## **Core Concept**
The primary goal of a root canal sealer in endodontic therapy is to fill the irregularities and minor discrepancies between the root canal walls and the obturation material, typically gutta-percha, ensuring a complete seal of the root canal system.

## **Why the Correct Answer is Right**
The root canal sealer serves to fill in the microscopic irregularities of the canal walls and the space between the canal walls and the gutta-percha points, providing an impervious seal. This seal prevents bacterial leakage and the passage of fluids and ions, which could lead to treatment failure. The sealer also helps in bonding the filling material to the canal walls.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option might suggest a primary mechanical function, which, while partially true, does not accurately represent the main purpose of a sealer.
- **Option B:** This could imply antimicrobial properties as the primary purpose, though sealers may have some antimicrobial effect, it is not their main function.
- **Option C:** If this option suggests obturation as the primary purpose, it's misleading because obturation refers to the overall process of filling the canal, with the sealer being one component.

## **Clinical Pearl / High-Yield Fact**
A critical point to remember is that while sealers are essential for a successful root canal therapy, they are not a substitute for proper canal cleaning and shaping. The type of sealer used can also affect the outcome, with common types including zinc oxide-eugenol (ZOE) sealers, calcium hydroxide sealers, and newer materials like MTA-based and resin-based sealers.

## **Correct Answer:** D. Fill in the irregularities between the root canal walls and the obturation material.