## **Core Concept**
The question pertains to the properties and handling of Mineral Trioxide Aggregate (MTA), a material commonly used in endodontics and restorative dentistry. MTA, particularly white MTA, is utilized for its biocompatibility and ability to promote healing. The dissolution of set white MTA is relevant in certain clinical and procedural contexts.

## **Why the Correct Answer is Right**
The correct answer, **citric acid**, is a solution that can dissolve set white MTA. Citric acid is known for its chelating properties, which allow it to bind to calcium ions. Since MTA is primarily composed of calcium silicate cements, citric acid can effectively interact with and dissolve the set MTA by chelating these calcium ions, thereby disrupting the material's structure.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While EDTA (ethylenediaminetetraacetic acid) is also a chelating agent and can interact with calcium ions, it is not typically highlighted for dissolving set MTA in the same context as citric acid. EDTA is commonly used in endodontics for root canal irrigation to remove smear layers.
- **Option B:** This option is incorrect because the specific chemical or solution is not provided, making it impossible to assess its relevance.
- **Option D:** This option is incorrect as there is no provided solution or context to evaluate its effectiveness in dissolving set white MTA.

## **Clinical Pearl / High-Yield Fact**
A memorable point for postgraduate medical students, especially those in dentistry, is that citric acid can be used as an adjunct solution for dissolving set white MTA. This is particularly useful in procedures where MTA has been used and needs to be removed or adjusted.

## **Correct Answer:** . Citric acid