Normally pH in the mouth is around 6.8, which is neutral (neither acid nor alkaline).

When you take frequently fermentable carbohydrates, that include the obvious sugary foods, such as cookies, cakes, soft drinks and candy; less obvious food, such as bread, crackers, bananas and breakfast cereals, the bacteria present in the mouth (most
commonly Streptococcus mutans and lactobacilli) produce lactic acid and
cause the pH of the mouth to drop.

When pH reaches 5.5 that is critical and that will cause acid attack. But also high sugar consumption can result in an increased population of S. mutans, which in turn produce more lactic acid hence higher caries rate.

Acid attack

After eating fermentable carbohydrates that easily fermement in the mouth by S. mutans and lactobacilli bacteria to produce lactic acid, teeth will be attacked by lactic acid.

During an acid attack, the part of Enemel (outermost part of the tooth crown) ; calcium hydroxyapatite begins to
dissolve as calcium and phosphate ions leave the tooth and pass into the saliva. This is demineralisation and it is the first stage in the development of tooth decay.

Saliva contains bicarbonate ions, that are able to neutralise acid. And if no more sugar is consumed, the calcium and phosphate ions
return to the enamel and the pH returns to normal. This is remineralisation and it will take between 30 and
60 minutes.

So tooth decay will occur when episodes of demineralisation become more than episodes of remineralisation.

Here is venn diagram representing factors for tooth decay to occur.

So to conclude, for a tooth decay will occur when you consume fermentable carbohydrates (simply snacks or other fermentable carbohydrates) then they are fermented by S. Mutants and lactobilli bacteria, that produce lactic acid which causes demineralisation. All of them will depend on frequency of consumption and time of exposure.

Disclaimer:
✔ This article is not for dental professionals or dental students. This article and the language used were simplified for the public to better understand. Professionals and students are advised to use books that detail everything we talked about.
✔ All images used are from royalty free image stocks except venn Digram that I got from the reference book.

Reference

#Book: Basic Guide to ORAL HEALTH Education AND PROMOTION (2nd edition) by ANN FELTON, ALISON CHAPMAN and SIMON FELTON.

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