What characteristic of zinc phosphate makes it less favorable for deep restorations?

Zinc phosphate's high solubility is a significant characteristic that makes it less favorable for deep restorations. In the context of dental materials, solubility refers to the ability of a substance to dissolve in a solvent—in this case, saliva or other oral fluids. When a material is highly soluble, it can gradually wash away when exposed to these fluids, leading to compromised restoration integrity over time.

In deep restorations, it is crucial for the material to provide a durable seal and maintain its structural integrity long-term, especially in environments that undergo fluctuations in moisture and pH levels. Therefore, materials used for deep restorations must exhibit low solubility to ensure they can withstand such conditions without degrading.

Other options, while they may seem relevant, do not capture the primary concern in the context of deep restorations. For instance, low strength would affect the material’s ability to endure occlusal forces but not directly speak to its suitability for long-term use in deep applications. High acidity can lead to pulp irritation but does not inherently dictate the longevity of the material's structural integrity. Poor adhesion, though an important factor, is less directly related to the issues posed by solvent effects in deep cavity restorations compared to solubility. Thus,