local anesthesia / orthodontic courses by indian dental academy

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.”


METHODS OF INDUCING LA:

• Mechanical Trauma• Low temperature• Anoxia• Chemical irritants• Neurolytic agents (alcohol & phenol)• Chemical agents(local anesthetics)


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.


• 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.


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.


ANOTOMY OF NERVE:

SENSORY NERVE

NERON OR NERVE CELL:

•Cell body

•Axon

•Dendrites


MOTOR NERVE


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.


•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.


CLASSIFICATION OF NERVE FIBRES:


NERVE TRUNK:


ELECTRO PHYSIOLOGY AND CHEMISTRY OF NERVE CONDUCTION:


• RESTING STATE: Nerve membrane is

Slightly permeable to sodium ionsFreely permeable to potassium ionsFreely permeable to chloride ions

• DEPOLARIZATION – 0.3msec

• REPOLARIZATION – 0.7msec


• 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.


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


• The nerve membrane.• Sodium receptor channel.


IMPULSE SPREAD:

Slow forward creeping conductionSaltatory conduction


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


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


• 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


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


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


BASED ON ACTION ON RECEPTOR SITE


THANK YOUTHE HUMAN TOUCH HEALS ALL THE PAINS; LIVE AND LET LIVE.


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local anesthesia / orthodontic courses by indian dental academy

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