Local anesthetic solution is injected to block the production of nerve impulses that relay sensory information. This is accomplished by decreasing the permeability of the ion channels to sodium ions. The decrease in the sodium conductance causes a failure to reach the threshold level of depolarization for the production and propagation of an action potential.
Local infiltration (supraperiosteal injection) is the injection of local anesthetic into a relatively small area with the aim of anesthetizing the terminal nerve branches in the area of the planned procedure. This is most effective for procedures of limited scope.
A nerve block requires the deposition of anesthetic in proximity to the trunk of a nerve usually at a site somewhat distant from the area of the procedure. This usually results in a larger area of anesthesia and is useful for multiple or more extensive procedures.
Commonly used syringe is a metallic, breech loading cartridge type. These can be of an aspirating or self-aspirating type. Alternatives include various disposable plastic syringes that accommodate the cartridge and computer-controlled local anesthetic delivery systems.
Sensory innervation to the mandibular arch, including teeth, supporting structures, and soft tissue, is derived from the mandibular division of the trigeminal nerve (V3). The specific branches of V3 involved are the inferior alveolar, the lingual, and the buccal. The inferior alveolar further divides into the mental and incisive branches. Block injections are usually chosen due to the anatomy and thickness of the bone of the mandible. The specific dental procedure planned determines which block injection is used.
Nerves targeted: the inferior alveolar before it enters the mandible at the mandibular foramen, which will include the mental and incisive branches of the inferior alveolar, and the lingual, which is just anterior and medial to the inferior alveolar when it enters the foramen (a-1).
Anesthetizes: all the teeth and supporting structures to the midline; buccal soft tissues anterior to the mandibular first molar, the lower lip, and chin to midline; and lingual soft tissues, floor of oral cavity, and the anterior two-thirds of the tongue (a-2).
Anatomic landmarks: coronoid notch, the greatest concavity on the anterior border of the ramus of the mandible; pterygomandibular raphe, a mucosal fold spanning from posterior of the mandibular dental arch toward the maxilla; and the occlusal plane of the mandibular dental arch.
The needle is advanced beyond the posterior border of the mandible, it enters the parotid gland space, and injection will affect the facial nerve (VII) to cause paralysis of the muscles of facial expression (Bell’s palsy).
Inferior alveolar or lingual nerves may be contacted by the needle during the injection, resulting in a “shock” sensation to the patient. This usually results in rapid and profound anesthesia. This seldom results in nerve damage.
Anatomic variations that should be considered effect the position of the mandibular foramen. In children, it is relatively farther posterior on the ramus of the mandible. In adults with a protrusive mandible, it is relatively higher on the ramus.
Fig. 27.1 (a-1) Syringe position for the inferior alveolar nerve block, left lateral view. (a-2) Areas anesthetized by inferior alveolar nerve block, superior view. (a-3) Intraoral injection site for inferior alveolar nerve block. (a-4) Transverse section just above the occlusal plane of the mandibular teeth, superior view.
Considered to be a true mandibular nerve block, this injection is a variation of the inferior alveolar nerve block in which the anesthetic deposition is very high in the pterygomandibular space and should affect all branches of the mandibular nerve (V3).
Anesthetizes: all the teeth and supporting structures to the midline; buccal soft tissues of the same side of the mandibular arch; lingual soft tissues, floor of oral cavity, and the anterior two-thirds of the tongue; skin of the cheek and anterior temporal region (b-1).
The syringe barrel should be positioned toward the injection site from the corner of the mouth on the opposite side. The syringe must be parallel to a line from the angle of the mouth to the lower edge of the tragus of the ear on the side of the injection.
Anesthetizes: all the teeth and supporting structures to the midline; buccal soft tissues anterior to the mandibular first molar, the lower lip, and chin to midline; lingual soft tissues, floor of oral cavity, and the anterior two-thirds of the tongue (c-1).
Anatomic landmarks: junction of the gingiva and mucosa superior to the maxillary third (or second) molar, the maxillary tuberosity, and the coronoid notch on the anterior border of the ramus of the mandible.
The needle should penetrate the buccal mucosa and be oriented slightly laterally to a depth of about 25 mm from the maxillary tuberosity (c-2). No bony contact should be expected. At this point, the tip of the needle should be in the middle of the pterygomandibular space.
The needle is directed too far medially, medial to the sphenomandibular ligament, if the lateral flare of the mandible is underestimated. The path of the needle should parallel the ramus of the mandible.
Inserting the needle too far or not far enough. There is no bony contact to help judge the depth of penetration. The 25-mm recommendation if for average patients. It has to be adjusted for larger or smaller individuals.