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Dental Anesthesia

Local Anaesthesia

11/30/2009

Question:

I have had local anaesthesia many times in my life for various dental procedures. It has always proven effective. During the last 2 years, I have had 5 dental procedues by 3 different dentists where the local anaesthesia had little or not benefit. In the last instance, I informed the dentist of my anxiety about "not getting numb" and he reassured me that the medication that he was giving me would keep me numb for 7 or 8 hours. Fortunately, I was numb during the procedure(it only lasted approximately 3-5 minutes though). However, by the time I got into my car to drive home I was no longer numb at all. Even though I was quite relieved to be numb during the procedure, I am sure that had the procedure been more time consuming I would not have been. Why do I no longer benefit from local anaesthesia?

Answer:

The dentist undoubtedly used bupivacaine (Marcaine) because it has a reputation of being a long-acting local anesthetic. While that is true, it is only a long-acting anesthetic in dentistry if it is used to numb one side of the lower jaw by what is called an inferior alveolar nerve block because the drug can be deposited right next to the nerve. Because this particular local anesthetic has difficulty penetrating through bone and the tough fibrous covering over the bone called the periosteum in order to reach the dental nerves in the upper jaw, only a small portion of the drug can get to the nerves in the upper jaw to numb those teeth. Thus bupivacaine does not numb the upper teeth for an extended period of time, only the lower teeth.

While you didn't mention which teeth were last treated, I suspect that they were upper teeth. Additionally, the upper jaw has a much greater blood supply compared to the lower jaw, so that the local anesthetic is more rapidly swept away from the nerves, so that more rapidly allows the numbing effect to disappear.

Finally, research has demonstrated that some teeth are much more difficult to numb compared to others in the same person. For instance, lower front teeth are much more difficult to numb than others in the lower jaw. So while you may have had excellent results when some teeth were anesthetized, other teeth that the dentist might be working on may have less satisfactory numbing.

The bottom line is that whenever the numbness is ineffective or wears off too quickly, please inform the dentist. Some dentists use alternative or supplemental injection techniques when their primary techniques are less than totally effective. They might include:

1. Re-injection of additional anesthetic at the same site
2. Injecting additional anesthetic into the periodontal ligament, a narrow space between the tooth root and the bone
3. Injecting more anesthetic directly into the bone (Intraosseous injection) via a tiny hole drilled into the bone (usually quite painless)
4. Infiltrating the soft tissue around the tooth with a local anesthetic drug called Articaine which may penetrate better into the bone than others.

For more information:

Go to the Dental Anesthesia health topic, where you can:

Response by:

Steven I Ganzberg, SB, DMD, MS Steven I Ganzberg, SB, DMD, MS
Formerly, Clinical Professor of Dentistry
College of Dentistry
The Ohio State University