Anesthesia is an amazing phenomenon for dentistry and medicine that allows us to perform miraculous procedures that would otherwise be impossible to accomplish. Can you imagine going to have any major surgery or dental procedure without anesthesia? The concept of anesthesia invokes the simple principle of separating an area of the body from the brain so it does not interpret pain. How does anesthesia work or more specifically for this article, how does dental anesthesia work?
According to Stanley Malamed, author of The Handbook of Local Anesthesia, several things happen at a cellular level when anesthesia is placed into an area of the mouth. Nerves normally transmit information from countless areas in the mouth to our brains like a telephone wire. This transmission of information, including pain, causes the action of sodium ions to move within the nerve fibers and results in the nerve sending the pain message to our brain for a reaction from our body. The more pain involved, the more cellular activity that occurs and the “louder” the transmission to our brain. Dental anesthesia works by binding to the nerve with a stronger affinity than natural elements in the area, specifically blocking sodium activity so there is no transmission of any nerve signals, (including pain), which permits several hours of working time to complete dental treatment.
The most commonly used local dental anesthetic is Lidocaine (also called Xylocaine or Lignocaine), an amide-type anesthetic, popular because amide anesthetics rarely cause allergies. Replaced by the amide anesthetics in the 1940s, a still commonly referred to anesthetic is Novocaine, seldom used today because of allergic reactions. Other local anaesthetics in current use include Septocaine, Marcaine (a long-acting anesthetic), and Mepivacaine. Most dental anesthetics come in two forms: with and without epinephrine. Epinepherine is added to dental anesthetic to make it last longer and is most commonly used in Lidocaine anesthesia. This agent can occasionally mimic adrenaline reactions for patients (especially women) by causing slight increase in heart rate and although this is normal and safe, it can be disturbing. Pregnant women and patients with high blood pressure receive epinephrine-free anesthesia.
Dental anesthesia is best delivered by use of recent technology known as “computer anesthesia”, which is a very comfortable and consistent way of “numbing” a patient.
Upper teeth are easily “numbed” by infiltration injections where the anesthesia is delivered above each tooth individually. It is easy and predictable. The most common technique for “numbing” the lower teeth and jaw is called an inferior alveolar nerve injection anesthesia or a block. This “numbs” half of the lower jaw and lower teeth to the midline of the lower lip, and can often involve half of the tongue. The tongue gets numb because of a nerve branch called the lingual nerve. Block injections sometimes require booster injections because the nerve position can vary slightly from person to person and often requires targeting different areas to achieve numbness. If the dentist only wishes to numb the lower middle or front teeth, they can numb adjacent to the teeth just as explained for the top teeth. This works because of a nerve called the mental nerve, which supplies nerves to the lower premolars (middle teeth) and lower front teeth. The facial nerve lies some distance from the inferior alveolar nerve, but in rare cases anesthetic can diffuse far enough to temporarily anesthetize a small area of the face as well.
Another anesthetic includes Nitrous Oxide (N2O), also known as “laughing gas”. This is a great adjunct to dental care for relaxing patients, especially those that experience dental anxiety. This is inhaled and easily crosses the alveoli of the lung and is dissolved into the passing blood, where it travels to the brain, leaving a dissociated and euphoric feeling for most patients. It does not put patients to sleep, like general anesthesia. Further, a patient can drive themselves to and from a dental appointment safely without because the effects of Nitrous Oxide are quickly reversed at the end of the dental appointment. Nitrous Oxide does not cause any numbing of the teeth and patients still require normal dental anesthesia during use of Nitrous Oxide.
The network of nerves in the oral cavity is relatively complex, but consistent, with only slight variation of the inferior alveolar nerve as described above. Knowledge of dental nerve anatomy is important to understand the best avenues for numbing teeth easily and effectively. This permits the routine administration of dental anesthesia, which is predictable and comfortable for patients so that dental treatment can be performed.