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Dental Anesthesia - Part 2

I have had questions from my patients concerning anesthetic technique. Probably the most common question is what the dentist might be doing to reduce the discomfort of the injection of local anesthetic. 

There are several common techniques aimed at reducing this discomfort.

Most dentists today are using topical (placed on the surface of the tissue) anesthetics at the site of injection.  These preparations are often a gel with colouring and flavouring.  They usually contain 20% Benzocaine and often one or several other types of topical anesthetics.  The flavouring is added because topical anesthetics taste nasty without it.  A topical anesthetic makes the area it is placed somewhat numb.  Topical anesthetics used on dental injections sites before injection of local anesthetic are usually placed on a Q tip or something similar to it and are swabbed in the area the needle is about to penetrate.  The topical anesthetic can also be delivered to the area using a spray system.  There have been several studies that have looked into the effectiveness of the agents used.  The consensus is that these agents are effective to a point.  Most of their effectiveness is not physiologic, but the mind is a powerful thing.  Apparently, the person feels the slight numbing of the topical anesthetic agent and is calmed by it somewhat so the perception is that penetration of the needle placing the local anesthetic is less painful.  The topical agents are not as effective as one would hope, but they are more effective than nothing at all.

Making the tissue where the needle is to penetrate tight by stretching it a little also makes the sensation of the needle less troublesome to the patient.  In the past, many dentists heated the anesthetic cartridges because the thinking was that it was the cold of the anesthetic agent when it was placed under the surface that was causing some of the discomfort.  I had the pleasure to be a part of one of the studies testing this idea.  We had 72 dental students who were anesthetized by one of our dental professors.  The same injection type and technique was used by the same person with anesthetic that had been heated to body temperature placed on one side and unheated anesthetic placed on the other side.  The study designer had removed the labeling on the cartridges and placed a unique numbering system on the cartridges that was known only to him at the time of anesthetic administration.  Neither the student nor the professor delivering the anesthetic to the student knew which was heated and which was not.  (This is termed a double blind study and is the so called “gold standard” method of doing scientific research).  Out of 72 students, none could tell which cartridge was heated and which was not.  So, heating the anesthetic to body temperature was a nice idea, but was not effective.  That is why you will find it has all but disappeared in dental practice.  The same is true of the ever diminishing diameter of the anesthetic needle.  A 27 gauge needle is the standard in the dental field.  A 30 gauge needle is quite a bit narrower.  The feeling was that narrower would be less painful, but with studies much like the one described above, patients could not feel the difference between a 27 gauge needle and a smaller gauge needle. 

Over the years, there have been electrical devices, some very impressive with lights and electronic beeps, but they have also been found to be little more than distractions to the patient.  However, a distraction is effective on some patients in reducing the perception of pain.  Pain is a complicated thing.  Some of it is physiologic, and some of it is clearly the mind playing out its fears.

So what works?  Since the innervation of the lower face is quite extensive, simply placing the anesthetic in very quickly categorically will not reduce pain when the anesthetic is expelled quickly through the needle, but will intensify it significantly.  However, placing the anesthetic into the tissue very slowly is really the most effective method we currently have.  About a minute to place one cartridge reduces the pain of placement very significantly when compared to placing it in a few seconds.  Two minutes reduces pain even more.  Patients quite often mistake the well intentioned, well trained, and disciplined dentist who is placing anesthetic in this slow manner for one who is trying to elongate the process and intensify the pain of anesthetic placement.  Rest assured, however, that when the dentist takes a long time to put in a cartridge of anesthetic it is your best interest that is being served.  Quick administration of local anesthetic is painful, and nobody likes pain.  So the dentist will likely place topical anesthetic, stretch the tissue a little, and then place the anesthetic slowly.  At present, this is arguably the best technique we have, but many in the field are looking for something better.  Ask your dentist if you would like to learn more about local anesthesia in dentistry. 

- 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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