Scaling cannot expose dentin. These are ultrasonic instruments and not drills. So don't worry. Unless if there was no enamel already and was covered by deposits. It happens if your adjacent tooth is lost. Over time, the gum recedes and your root gets exposed. Or sometimes due to wrong brushing, you get toothbrush abrasion where enamel Is lost. Or sometimes there is no loss of enamel but After scaling, your teeth covered previously by deposits are now new to oral environment and are a little sensitive. They settle in 2 weeks. You will be given toothpaste and mouth wash to reduce sensitivity. Please revisit or call your dentist