Question

What is the role of toothpaste in preventing cavities?

Answer 1

Tooth decay

• Tooth decay starts when the pH of the mouth is lower than $5.5$.
• Tooth enamel, made up of calcium hydroxyapatite (a crystalline form of calcium phosphate) is the hardest substance in the body. It does not dissolve in water but is corroded when the pH in the mouth is below $5.5$.
• Bacteria present in the mouth produce acids by degradation of food particles and sugar remaining in the mouth after eating.

Role of toothpaste in preventing cavities

• Using toothpaste, which is generally basic, for cleaning the teeth can neutralize the excess acid and prevent tooth decay.
• Fluoride is found in toothpaste, and it is the most effective approach to preventing tooth decay.
• By converting hydroxyapatite$\left[3\right({\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2.\mathrm{Ca}{\left(\mathrm{OH}\right)}_2]$ into the considerably harder fluorapatite$\left[3({\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2.{\mathrm{CaF}}_2\right]$, the ${\text{F}}^{-}$ ion makes the enamel of teeth much harder.
• However, ${\text{F}}^{-}$ ion concentration above $2\mathrm{ppm}$ causes brown mottling of teeth.