There are certain anesthetic injections we learn about in dental school that many of us remain wary of, perhaps deeming them “difficult,” and consequently, we don’t use them very often. Leading this list are the Posterior Superior Alveolar Nerve Block (PSA) and its “bigger sibling,” the Maxillary Nerve Block.
Many of us simply rely on standard infiltration when extracting an upper tooth, and this can certainly work well in numerous cases. However, when you encounter a challenging extraction, a tooth with a large, swollen abscess, or if you need to extract several teeth on the same side, you’ll often find that infiltration just isn’t effective, and the patient continues to experience pain.
This is precisely where the PSA and Maxillary Nerve Blocks come into play. These aren’t just mere injections; they are powerful “weapons” in your armamentarium if you know how to wield them correctly. In this article, we’ll demystify both of these blocks, walking you through, simply and thoroughly, when to use them and how to administer them correctly right from your very first attempt.
When Should You Consider Using the PSA or Maxillary Nerve Block?
These injections aren’t for everyday use, but they can be an absolute lifesaver in specific clinical situations:
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Maxillary Molar Extraction: Especially when you’re working on the upper sixth, seventh, or eighth molars, particularly if the extraction is expected to be somewhat difficult.
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When You Want to Avoid Multiple Injections: Instead of giving an individual injection for each tooth, a single PSA block can effectively anesthetize three molars simultaneously.
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In Cases of Infection and Abscess: When there’s a large abscess, the tissues become acidic, causing standard infiltration to completely fail. A nerve block like the PSA works away from the inflamed area, making it highly effective.
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For Major Surgeries: Such as sinus lifting procedures or the removal of large cysts in the posterior region of the maxilla.
Anatomy of the PSA Block: What Exactly Does it Anesthetize?
When you successfully administer a PSA block, you’re anesthetizing the Posterior Superior Alveolar Nerve. This nerve is responsible for innervating:
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The entire Pulp of the upper seventh and eighth molars.
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The Pulp of the upper sixth molar in most instances.
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The Investing Structures (bone and surrounding soft tissues) of these molars.
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A portion of the Maxillary Sinus.
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The Buccal Mucosa in the area of these molars.
A Crucially Important Anatomical Point: In approximately 28% of individuals, the Mesiobuccal root of the upper first molar does not receive its nerve supply from the PSA. Instead, another nerve, the Middle Superior Alveolar Nerve (MSA), is responsible for its innervation (1).
What does this mean practically? It implies that even if you administer a perfect PSA injection, the patient might still feel pain during the extraction of the upper first molar. If this occurs, you’ll need to provide an additional infiltration injection specifically over that root to ensure complete anesthesia.
Steps for the PSA Block: The 45-Degree Technique
This injection might seem daunting, but it genuinely relies on your understanding of anatomy and your ability to visualize the needle’s path. Your objective is to guide the needle to the region of the Foramina through which this nerve enters, located on the posterior surface of the maxilla.
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Point of Insertion:
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Grab a long needle.
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Ask the patient to open their mouth halfway and gently shift their mandible towards the side you’re injecting. This simple movement provides excellent access.
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The insertion point is at the highest part of the Mucobuccal fold, positioned superior to the Upper 7th Molar.
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Needle Angulation:
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This is the core secret. The needle absolutely must move in three directions simultaneously, maintaining a 45-degree angle on each axis. Imagine you’re holding the needle and moving it:
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Upward: To reach the level of the foramina, which are higher than your insertion point.
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Inward: To approach the bone surface of the maxilla.
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Backward: To reach the posterior surface of the maxilla.
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This 45-degree angle is paramount. If the needle is parallel to the tooth, it will hit bone. If it’s too horizontal, it will stray far from your target.
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Needle Depth:
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On average, you’ll need to insert the needle to a depth of approximately 16 mm in an adult (2).
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Injection:
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Once you’ve reached the desired depth, and before injecting anything, perform an Aspiration. You absolutely must confirm you are not within a blood vessel.
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If the aspiration is negative, slowly inject about 1.5 ml of the anesthetic solution.
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Critical Warning:
If you insert the needle Too Posteriorly or Too Laterally, you risk encroaching upon an area rich with veins called the Pterygoid Plexus of Veins. Injecting into this region can lead to a sudden and significant Hematoma.
The Next Level: The Maxillary Nerve Block
This injection is truly the “big sister” to the PSA. Here, you’re not just anesthetizing a single branch; you’re blocking the entire Maxillary Nerve before it branches out.
The Technique:
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It’s precisely the same technique as the PSA block—the identical insertion point and the same 45-degree angulation in all directions.
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The only difference lies in the needle depth: here, you’ll need to insert the needle much deeper, approximately 30 mm, to reach a specific area known as the Pterygopalatine Fossa, where the main nerve trunk travels (3).
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Anesthetic Volume: You’ll typically inject nearly the entire cartridge (1.8 ml).
What Gets Anesthetized?
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All teeth on that side, from the upper eighth molar all the way to the central incisor.
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The surrounding bone and soft tissues.
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The skin of the upper lip, alongside the nose, and the lower eyelid. The patient will likely report a “numb” sensation in this part of their face.
Complications and How to Avoid Them
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Hematoma: This is the most common and potentially serious complication. It happens when you injure the Pterygoid Plexus. The Solution: Strictly adhere to the correct angles and depth, and always perform Aspiration before injecting.
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Mandibular Anesthesia: This is an unusual occurrence that can happen if your needle isn’t inserted sufficiently Inward. In such a scenario, the anesthetic solution might inadvertently spread close to the Foramen Ovale, through which the Mandibular Nerve passes. You’ll then find the patient complaining that their lower jaw feels numb (4).
In Summary:
The PSA and Maxillary Nerve Blocks are not inherently difficult injections. However, they demand two key things from you: a solid understanding of Anatomy and precise Technique application. Once you master these, you’ll find yourself approaching challenging extraction and surgical cases with far greater confidence.
