Posterior Superior Alveolar Nerve Block

For reasons already described, the posterior superior alveolar nerve block is used to anesthetize the second primary molar in the primary and mixed dentitions and the permanent molars in the mixed and permanent dentitions. The mesiobuccal root of the first permanent molar is not consistently innervated by the posterior superior alveolar nerve. Complete anesthesia of the tooth may need to be supplemented by a local infiltration injection (Figure 13).

posterior superior alveolar nerve block 1
Figure 13. Posterior superior alveolar nerve block

The injection is indicated when a supraperiosteal injection is contraindicated (infection or acute inflammation) or when supraperiosteal injection is ineffective. It is contraindicated in patients with blood clotting problems (hemophiliacs) because of the increased risk of hemorrhage in which case a supraperiosteal or PDL injection is recommended.


  • A 25 or 27 gauge short needle is acceptable.
  • The area of insertion is the height of the mucobuccal fold above and distal to distobuccal root of the last molar present in the arch.
  • Retract the cheek so the tissue of the mucobuccal fold is taut.
  • Apply topical anesthetic.
  • Orient the needle bevel toward the bone.
  • Insert the needle into the height of the mucobuccal fold over the last molar.
  • Advance the needle slowly in an:
    • Upward (superiorly at a 45 degree angle to the occlusal plane).
    • Inward (medially toward the midline at a 45 degree angle to the occlusal plane).
    • Backward (posteriorly at a 45 degree angle to the long axis of the molar) to a depth of 10-14mm.
  • Aspirate.
  • Slowly deposit ½-1 cartridge of solution (aspirate several times while injecting).
  • The needle is withdrawn and recapped.
  • Wait 3-5 minutes before commencing with dental treatment. If anesthesia is incomplete, supplement with a supraperiosteal or PDL injection.