**Question:** The best sustaining topical effect of fluoride is obtained by:

A. Fluoride varnish
B. Fluoride gel
C. Fluoride mouthwash
D. Fluoride toothpaste

**Core Concept:** Fluoride is an essential element for dental health, especially in preventing dental caries. Topical fluoride application refers to placing fluoride directly onto the teeth through various formulations.

**Why the Correct Answer is Right:** Fluoride varnish (A) is a liquid fluoride solution that has a high fluoride concentration and is coated onto the tooth surface using a brushless applicator. The high concentration allows for a rapid fluoride release, ensuring a sustained topical effect over a longer duration compared to other options.

**Why Each Wrong Option is Incorrect:**

Option B (fluoride gel) has a lower fluoride concentration than varnish, making it less effective for sustaining a topical effect.

Option C (fluoride mouthwash) is intended for swallowing, not directly applied to teeth. Although it may provide some systemic fluoride protection, it is not the best for sustaining a topical effect.

Option D (fluoride toothpaste) is primarily designed for oral hygiene and cleaning, with fluoride acting as a secondary benefit. Toothpaste fluoride's release is primarily for caries prevention during brushing and is not tailored for sustained topical effect on teeth.

**Clinical Pearl:** Fluoride varnish is often used in dental clinics for caries prevention in high-risk patients, particularly children and adolescents during the developmental stage when tooth enamel is more prone to caries formation. Fluoride varnish application is recommended at 6, 12, and 18 months, followed by yearly applications in high-risk patients.

**Correct Answer:** Fluoride varnish (A) is the optimal choice for sustaining a topical fluoride effect on teeth, making it the best choice among the given options.