How should the polishing paste be applied?

The polishing paste should be placed in the rubber cup before making contact with the tooth surface to ensure effective and efficient application during the polishing process. By adding the paste to the rubber cup first, it allows for a consistent and controlled distribution of the paste across the surface of the tooth as the dental professional begins polishing. This technique facilitates the removal of plaque and surface stains while minimizing the risk of any undue abrasion to the enamel.

In contrast, applying the paste after polishing is complete, as suggested in another choice, would not serve any purpose, as polishing requires the paste to enhance the effectiveness of the procedure while it's ongoing. Not using the paste at the beginning can compromise the polishing outcomes, as it is an essential component for achieving the desired smoothness and shine on the tooth surface. Mixing the paste with water is unnecessary and could dilute its effectiveness, leading to unsatisfactory results. Overall, the correct application technique ensures both safety and effectiveness in coronal polishing procedures.