1. B. Inhibition of inward migration of Na+ can result in complete block of conduction and therefore abolition of pain transmission. This block of conduction is not a feature of alteration of any of the other ions.
2. C. A block at this level will affect only the sympathetic nerves, not parasympathetic activity.
Application to the nerve cell ending would result only in topical anesthesia, and blockade of the neuromuscular junction could produce respiratory failure. Administration to the spinal cord is too general an answer. The injection must be near a nerve or nerve plexus proximal to the surgical site.
3. D. Epinephrine is by far the most commonly employed vasoconstrictor. Phenylephrine is occasionally used with procaine for dental procedures. Levonordefrin is also used rarely in dental procedures. Dopamine has no vasoconstrictor activity. Cocaine is itself a local anesthetic with some vasoconstrictor properties. However, cocaine, because of its abuse potential and toxicity, is seldom used. Its only use is topical.
4. C. Lidocaine is well tolerated and has a rapid onset and an adequate duration of action for most procedures. Bupivacaine has a particularly long duration of action. This may be advantageous in certain procedures, but not in most. Procaine has a relatively slow onset of action as well as a short duration of action. Etidocaine shows a preference for motor rather than sensory block; this limits its effectiveness in obstetrics.
5. B. Allergic reactions occur only to the ester type of local anesthetics. This is because the metabolism of all ester-linked local anesthetics leads to the formation of PABA, which is known to be allergenic to some individuals. Both cocaine and procaine are esters. However, cocaine is not employed in dental procedures. Therefore, the best choice is procaine.
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