Why does tooth decay start when the pH of mouth is lower than 5.5?

Explanation

1) Tooth decay starts when the pH of the mouth is lower than 5.5.
2) Tooth eN/Amel, made of calcium phosphate is the hardest substance in the body.
3) It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5.
4 ) Bacteria present in the mouth produces acids by degradation of sugar and food particles remaining in the mouth
Preventions:
1) Clean the mouth after eating food.
2) Using tooth pastes. Which are generally basic neutralize the excess acid and prevent tooth decay.