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Anterior Middle Superior Alveolar (AMSA) Injection Technique

 

The AMSA is an exciting addition to local anesthesia techniques.  It will allow the operator to achieve pulpal anesthesia from the maxillary central incisor through the second premolar including the palatal tissue and mucoperiosteum from a single needle penetration. The recommended dosage is from 3/4 to 1 cartridge of anesthetic and the expected duration of anesthesia is approximately 60 minutes.  A bilateral AMSA anesthetizes 10 maxillary teeth extending from the second premolar to the opposite second premolar and the associated palatal tissue from just 1 1/2 to 2 cartridges of anesthetic.  The lips, face and muscles of expression are not anesthetized with the AMSA resulting in greater patient comfort operatively and post operatively. In addition, esthetic smile-line assessments are not hampered by facial distortion associated with traditional mucobuccal fold injections. To enhance buccal soft tissue anesthesia a small volume of anesthetic is administered within the surface mucosa of the mucobuccal fold.

 

The AMSA is easily administered, requiring up to 4 minutes to complete.  Anesthesia is achieved within approximately 5 - 7 minutes of injection. The patient should be prepared for the extra time required to administer an AMSA and advised they will likely experience only a minor sensation from the injection. They will appreciate the lack of numbness to the face and lips.

 

A 30 gauge extra-short needle is recommended.  It is inserted in a position that bisects the premolars and is approximately halfway between the mid-palatine suture and the free gingival margin.  On patients with either a flat or excessively high palatal vault, the landmark is adjusted closer to the mid-line. If desired, topical anesthetic may be applied. The needle bevel is initially oriented parallel to the palatal tissue.  A sterile cotton tip applicator is employed to apply pressure on the needle to “seal” the bevel to the tissue for the “pre-puncture” phase of the insertion. (see pre-puncture section) The foot control is depressed slightly to activate the slow flow rate for 4 - 6 beeps prior to slow needle insertion. The cotton tip will help catch any anesthetic drips that occur before the bevel is completely within the tissue. The needle movements are extremely slow and gentle during penetration while the slow flow rate is maintained. The needle is reoriented to a 45º angle as it is advanced until it contacts the bone. 

 

Perform aspiration. Maintain contact on bone and deliver the required dosage of 3/4 to 1cartridge. Significant blanching of the palate will be observed (with anesthetics containing vasopressor) and care should be taken upon needle removal to reduce anesthetic solution from dripping down the posterior palate.

 

Note: It is critical that only the slow rate be used for this injection.  Using the fast rate of flow may cause excessive ischemia and tissue damage. It is recommended that anesthetic containing vasopressor concentration of 1:100,000 or 1:200,000 be used.  Caution should be exercised with 1:50,000 concentration of vasopressor. Excessive ischemia can result in soft tissue damage.

 

 

 

 

REVIEW OF THE AMSA INJECTION TECHNIQUE

 

1.         Prepare the patient for a slow injection experience.

2.         Place topical anesthetic on the palatal tissue if desired.

3.         Orient a 30 gauge extra-short needle, bevel parallel to the palatal tissue at the landmark which bisects the premolars and is midway between the free gingival margin and the mid palatine suture.

4.         Place a sterile cotton tip applicator to absorb any anesthetic drip prior to needle penetration.

5.         Perform pre-puncture technique.

6.         Rotate needle slightly upon entering tissue and during movement to final site.

7.         Initiate the slow flow rate at the moment that the needle enters the palatal tissue and maintain this rate continuously. Reorient needle to 45º and       advance the needle very slowly until it contacts bone.

8.         Perform aspiration.

9.         Cruise control can be activated if desired.

10.       Continue to inject until approx. 3/4 to 1 full cartridge has been deposited.

11.       Remove the needle slowly and try to avoid any excess anesthetic dripping.

Repeat on the contralateral side if required