Local anesthetics are drugs which on topical application/local injection cause reversible loss of sensory perception (Pain) in a restricted area of the body.
Classification of Local anesthesia
Injectable:
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- Low potency, short duration: Procaine, Chloroprocaine
- Intermediate potency & duration: Lignocaine, Prilocaine
- High potency, long duration: Tetracaine, Bupivacaine, Ropivacaine, dibucaine
Surface anesthetics:
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- Soluble: Cocaine, Lignocaine, Tetracaine, Benoxinate
- Insoluble: Benzocaine, Butylaminobenzoate, Oxethazaine
Ester linked LA: Cocaine, procaine, chloroprocaine, tetracaine, benzocaine
Amide linked LA: Lignocaine, Bupivacaine, dibucaine, prilocaine, ropivacaine
Mechanism of action
Block nerve conduction by reducing the influx of sodium ions into the nerve cytoplasm. Acts by blocking voltage dependent Na+ channels. Block sensory nerve endings, nerve trunks, neuromuscular junction, ganglionic synapse & receptors smaller, myelinated fibers are blocked first order of sensory function block: pain → cold → warmth → touch → deep pressure → motor. The recovery in reverse order.
Actions
- Effect of Fiber Diameter: Preferentially block small fibers
- Effect of Firing Frequency: Blockade is more marked at higher frequencies of depolarization
- Effect of Fiber Position in the Nerve Bundle: In large nerve trunks, fibers located circumferentially are the first to be exposed to the local anesthetic
Procedures requiring local anesthesia in dental clinic
- Root canal treatment
- Removal of teeth
- Deep dental fillings
- Periodontal gum surgeries
- Cosmetic dental procedures
- Crown and bridge work
- Implants
- Oral surgical procedure
Nerve blocks
- Posterior superior alveolar nerve block: anesthetize maxillary first, second and third molars
- Middle superior alveolar nerve block: Pre-molars
- Anterior superior alveolar nerve block: Anterior teeth on one quadrant
- Greater palatine nerve block: palatal soft tissues & osseous tissue treatment distal to the canine in one quadrant
- Nasopalatine nerve block: palatal soft tissues & osseous tissue treatment from canine to canine
Note on Conduction block
LA injected around nerve trunks so that area distal to injection is anesthetized & paralyzed.
Field block: Inject LA SC blocking all nerves coming to a particular field e.g. herniorrhaphy, appendicectomy, scalp stitching, operations on forearm & legs
Larger area can be anesthetized
Nerve block: LA injected around anatomically localized nerve trunks or plexuses
Larger area is anesthetized “flooding technique” is used; larger volumes required
Longer lasting
Adverse effects
- CNS effects: light headedness, dizziness, auditory & visual disturbances, mental confusion, disorientation, shivering, twitching, tremors, convulsions & respiratory arrest
- CVS effects: Bradycardia, hypotension, cardiac arrhythmias & vascular collapse
- Injection: painful; local tissue necrosis
- Hypersensitivity reactions: rashes, angioedema, dermatitis, asthma & anaphylaxis
Article by Dr. Siri P.B.
