How should the polishing cup be positioned against the tooth?

The rationale for positioning the polishing cup such that the rim hugs the tooth contour is essential for effective coronal polishing. This method ensures that the polishing cup can effectively adapt to the varying contours of the tooth surface, allowing for thorough plaque removal and smoothening of the enamel. When the rim of the cup follows the natural curve of the tooth, it maximizes contact with the surface, thereby improving the efficacy of the polishing procedure. Proper positioning also minimizes the risk of damaging the gums and adjacent structures, which is crucial for maintaining patient safety and comfort.

In contrast, positioning the cup at a 90-degree angle to the tooth could lead to ineffective polishing, as it would not adequately follow the tooth's structure, potentially leaving areas untreated. Similarly, maintaining a gap to avoid injury does not optimize the cleaning process and could result in missed plaque and debris, while being perpendicular to the gumline is aimed at a specific angulation that may not align with effective tooth contour polishing. Therefore, hugging the tooth contour is the best practice for ensuring a thorough, safe, and effective coronal polishing procedure.