How Does A Tooth Get A Cavity?

Now I have finished the most common decades of life and what can be expected to happen to most people’s mouths, I will address questions either from you or questions that come up frequently in my practice. Some of you will likely remember the articles I wrote in a similar column in 1998. Some of those articles generated quite a bit of interest from our patients. For the next couple of weeks, I will again provide a few of those articles with some updates. Please feel free to contact me at my e mail address,, or my office by telephone 468-9866 if you would like to submit a question. 

Question: How does a tooth get a cavity?
Tooth decay is the end product of the action of bacteria on the teeth. Bacteria live in every person's mouth all the time. Only a couple of kinds of all the many types of bacteria that live in a person's mouth are capable of damaging the teeth. It happens like this: Bacteria live in the saliva all the time. In a few hours, bacteria colonize on any hard surface in the mouth, like a denture, braces, fillings, or teeth. Once the bacteria form a thick mass on the tooth, the bacteria is called plaque. Plaque is a large community of living bacteria. The bacteria in plaque will eat anything, but they grow fastest on sugar and other fairly simple carbohydrates like bread, or potatoes. After the bacteria use the food they are provided, they produce lactic acid as a byproduct of their life process. Lactic acid is a very weak acid. It is not even as strong as lemon juice. It is the same acid produced in a person's muscles when that person exercises vigorously and the muscles ache. The teeth are bathed in this lactic acid and slowly the calcium and phosphorus in the tooth are dissolved away leaving just a sticky brownish protein. After this dissolution process has begun in the tooth, in time pieces of the surface of the tooth will chip away leaving a hole (a cavity) needing to be cleaned out and filled up to prevent further damage from occurring to the tooth.

A person can keep bacteria in the mouth from harming the teeth. Bacteria in the mouth can only harm the teeth if it is allowed to form a mass (plaque) on the teeth. Depending on the food a person is eating and a few other factors, plaque takes about 12 to 24 hours to form a covering on the teeth and start to produce acid. If the plaque mass is removed from the teeth, the bacteria have to stop producing acid and begin to try to attach themselves onto another hard surface in the mouth. As mentioned earlier, this attachment process takes many hours for the bacteria to accomplish. A toothbrush will remove plaque from teeth nicely. Floss is for removal of plaque from areas where a toothbrush will not reach easily, like between teeth. So, by using a toothbrush and floss, a person can stop bacteria in the mouth from harming the teeth.

In the last few years, scientists have learned that plaque does not need oxygen to produce the acid that causes tooth decay. It had been thought for many decades that tooth decay was a strictly aerobic (needing oxygen) process. Now it is known that even without oxygen, the bacteria that cause tooth decay can still dissolve calcium and phosphorus from the teeth. This is significant in that even the last bits of tooth decay must be scrupulously removed before anything is bonded onto the tooth. This includes sealants. If even a small amount of decay is not detected on the grooves of the teeth before a sealant is placed, the decay will slowly continue to dissolve the tooth even though oxygen may be unavailable to the bacteria. Stains are available to detect decay before fillings or sealants are placed, but experts have deemed them not accurate in many instances. This is where the experience and interpretive skill of the dentist must be relied upon since there is, as of yet, no other way to completely discern when all of the decay has been removed. Fortunately, dentists are quite skilled at discerning when the decay is adequately (completely) removed.

This article was written by Dr. Mike Christensen and published in the Daily Miner and News, and Enterprise. Local Kenora News Publicatons (1998-2006)