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WHAT IS IT?
In the world of oral anesthesia this injection is still considered the new shot on the block. If you have been practicing for more than 7 years you may not have been introduced to it in your pain management courses, but it's steadily gaining popularity. Particularly for its potential uses in cosmetic dentistry and Non-Surgical Periodontal Therapy (NSPT…aka… SRP). I learned it over 10 years ago and thought it was magic!
The Anterior Middle Superior Alveolar (AMSA) injection is a palatal injection which anesthetizes pulpal tissue of the teeth, from the midline thru premolars, including the facial periodontium and all the palatal tissue on the side injected. This injection impacts the Anterior Superior Alveolar (ASA), Middle Superior Alveolar (MSA) nerves and the plexus of nerves found on the palate. It was introduced to the dental field around 1997 when the Computer Controlled Local Anesthesia Delivery system (CCLAD) emerged.
The AMSA can be described as a field block since it anesthetizes a broad area in the mouth. Because the anesthetic is deposited by palatal process of the maxilla, which is relatively thin and porous, the anesthetic diffuses easily. Which will anesthetizes all those nerves! The bonus is the nerves innervating the upper lip are not affected. Because the facial nerves which innervate the lip are so far away from the administration point they do not receive any of the anesthetic solution. That means our patients will maintain upper lip function…how cool is that?!?!
ADMINISTRATION
This injection can be done manually or with a computer-controlled delivery device. Placing topical and the use of pressure anesthesia prior to injecting helps reduce injection discomfort for your patient (Palatal Injection Success). Using a 27- or 30-gauge short needle is best. The point of insertion is halfway between the gingival margin of the maxillary premolars and the palatal midline raphe, this is where the horizontal and vertical portions of the maxilla join. Align your barrel at about a 45-degree angle and between the first and second premolars. Insert the needle until bone has been contacted, I like to have the bevel of the needle facing the bone. After a negative aspiration deposit the local anesthetic, about one-half cartridge (0.9 mL). As the anesthetic is deposited the palatal tissue will begin to blanch, allowing you to see where the anesthetic is working. The delivery time can be slow when performed manually due to the nature of the palatal tissue. The use of a computer aided delivery device is usually recommended due to hand fatigue and the duration of deposit time. However, I and many other clinicians have successfully used manual deposition with great success.
POINTS TO REMEMBER
There are several pros with this injection. Due to the wide field of tissue anesthetized few injections are needed for quadrant anesthesia. A traditional approach to anesthetizing an entire maxillary quadrant would require four to five injections. The posterior superior alveolar (PSA), MSA, and ASA, nasopalatine (NP) and greater palatine (GP) injections are the five injections to get that quad numb. When using the AMSA the clinician may only need to perform two injections, the PSA and the AMSA. Another benefit is the patient’s upper lip will retain normal sensation and function. Making it easier for restorative esthetic dentistry, and for the patients ease of life after the procedure. Just think how happy your patient will be when he or she has a meeting they need to attend after the dental appointment. Now, they can continue with normal lip function, smiling and talking without a problem. Due to fewer injections the potential to use less anesthetic is a great bonus.
In my opinion, 4% Articaine with 1:100,000 mg of epinephrine and the AMSA are a match made in oral anesthesia heaven. Due to the potency of this anesthetic the clinician can achieve profound anesthesia with less anesthetic than 2% Lidocaine with 1:100,000 mg of epinephrine. So, what does that mean? It means you can get the same impact with less anesthetic and reduce how long the injection takes (lowering hand fatigue potential).
The drawbacks to this approach are important to consider as well. Due to the dense palatal tissue, manual deposition can take longer than expected, and the clinician may develop hand fatigue. Also, due to crossover innervation there is a potential for the central incisors to have some sensation (but this is true for all quadrant injections) Depositing more anesthetic using the infiltration technique easily remedies this problem…. but can negate the benefit of upper lip function. Another option to consider, would be to give the NP injection. Usually, the papilla is already numb, but if you give this injection there is no guarantee of pulpal anesthesia, but the patient will still have lip function. It all depends on what you and your patients’ needs are.
Something to keep in mind, is patients who have a history of poor healing could develop a post injection ulcer if high amounts of vasoconstrictor is used. I have only seen this once and the individual was severely immunocompromised. Also, it's important to monitor the blanching of the palatal tissue. Blanching is a sign of vasoconstriction. Every patient is different. As you administer anesthetic solutions which contain vaso's, you will see the the blanching spread towards the incisive papilla and back to the posterior palate. Once those regions have become pale you can stop delivering anesthetic. This means you may give about 1/2 cartridge, maybe a little more. I caution you from using more than 2/3 of a cartridge, unless it's a plain anesthetic.
THERE IS A LEARNING CURVE...
When you first begin to give this injection, you may not have the success with it right away. Be patient as you progress. You will find that this injection is very forgiving regarding deposition site, unlike many of the other injections we administer.
You can learn more and see the AMSA tutorial in the CE course Hit Me With Your Best Shot. Head to www.teachertina.thinkific.com to sign up.
I can’t wait for you to give this a try in your practice. Maybe you'll think its magic too. It really is a simple and effective injection to give. I know you’ll give your best shot!
CHEERS!
Tina
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