An Analogy of Tooth Decay – How our Teeth Stay Strong

Dr. Terri Baarstad

I have a little analogy that I use with my patients that seems to help them understand. I say something like:

There are bacteria in your mouth that “eat” carbohydrates. These bacteria have waste products and those waste products are acidic. Acid “dissolves” our teeth and makes it so we get cavities.

Imagine that your teeth are brick walls. They have all these bricks going in and out of the wall all the time- they are not static, they change. So when your mouth is at PH7 –that is neutral- the bricks go in and out at the same rate- there is no net change. Teeth stay healthy. But, when you eat or drink anything that has carbohydrate (sugar, bread, pretzels, even croutons) the PH of your mouth drops and the environment becomes acid. When your mouth is in acid- more bricks go out than come back in, so there is net loss of tooth structure. It takes about 20 minutes for your mouth to return to neutral after eating, so, if you are snacking, taking a bite or a sip of a soda pop every few minutes over an period of time, say 2 hours, then your mouth will be in acid for 2 hours and 20 minutes. If this occurs regularly over time, there is more net loss of “bricks” and eventually there begins a cavity. Once the cavity begins there is more acid because the bacteria have multiplied and they make more acid, leading to more cavities. The cure for the cavity is to have it treated with a filling or a crown. But the cure for not getting more cavities is reducing “exposure” to the acids. Fluoride on and in the teeth is like having mortar for those bricks- it makes it so much more resistant to acid.

Knowing the way that teeth “dissolve” you can understand what might help slow down this process

If you brush your teeth, chew sugarless gum, or rinse vigorously with water after eating, the Ph raises to neutral more quickly. Conversely, a dry mouth doesn’t return to neutral very quickly. The dry mouth patient is also at a higher cavity risk because the acid is that much more concentrated. Water, mints and gum, or even a change of medications might be in order.

Since it is all about acid, and acid comes from bacteria, and the bacteria live in plaque, reducing plaque (by brushing and flossing) reduces acid and therefore cavities. Xylitol (gum and mints) reduce bacteria and increases saliva flow, thereby minimizing acid exposure. Eating your food less frequently (eating the entire candy bar or drinking the entire soda all at once) will decrease exposure time, thereby reducing the risk.


Dr. Baarstad appreciates the value of community service, and devotes herself to improving the dental health of those who live around her.  After attending the University of Oregon, Dr. Baarstad graduated as a DMD from the Oregon Health Sciences University in Portland. She is an active member of the American Dental Association, the Oregon Dental Association and the Academy of General Dentistry, and a recipient of the Dr. William Howard Award for Excellence in Fixed Prosthetics. She donates services to charitable organizations and sponsors many community events, including high school fundraisers. Dr. Baarstad expresses a special interest in helping young men and women explore a career in dentistry through volunteering at local high school career symposiums.

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