Local Anaesthesia

Dr. Daniel Haas
Authored By:
Dr. Daniel Haas

The ability to anaesthetize, or “numb”, areas of the mouth is of great benefit to patients who would otherwise experience unpleasant sensations during some types of dental treatment. In dentistry, the term “local anaesthesia” refers to a procedure where a “local anaesthetic”, which is a drug which numbs a small area of tissue, is delivered to block sensations from an area of the mouth. The original local anaesthetic (LA) in the 1800’s was cocaine, followed by procaine (which goes by the trade name of Novocaine), and eventually by lidocaine, which is still the main LA in use today. Now there are five highly effective and safe LA’s available for use in dentistry. Getting “frozen” makes the dental experience far more pleasant than it used to be. Here’s how it works.

All of our teeth are supplied by nerves. That is why they can normally feel hot, cold, pressure, vibration, sweetness and sometimes pain. Pain messages are carried through the body by electrical signals; this transmission can be blocked by chemicals.

The dental needle is placed close to the nerve(s) supplying the area(s) to be worked on, and LA is injected into the region. As the nerves of interest are bathed in LA, their ability to carry messages is interrupted; that area is numb or “frozen” and the dental work can be carried out without patients feeling pain. Sometimes dentists will pre-treat the injection site with topical anaesthetic gels.

For work in the maxilla (the upper jaw), LA can usually be placed right next to the teeth to be worked on. This is because the bone there is fairly porous so that the LA can soak into the bone and bathe the nerves that provide sensation to the teeth and gums in that area. The mandible (lower jaw) is quite different. The outer layer of bone (cortical bone) is thick and non-porous. Local anaesthetics will not soak into this bone and get to the nerves. This means that in order to freeze most of the lower teeth, we must use a nerve block. There are three specific techniques to achieve a nerve block. All of them involve putting the needle toward the back of the mouth, where the main nerve that supplies these teeth, the inferior alveolar nerve, is not encased in cortical bone.

Freezing or numbness wears off because the LA is picked up by the bloodstream and taken away from the area of interest (redistribution). Later, the drug is broken down through chemical processes in the body (metabolism). Because circulation is greater in the maxilla than in the mandible, the duration of anaesthesia is shorter in the upper jaw.

After your appointment your mouth is likely to still feel different. It may also feel like you can’t move your lips, but you probably can. That is because freezing affects mostly the sensory nerves as opposed to the motor nerves. This means it affects what you feel, but does not prevent you from using your mouth. After the appointment, you’ll have to be careful not to bite your lip or tongue. This is especially important for children. The soft tissues of the lips and gums stay numb for longer than the teeth. For the adults, if you’re a coffee aficionado, wait a while for your cuppa – if you burn yourself, you won’t know until later.

Local anaesthesia is arguably the most important advancement in modern dentistry as it provides the ability to deliver dental care without pain. Feel free to ask questions of your dentist about how best to enhance your comfort during treatment.