Anatomy and Course of the Canal
The mandibular canal originates in the mandibular ramus (ramus mandibulae) and courses through the body (corpus mandibulae) of the mandible.
- Origin: Located on the medial (inner) surface of the mandibular ramus, inferior to the mandibular notch, is the mandibular foramen (foramen mandibulae). It is bounded anteriorly by a bony projection known as the lingual of the mandible (lingula mandibulae). The canal begins at this foramen.
- Course: The canal runs anteroinferiorly through the body of the mandible.
- Termination: It opens onto the lateral (outer) surface of the mandibular body as the mental foramen (foramen mentale), which marks the terminal end of the mandibular canal (canalis mandibulae).
Anteroinferior to the lingula on the inner surface of the bone runs the mylohyoid groove (sulcus mylohyoideus).
Contents of the Mandibular Canal
The canal contains a neurovascular bundle consisting of:
- Inferior alveolar nerve (n. alveolaris inferior) — the largest mixed branch of the mandibular nerve ($V_3$). In most cases (about 80%), it travels through the canal as a single trunk. In approximately 20% of cases, the nerve forms a dental plexus in the proximal part of the canal. Branches to the teeth, gingiva, and bone arise from this trunk or plexus.
- Inferior alveolar artery and vein — vessels that accompany the nerve within the mandibular canal.
Related Nerve Branches
- Mylohyoid nerve (n. mylohyoideus) — a motor branch that branches off from the inferior alveolar nerve prior to its entry into the mandibular canal. It innervates the mylohyoid muscle and the anterior belly of the digastric muscle.
- Mental nerve (n. mentalis) — a large terminal branch representing the extracanalicular continuation of the inferior alveolar nerve after exiting the mental foramen. It emerges through the mental foramen to supply the skin and mucous membrane of the lower lip, as well as the skin of the chin.
- Incisive branch (ramus incisivus nervi alveolaris inferioris) — the intraosseous continuation of the nerve supplying the canine and incisor region after the mental nerve branches off.
Clinical Significance in Dentistry and Surgery
- Inferior Alveolar Nerve Block: During mandibular anesthesia, the needle is advanced approximately 2 cm to the bony sulcus—the site where the nerve enters the mandibular foramen.
- Mental Nerve Block: To anesthetize the premolars, canine, and incisors, the needle must be inserted into the canal through the mental foramen to a depth of 3–5 mm. A characteristic "drop" sensation serves as a landmark. If the needle fails to enter the canal, anesthesia remains limited to the soft tissues of the chin and lower lip.
- Intraosseous Anesthesia: Due to high injection pressure, local anesthetic solution penetrates intraosseous arteries and pulp vessels both with and against the direction of blood flow, causing near-total ischemia of the dental pulp and periodontal tissues.