Which component must be present during the setting of carboxylate cement?

The presence of water is crucial during the setting process of carboxylate cement because it acts as a solvent that activates the powder components, allowing for the chemical reaction necessary for the cement to set properly. Carboxylate cements rely on a specific formulation that includes water to mix the powdered components (which typically include zinc oxide and polyacrylic acid).

In the absence of water, the cement would not properly hydrate, resulting in an insufficient setting and potentially compromising the material's properties such as adhesion, strength, and longevity. Thus, water plays a vital role in achieving the desired physical and chemical characteristics of carboxylate cement, ensuring its effectiveness for dental applications.

Other components like chemically treated paper, bonding agents, or base materials do not fulfill the essential role that water does in the setting process of this specific type of cement.