Which of the following should not be polished due to potential increased sensitivity?

Exposed dentin should not be polished due to the risk of increased sensitivity. Dentin is the layer of tooth structure beneath the enamel, and when it is exposed, it is much more vulnerable to external stimuli, such as temperature changes and pressure. Polishing this area can further irritate the nerve endings that are present within the dental tubules, leading to heightened sensitivity or discomfort for the patient.

In contrast, polishing enamel surfaces, healthy gums, and polished composites poses minimal risk of increasing sensitivity. Enamel is the hard outer layer of the tooth and is designed to withstand wear, while healthy gums should not be subjected to polishing as they are soft tissue. Polished composites can safely be treated as they are designed for aesthetic and functional longevity without affecting underlying sensitivity. Thus, the correct focus on exposed dentin highlights the careful consideration needed when performing coronal polishing procedures.