Question

A dental caries characterised by mottling of teeth is due to presence of certain chemical elements in the drinking water. Which of the following is that element?
a. Fluorine
b. Boron
c. Mercury
d. Chlorine

Answer 1

Hint: This element when it is in correct concentration it is beneficial for the tooth. It prevents demineralisation. It is also used as a topical agent to preserve the tooth as a whole.

Complete answer:
Dental caries is an Infectious disease caused by the interaction of bacteria that cause caries with carbohydrates from the food in the oral cavity over time. These bacterias produce organic acids as an end product on the tooth surface. The bacteria and the end products adhere on the tooth surface and result in formation of plaque. There is a decrease in the ph making it favourable for bacteria to grow.

Tooth has various zones:
The outer is enamel, followed by dentin and pulp which is the innermost.
Enamel is composed of hydroxyapatite crystals i.e. phosphorus and calcium ions. When the ph drops it starts to cause demineralisation of the tooth enamel. When the ph starts to return back to normal, the minerals reincorporate on the tooth surface causing remineralisation on the enamel.

Fluorid in normal value is beneficial as it replaces calcium and forms fluorapatite crystals which are more resistant to demineralisation. When this concentration is increased more than 2 mg/L white patches or streaks are seen on tooth surface.

Hence, the correct answer is option (A).

Note: The normal concentration of fluorine is 1 ppm. It is nowadays added to water supply both in community and schools to provide fluorine in deficient regions. Topical pit and fissure sealants have also been popular to preserve the newly erupted tooth.