Freezing the lower jaw: The infamous inferior alveolar nerve block

Have you ever experienced the frustration of getting dental work done, only to find that your lower teeth never seem to get numb quite like the top ones? It's a common complaint among dental patients, and it can leave you feeling uncomfortable and anxious during procedures. But why does this happen?

The answer lies in the anatomy of your bone and nerves in your mouth. When your dentist administers local anesthesia, they're targeting specific nerves to numb the area being worked on. In the upper jaw, the bone is very thin and porous, allowing any local anaesthetic deposit to diffuse through the bone directly to the nerve. However, the lower jaw presents a greater challenge in that it contains more dense bone (thicker, more corticated), which can impede the diffusion of the anesthetic solution. To overcome this challenge the anaesthetic must be deposited before the nerve enters the thick bone through a hole called the mandibular foramen.

This delivery technique is called the ‘inferior alveolar nerve (IAN) block’ and it is the least successful injection dentists do, with a failure rate of 20-25% supported in the literature. But why is it so difficult?

If you look at this picture you can see the needle here is aimed directly at the mandibular foramen, a perfect position, however in reality this foramen’s location varies from person to person and is hidden by soft tissue.

Every time freezing on your lower teeth hasn’t worked it’s very likely the case that the dentist injected the anaesthetic too low, where the nerve has already entered your bone. Since the bone is too thick the anaesthetic can’t then reach your nerve and you end up not getting numb. It’s unfortunate for patients, it’s unfortunate for dentists to feel they’ve let their patients down. There’s a common misconception today that dentists will ‘miss’ this nerve when freezing solely based on the rationale that every patients anatomy is different. While that may be true to some extent, research has shown now that failure of anesthesia is mainly due to technical errors in the local anesthetic administration technique by the dentist/surgeon.

The most common method for an IAN block taught in dental school in North America is the ‘standard block’, which injects about halfway down an imaginary line from the coronoid notch and the occlusal plane. This method is usually easier to learn and landmark however its success rate ranges from 46%-86%, usually compromising the majority of cases where the patient did not get frozen. In my practice I utilize a different technique to achieve more predictable anaesthesia: the Gow-Gates injection. With proper technique anaesthesia can be achieved 99% of the time.

In the Gow-Gates technique the anaesthetic is delivered higher up, lowering the chance missing the nerve before it enters the mandibular foramen. I first palpate the coronoid notch with my thumb and place my middle finger just outside the ear, below the tragus. The syringe is aimed from between the lower premolars on the opposite side pointed at my finger positioned below the tragus of the ear. After approximately 20-25mm I should contact bone just below the mandibular condyle. Once this happens I withdraw 3-4mm, aspirate to ensure I am not injecting into a blood vessel, and then inject 1.8ml of 2% Lidocaine 1:100,000 epinephrine. It is important to use a 2% solution, rather than a 4% solution like Articaine, to minimize the risk of post-operative nerve damage.

Communication between you and your dentist is key in addressing any discomfort or lack of numbness during dental procedures. If you're experiencing persistent discomfort, don't hesitate to voice your concerns. Your dentist can adjust their approach or explore alternative options to ensure your comfort throughout the treatment process. While achieving consistent numbness in the lower teeth may be more challenging, advancements in dental techniques and anesthetics continue to improve patient comfort and satisfaction. By understanding the factors at play and working closely with your dentist, you can ensure a more comfortable and successful dental experience.