cavities / tooth decay / dental caries

A person doesn't develop cavities just overnight. It typically takes months or even years for a cavity to form. This is because conditions aren't always right for the tooth demineralization process.

As you know, there has to be both dental plaque and dietary sugars present for tooth decay formation to occur. These conditions don't always exist but each time they do some tooth demineralization will occur. Over time there can be a point where the cumulative effect of each episode of demineralization has resulted in the formation of a cavity.

There is another important dynamic that takes place related to tooth decay formation besides just the demineralization of the tooth. If conditions are right, a tooth can undergo a remineralization process. Remineralization helps to counteract the damage done during demineralization. Remineralization in effect is somewhat like tooth decay in reverse.

What is the remineralization process and how does it attempt to reverse tooth decay formation?

When conditions at a tooth's surface are non-acidic a remineralization process can take place. During this event minerals found in the oral environment can be re-incorporated into a tooth, thus reversing, or at least minimizing, the damage that was done to the tooth during the demineralization process (tooth decay formation). This repair process will continue until the repair has been completed, or else the next attack by bacterial acids has begun.

This tug of war action between the demineralization and remineralization processes, each of which can occur several times a day, is one reason why cavities can take many months to form. Actually, in some cases a tooth's remineralization can balance out the damage done during the demineralization stage. However, in those cases where there is heavy dental plaque accumulation or the person has a high sugar intake, the balance will tip to the side of tooth decay formation.

On to page 4 and more about tooth decay formation.  >  

What does a dentist see when they read a dental x-ray?

When a dentist evaluates a dental x-ray (a radiograph) for evidence of tooth decay they are actually examining the image on the film for hints of changes in the density of the tooth's enamel and dentin.

The principle associated with taking of dental radiographs is that hard mineralized tooth tissues will block out some of the x-rays attempting to pass through the tooth on their way to reaching the x-ray film. So, the parts of the dental film that lie protected behind a tooth's enamel and dentin portions will be less exposed (have fewer x-rays hit them), and thus look lighter in color on the x-ray film (radiograph).

Since areas of tooth decay are a demineralization of the tooth's hard tissues, or even a frank hole in the tooth if the decay process has progressed far enough, those locations on the tooth where decay has formed will appear as darkened areas on a radiograph. This is because the decayed portion of the tooth is less "hard," or less intact, and therefore the x-rays can penetrate that portion of the tooth more easily and expose the dental film to a greater degree.

Our mockup of a dental x-ray shows some of the stages that the decay process can undergo.

• Frame A: This frame illustrates the earliest stage of tooth decay that will show up on a dental x-ray. Notice how there is just ever so slightly a darkened area in the enamel portion of the tooth right exactly where it touches its neighboring tooth. That's the decay. This person has not been flossing enough.
        Most dentists won't recommend placing a filling until the dental x-ray shows that the decay has completely penetrated the enamel layer of the tooth (as shown in Frame B). The lesion shown in Frame A may not progress further if this person starts to floss effectively.
  
  
• Frame B: Once a dental x-ray shows that the tooth decay has penetrated through the tooth's enamel and into its dentin layer a dentist will recommend placing a filling.
  
  
• Frame C: As discussed previously, the dentin portion of a tooth is less mineralized ("hard") than a tooth's enamel layer. This means that dentin will decay at a faster rate than tooth enamel. Notice how in Frame C the size of the lesion in the enamel layer has only slightly increased in size while the tooth decay present in the tooth's dentin has advanced significantly.
  
  
• Frame D: Frame D illustrates a worst-case scenario situation. If decay is left unchecked, it can advance all the way to the tooth's nerve. If it does, not only must the decay be removed and the damaged tooth structure repaired but additionally the tooth's nerve will require root canal treatment. Clearly the early control of tooth decay (preferably at the point shown in Frame B) is a case where a stitch in time saves nine.