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INSIDE A TOOTH


Some people are surprised to learn that inside the outer shell of a tooth is soft living tissue with cells, nerves, and a blood supply. The outside of a tooth may feel hard to your tongue, but don’t imagine your teeth as a row of stony pebbles in your mouth. If they were, it would be fine to scrub, bleach, and polish them because then, the more you scrubbed and polished, the brighter they would be. The fact is that the outer enamel of a tooth is a delicate mesh of minerals that is easily rubbed away, dissolved, and damaged, particularly by acidity or inappropriate scrubbing and polishing.

OUTSIDE A TOOTH

Weakness in the outer layer of your tooth can allow liquids, bacteria, and stains to travel toward the center part, which will irritate the nerve and potentially lead to an infection that can threaten the life of your tooth. Protecting tooth enamel is important for many reasons, but especially in order to keep the center of your tooth healthy and disease free.
The enamel on the outside of your tooth is constantly changing in strength and hardness, becoming softer for a while and then naturally hardening up again. People have known for years that there is a similar chemistry to keep our skeleton healthy. Minerals are deposited into bones and then removed in a natural process of breakdown and rebuilding. Healthy bone exists when the repairs balance the wearing away. Even under normal, healthy conditions, the strength of tooth enamel is always in balance, as the outer enamel builds up and breaks down all day and all night.6

Strong Teeth

As we grow older, or if sickness changes our body chemistry, repairs to our skeleton may slow down, and osteoporosis (thinning of the bones) can occur if there is not enough building up of bones to counter the wearing away. Changes in the balance make it difficult to maintain bone strength, and the same goes for teeth. For bone health, women are encouraged to build the strength of their bones before they become weak or damaged. They should similarly work to protect and maintain the strength of their teeth, even before they see any signs of damage.
The difference between maintaining healthy bones and teeth is the ease with which we can control the balance for our teeth and prevent any loss of strength in the enamel, no matter our age or our state of general health. Our teeth are in direct contact with mouth liquids that can either soften and wear teeth away or build them up. Everything we consume touches our teeth directly or mixes with mouth liquids to flow around them, into every groove or pit on their surface. Food particles dissolved in mouth liquids contribute either to tooth erosion or tooth repair, depending on the chemistry of the resulting liquid. When any corrosive or acidic mouth liquid flows over teeth, it interacts with the surface of the enamel and dissolves it.

MINERALS

If you examined healthy enamel with a microscope, you would see that it is made up of a skeleton with crystals in between a lattice-shaped structure. These crystals are packed tightly together, with only a very thin, watery film between them. Even when enamel is healthy and made up of these densely packed crystals, mouth liquids can flow between them, working through the tiny spaces around each crystal.
Tooth enamel is built from calcium and phosphate, two minerals that occur naturally in saliva. Under the correct conditions, these minerals combine to form crystals called calcium hydroxyapatite. These crystals are packed together tightly, like little grains of salt, within a lattice-type skeleton that creates the structure of tooth enamel. The appearance of enamel is like a honeycomb, and you can imagine the skeleton as the comb and the crystals like the honey that fills in the spaces.
When your saliva is alkaline, calcium and phosphate flow into tooth enamel and build more crystals that form strong and dense enamel that is resistant to damage. As you will see in chapter 5, on mouth acidity, in a moist and alkaline mouth, enamel crystals grow large and thick because minerals are plentiful. Most people are aware that fluoride helps to strengthen teeth and fluoride works by encouraging the formation of these large and well-formed enamel crystals.
In a moist and alkaline mouth, dilute concentrations of fluoride can increase the speed at which minerals from saliva turn into enamel crystals. Fluoride is really an activator—in scientific terms, fluoride would be called a catalyst. The interesting thing is that when enamel crystals form in the presence of fluoride, a tiny particle of fluoride is incorporated into the crystals. The scientific name of this crystal is calcium fluorapatite, and it has a different chemistry from the calcium hydroxyapatite crystal of regular enamel. Calcium fluorapatite is larger than regular enamel crystals and has a more perfect shape. Tooth enamel formed with this kind of crystal appears smoother, shinier, and stronger and is less easily damaged by acids and the wear and tear that can harm teeth.
On the other hand, when teeth are bathed in acidic saliva or corrosive foods and drinks, minerals flow out of the tooth, enamel crystals melt or dissolve, and the framework (the skeleton) becomes less densely packed, with smaller crystals. As the crystals melt (imagine an antacid tablet melting or dissolving in a glass of water) and become smaller, spaces or gaps, called pores, form between each crystal. As the spaces enlarge, they fill up with liquid. In this way, enamel under acidic attack loses its density and becomes more porous, and porous teeth are more likely to break, chip, or crumble. Porous teeth also stain more easily as colors from foods and drinks soak into their surface.
Understanding the difference fluoride can make to the outer shell of teeth explains why people with acidic mouths and damaged teeth should use dilute fluoride rinses to strengthen and protect them from any future acidity or dental damage.
When a dentist puts a white filling on the surface of a tooth he or she will etch the surface of that tooth with some acid, using this crystal “melting” process to purposefully remove minerals and open up pores in your tooth enamel so that he or she can attach the white filling material to the tooth surface. An acidic liquid is coated over the enamel and allowed to soak for a few seconds. The acidic liquid shrinks the enamel crystals and opens up pores between them. The acidic liquid is then washed away, and filling material is flowed onto the enamel and allowed to soak into the surface and into these microscopic holes. This method creates what appears to be (under the microscope) a mass of mini-fingers or tentacles clinging in the pore holes. To the patient, the white filling appears to magically stick onto the surface of the tooth. In fact, this has been a great demonstration of how quickly and easily tooth enamel crystals can be dissolved by acidity and how porous they make the tooth surface.

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