Sugar is not corrosive, in any sense of the term, so how does it causwe decay in our teeth?
Well let’s start by considering what teeth are, and what could possibly be corrosive to them.
Teeth are an inorganic composite – calcium phosphate. Any phosphate will dissolve in an acid, so that’s probably a good place to start looking.
What could be in our mouths that’s acidic? An obvious culprit is orange juice, containing citric acid.
The problem with that theory however is that citric acid is just not that acidic, and in any case, once we swallow it how much of it remains left behind on their teeth?
No, we have to look elsewhere.
In fact, sugar is indeed the culprit, but by a roundabout sort of route. What happens is that the sucrose (sugar) combines with proteins to form glycoproteins, which stick to our teeth like glue. This, in fact, is what plaque is, and this process is the beginning of plaque formation on their teeth.
What happens next is that bacteria in your mouth convert the fructose part of the sucrose molecule to glycogen, to get energy. The end result of this process is lactic acid.
We all know what lactic acid is, particularly those who exercise. It’s that burning sensation in your muscles when you are working them too hard. And running out of breath. In fact we know this is due to lack of oxygen as lactic acid forms under anaerobic conditions. And the same is true in your mouth – locked away between your teeth and your gums, the bacteria can’t get enough oxygen, therefore they use an anaerobic process to make the lactic acid.
How acidic is lactic acid? The answer is it’s about 10 times more acidic than acetic acid (vinegar) which is itself acidic enough to be used as a cleaning agent in many household formulations.
So yes, lactic acid is well and truly acidic enough to dissolve the calcium phosphate in your teeth. This is why many toothpastes now contain sodium bicarbonate – this raises the pH and neutralises the acid, thus protecting your teeth.