Dental Anasthesia: Posterior Superior Alveolar Nerve Block

The posterior superior alveolar (PSA) nerve is a branch of the maxillary division of the trigeminal nerve. It parts from the main trunk in the pterygopalatine fossa, passes inferiorly along the posterior wall of the maxilla, and enters the bone about 1 cm superior and posterior to the third molar tooth. The PSA nerve supplies the buccal gingivae, periodontium, and alveolus associated with the upper molar teeth. It provides innervation to the pulps of all the upper molar teeth with the possible exception of the mesiobuccal pulp of the first molar, which is supplied by the middle superior alveolar (MSA) nerve in approximately 50% of individuals.

Branches of the maxillary nerve

Injection for the PSA nerve block is performed in a highly vascular area, and formation of a hematoma is a recognized side effect, especially when the needle is advanced more than 15 mm. Immediate hemorrhage is controlled by pressure, but postinjection trismus may last for weeks. Antibiotic therapy should be prescribed if the hematoma is large. 

Technique: Posterior Superior Alveolar Nerve Block

1. Use a short or long needle, no less than 27 gauge.
2. Instruct the patient to open the mouth only slightly, and move the lower jaw over to side of injection.
3. Retract the lip and cheek with the thumb or first finger of left hand.
4. Insert the needle at the height of the maxillary buccal sulcus at distal aspect of second
   molar.
5. Advance the needle posteriorly, superiorly, and medially (at 45-degree angle to each plane) to a depth 15 mm.
6. Perform aspiration.
7. Inject 1.5 ml of solution slowly.
8. If bone is contacted before a depth of 1.5 ml achieved, alter the angle of approach by
   withdrawing slightly and positioning the syringe medially.

Normal orientation of needle for posterior superior alveolar nerve block. From Jastak JT, Yagiela JA, Donaldson D: Local anesthesia of the oral cavity, Philadelphia, 1995, Saunders.

Palpation of zygomatic process in posterior superior alveolar nerve block. Point of needle insertion lies within mucosal pocket posterior to palpating finger.

 

Source : Dionne RA. 2002. Management of Pain and Anxiety in the Dental Office. W.B. Saunders. Philadelphia