Which instrument is NOT commonly used in coronal polishing?

Hand scalers are primarily used for the removal of calculus and plaque from the teeth, rather than for coronal polishing. Coronal polishing focuses on the polishing and smoothing of the tooth surfaces after plaque and stains have been removed, which is best achieved using instruments like polishing cups and brushes that are designed for this specific purpose.

Polishing cups are specifically designed to hold polishing paste and fit onto a handpiece, making them ideal for achieving a smooth, polished finish on the enamel surface. Similarly, electric handpieces are commonly used in coronal polishing for their efficiency and ease of use, allowing the dental professional to perform polishing quickly and effectively.

Air water syringes, while not directly involved in the polishing itself, are often used to rinse and dry the teeth during the procedure to maintain visibility and ensure optimal results. Thus, hand scalers do not fit into the context of instruments used specifically for coronal polishing, making them the correct choice regarding which instrument is not commonly used in that process.