This first part will give the background about tooth decay and set the stage for the use of fluoride.
The crystals in bones, enamel, and dentin (all the hard tissues of the body) are a form of calcium hydroxyapatite. It's a complicated crystal of calcium, phosphates (PO4), and hydroxide (OH) groups. Intermixed is a meshwork of proteins that promote the collection of these minerals and allow soaking and diffusion of substances throughout the tooth structure to a small extent.
Most minerals can dissolve in water to some extent and each mineral has a different amount they will dissolve to and this depends on acidity and temperature of the fluid. An acid is a substance that can easily let go of a proton, or, a hydrogen that has lost its electron (H+) or it can be a fluid with lots of extra H+'s in it, as specificed by pH (1 is most acidic, 7 neutral, and 14 most basic/alkaline). Each person has taste buds for acids, it's known as sour/tart.
Hard water deposits are an easy example. When in the hot-water pipes, the minerals remain dissolved, but upon cooling, they "precipitate" out and form deposits/stones/crystals on the insides of some pipes, tiles, showerheads, etc. Limestone that has been eroded by acid rain is an example of acid dissolving. The crystals that make enamel are similar. When acids get to them, they will dissolve a bit. Over time, this erodes tooth structure and decays the tooth.
Dental Caries is the disease of tooth decay. It is influenced by diet, personal behavior, and bacterial species that live in the mouth. Some people have more virulent and dangerous species of bacteria in their mouth than others and these can spread from person to person, or the bad species can dominate the other less-bad species if given the chance. All the bacteria in the mouth take simple sugars (glucose, fructose, sucrose, etc), and use them to create meshes of plaque that stick to teeth where they hang out in permanent residence and hide from oxygen and do their thing. This involves eating sugar and spitting out the remains as various acids: lactic acid (the same that cultures milk into yogurt, made by lactobacillus bacteria), acetic acid (aka vinegar), propionic acid, and formic acid. Lactic is made by the most damaging species: streptococcus mutans and the lactobacillus groups and when lactic acid is the dominant acid found in the mouth, it's a sign that S. Mutans and LB's have taken over.
The longer these bacteria remain, the more damage they do, since they just hang out sharing in the food you eat and spitting out the remains to dissolve your teeth more and more. To combat this, the minerals in saliva will settle into teeth and remineralize them, buying time, but not combating the source of the problem. Brushing helps, eating less sugar helps, and killing off the bacteria in your mouth with antibacterial mouthrinses helps, but if you've got the really bad guys in your mouth, teeth are still the losers in the end. There are stronger mouthrinses available, and are sometimes necessary to gain an advantage and get ahead of the infection. They're not for the squeamish and contain either sodium hypochlorite (aka bleach/"pool chlorine") or chlorhexidine (which does funny things to taste buds and can cause removable surface stains on teeth). They are flavored and sweetened with xylitol, but it still takes some bravery to use them. They apparently work pretty well. Having a mouth full of bad-uns, myself, my wife and I plan on trying them out in the near future to take care of chronic teeth problems I've got. I plan on recording the use and results for faculty to use in an ongoing study.
Side note: Xylitol is similar to sugar in taste and structure, but different enough that bacteria usually don't have the ability to use it for food. Thus, they eat it and it plugs up their enzyme machinery. In people, xylitol sweetens food while providing about 2/3 the amount of calories (we have enzymes that can use it, bacteria don't). It's found naturally in many plants and fruits to small extents.
When a person eats, the pH of their mouth drops from a safe 6-7 range down into the acidic low 5's and 4's. Calcium hydroxy apatite begins to dissolve below 5.5. It takes some time for saliva to clean out the mouth and restore the pH back to safety. The whole time, tooth structure is being slowly lost. Once restored to normal, the minerals in saliva precipitate/deposite onto the dissolved areas and make it normal again too (provided too much isn't lost and that saliva can reach the eroded areas).
Important to remember is that any acid will dissolve teeth whether it's sports drinks, sodas, and lemonade (with pH's down in the 2-3 range) or stomach acid (also with pH down in the 2 range) from bulimia or acid reflux. Bacterial acids are especially dangerous, because they are always in the mouth and maintain permanent residence on the tooth surface.
That's where fluoride steps in. Fluoride ions fit nicely into calcium hydroxyapatite crystals by replacing the hydroxy (OH) groups. The flouride doesn't leave as easily and postpones dissolving until the pH drops below 4.5. This makes teeth significantly more resistant to acidic dissolvement, erosion, and decay, but the dilemma is, how much do we need, and how do we get it?
to be continued.....
1 comment:
That's very interesting stuff. Thanks for putting it in understandable terms! It seems that some of us are just doomed to tooth problems! Ughh!
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