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Local Anesthetic

What are some of the challenges with local anesthetic?

One of the parts of most visits to the dentist is local anesthetic or getting frozen as people often say. It is interesting to note that the first local anesthetic was actually cocaine. Cocaine was first isolated in the 1860’s and first used clinically in 1884. While the local anesthetic effect was a good thing, the addiction it produced, of course, was not. In 1905, chemists managed to change the cocaine molecule in such a way that the addictive effects were eliminated and much of the local anesthetic effect was retained creating procaine (Novocaine). The disadvantages of this new local anesthetic included a high allergic potential, it took a long time to produce numbness, and it wore off very quickly. The first modern local anesthetic was lidocaine which was invented in the 1940’s. Lidocaine produced much deeper local anesthesia, had a much shorter onset, and with the addition of epinephrine, lasted several hours. Lidocaine was the first of the broad category of the local anesthetics used today (called amide type anesthetics). The latest addition to the local anesthetic lineup is Articaine and represents a major advancement in anesthetic technology. It diffuses through bone much more effectively than previous types of anesthetic thus nearly eliminating the need for difficult and less reliable block type anesthesia on all but the lower molars. Articaine has been used in Europe since 1976, Canada since 1983, and was only approved for use in the USA in 2000. There are other kinds of anesthetic in this amide type group. Each has its own advantages and disadvantages.

For all but the lower molars, infiltration (placing the anesthetic right next to the tooth needing to be numb) is the method of choice. Infiltration is reliable, usually gets only a small area numb, and takes effect within only a few minutes. This type of anesthesia presents little challenge most of the time. However, for the lower molars, the situation is quite different. The bone in the lower molar region is too dense for infiltration to be effective. This area requires another anesthetic technique called block anesthesia. In block anesthesia, the anesthetic is placed near the entrance into the lower jaw of the nerve supplying the lower molars (the inferior alveolar nerve) quite far behind where the teeth are located. Individual anatomy presents a unique challenge to anesthetizing (freezing) the lower molars. The opening for the inferior alveolar nerve can be located in a spot that is not the most common spot. As well, there can be several openings for the nerve, all of which would have to be anesthetized in order to achieve numbness of the lower molars. There is little chance the dentist will have access to the kind of imaging required to know of these significant anatomic irregularities in his individual patient. Block anesthesia typically anesthetizes a much larger area than infiltration and takes quite a bit longer to take effect and to leave the area after the work is done. Success rates for profound anesthesia to the desired teeth approach 100% when infiltration can be used, but when block anesthesia has to be used (for lower molars), success rates for the first cartridge of anesthetic deposited in the area range between 21% and 67%. Another cartridge is often required, and sometimes a supplemental technique is also required in order to achieve the required amount of numbness in the tooth to be treated.

Other challenges to anesthetizing patients include substance abuse. Patients who abuse alcohol regularly or are recreational drug users present unique problems to effective anesthesia for dental procedures. Often, these patients require more anesthetic and more time for the anesthetic to begin to be effective. Active glue sniffing presents significant anesthesia problems that often cannot be overcome with regular techniques. As well, the mind is a powerful force. People who are very afraid or who are certain they cannot become numb will have difficulty being anesthetized. Medications to alleviate anxiety can be considered for this kind of person.

There is ongoing research on alternate anesthesia techniques including electrical devices as well as acupuncture. Continued advancement in the chemistry of injection type anesthetics is probable. Make sure you communicate any fears you might have or other concerns about local anesthesia to your dentist. Ask your dentist if you would like more information about local anesthesia.

- This article was written by Dr. Mike Christensen and published in the Daily Miner and News, and Enterprise. Local Kenora News Publicatons (1998-2006)

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