**Core Concept**
Pulpotomy is a dental procedure aimed at preserving the vitality of the pulp tissue within a tooth, typically by removing the inflamed or infected portion of the pulp while maintaining the remaining healthy pulp. The decision to perform a pulpotomy depends on various factors, including the extent of pulp exposure, the tooth's developmental stage, and the presence of sufficient crown structure.

**Why the Correct Answer is Right**
Pulpotomy is generally contraindicated in cases of small pulp exposure since 1 hour, as the likelihood of successful pulp preservation is high with immediate access to the affected area. In such scenarios, a more conservative approach, such as a direct pulp cap or pulpal debridement, might be preferred to avoid unnecessary removal of healthy pulp tissue. The primary objective of pulpotomy is to manage pulp exposure in situations where the pulp is likely to be irreversibly damaged or infected.

**Why Each Wrong Option is Incorrect**
**Option B:** Pulpotomy can be indicated in permanent teeth with open apex, particularly when the exposure is large or the tooth is in a non-vital state. This scenario often necessitates a more extensive pulpal management approach.
**Option C:** Pulp exposure in a permanent tooth with a closed apex treated immediately after injury may indeed require a pulpotomy, as the goal is to preserve the remaining healthy pulp tissue. This scenario is often associated with a higher likelihood of successful pulp preservation.
**Option D:** Insufficient crown structure remaining is a relative contraindication for pulpotomy, as the remaining tooth structure may compromise the procedure's success or make it difficult to maintain the tooth's integrity post-procedure.

**Clinical Pearl / High-Yield Fact**
When dealing with pulp exposure, it's essential to assess the tooth's developmental stage, the extent of pulp exposure, and the presence of sufficient crown structure to determine the most appropriate pulpal management approach.

**✓ Correct Answer: A. Small pulp exposure since 1 hour**