Local Anesthesia

Techniques of administrating LA

Nerve block in maxilla and mandible

1. Inferior alveolar nerve block: Mandibular posterior teeth


  • Between pterygomandibular raphe and coronoid notch (feel with thumb)
  • Insert from contralateral side, 1cm above occlusal plane
  • Contact bone, withdraw slightly and give LA

2. Mental nerve block: Mandibular anterior teeth


  • Between 1st and 2nd premolar

3. Anterior, middle, posterior superior alveolar nerve block: Maxillary teeth


  • At junction of mucobuccal fold

4. Greater palatine nerve block: Maxillary posterior teeth


  • In front of 1st molar at junction of vertical and horizontal hard palate
  • Withdraw after contacting bone

5. Nasopalatine block: Maxillary anterior teeth


  • Insert in incisive papilla

6. Infiltration: Picture

  • At mucogingival level

7. Buccal Infiltration: Picture

  • Parallel to occlusal plane
  • Distal to 2nd molar

8. Intrapapillary: Picture

9. Intraligamentary (supplemental): Picture

10. Intrapulpal (supplemental): Picture

11. Intraosseous (supplemental): Picture

12. Gow-Gates technique: Video

13. Vazirani-Akinosi technique: Video

Calculating LA dosage

Use the app Dental Drugs (App store, Play store) to quickly refer for prescribing medications, calculating maximum anesthetic dosages or recalling common treatment protocols in practice

Desirable properties of LA

  • Non irritant
  • Reversible effect
  • Long enough duration for procedure
  • Low toxicity
  • Fast onset of action
  • Potent

Mechanism of action of LA

LA = Tertiary amine base [B] + Water soluble hydrochloride [B.HCl]

  • Injected into tissues
  • Base liberated in alkaline pH of tissues

B.HCl + HCO3 = B + H2CO3 + Cl

  • Base diffuses through nerve sheath into axoplasm and partially ionizes

B + H+ = BH+

  • Ionized form of BH+ enters sodium channel from interior of nerve and combines with a specific receptor in the channel to block sodium influx into the nerve and therefore prevent action potential initiation

BH+ + Receptor = Block sodium influx

Mechanism of action of local anesthesia

Structure of LA

Aromatic group – Intermediate bond (amide/esters)- Tertiary amine

Structure of local anesthesia


  • Lignocaine
  • Prilocaine – metabolism in liver and lungs. Primary product of metabolism is ortho-Toluidine – associated with methemoglobinemia
  • Mepivacaine
  • Bupivacaine


  • Cocaine – Only cocaine causes vasoconstriction
  • Procaine – used in case of drug induced arteriospasm. Procaine broken down to PABA – associated with allergic reaction.
  • Amethocaine
  • Chloroprocaine

Factors affecting LA action

1. pKa (physiologic pH): ↓ pKa leads to faster onset of action as ↑ molecules diffuse through the nerve sheath

2. Lipid solubility: ↑ lipid solubility leads to ↑ potency and therefore block conductions at low concentration

3. Protein binding: ↑ protein binding leads to ↑ duration of action as it firmly attaches to proteins at receptor sites

4. Non nervous tissue diffusibility: ↑ diffusibility leads to slower time of onset

5. Vasodilator activity: ↑ vasodilator activity leads to ↑ blood flow to region and therefore ↑ removal of anesthetic molecules and so ↓ potency and duration

6. Tachyphylaxis: ↑ tolerance when injected repeatedly. Mop up of HCO3, alkaline pH of tissues not sustained

7. Infection: Acidic pH therefore prevent ready formation of free base

Contents of LA

Local anesthetic agentLignocaine HCLBlock nerve conduction
VasoconstrictorEpinephrine– Increase duration by decreasing absorption of LA
– Control bleeding
– Prevent systemic toxicity
Reducing agentSodium metabisulphiteAntioxidant
PreservativeMethylparabenBacteriostatic and antioxidant
Isotonic solutionSodium chloride or Ringer’s solution
Diluting AgentDistilled water
To adjust pHSodium hydroxide
Nitrogen bubble1-2mm in diameterTo prevent oxygen from being trapped in the cartridge and potentially destroying the Vasopressor or vasoconstrictor
Contents and their function in LA

Pharmacokinetics of LA

1. Uptake:

  • LA causes vasodilation and increased uptake into circulation
  • Esters cause more vasodilation
  • Procaine used in case of drug induced arteriospasm
  • Only cocaine causes vasoconstriction

2. IV of LA:

  • May cause increased toxicity/adverse effect
  • Used to treat ventricular dysrhythmias
  • Local and systemic toxicity effects:
Local and systemic complications of LA
LA systemic toxicity

3. Toxicity: Balance between absorption into circulation and rate of elimination from circulation

4. LA crosses blood brain barrier (BBB) and placental barrier

5. Esters metabolized by pseudocholinesterase

  • Atypical pseudocholinesterase – cannot metabolize esters – increase toxicity
  • Pseudocholinesterase also metabolize succinylcholine – therefore atypical pseudocholinesterase associated with difficult general anesthesia (sleep apnea). Succinylcholine used to cause short term paralysis as part of GA
  • Procaine broken down to PABA – associated with allergic reaction

6. Amides metabolized in liver

  • Liver perfusion and function important to determine rate of amide elimination
  • Liver cirrhosis, hypotension and congestive heart failure – reduce rate of elimination and therefore increase toxicity
  • Prilocaine metabolism in liver and lungs. Primary product of metabolism is ortho-Toluidine – associated with methemoglobinemia

Contraindications of LA

AbsoluteLA allergyEg. to estersGive amide
AbsoluteSulfur allergyAvoid articaineGive non sulfur containing LA
AbsoluteBisulfite allergyAvoid LA with vasoconstrictorGive LA with no vasoconstrictor
RelativeAtypical pseudocholinesteraseAvoid estersGive amide
RelativeMethemoglobinemia Avoid articaine and prilocaineGive other LA
ASA (III-IV)Significant liver dysfunctionAvoid amidesGive esters judicially
ASA (III-IV)Significant renal damageAvoid amides and estersGive LA judicially
ASA (III-IV)Significant CVDAvoid high concentration of vasoconstrictorGive LA with epinephrine concentration 1:100,000 or 1:200,000
ASA (III-IV)Clinical hyperthyroidismAvoid high concentration of vasoconstrictorGive LA with epinephrine concentration 1:100,000 or 1:200,000
Contraindications of LA

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