Local anesthesia, often referred to simply as dental numbing, is a medication used to temporarily stop the transmission of nerve signals in a targeted area of the mouth. This temporary blockage is necessary to prevent the sensation of pain during various dental procedures, such as fillings, extractions, or crowns. While the anesthesia eliminates the pain, you may still feel pressure or movement during the procedure.
Typical Duration for Dental Anesthesia
The duration of numbing is complex because the time the tooth remains numb is usually far shorter than the time the surrounding soft tissues are affected. Most standard dental anesthetics, such as lidocaine, are combined with a vasoconstrictor like epinephrine to restrict blood flow, which extends the numbing effect and provides sufficient pain relief for the procedure.
Pulpal anesthesia, which is the numbing of the tooth pulp, typically lasts between 60 and 90 minutes for standard procedures. However, soft tissue anesthesia, involving the lips, tongue, and cheek, lasts significantly longer. For commonly used agents like lidocaine or articaine, this soft tissue numbness often persists for two to five hours. The drug works by binding to sodium channels on the nerve cell membrane, blocking the electrical signal that the brain interprets as pain.
Longer-acting anesthetics, such as bupivacaine, may be used for complex surgical procedures like extractions. Their effects on soft tissue can last up to 12 hours, providing prolonged post-operative pain relief and delaying the need for oral pain medication.
Why Numbing Times Vary
The overall time the numbing sensation lasts differs significantly between individuals due to physiological factors and the specific injection technique used. A major variable is the patient’s metabolic rate, which dictates how quickly the liver enzymes break down the anesthetic drug. Individuals with a faster metabolism, such as younger or healthier adults, may experience a shorter duration of numbness compared to others.
The inclusion of a vasoconstrictor, most often epinephrine, plays a substantial role in extending the numbing time. Epinephrine constricts the local blood vessels, which slows the rate at which the anesthetic is absorbed into the general circulation. This action keeps the drug concentrated at the injection site for a longer period, effectively prolonging both the pulpal and soft tissue anesthesia.
The injection technique also influences duration, as block injections generally last longer than infiltration injections. A block injection, such as one used for the lower jaw, deposits the anesthetic near a major nerve trunk, resulting in a broader area of numbness that takes longer to dissipate. In contrast, an infiltration injection, typically used for upper teeth, targets only the small nerve endings near the tooth root, leading to a more localized and shorter-lived effect. Furthermore, the total dose and concentration of the anesthetic administered directly impacts the duration, where a higher volume results in a longer lasting effect.
What to Do While You Wait for Numbness to Fade
While waiting for the numbing sensation to completely fade, it is important to take safety precautions to prevent accidental injury to the mouth. Since the loss of sensation means you cannot feel temperature or pain, avoid chewing any food until full feeling returns to your lips and tongue. Biting down on a numb cheek or tongue can cause significant, unnoticed trauma that only becomes painful later.
It is also important to refrain from consuming hot beverages, as the absence of temperature sensation can lead to accidental burns on the lips or inside of the mouth. Stick to cool or lukewarm liquids and soft foods that do not require chewing until the numbness is gone. Once the anesthesia begins to wear off, you may notice common sensations like tingling, itching, or mild throbbing in the area.
If the injection site feels tender, over-the-counter pain relievers, such as ibuprofen, are recommended and can be taken before the numbing fully disappears to manage discomfort. You should contact your dentist immediately if the numbness persists beyond the expected five to six hours, or if you experience severe, persistent pain that is not managed by medication. Rare but serious signs, such as a spreading rash, swelling, or difficulty breathing, require immediate medical attention as they could indicate an allergic reaction.