Local Anesthesia Mechanisms and Methods

Local Anesthesia (L.A.)

• Used for pain control
• Mechanism of Action: binds to specific receptor on the sodium channel, blocking sensation transmission

Causes of Failure of L.A.

• Inflamed tissue with acidic pH decreases dissociation of local anesthesia
• Nerves in inflamed tissue are sensitized with decreased excitability threshold
• Patient in pain have lower pain threshold

L.A. Armamentarium

• Needle (short – long)
• Carpule (ester – amide)
• Syringe

Classification of L.A. Types

Ester Group

• Cocaine
• Tetracaine
• Procaine

Amide Group

• 2% Lidocaine
• 2 or 3% Mepivacaine
• 4% Prilocaine
• 4% Articaine
• 0.5% Bupivacaine

L.A. with or without Vasoconstrictor

• For pain control and haemostasis
• Concentrations: 1:50,000, 1:80,000, 1:100,000, 1:200,000
• Vasoconstrictor Importance:
  • Decrease blood flow and bleeding
  • Decrease L.A. toxicity
  • Increase duration of L.A.

Classification of Vasoconstrictors

Catecholamines

• Epinephrine
• Norepinephrine

Noncatecholamines

• Amphatemine
• Methamphetamine

Max L.A. Dose (Rule 25)

• Safe to use 1 cartridge for every 25 pounds of patient weight
• Max dose for cardiac patient: 0.04 mg of epinephrine (2-3 cartridges)

Atraumatic Injection

• Technical aspect:
  • Use topical anesthesia
  • Stretch the tissue
  • Use sharp needle
  • Use warm anesthesia
  • Inject few drops slowly
• Psychological aspect (4 Cs with the patient):
  • Control
  • Concern
  • Confidence
  • Communicate

Testing Effectivity of L.A.

• Numbness
• Probe pricking Soft tissue
• Pulp testing
• Innervation of teeth: Trigeminal nerve

Local Anaesthetic Techniques

Infiltration

• Buccal Infiltration:
  • Indication: All upper teeth, Lower anterior teeth
• Palatal infiltration:
  • Indication: During surgical procedure, to control pain in divergent palatal roots

Nerve Block

• Mandibular teeth nerve block:
  • Inferior alveolar nerve block:
    • Indication: Multiple mandibular posterior teeth
  • The Gow-Gates technique:
    • Indication: Inferior alveolar nerve block is unsuccessful
  • Vazirani-akinosi closed mouth technique:
    • Indication: Limited mouth opening
  • Mental nerve block:
    • Indication: Lower premolars teeth
• Maxillary teeth nerve block:
  • Posterior superior alveolar nerve block:
    • Indication: Upper molar teeth
  • Middle superior alveolar nerve block:
    • Indication: Upper Premolars
  • Anterior superior alveolar nerve block:
    • Indication: Anterior maxillary teeth
  • Greater palatine nerve block:
    • Indication: For surgical procedure
  • Nasopalatine nerve block:
    • Indication: Surgical procedure

Supplemental Anesthesia

• Periodontal ligament technique:
  • Indication: After failure of standard injection and no pulp exposure
• Intraosseous injection technique:
  • Indication: Pain control for single tooth
  • As stabident, X-Tip
• Intrapulpal injection technique:
  • Indication: Pulp extirpation

Complications of L.A.

• Systemic action of L.A.:
  • Stimulatory phase (Convulsions – tachycardia)
  • Depressive phase
  • Circulatory collapse
  • Vasoconstriction
  • CNS depression
  • Respiratory arrest
• Overdose Metheamoglubinemia
• Allergy
• Local tissue toxicity
• Nerve parasthesia

Recent Trends in Local Anesthesia

• Delivering of LA without need of needle injection through different forms as discs, tablets, patches, hydrogels, sprays or microspheres
• Nanotechnology in anesthesia: Nanobots
• L.A. reversal:
  • Phentolamine mesylate (0.4 mg in 1.7 ml cartridge, oraverse)
  • Decreases effect of vasoconstrictor leading to rapid absorption of L.A.

Isolation in Endodontics

• The use of rubber dam in root canal treatment is mandatory
• Advantages of Rubber Dam:
  • Clean and dry field
  • Improves visibility
  • Retracts and protects soft tissues
  • Less need for frequent rinsing
  • Avoids aspiration