The % reduction in caries to be expected by the application of neutral fluoride solution is:
**Core Concept:** Neutral fluoride solutions are commonly used for caries prevention as they can penetrate tooth enamel and reduce caries by promoting remineralization of the enamel, which makes it more resistant to acids produced by dental plaque bacteria. Fluoride ions (F-) bind to hydroxyapatite crystals in the enamel, making the crystals more resistant to dissolution by acidic plaque bacteria.
**Why the Correct Answer is Right:**
The correct answer is **D**: a 20% reduction in caries is expected by the application of neutral fluoride solution. Fluoride ions (F-) promote remineralization of the enamel, making it more resistant to demineralization caused by dental plaque bacteria. This results in a significant decrease in caries incidence.
**Why Each Wrong Option is Incorrect:**
A) A 50% reduction in caries is not typically achieved with neutral fluoride solutions. The remineralization process is not complete and thus does not lead to such a high reduction.
B) A 30% reduction in caries is not as significant as 20%. The difference between 20% and 30% is subtle but crucial for the understanding of the effectiveness of fluoride application.
C) A 10% reduction in caries is too low for practical use. Fluoride therapy aims to significantly reduce caries, and a 10% reduction is not considered clinically meaningful.
E) A 40% reduction in caries is more than the 20% reduction achieved with neutral fluoride solutions. This option is incorrect as neutral fluoride solutions are known to provide a more modest reduction in caries, typically around 20%.
**Clinical Pearl:** Fluoride therapy, including the use of neutral fluoride solutions, is a well-established preventive measure for dental caries. Fluoride ions (F-) bind to hydroxyapatite crystals in the enamel, enhancing its resistance to demineralization mediated by dental plaque bacteria. The 20% reduction in caries is considered a clinically meaningful outcome, as it results in a significant decrease in caries incidence while minimizing potential side effects of excessive fluoride intake.