I have others that  unfortunately are cavity prone, that is, it will be more common than not that I find a cavity when they come in for their six month check up.

​As a dentist one of my primary duties is to advise my patients on how to prevent cavities.   In this article I will discuss some basic do's and don’t’s which will hopefully help keep you cavity free and will give you a better understanding of the cavity process.

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 What is a cavity

A cavity is a  softening or destruction of a tooth caused by bacteria.  We also use the term tooth decay to describe the cavity process as the tooth is decaying or literally  rotting.

A cavity  can take on many different appearances, for example:

• it can look like small pinpoint sized  defect in a tooth.  However appearances can be deceiving, for cavities that look small on the outer surface can actually involve a large inner part of the tooth.  More on this later.
• it can look like a  brown or black  discoloration in the grooves or crevices of a tooth or on the smooth   surface of a tooth, and can be found  along the gumline or on exposed roots where the gums have receded.
• they can get develop into a sizeable hole in the tooth
• cavities can form in between the teeth and are often not visible and are  only detectable with a dental x-ray
• (Not all dark spots you see on your teeth are cavities;  some are simply stains or harmless discolourations)
                 

How do you know if you have a cavity?

Interestingly, sometimes a tooth with a cavity will be sensitive and sometimes it won’t.
I have seen patients with a small cavity that is sensitive whenever  they eat something sweet or have a cold drink while I have seen other patients with a huge cavity that has not given them the slightest trouble.

 The latter can be a bigger problem as sometimes a painless  cavity will get so deep that by the time it finally does become painful or sensitive the cavity has reached a point when  the tooth will need a root canal treatment or  removal.

Since cavities can be sometimes symptom-free even when they are fairly large or deep it is important  that you get your teeth checked for cavities every six months,  and for the typical patient  the  teeth at the back of the mouth should be x-rayed to check  for cavities once per year. 

The cavity process

If a cavity is going to develop you need two things: bacteria on the tooth  and food for the bacteria, which is sugar in some form.

First, a few words about bacteria:   At this moment there are  between 100 to 200 different types of bacteria in your mouth, But only a few types of these bacteria are responsible for causing cavities.

As well, right now you have anywhere from 1,000 to 100,000 individual bacteria on each of your teeth, assuming you do a decent job when you brush and floss.  

These bacteria are  single celled creatures that cause cavities in the following way:  when you eat or drink anything containing sugar, certain types of  bacteria will ingest this sugar and produce  acid.  The acid is secreted on the tooth surface and can start to dissolve the enamel (or other parts of the tooth),  a process called demineralization (the breakdown of the mineral content of the tooth).

To combat this acid attack, our saliva normally washes away the acid and sugar from the tooth surface  and also delivers calcium, phosphate and fluoride  to the tooth  to rebuild the enamel that has been demineralized, a process called remineralization.

Therefore, there is a constant and delicate balancing act occurring constantly on our tooth surface wherever this bacteria or plaque exists, plaque being the name we give to clumps of bacteria.

If the bacteria or plaque has a ready supply of sugar this will  result in more and more acid production on the tooth which will lead to the acid eating a hole in your tooth,  and a cavity is born.

If you don’t brush or floss well or regularly,  this will result in more bacteria on the tooth and will promote cavity formation.

So whether you get a cavity comes down to this fine balance between the dissolving of tooth structure by acid produced by bacteria and remineralization of the tooth from calcium delivered in your saliva.  

If an area on your tooth that is being dissolved by acid can remineralize a cavity will not develop, however if  the amount of acid present on the tooth overwhelms the  ability of the saliva  to remineralize the tooth a cavity  will form.

The Tip of the Iceberg

The same way that ninety percent of an iceberg is below the surface of the water and be dangerous to a passing ship, a cavity that looks small and  innocent on the surface can sometimes  be large and troublesome.  The reason for this has to do with way that some teeth form when you are very young.

While some people have very well formed and decay resistant teeth,  other people have teeth that are more prone to developing cavities in the grooves and pits of their teeth.

The tooth pictured in Figure 1 is well formed and has shallow grooves.  This means that bacteria is less likely to accumulate in the grooves of the tooth,  as it is easily washed away by  saliva or more easily scrubbed away by a toothbrush.

The other key point is that the entire groove is lined with enamel, a very hard tissue which is harder than bone and more resistant to acid attack than other materials that make up a tooth.

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The tooth pictured in Figure 2 has deeper grooves that attract plaque/bacteria.  The deep grooves provide a safe haven for the bacteria.  As well the crucial thing is that there is no enamel lining the floor of the  deep groove of the tooth in figure 2.  Instead the floor of the groove is lined with dentin, which is softer than enamel and less able to withstand acid attack by the bacteria in the groove.

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In a deeply grooved tooth, if there is a hint of decay in the grooves it is far better to clean out the decay and place a shallow filling than to watch and wait, as the deep cavity  pictured in Figure 3 is the result.

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What increases your  cavity risk?

1) The frequency that you eat or drink food that contains sugar:  

• exposing your teeth to sugar  often
• for example,  if you suck on  throat lozenges or mints  that contain sugar several times each day  this will result in excessive  acid production on the surface of your teeth increasing the likelihood of developing cavities

2)  The duration of the exposure  of your teeth to sugar:  

• If the sweets or sugar exposure occurs over long periods of time during the day.
• For example, if you like to  have a coffee or tea with sugar sitting on your desk at work and you take sips at it all morning long,  or if you sip on  a soft drink or glass of juice or iced tea with sugar for an hour each night while you watch television,  this promotes acid production on your teeth and does not allow time for your teeth to remineralize from the acid attack.  This favours cavity formation.

3)  Having a dry mouth.  

• Having a dry mouth  is a problem that occurs far too often, especially in people who are taking certain medications such as  for high blood pressure,  anxiety  and depression to name a few.
• A dry mouth means less saliva is available  to wash the tooth,  which promotes the buildup of plaque and favours acid production.
• Less saliva also means less calcium, and other minerals  will be delivered to the surface of teeth meaning less remineralization is going to occur.
• People with a dry mouth also may drink sugary drinks or suck on candies that contain sugar, which are the worst things you can do for your teeth.  Extensive cavities usually will result.

4)  Poor oral hygiene

• incorrect brushing technique,  not brushing often enough or for long enough.
• I am always surprised by how many patients tell me they only brush once a day or even miss days.  These are unfortunately often  the same patients who develop cavities.
• Brushing removes bacteria  (plaque) from our teeth.  Less plaque means fewer cavities.
• And don’t even get me started on flossing.  If you have read my articles “Why you should be flossing:  Parts 1, 2 and 3”  you will see why flossing matters.  Flossing simply removes plaque that is lives in between our teeth  where  toothbrush doesn’t reach.  If you floss daily you are far less likely to get cavities in between your teeth.

5)  Having deeply pitted or grooved teeth.    This was discussed earlier in the article.

6)  A tooth with poorly formed enamel.

•  I unfortunately occasionally see children in my practise who have poorly formed permanent teeth  with weakened enamel due to poor calcium content in the enamel.  This is usually due to genetics or some disturbance in the way the enamel formed in that tooth while it was developing.  Fortunately I find in these patients  that usually only one or two teeth in their mouth is affected.

6)  Crowding:  teeth that overlap one another can be bacteria or plaque traps and can be harder to keep clean.

Ways to Decrease your Cavity Risk

1.   Switch to sugarless candies or mints.  

• Check the labels of mints or breath fresheners before you buy them.
• Even better, try to find ones that contain the sugar substitute  Xylitol, which has been shown to prevent bacteria from producing acid by interfering with the acid producing mechanism inside the bacteria itself.
• Candies, mints or gum sweetened with xylitol can reduce cavity rates more than those sweetened with other artificial sweeteners such as sorbitol, aspartame and mannitol.

2.   If you like soft drinks try diet versions.

• They don't contain sugar but note: almost all soft drinks,  both diet and regular contain acid that can wear down (erode) your enamel if you overindulge, so limit use.

3.  Reduce the frequency you eat sugary foods and drinks

• I will admit I do like chocolate but I only buy it occasionally and in small amounts so I won't be tempted to eat it everyday.  
• If you absolutely need to put sugar in your coffee or you crave pop with sugar try to only have it    occasionally or once a day at most.   
• Stop putting sugar in your coffee or tea or switch to a  sugar substitute such as Splenda

4.  Reduce the duration that sugar stays in your mouth.  

• A lollipop with sugar will provide sugar to bacteria on the teeth and promote acid production and cavities.  Same with sticky candies such as  gummy worms, jujubes and the like.
• As well, if you do have a drink that contains sugar such as coffee, tea, pop, juice or milk (milk has the natural sugar lactose that can cause cavities) drink it with a meal or snack but don't sip at it for hours on end.  
• If you need to carry a drink with you during the day or if you  like sipping on a drink continually while at  work or relaxing, switch to water.  Sipping on the following drinks for long periods of time during the day for several  times a week will increase your risk of developing cavities:  sports drinks,coffee or tea with sugar, soft drinks, iced tea with sugar milk and juice, to name a few.        
•  Dried fruit such as raisins and dried mangoes are healthy for you in moderation but do stick to your teeth increasing cavity risk.

 5.  Brush well and longer: aim for two minutes each time you brush.  Brush two to three times each   day.   

 6.  Consider switching to an electric toothbrush to get more plaque off your teeth.

 7.  See your dentist regularly to catch cavities while they are small.  Every six months is ideal.

 8.  Use a daily fluoride mouthwash and/or a high content Fluoride toothpaste if you are cavity
      prone.

9.   A paint-on fluoride varnish can be applied to your teeth if you are cavity prone

10.  Sealants can be placed in teeth with deep grooves to seal out bacteria.  I will place sealants on  permanent molars when they are deeply grooved.

11.  If you are on a medication that is causing dry mouth ask your doctor for an equally effective
         drug that does not reduce saliva flow.

To conclude,  your  biology, tooth anatomy, diet and habits are unique and all combine to result in whether or not cavities will form on your teeth.

I hope this article has given you a few tips and better insight into how cavities form and how they can be prevented so that hopefully at your next dental visit you will be less likely to hear those four unpleasant words: “  you have a cavity.”

​If you have any comments, questions or suggestions for future articles please feel to leave a comment below.
Jeff Shnall DDS BSc

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