What would be a potential disadvantage of using zinc phosphate in deep cavities?

The potential disadvantage of using zinc phosphate in deep cavities is primarily due to its irritant properties pertaining to the dental pulp. Zinc phosphate cement, while widely used for its strengths and durability, can lead to pulp irritation when placed in deep cavities. This occurs because the cement can produce exothermic reactions as it sets, potentially leading to discomfort for the patient and posing a risk to the pulp if there is insufficient insulation or if it is placed too deeply.

While the other options present characteristics of zinc phosphate, they do not highlight the critical concern regarding pulp health. For instance, excellent moisture tolerance (first choice) is actually advantageous in many clinical situations, and while it can be challenging to remove once set (third choice), that aspect does not directly impact the health of the tooth structure in the same manner. Similarly, although zinc phosphate does not form a bond with dentine (fourth choice), this is more relevant to its mechanical properties rather than a direct disadvantage affecting the pulp if used inappropriately in deep cavities. Therefore, the irritant nature of zinc phosphate to the dental pulp is the most significant concern when considering its use in deeper restorations.