Local Anesthesia for the Local Anesthesia for the Dental HygienistDental Hygienist

Dr. R. Cordell JohnsDr. R. Cordell Johns

Old Dominion UniversityOld Dominion University

Unit 1Unit 1

MECHANISM OF ACTIONMECHANISM OF ACTION

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MECHANISM OF ACTIONMECHANISM OF ACTION

There are board questions be sure to review your physiology– Parts of a nerve cellParts of a nerve cell– Myelinated vs. non-myelinated Myelinated vs. non-myelinated – Fiber diameter effects speed and type of painFiber diameter effects speed and type of pain– Nerve trunk vs. gangliaNerve trunk vs. ganglia– Resting nerve membraneResting nerve membrane– Permeability of cell membrane with sodiumPermeability of cell membrane with sodium– Minimal threshold stimulusMinimal threshold stimulus– ExcitationExcitation– Action potentialAction potential– etcetc

CHEMICAL STRUCTURECHEMICAL STRUCTURE

Two basic classes of local anesthetics exist, the Two basic classes of local anesthetics exist, the amino amino amidesamides and the and the amino estersamino esters. Amino amides have an . Amino amides have an amide link between the intermediate chain and the amide link between the intermediate chain and the aromatic end, whereas amino esters have an ester link aromatic end, whereas amino esters have an ester link between the intermediate chain and the aromatic end. between the intermediate chain and the aromatic end. Some common amides are lSome common amides are liidocadocaiine, mepne, mepiivacavacaiine, ne, prpriilocalocaiine, bupne, bupiivacavacaiine, etne, etiidocadocaiine, and dne, and diibucabucaiine ne (An easy way to remember which drug belongs in which (An easy way to remember which drug belongs in which category is that all of the amcategory is that all of the amiino amno amiides contain the letter des contain the letter "i" twice, as does the term "amino amides.) "i" twice, as does the term "amino amides.) Amino esters are much more likely than amino amides to Amino esters are much more likely than amino amides to cause true allergic reactions. cause true allergic reactions.

PHYSIOLOGIC ACTIVITYPHYSIOLOGIC ACTIVITY

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

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

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