**Core Concept:** Following a dental procedure like amputation of the coronal portion of the pulp in an immature permanent first molar, it is crucial to cover the exposed dentin and pulp stump to prevent complications such as pulpal and periapical infections, dentigerous cyst formation, and resorption of the residual root.

**Why the Correct Answer is Right:** The correct answer is D, which refers to placing a rubber dam isolating agent over the tooth before performing the procedure and then capping the exposed pulp stump with mineral trioxide aggregate (MTA). MTA is a biocompatible material that forms a barrier between the oral environment and the pulp stump, preventing bacterial invasion and associated complications. Additionally, MTA promotes root formation and apical closure in immature teeth, which is essential for the tooth's long-term prognosis.

**Why Each Wrong Option is Incorrect:**

A. Calcium hydroxide (CH) is also used as a pulp capping material, but it is not as effective as MTA in sealing the pulp stump and stimulating root formation in immature permanent teeth.

B. Calcium hydroxide is only effective for pulp capping when the vital pulp is exposed, not when the coronal portion of the pulp is amputated.

C. Glass ionomer cement (GIC) is a restorative material and not specifically designed for pulp capping. It does not seal the pulp stump as efficiently as MTA, increasing the risk of complications.

**Clinical Pearl:** In clinical practice, MTA is the preferred material for capping the exposed pulp stump after coronal pulp amputation in immature permanent teeth to prevent complications and promote long-term tooth survival.