Final answer:
Topical anesthetics in dentistry numb the tissue surface before an injection by acting as sodium channel blockers, preventing nerve impulses and pain sensation. Examples include lidocaine and novocaine.
Step-by-step explanation:
Topical anesthetics are mainly used in dentistry to numb the tissue surface before an injection. These anesthetics, such as lidocaine and novocaine, act as sodium channel blockers, preventing sodium ions from moving across the neuronal membrane. By disrupting ion movement, nerve impulses are not transmitted, resulting in a temporary loss of sensation or pain. For example, when a dentist injects an anesthetic into the gum before a tooth extraction, the patient will not sense pain until the anesthetic wears off.