Which instrument is commonly used for coronal polishing?

The instrument commonly used for coronal polishing is a rubber cup or prophy cup attached to a low-speed handpiece. This choice is correct because the prophy cup is specifically designed for polishing teeth. It is made from a soft rubber material that can effectively hold and distribute polishing paste, allowing for the removal of plaque and stains from the tooth surface without damaging the enamel.

A low-speed handpiece is ideal for this procedure as it provides better control and precision, ensuring that the polishing is performed safely and effectively. The use of a rubber cup allows the dental professional to access all parts of the tooth, including the surfaces that may be difficult to reach with other instruments.

In contrast, a high-speed handpiece is typically used for cutting and shaping teeth rather than polishing, a periodontal scaler is designed for removing calculus and plaque from below the gum line, and a dental mirror is primarily for visualization during procedures but does not serve a polishing function. Therefore, the rubber cup on a low-speed handpiece is the most appropriate choice for coronal polishing.