Dental Anesthesia- A Horse of a Different Color

August 2006

By: Dr. Scott R. Harden

Historically, a “toothache” as incurred by the masses, has been regarded as the worst infliction experienced by mankind since times immemorial. Toothaches are the most common manifestation of dental disease and the advent of dental anesthesia can be acclaimed as a cornerstone in the development of modern dentistry.

In the early 1800’s, before there were dental schools, before dentistry was considered a science, and before dental anesthesia was invented, many undesirable remedies for toothaches were attempted. Historically, it was commonplace for a person with a toothache (or victim in this case) to be lead to an open field and have a thread tied around the offending tooth. In the absence of anesthesia, and what we now would consider common sense, two gentlemen would hold the patient down while the thread was pulled by a horse galloping at full speed! At some point, dentists were told to stop horsing around, and they listened. Dentists, in the 1880’s, traded their use of horses for the first dental anesthetic, known as cocaine – not the best choice. It was realized by the late 1890’s that cocaine was very addictive, and in 1905 Alfred Einhorn invented a non-addictive dental anesthetic, named “Novocaine”. People still commonly refer to dental anesthesia as “novocaine”, over 100 years later, despite the fact that “Lidocaine” has been the most popular anesthetic for many years. In honor of dental history, you could say lidocaine is the workhorse of today’s dentistry.

TYPES OF ANESTHESIA

There are several types of dental anesthesia. Lidocaine typically has a 2-4 hour duration, ideal for the high majority of dental procedures. Bupivicaine lasts 10-12 hours and is ideal for oral surgery and root canal procedures to maintain comfort after the procedure is completed. Carbocaine benefits patients that are sensitive to heart palpitations (“the jitters”), are pregnant, or have a medical condition such as high blood pressure or hyperthyroidism.

Several types of anesthesia contain epinephrine (similar to adrenaline). This product is a vasoconstrictor, meaning that it constricts blood vessels in the area where it is injected, thereby prolonging the action of the anesthetic. Occasionally, this can produce a detectable but safe increase in heart rate similar to when you are scared or angry, and will last for about two minutes.

HOW DOES ANESTHESIA WORK?

  • Local anesthetics create a chemical roadblock between the source of the pain or stimulation – and the brain. The function of a nerve is to carry messages from one part of the body to another. These messages are in the form of electrical signals called “action potentials”.
  • Local anesthetics block the operation of a specialized gate, called the “sodium channel”. When the sodium channel of a nerve is blocked, nerve signals cannot be transmitted.
  • The vasoconstrictor, such as epinephrine, works by slowing the removal of the anesthetic from the vicinity of the nerve.
  • The potency of a local anesthetic is directly related to its lipid solubility, since 90% of the nerve cell membrane is composed of lipid.
  • Finally, the better the local anesthetic molecule binds to the protein in the sodium channel of the nerve, the longer the anesthetic will be effective.

WHY DON’T PEOPLE ALWAYS GET FULLY NUMB?

  • An imperfect injection technique is the most common cause of why patients do not develop profound anesthesia.
  • Another common cause of problems is that local anesthetics do not work well in an acidic environment – such as an inflamed or abscessed area. It is therefore sometimes useful to control a dental infection with antibiotics before a local anesthetic can be successfully used.
  • All other factors being equal, the single most important determinant of local anesthetic potency is its lipid solubility based upon nerve anatomy.
  • A doctor’s understanding of nerve and tooth anatomy is fundamentally important to allow positioning of the anesthesia to key areas for proper numbing. An upper molar for example can often require two injections to attain a proper effect.
  • When anesthetizing upper teeth, the dentist will provide an “infiltration”, administered proximal to the tooth. This is isolated to each tooth. For lower back teeth, proper anesthesia requires a “block” injection, which numbs one half of the lower jaw. Lower front teeth can receive infiltrations similar to upper teeth, without the need of a block injection.

CONTRAINDICATIONS TO DENTAL ANESTHESIA
Local anesthetic should not worry you. They are administered more than 300 million times annually in the United States. There are virtually no absolute contraindications to the administration of anesthetic agents, excepting allergy to the solution, which is extremely rare. There are some conditions where it is not advisable to give the full concentration of the drug. High blood pressure or hypertension is one such condition where adrenaline is not included in the anesthetic solution. All the other components are the same. Dental anesthesia is so safe in fact, that a very low percentage of obstetricians surveyed wish to be consulted prior to administration of local dental anesthetic.involving their pregnant patients.

LASEST ACTIVITY IN THE DENTAL FIELD
Currently, there are several wonderful advances allowing dental injections to be painless and predictable every time. This is true for three year olds that will be quite honest with their experience to adults alike. Computer technology, jet injectors, and microchips all have been incorporated to permit a slow transmission of the fluid under the skin at a rate undetectable to the nerves. This means no pain.

Overall, dental anesthesia remains the wonderment of modern dentistry and permits all of us to live comfortable lifestyles free of toothaches and chronic agony. We are all actually very fortunate in to live in this modern age of dentistry and need to appreciate how simple dental procedures have become. Just imagine your great grandfather being held by two men while the crack of the whip startled two horses into a gallop to remove his tooth. We have truly come a long way.