Final answer:
Topical anesthetics are effective at a shallow depth, typically less than 2-3 mm, as they are designed to numb the surface for minor procedures and are not intended to penetrate deeply into tissues.
Step-by-step explanation:
The question is asking about the effective depth that a topical anesthetic can penetrate into tissues to provide numbness or pain relief. Topical anesthetics are applied to the surface of the skin or mucous membranes and are not intended to penetrate deeply into tissues. They are primarily used to numb the surface for minor surgical procedures, wound care, or other surface-level interventions.
The depths mentioned in the question options (i.e., 2-3 mm, 3-4 mm, 4-5 mm, and 6 mm and more) are generally not achievable by topical anesthetics alone. Most topical anesthetics are effective at much shallower depths, typically less than 2-3 mm.
Therefore, the correct answer to the question 'How deep can topical anesthetic be effective on tissues?' is:
a. 2-3 mm
This depth is appropriate for achieving numbness in the top layer of skin, as topical anesthetics are not designed to permeate deep into tissues.