local anesthesia / orthodontic courses by indian dental academy
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LOCAL ANESTHESIA INDIAN DENTAL ACADEMY
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DEFINITION
‘ ‘Local anesthesia has been defined as a loss of sensation in a circumscribed area of the body caused by a depression of excitation in nerve endings or an inhibition of conduction process in peripheral nerves.”
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METHODS OF INDUCING LA:
• Mechanical Trauma• Low temperature• Anoxia• Chemical irritants• Neurolytic agents (alcohol & phenol)• Chemical agents(local anesthetics)
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IDEAL PROPERTIES OF LA
• It should not be irritating to the tissues to which it is applied.
• It should not cause any permanent alteration in the nerve structure.
• Its systemic toxicity should be low.
• It must be effective regardless of whether it is injected to the tissues or applied locally to the mucous membranes.
• Time of onset of anesthesia should be as short as possible.
• Duration of action must be long enough to permit completion of the procedure yet not so long as to require an extended recovery.
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• It should have potency sufficient to give complete anesthesia without the use of harmful concentrated solutions.
• It should be relatively free from producing allergic reactions.
• It should be stable in solution and readily undergo biotransformation.
• It should either be sterile or capable of being sterilized by heat without deterioration.
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CONCEPT OF ACTION OF LOCAL ANESTHETICS:
• Local anesthetics prevent both the generation and conduction of nerve impulse.
• They set up a chemical road block between the source of impulse and the brain.
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ANOTOMY OF NERVE:
SENSORY NERVE
NERON OR NERVE CELL:
•Cell body
•Axon
•Dendrites
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MOTOR NERVE
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NERVE MEMBRANE: Sensory nerve excitability and conduction are attributable to changes developing with in the nerve membrane.
Proteins are classified as transport proteins and receptor proteins.
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•MYELINATED NERVE
•UNMYELINATED NERVE MYELIN SHEATH:
•75% lipids•20% proteins•5% carbohydrates
Node of Ranvier – are constrictions located at regular interval- 0.5 to 3mm.
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CLASSIFICATION OF NERVE FIBRES:
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NERVE TRUNK:
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ELECTRO PHYSIOLOGY AND CHEMISTRY OF NERVE CONDUCTION:
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• RESTING STATE: Nerve membrane is
Slightly permeable to sodium ionsFreely permeable to potassium ionsFreely permeable to chloride ions
• DEPOLARIZATION – 0.3msec
• REPOLARIZATION – 0.7msec
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• The firing threshold is actually the magnitude of decrease in negative transmembrane potential that is necessary to initiate action potential.
• A decrease in negative transmembrane potential of 15 mV is necessary to reach the firing threshold.
• Exposure of nerve to local anesthetic raises its firing threshold.
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MEMBRANE CHANNELS:
• Lipoglycoprotein aqueous pores firmly situated in the membrane.
• Internal diameter – 0.3nm to 0.5nm.• Hydrated sodium ions have radius of 3.4 AO
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• The nerve membrane.• Sodium receptor channel.
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IMPULSE SPREAD:
Slow forward creeping conductionSaltatory conduction
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MODE OF ACTION OF LOCAL ANESTHETICS:
• Alter the basic resting potential potential of nerve membrane.
• Alter the threshold potential
• Decreasing the rate of depolarization
• Increasing the rate of repolarization
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CLASSIFICATION BASED ON CHEMICAL STRUCTURE
• ESTER GROUP A) Benzoic acid esters
1) Cocaine 2) Benzocaine B) Para amino benzoic acid esters 1) Procaine 2) Tetracaine 3) Propoxycaine 4) 2-Chloroprocaine
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• NON ESTER GROUP A) Anilide 1) Bupivacaine
2) Etidocaine 3) Lidocaine 4) Mepivacaine 5) Prilocaine 6) Articaine 7) Ropivacaine 8) Dibucaine B) Quinoline 1) Centbucridine
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BASED ON DURATIOIN OF ACTION A) Ultra short acting – Less than 30 mins. 1) Procaine 2) 2- Chloroprocaine with vasoconstrictor 3) 2% Lidocaine 4) 4% Prilocaine
B) Short acting – 45-75 mins 1) 2% Lidocaine with 1:1,00,000 Epinephrine 2) 2% Mepivacaine with 1:20,000 Levonordephrin 3) 4% Prilocaine 4) 2% Procaine with vasoconstrictor
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C) Medium acting – 90-150 mins 1) 4% Prilocaine with 1:2,00,000 Epinephrine 2) 2% Lidocaine with vasoconstrictor
D) Long acting – 180 mins or longer 1) 0.5% Bupivacaine with 1:2,00,000 Epinephrine 2) 0.5% or 1.5% Etidocaine with 1:2,00,000
Epinephrine
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BASED ON ACTION ON RECEPTOR SITE
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THANK YOUTHE HUMAN TOUCH HEALS ALL THE PAINS; LIVE AND LET LIVE.
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