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(a)Which chemical substances is present ...

(a)Which chemical substances is present as enamel on the surface of the teeth ?
(b)Traces of fluoride ions `(F^-)` in drinking water (about 1 ppm) greatly reduce the incidence dental cavities (tooth decay ) . What is the reason for reduction in cavities ?

Text Solution

Verified by Experts

(a)The chemical substance present as enamel on the surface of the teeth is `3 Ca_3(PO_4)_2 . Ca(OH)_2`
(b)The fluoride ions `(F^-)` convert to enamel to much harder `3Ca_3(PO_4)_2. CaF_2` . Hence, the incidence cavities is greatly reduced.
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Answer question numbers (a) – (d) on the basis of your understanding of the following paragraph and related studied concepts 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 of the mouth is below 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. The best way to prevent this is to clean the mouth after eating food. Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay. What is the composition of the material of teeth ?

Answer question numbers (a) – (d) on the basis of your understanding of the following paragraph and related studied concepts 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 of the mouth is below 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. The best way to prevent this is to clean the mouth after eating food. Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay. What should be the pH of the mouth to prevent damage to the teeth ?

Knowledge Check

  • The recommended concentration of fluoride ion in drinking water is up to 1 ppm as fluoride ion is required to make teeth enamel harder by converting [3 Ca_3(PO_4)_2. Ca(OH)_2] to

    A
    `[CaF_2]`
    B
    `[3 (CaF_2). Ca(OH)_2]`
    C
    `[3Ca_3 (PO_4)_2. CaF_2]`
    D
    `[3(Ca(OH)_2. CaF_2)]`

  • The recommended concentration of fluoride ion in drinking water is up to 1 ppm as fluoride ion is required to make teeth enamel harder by converting [3Ca_(3)(PO_(4))_(2).Ca(OH)_(2)]

    A
    `[3{Ca(OH)_(2)}.CaF_(2)]`
    B
    `[CaF_(2)]`
    C
    `[3(CaF_(2).Ca(OH)_(2)]`
    D
    `[3Ca_(3)(PO_(4))_(2).CaF_(2)]`

  • Assertion : Soluable fluoride is often added to drinking water to bring its concentration up to 1 ppm. Reason : F^(-) ion concentration above 2 ppm causes brown mottling of teeth.

    A
    If both assertion and reason are true and reason is the correct explanation of assertion.
    B
    If both assertion and reason are true but reason is not the c orrect explanation of assertion.
    C
    If assertion is true but reason is false.
    D
    If both assertion and reason are false.

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