When pouring suppository molds, why should you fill slightly over the edge of the mold?

Filling the suppository molds slightly over the edge is primarily done to account for the contraction of the material as it cools. As the molten suppository base cools, it will typically shrink slightly. By overfilling the mold, you ensure that once the suppository solidifies and contracts, it will have the desired shape and full volume without any gaps or voids that could occur due to this shrinkage. This practice helps maintain the quality and efficacy of the suppository, ensuring that it remains uniform and effective for its intended use.

The other options, while they may have some relevance to suppository preparation, do not adequately address the specific reason for slight overfilling. For example, overfilling isn't primarily about preventing leakage or improving shape, though these can be secondary benefits. The key focus remains on ensuring that the final product conforms to the expected dimensions and volume after cooling.