By Neil Melker, D.D.S.

The Normal Human Mouth

The condition of the average modern human mouth is the strongest example of the effect of industrial-agricultural society on the human body. Whenever a pre-Columbian native North American skull is found, it is remarked that the dentition is fully intact. Even in individuals of advanced age, the only distress is wear -- no periodontal disease, caries (cavities), or orthodontic problems. This same condition is found in the remains of other past hunter-gatherers and to a smaller extent in some present-day more “primitive” cultures. It seems that the mouth is particularly sensitive to the way we live, since if other organs were as distressed they would barely function.

Tooth Decay in General

Tooth decay, technically dental caries, is due to the effect that normal oral bacteria have on the teeth. Human tooth enamel is the strongest and hardest material made by life. It is a nearly inorganic (not carbon containing) calcium-hydroxyapatite crystal; that is a regular symmetric crystal quite like quartz crystal. Besides trauma, the only threat to this armor-like outer tooth layer is strong acid.

Let’s digress: The healthy mouth is home to at least 700 different bacterial species. The mouth is an ecosystem and, like the other end of the digestive tract, must have a resident bacterial population for proper function. In fact, bacteria-free mouths are quickly colonized and attacked by yeast. The most common bacteria are lactobacillus and streptococcus mutans which are gram-positive aerobes, all humans have them in their mouths. They are beneficial species; they control the populations of not only yeast but also more potentially harmful bacteria. Strep mutans and lactobacillus however have one bad side. In the presence of sugar, they produce lactic acid. This is not a problem when the diet has little sugar, but when the mouth is frequently loaded with sugar the strep mutans and lactobacillus population soar and their waste product, lactic acid, reaches a high enough concentration to dissolve tooth enamel.

Humans were designed to process raw vegetables. The complex carbohydrates in these vegetables take long to break down, so the digestive process begins in the mouth with the mixing of saliva and ground-up food. The saliva contains ptyalin, an enzyme that converts starch (one form of carbohydrate) to sugar (another form of carbohydrate). So far so good.

However let’s introduce our modern diet into this environment full of enzymes and bacteria.

Finely ground wheat and rice are the most concentrated and easily metabolized sources of food energy available. Therein lies the problem: the finely ground wheat is quickly converted to sugar by the salivary maltase and this sugar nourishes the bacteria, which in turn produce large amounts of acid, which in turn dissolves tooth enamel, making holes in it called cavities.

Decay occurs within twenty minutes after sticky, finely ground starch adheres to the tooth surface. That is the time it takes for the bacteria population to increase to significant enough levels to produce enough acid to initiate or propagate decay.

Childhood Caries

Primary (baby or milk) teeth usually enter the mouth during the first year of life. There are twenty of them. They are similar in shape and structure to the permanent or secondary teeth that replace them. They are smaller and thinner than the permanent teeth, with much thinner enamel and are thus more easily disrupted by decay. In addition, the young mouth is particularly susceptible to decay for several reasons:

When all the teeth are present, they function as a self-cleaning mechanism. Upper teeth fit closely into lower teeth thus removing any food material on their surfaces. When teeth first erupt, they don’t have the opposing partner for some time, enough time for decay to occur.

Young children are often poorly nourished from a dental point of view: Popularly acceptable food for young children includes starchy crackers (toasted bread is often the first food), processed cereal, cheddar cheese goldfish, organic cheerios, etc. This sticky-starchy mass is then wetted with sugar filled drinks (kool-aid, organic apple juice, and breast milk are all equivalent from a bacterium’s point of view) and the result is a highly acidic environment around each tooth, enough to eat holes in the enamel.

Parents don’t know any better. Most publicly disseminated parenting information in this society is commercial in nature and the best ways to prevent tooth decay don’t involve buying anything.

Children can easily become carbohydrate/sugar addicts. Not only do frequent snacks of finely ground starches, sweet drinks and sucking candy cause the teeth to rot, but also this sugar-high cycle disrupts attention and adversely affects behavior. The best snacks from a dental point of view are better nutritionally as well. When age and allergy concern appropriate, nuts, cheeses, hard fresh fruit, e.g., carrots, apples, celery are all noncariogenic (that is not cavity producing) and in fact help clean other debris from the tooth surface. Also, avoid dried fruit such as raisins, fruit leather or roll-ups, these fit the description of cariogenic foods, they are sticky and full of sugar. Incidentally, ice cream, frozen yogurt and other like treats are generally noncariogenic, since they do not stick to the tooth provided there are no candy bars and other similar inclusions mixed in.

Does all this discussion mean that children’s diets should contain no breadstuffs or rice at all? Certainly not, but there must be no residue of them in the teeth immediately after the meal or snack. This involves designing meals to be self-cleaning. If the last course of a meal or part of a snack is an apple, carrot, nuts, or celery stalk, all the bad stuff is worked off the tooth surface as well as after a good tooth brushing.

The best way to determine if there is the possibility that your child’s last meal is about to cause tooth decay, just look inside his or her mouth. If you see light colored sticky masses in the biting surfaces of the back teeth or around the gum line of any tooth some sort of cleaning is in order. This inspection is especially important at bedtime, since during sleep salivary flow is diminished and therefore its decay fighting is reduced as well.

Despite the fact that in some circles, gum chewing is unacceptable, and schools forbid it because there is just so much room on the underside of chairs, it remains as one of the best ways to clean the teeth. Hard gum, not bubble gum or gum candy is extremely effective in removing even the smallest particles from the biting surfaces of teeth. Sugared or non sugared seem to work equally effectively in preventing decay (recent studies support the effectiveness of xylitol sweetened gum however) since the starchy plaque is usually removed so quickly that the bacteria in it have no time to produce acid. In addition, gum chewing elicits high salivary flows that further cleanse the mouth.

An important note to the choice of school-day snacks: The classic crackers and juice is perhaps the worst possible prescription for tooth decay. Apples, carrots, nuts and nut butters, celery and other hard, uncooked fruit are better selections for many reasons.

To cite this page: Melker, Neil D.D.S. Tooth decay: Its causes and prevention in children.