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The posterior superior alveolar (PSA) nerve block is a commonly used dental nerve block.  Although it is a highly successful technique, several issues may arise.  These include the extent of the anesthesia produced and the potential for hematoma formation.  When used to achieve pulpal anesthesia, the PSA nerve block is effective for the maxillary third, second, and first molars.  However, the mesiobuccal root of the maxillary first molar is not consistently innervated by the PSA nerve.  Therefore, a second injection, usually supraperiosteal, is indicated after the PSA nerve block when effective anesthesia of the first molar does not develop.

As a means of decreasing the risk of hematoma formation after a PSA nerve block, use of a “short” dental needle is recommended for all but the largest of patients.  The average depth of soft tissue penetration from the insertion site to the area of the PSA nerves is 16mm, the short dental needle (about 20mm) can be successfully and safely used.  The PSA injection is normally atraumatic because of the large tissue space available to accommodate the anesthetic solution and that bone is not touched.  Aspiration needs to be performed several times before and while slowly depositing the solution to avoid inadvertent intravascular injection.  The nerves that are anesthetized are the posterior superior alveolar and branches.  The areas that are anesthetized are the pulps of the maxillary third, second, and first molars (entire tooth= 72%; mesiobuccal root of the maxillary first molar not anesthetized= 28%) and the buccal periodontium and bone overlying these teeth.

Proper technique:

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  1. 25 or 27-gauge short needle is recommended 

  2. Area of insertion: height of mucobuccal fold above the maxillary second molar

  3. Target area: PSA nerve- posterior, superior, and medial to posterior border of the maxilla

  4. Landmarks

    • Mucobuccal fold​

    • Maxillary tuberosity

    • Zygomatic process of the maxilla

  5. Orientation of the bevel: toward bone during injection (if the bone is accidentally touched, the sensation is less unpleasant) 

Procedures:

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  1. Correct patient & clinician positioning

    • Right PSA, right-handed clinician sit at 8:00 facing patient / left-handed clinician sit at 4:00 facing patient

    • Left PSA, right-handed clinician sit at 10:00 facing patient / left-handed clinician sit at 2:00 facing patient​

  2. Prepare tissue at the injection site

    • Dry with gauze or blow air with air/water syringe​

    • Apply topical anesthetic for minimum of 1 minute

  3. Orient needle so bevel faces bone

  4. Using mirror or index finger, partially open the patient's mouth, pulling the mandible to the side of the injection & retract the patient's cheek for visibility

  5. Pull tissue at the injection site taut

  6. Insert needle into height of mucobuccal fold over second molar

  7. Advance needle slowly in upward, inward, backward direction in one movement

    • Upward 45-degree angle to occlusal plane​

    • Inward medially toward midline at 45-degree angle to occlusal plane

    • Backward posteriorly at 45-degree angle to long axis of second molar

  8. Advance needle further through soft tissue

    • There should be no resistance and therefore no discomfort to the patient​

    • If resistance (bone) is felt, angle of the needle in toward the midline is too great

      • Withdraw needle slightly (but do not remove entirely from the tissue) and bring syringe barrel closer to occlusal plane​

      • Re-advance the needle

  9. Further advance needle to desire depth (Goal: deposit local anesthetic close to PSA nerves, located posterosuperior and medial to maxillary tuberosity)

    • In adults of normal size, penetration to the depth of 16mm will be about 1/2 to 3/4 of a short needle​

    • For smaller adults and children, penetration of depth will be about 10-14mm

  10. Aspirate in at least two planes

    • Rotate syringe barrel (needle bevel) 1/4 turn and re-aspirate

  11. If both aspirations are negative:

    • Slowly, over 30-60 seconds, deposit 0.9-1.7mL of anesthetic solution (1/2 to one whole cartridge)​

    • Aspirate several additional times (in one plane) during administration

  12. Slowly withdraw needle and safely recap

  13. Wait 3-5 minutes before starting dental procedure​

P O S T E R I O R   S U P E R I O R   A L V E O L A R  ( P S A )

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