Which instrument is NOT commonly used in coronal polishing?

The reason the dental scaler is not commonly used in coronal polishing is that its primary purpose is to remove calculus and plaque from the teeth surfaces, especially in subgingival areas. Coronal polishing, on the other hand, focuses on the smoothening and polishing of the tooth surfaces above the gum line after the majority of calculus and plaque has been removed. The instruments typically used in coronal polishing, such as rubber cups, handpieces, and prophy angles, are designed specifically to apply polishing agents and perform the polishing action without the need for vigorous scraping that a scaler provides. This distinguishes the scaler from the other tools, as it is not intended for the polishing process.