p 9 How teeth decay.

 pH is a measure of the acidity (or alkalinity) in a material: neutral is pH 7: the more acid in the material, the lower the pH.

Saliva in a clean mouth is about pH 6.5. Below pH 5.5, teeth begin to decay.

   The action of bacteria on sugar produces type 1 acid very quickly indeed - a few minutes. A small sweet on its own should not be converted to enough acid to defeat the buffers in the saliva. In the description below, read any small quantity of sugar in place of "sweet".


  If a single sweet is eaten, the acid produced causes a fall in th pH, but too little for it to fall below 5.5. The saliva washes it all away after 20-30 minutes or so and the pH returns to normal.

If a second sweet is eaten after, say, that 30 minutes, the same happens again and the teeth are safe.


 In general terms, the younger the person, the more vulnerable the teeth. One reason for this is that throughout life we pick up chemicals (like the fluorides in tea) from our food and drink which make the enamel somewhat more resistant to acid attack.

The teeth will still decay of course but less readily.


 If, however, the second sweet is eaten sooner than the pH has had time to return to normal, say in less than 30 minutes, the the remaining acid in the saliva from the first sweet is added to that produced by the second. So the total amount of acid present makes the pH fall lower than one sweet alone.  

 If the third sweet and fourth sweets are eaten in the same way, the pH at some time drops below 5.5 - into the decaying now zone.

The lower it drops, the greater the time taken by the saliva to recover and so the greater the total tooth damage.


 Look again at the types of acid after 'How does it all happen' (page8). If an acid drink (type 2) with no sugar in it is drunk, the pH drops like a stone, way below pH 5.5 - but there is no decay - wrong acid!    But, with, say, a sugar-free drink, or diet drink, or low calorie drink, or a slice of fresh lime or lemon, plus only one sweet, OR even unsweetened fruit juice which is always acid with some natural sugar, the teeth start decaying immediately. because the type 2 acid has done the pH-dropping job to decay level!

So, to prevent decay, be very, very careful with the sweets - a mint every 15-20 minutes is disastrous to teeth. A sugar-free drink (totally sugar-free, no naturally- occurring sugar like in fresh orange) is ok on its own without anything else with any sugar at all in it. Corrodes the teeth, mind, but doesn't decay them.

Diet drinks - you're ok - corrodes the teeth too but doesn't decay them. But an acid drink with the smallest amount of sugar in it is curtains to teeth. So fresh fruit juice (FFJ) is bad news - don't touch the stuff.

FFJ with no added sugar - so what? Even the naturally-occurring stuff has plenty of sugar. FFJ is about pH 2.0: with the sugar already in it, it's dynamite to teeth!

Diluting juice (no added sugar or not) - all the same as FFJ: acid and any sugar - and you can't have a biscuit, or a sweet or a choccy bar at the same time or your teeth will be on the skids. I don't know what all the other ingredients do to you when mixed with acids - not my field (ask your Doctor).

FFJ with "added vitamins"? That's just not fair! There's nothing wrong with fruit juice if you know how to drink it (or if you have lost your teeth.) Your vitamin needs are your affair too. But trying to fool the buyer into thinking a criticised product is healthy or giving it more 'buyer-attraction' by adding a well-recognised health requirement such as vitamins to it is not only not right - it's positively disgraceful! How about smoking in an oxygen tent?

Phew! You deserve a rest after all that!
 Walking in the wild bits of Scotland

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