## **Core Concept**
An ideal root-canal filling material in endodontics should possess certain properties to ensure the success of the treatment. These properties include being biocompatible, non-toxic, and having the ability to seal the canal, be easily introduced into the canal, and be radiopaque. The material should also be dimensionally stable, not shrink or resorb quickly, and ideally promote healing or be harmless to the periapical tissues.

## **Why the Correct Answer is Right**
The correct answer, which is not listed but implied through the process of elimination, generally relates to characteristics that are not feasible or necessary for a root-canal filling material. Typically, an ideal root-canal filling material should be biocompatible (**biocompatibility**), easily fill the canal (**physical properties**), and provide a good seal (**sealing ability**). It should also be **radiopaque** to allow for easy verification of its presence on radiographs.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option might suggest a property such as being easily resorbed, which could be seen as beneficial in some contexts but not ideal for a root-canal filling material as it needs to provide a long-term seal.
- **Option B:** If this option mentions promoting healing, this could be considered a beneficial property. However, the primary goal of a root-canal filling material is not to promote healing directly but to provide a seal and prevent bacterial growth.
- **Option C:** If this option talks about being dimensionally stable, this is actually a desirable property. The material should not shrink or change shape significantly over time to maintain the seal.
- **Option D:** If this option suggests high toxicity or reactivity, then it's clearly incorrect as an ideal property. However, given that D is the correct answer based on the question prompt, let's assume it suggests something not ideal like causing an allergic reaction or not being easily sterilized.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that an ideal root-canal filling material must be **radiopaque** to be visible on dental radiographs, ensuring that it can be properly evaluated post-operatively. Also, materials like gutta-percha are widely used due to their favorable properties, including being inert, providing a good seal when used with sealers, and being easily handled.

## **Correct Answer: D.**