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Updated: Apr 13, 2021

You may have learned this injection while you were in school or had a coworker teach you. However, you might be one of the many hygienists that never learned this injection and are unsure if it is one you could confidently give. Let me tell you a little secret…often clinicians give this injection and don’t even realize it.

WHY?!?.... because it is so like the Middle Superior Alveolar (MSA) injection.

The IO (Infraorbital) was one I hated when I first learned it in hygiene school. Probably because my classmate kept chattering the needle across my alveolar process as she was reaching the final target…OUCH.

That experience, along with nearly fourteen years of teaching anesthesia helped me know what not to do when giving this injection, and helped me gain the appreciation of giving it. My friend when you can give this injection well it will leave your patients saying "HIT ME WITH YOUR BEST SHOT!"


This maxillary injection anesthetizes the pulpal and facial tissues of the premolars thru the midline on the side injected. Allowing the clinician to get all those teeth numb with only one injection, instead of using both the ASA (Anterior Superior Alveolar) and the MSA. Making it well suited for restorative work involving the premolars and anterior teeth. Even for perio therapy that doesn’t have extensive palatal involvement.

drawing of the IO nerve as it exits the IO foramen
Infraorbial Nerve

Let’s take a deeper dive into how this works.

As the maxillary branch of the trigeminal nerve exits the skull it branches into several small nerves. One of those nerves is the infraorbital nerve. It travels along the floor of the orbit then into the infraorbital canal finally exiting out of the infraorbital foramen, just below the infraorbital rim. The branches of the MSA and the ASA nerves are formed from the IO inside of the canal. So, when the anesthetic goes inside the canal it bathes those nerves. Which means the anterior teeth and premolars are numb.


The first step to a successful injection is to locate the infraorbital foramen. This is located just inferior to the orbital rim. Palpating inferior to the rim you may feel the indentation of the foramen. Your patient may even feel a slight twinge in the canine region from the pressure created from palpating. Another way to identify it is by having your patient looks straight ahead and create a line straight down from the pupil. Palpate the area again, you should feel the foramen. This will probably align superior to the 2nd premolar or in between the 1st and 2nd premolar. Understanding the location of the foramen is important since it is the site of deposition.

The other boney obstacle to recognize is the zygomatic process of the maxilla. As we know each person has unique anatomy. This extension can be as far anterior as the canine or as far back as the molars. This will impact the accessibility of reaching the foramen.


Because I often have the supplies handy for anesthesia before patient care begins, I normally grab a 25- or 27-gauge long needle. The reason for a long needle is due to the anatomical variation for each patient. The depth of the needle could be as little as 10 millimeters or as much as 24. If you can, determine vestibule height and location of the foramen prior to injection you will have a better understanding of which needle you will need. However, it is always a safe bet to go with a long needle I lean towards the side of safety in making sure the tissue is not close to the hub when final deposition site has been reached.

Site of insertion for the IO injection between the 1st and 2nd premolars

Insert at the height of the mucobuccal fold, below the IO foramen and parallel to the angle of the alveolar process (about the same region as the MSA injection). Near the apex between the 1st and 2nd premolar. Make sure the needle is a couple of millimeters away from the alveolar process to avoid the needle skidding across the bone as you reach the final target. Insert until contact with bone near the infraorbital foramen has been made. Once contact is made withdraw one millimeter, aspirate, and deposit solution (about ½-1 cartridge). Upon completion massage the anesthetic into the foramen. This one step will make or break your injection. This key step allows the anesthetic to flow over the infraorbital nerve which rests inside the infraorbital canal.

Keep the barrel parallel with the midline and in line with the pupil.

Do not over correct the angle away from the bone either. I have seen clinicians angle the needle too far away from the maxillary bone and end up with the needle tip piercing the cheek....that sounds a lot worse than it really is.

This injection might be intimidating to some providers due to the needle traveling towards the eye. However, you have the boney roadblock of the infraorbital rim. Which keeps the needle from moving superior and gives you the confidence you are at the correct deposition site.

Even with all these considerations it is a very safe injection to give. One could even argue it is just like the MSA injection, just a little deeper. With careful palpation and angulation, I know you will give your best shot!



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I have used this injection successfully.

I recently had a patient that could not close eye afterwards. Needl

concerned! I felt really bad. I explained the situation to the patient and he understood but I am now hesitant to use the IO.

how can I be sure this doesn’t happen again. The EYE! That is unnerving to me. Thanks

Replying to

Sorry about the missing text. Not sure what happened there. Needless to say, I was concerned

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