For reasons already described, the posterior superior alveolar nerve block is used to anaesthetized 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.
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.