**Core Concept**
Sodium fluoride is a compound used in dentistry and public health to prevent dental caries. It inhibits the enzymatic activity of acidogenic bacteria, thereby reducing the production of acid and the demineralization of tooth enamel.

**Why the Correct Answer is Right**
Sodium fluoride is added to community water supplies to prevent dental caries. It works by inhibiting the enzyme enolase, which is involved in the glycolytic pathway. By inhibiting enolase, sodium fluoride reduces the production of lactic acid, which is a key contributor to the development of dental caries. This leads to a reduction in the acidification of the oral environment and a decrease in the demineralization of tooth enamel.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because sodium fluoride is not typically added to salt for the prevention of dental caries.
**Option B:** This option is incorrect because sodium fluoride is not added to toothpaste for the treatment of periodontal disease.
**Option C:** This option is incorrect because sodium fluoride is not added to mouthwash for the prevention of oral thrush.

**Clinical Pearl / High-Yield Fact**
One important fact to remember is that sodium fluoride is most effective when used in conjunction with good oral hygiene practices, such as regular brushing and flossing.

**Correct Answer: A. Community water supplies**