When preparing a tooth for a filling, dentists use local anesthesia to temporarily interrupt sensory signals traveling from the mouth to the brain. The anesthetic agent is delivered precisely near the targeted nerves, causing a localized loss of sensation while the patient remains fully conscious. This process blocks the transmission of pain impulses, ensuring a comfortable experience during the procedure.
The Trigeminal Nerve System
Sensory input for the face, teeth, and gums is managed by the Trigeminal Nerve (CN V), the fifth cranial nerve. It is divided into three major branches. The Ophthalmic division (V1) supplies the upper face and eyes. Dentists focus on the Maxillary division (V2) and the Mandibular division (V3). The Maxillary nerve carries sensation from the upper teeth, gums, and palate. The Mandibular nerve supplies the lower teeth, lower lip, and tongue. These two divisions contain the specific dental nerves that must be blocked during restorative procedures. The Maxillary and Mandibular divisions split into smaller branches that enter the jawbones to innervate individual teeth. For instance, the inferior alveolar nerve, a branch of the Mandibular nerve, controls sensation in the lower molars and premolars.
Injection Methods: Blocking vs. Infiltration
The procedural approach a dentist uses depends primarily on the location of the tooth and the density of the surrounding bone. The two main techniques for delivering local anesthesia are infiltration and nerve block.
Infiltration
Infiltration is generally used for the upper jaw (maxilla) because its bone structure is more porous. The anesthetic solution is deposited near the apex of the tooth root, allowing the drug to diffuse through the bone to reach the terminal nerve endings of that specific tooth. This technique typically numbs only one or two teeth and a small area of the surrounding gum tissue, making it a highly localized approach.
Nerve Block
For the lower jaw (mandible), the bone is much denser, preventing effective anesthetic diffusion. Dentists frequently use a nerve block technique, such as the Inferior Alveolar Nerve Block, which targets a main nerve trunk further back in the jaw. This method numbs an entire quadrant of the mouth, including several teeth, the corresponding gum tissue, and often the lower lip and tongue on that side.
The Chemistry of Numbness
Medications like Lidocaine or Articaine achieve numbness by chemically interfering with the nerve’s ability to transmit an electrical signal. Nerves propagate pain signals using a rapid influx of positively charged sodium ions through voltage-gated sodium channels embedded in the nerve cell membrane. These channels must open for the signal to continue toward the brain. Local anesthetic molecules stabilize the nerve membrane and physically block these channels. By preventing the entry of sodium ions, the anesthetic stops the electrical impulse (action potential) from forming. This interruption silences the nerve, preventing pain sensation from reaching the central nervous system. The block is temporary and reversible, lasting until the body metabolizes and clears the drug from the injection site.
Duration and Recovery
The duration of numbness varies based on the anesthetic type and the injection technique employed. Common agents like Lidocaine typically provide pulpal anesthesia for one to three hours, though soft tissues, such as the lip and tongue, may remain numb longer. A nerve block, which targets a larger nerve trunk, generally results in a longer period of numbness than infiltration near a single tooth. During recovery, patients must exercise caution, especially when eating or drinking hot liquids, until full sensation returns. Numbness prevents feeling if the lip, cheek, or tongue is bitten, which can cause accidental injury. Tingling is a common sensation as the anesthetic wears off, indicating nerve function is returning. If numbness persists beyond five hours, contact the dental office for guidance.