ANTERIOR SUPERIOR ALVEOLAR (ASA) INJECTION
Updated: Jun 7, 2021
The ASA injection is designed to anesthetize the anterior maxillary teeth and is a decent option for dental hygiene services.
This injection is considered a field block because it covers a small portion a region and may anesthetize smaller unnamed nerves. And, depending on which textbook you learned from, you may not have learned this particular injection. It would have been taught as an Infraorbital (IO) injection. There is a difference between the two, but that discussion is for a different day.
For now, let's take a look at what the ASA injection is.
The Anterior Superior Alveolar nerve is a bilateral structure and part of the maxillary nerve
family. It branches from the Infraorbital nerve as it travels through the IO
canal, providing sensation to the pulp and facial tissues of the canine thru the central incisor.
HOW DO YOU ADMINISTER?
Understanding the patient’s anatomy is important for this injection. You want to palpate the canine eminence. I consider this the “corner” of the maxillary arch. It is where the root of the canine is housed and helps keep our upper lip from sagging in. Once identified, use a short needle and insert on the mesial aspect of the eminence, at the height of the mucobuccal fold. Align the syringe so you are angled away from the midline about 5-10 degrees. Basically, you are inserting on the mesial aspect of the canine and depositing on the distal. The deposition site is apical and distal to the root of the maxillary canine. Insert about 3-6 mm depending on the height of the vestibule. After confirming a negative aspiration, deposit one-half to a full cartridge of anesthetic solution.
When inserting, make sure not to over angulate towards the alveolar bone. This will cause contact with the bone which can make your patient uncomfortable. To aid in patient comfort, not only should you apply topical but proper retraction can help too. Anytime you are inserting into the mucobuccal fold, pulling the lip away from the jaw causes the tissue to be tight. This allows the needle to penetrate the mucosa easily.
Look at the picture below to see how the lip is pulled out and the angle of the needle.
If freenums are at your point of insertion you can move the lip either toward or away from the midline. This moves this attachment out of your way. As you slowly insert, drip some anesthetic into the surrounding tissue. Once you’ve reached your point of deposition and aspirated, slowly deposit the solution. And I mean slowly…the slow pace reduces the burning sensation which can be more noticeable in the anterior region. Don't be surprised if your patient says they can feel the solution. This tissue is thin.
An important factor to remember is the midline of the maxillary arch is famous for having cross over innervation. If the central incisor still has pain reception, infiltrating over the mesial aspect of the central incisor takes care of this issue.
Often, clinicians struggle with stabilization for this injection. Once you have reached your site of deposition, relax the retraction hand, and rest your knuckle or the tip of your finger on the syringe (see picture). This makes it harder for the needle to move and if the patient moves you have a stabilized syringe.
Once you deposit the appropriate amount of anesthetic, recap your needle, take a deep breath, and remind your patient to breathe as well.
It’s not unusual to have post injection bleeding for this particular shot. There are several small blood vessels which can easily get nicked by the needle. If this happens simply grab some gauze and press it on the injection site for about 30-60 seconds. The bleeding should stop and then you can begin your treatment.
This is a simple injection to give but a little review is always great to have. Following these steps will help you give your best shot.
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Did you know you can get CE credit for all you are learning? Enroll in the course series HIT ME WITH YOUR BEST SHOT. You will review injection techniques (with cued videos) and anesthesia management.