Local Anesthesia for the Dental Hygienist Dr. R. Cordell Johns Old Dominion University Unit 1

MECHANISM OF ACTION Insert fig 1-14

MECHANISM OF ACTION There are board questions be sure to review your physiology –Parts of a nerve cell –Myelinated vs. non-myelinated –Fiber diameter effects speed and type of pain –Nerve trunk vs. ganglia –Resting nerve membrane –Permeability of cell membrane with sodium –Minimal threshold stimulus –Excitation –Action potential –etc

CHEMICAL STRUCTURE Two basic classes of local anesthetics exist, the amino amides and the amino esters. Amino amides have an amide link between the intermediate chain and the aromatic end, whereas amino esters have an ester link between the intermediate chain and the aromatic end. Some common amides are lidocaine, mepivacaine, prilocaine, bupivacaine, etidocaine, and dibucaine (An easy way to remember which drug belongs in which category is that all of the amino amides contain the letter "i" twice, as does the term "amino amides.) Amino esters are much more likely than amino amides to cause true allergic reactions.

PHYSIOLOGIC ACTIVITY A decrease in pH shifts equilibrium toward the ionized form, delaying onset of action. This explains why local anesthetics are slower in onset of action and less effective in the presence of inflammation, which creates a more acidic environment with lower pH. Local anesthetics, with the exception of cocaine, are vasodilators. This occurs via direct relaxation of peripheral arteriolar smooth muscle fibers. Greater vasodilator activity of a local anesthetic leads to faster absorption and, thus, shorter duration of action. To counteract this vasodilatation, epinephrine often is included in local anesthetic solutions

What should I do if I am exposed to the blood of a patient? ????