**Core Concept**
Calcium hydroxide apexification is a procedure used to induce the formation of a hard tissue barrier in the root canal of a non-vital tooth, with the goal of creating a solid foundation for future restoration. However, it has a significant drawback compared to other materials like Mineral Trioxide Aggregate (MTA).

**Why the Correct Answer is Right**
The main drawback of calcium hydroxide apexification is that it can lead to a reduction in the physical strength of the dentin. This is because calcium hydroxide can cause the dentin to become more brittle and prone to fracture. This is a result of the alkaline nature of calcium hydroxide, which can disrupt the normal mineralization process of the dentin. In contrast, MTA does not have this effect and can actually promote the formation of a stronger dentin.

**Why Each Wrong Option is Incorrect**
**Option A:** While calcium hydroxide apexification may require more treatment time compared to MTA, this is not the main drawback of the procedure.

**Option B:** Incomplete apical barrier is actually a potential complication of MTA, not calcium hydroxide apexification.

**Option C:** Incomplete coronal barrier is not a characteristic of calcium hydroxide apexification.

**Clinical Pearl / High-Yield Fact**
It's essential to note that MTA has become a popular alternative to calcium hydroxide for apexification due to its ability to promote the formation of a stronger dentin and its biocompatibility.

**Correct Answer Line**
✓ Correct Answer: D. Reduced physical strength of dentin