Chemistry of Teeth

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Chemistry of Teeth

Chemistry of Teeth

And I though O chem was just a filter class and that I could forget my chemistry...wrong! Read on but it could get boring...

Like anything in solution (ie our teeth in saliva), an equilibrium works to be established (between ions moving in and out of the solution). This equilibrium is affected by other ions added to solution, and pH; ie fluoride, calcium, phosphate, acidic or basic food/drinks in our diet, toothpastes, plaque (bacteria releasing organic acids) etc.

Our teeth are (ideally) composed of hydroxyapetite: Ca10(PO4)6(OH)2, which can dissociate into calcium (Ca2+), phosphate (PO4)3-, and hydroxyl (OH-)ions.
In reality there are impurities with magnesium, lead, sodium, potassium, strontium, barium... 

Our saliva is saturated with calcium and phosphate, which is why under normal conditions our teeth don't break down from calcium and phosphate leaving the tooth for solution. In acidic conditions, such as eating fruits, wine, sports drinks, colas, sour candies, cavities, etc, the hydroxyl (OH-) and phosphate (PO4)3- ions are grabbed by hydrogen (H+) ions. This shifts the equilibrium / acid base balance and OH- and (PO4)3- dissociate from our teeth. Now we have a breakdown of our teeth. The enamel (or top layer) of our teeth breaks down and we have acid erosion or a cavity. Once enamel is lost, it is irreplaceable. 

How does fluoride fit in? More about fluoride later, but for now:
The fluoride ion (F-) can take the place of the (OH-) in hydroxyapetite to make fluorapetite which is stronger and more resistant to acids (I suppose due to higher bonding energy?). Remember, there is always an equilibrium, a movement of ions in and out of solution. When the hydroxyls (OH-) move out, the F- with a higher affinity for (Ca2+) can bind, thus only topical fluoride use is necessary, NOT systemic. 
Once enamel structure is lost, it can't be replaced. But if it's just slightly damaged, the fluoride can help to "fix" it, or remineralize it. In these cases the F- may also need additional calcium and phosphate ions. This is one reason why cheese may be some dentist's list of good foods to eat. On the other side, some dentists believe once these damaged spots appear as a white spot it is already too late; supplementing calcium and phosphate with the fluoride won't work. Ask your dentist what they think. 

PS: I am a dentist, not a chemist. If there are any chemists out there let me know your thoughts, thanks!