Toothpaste prevents tooth decay by:
- (a)neutralizing the excess acidity.
- (b)means of emulsification.
- (c)the action of fluoride.
- (d)making a coat of calcium over the teeth surface.
Correct — A and C (the official key accepted both, so this was a grace item). Tooth decay begins when acids produced by mouth bacteria dissolve the enamel. Toothpaste fights this two ways: the fluoride in it (C) reacts with enamel to form acid-resistant fluorapatite and helps remineralise early damage, while its mildly alkaline formulation neutralises the excess mouth acidity (A). Because both mechanisms are genuine and both option A and option C describe them, UPSC awarded marks for either.
- (b)means of emulsification. — Emulsification (the detergent/foaming action) merely helps lift food debris and spread the paste; it does not prevent the acid attack that causes decay, so it is not how decay is prevented.
- (d)making a coat of calcium over the teeth surface. — Toothpaste does not deposit a calcium coating over the teeth. Fluoride strengthens the existing enamel by forming fluorapatite; it does not lay down a fresh calcium film, so this is incorrect.
Dental caries (tooth decay) is an acid problem: bacteria in dental plaque ferment sugars into acids that demineralise the hydroxyapatite of enamel. Toothpaste protects the tooth chiefly through fluoride, which converts hydroxyapatite into the tougher, less acid-soluble fluorapatite and promotes remineralisation; the paste's mild alkalinity also buffers the acid. Its abrasives and detergents clean the surface but are not the anti-decay agents.
The item is really testing what actually stops enamel from dissolving. Fluoride action (C) is the textbook answer, but neutralising the acid (A) is also a valid decay-preventing mechanism — which is why the commission accepted both and dropped the trickier distractors (emulsification and a supposed calcium coat).
- Decay starts when plaque bacteria ferment sugar into acids that demineralise enamel.
- Fluoride forms fluorapatite, which is more resistant to acid than natural hydroxyapatite, and aids remineralisation.
- Most toothpastes are mildly alkaline, helping to neutralise excess acidity in the mouth.
- Abrasives and foaming detergents clean the teeth but do not, by themselves, prevent caries.
- Choosing 'emulsification' because toothpaste foams — foaming cleans but does not stop acid attack.
- Believing toothpaste coats teeth with calcium — fluoride strengthens existing enamel rather than depositing a new layer.
Framed as an applied-chemistry item on how a daily-use product prevents decay, with two mechanisms both correct.
No directly related past PYQ was found.
- practice — not a real PYQ
Fluoride in toothpaste protects enamel mainly by:
- (a)bleaching the enamel white
- (b)converting hydroxyapatite into acid-resistant fluorapatite
- (c)killing all mouth bacteria permanently
- (d)coating teeth with a plastic film
Answer(b) converting hydroxyapatite into acid-resistant fluorapatite.
- practice — not a real PYQ
Tooth decay is fundamentally caused by:
- (a)acids produced by plaque bacteria demineralising enamel
- (b)excess saliva
- (c)hard tap water
- (d)cold drinks freezing the enamel
Answer(a) acids produced by plaque bacteria demineralising enamel.