## **Core Concept**
The question tests understanding of endodontic instrumentation goals, specifically regarding the obturation of the root canal system with gutta-percha. Effective containment of gutta-percha within the canal requires a well-instrumented and shaped canal that allows for a precise fit of the obturation material.

## **Why the Correct Answer is Right**
The correct answer, , implies that the instrumentation should result in a canal shape that has a **taper** which allows for the easy insertion and containment of gutta-percha. A commonly recommended taper for endodontic preparation is **0.02-0.04 mm/mm**, which facilitates the filling process while ensuring the structural integrity of the tooth. This taper allows for a balanced and controlled fill, reducing the risk of overfilling or underfilling.

## **Why Each Wrong Option is Incorrect**
- **Option A:** A taper that is too minimal may not allow for easy insertion of gutta-percha or may lead to over-instrumentation apically, increasing the risk of perforation or transportation.
- **Option B:** A very steep taper could weaken the tooth structure and make it difficult to achieve a tight seal with gutta-percha.
- **Option D:** A negative taper or insufficient taper could prevent the easy insertion of gutta-percha and make containment difficult.

## **Clinical Pearl / High-Yield Fact**
A critical aspect of endodontic treatment is achieving the **master cone fit** at the working length with a tug-back, ensuring a precise adaptation of gutta-percha to the canal walls. A taper of 0.02-0.04 mm/mm is often aimed for to facilitate this process.

## **Correct Answer:** . 0.02 taper.