**Core Concept**
Topical application of sodium fluoride solutions is a preventive measure to strengthen tooth enamel and reduce the risk of dental caries. However, the effectiveness of this therapy can be influenced by various factors, including the frequency and duration of application.

**Why the Correct Answer is Right**
The correct answer, **C. Patient must make four visits to the dentist within a relatively short period of time**, highlights a significant disadvantage of topically applied sodium fluoride solutions. This is because the application of fluoride varnish typically requires a series of four visits to the dentist within a short period, which can be inconvenient for patients with busy schedules. This limitation can lead to inconsistent application and reduced patient compliance.

**Why Each Wrong Option is Incorrect**
**Option A:** While it is true that a fresh solution should be prepared for each patient to ensure optimal efficacy, this is not a disadvantage of topical sodium fluoride application. In fact, using a fresh solution is a standard practice to prevent contamination and ensure the best possible outcome.

**Option B:** Taste is indeed a consideration for some patients, but it is not the primary disadvantage of topical sodium fluoride solutions. Many fluoride varnishes have a pleasant taste and are well tolerated by patients.

**Option D:** Allowing the solution to dry for 5 minutes is actually a recommended step to ensure optimal fluoride uptake by the tooth enamel. This is not a disadvantage, but rather a recommended protocol.

**Clinical Pearl / High-Yield Fact**
It's essential for dentists to educate patients about the importance of consistent fluoride application and the need for multiple visits to achieve optimal results. By understanding the limitations of topical fluoride therapy, patients can better appreciate the value of regular dental care and adhere to treatment plans.

**✓ Correct Answer: C. Patient must make four visits to the dentist within a relatively short period of time**