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: 

• • Low potency, short duration: Procaine, Chloroprocaine 
  • Intermediate potency & duration: Lignocaine, Prilocaine 
  • High potency, long duration: Tetracaine, Bupivacaine, Ropivacaine, dibucaine 

Surface anesthetics:  

• • 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.