What are the structural parts of the body of the mandible?
- Base of the mandible (Basis mandibulae) — the lower, thickened border of the bone.
- Alveolar part (Pars alveolaris) — the upper border that forms the alveolar arch (Arcus alveolaris). It contains dental alveoli (Alveoli dentales), which are separated by interalveolar septa (Septa interalveolaria) and interradicular septa (Septa interradicularia). The outer surface features alveolar juga (Juga alveolaria). Posterior to the last molar lies the retromolar triangle (Trigonum retromolare) containing the retromolar fossa (Fossa retromolaris).
External and Internal Surfaces: Topography and Landmarks
External (Lateral) Surface: Along the midline is the mental protuberance (Protuberantia mentalis), flanked by the paired mental tubercles (Tuberculum mentale). Laterally, the mental foramen (Foramen mentale) opens as the termination of the mandibular canal (Canalis mandibulae), which runs through the bone body.
Internal (Medial) Surface: Along the midline lie the mental spines (Spinae mentales — superior et inferior). Laterally to these is the digastric fossa (Fossa digastrica). Superior and posterior lies the sublingual fossa (Fovea sublingualis), while inferior and posterior lies the larger submandibular fossa (Fovea submandibularis). These two fossae are separated by the mylohyoid line (Linea mylohyoidea).
Clinical Examination and Topography
- Bone Palpation: Performed systematically from the condylar process down the ramus, and then anteriorly along the body of the mandible (Corpus mandibulae).
- Valle's Points: The third division of the trigeminal nerve (n. mandibularis) gives rise to its terminal branch, the mental nerve (n. mentalis), exiting through the foramen mentale. The projection of the foramen mentale is located approximately 0.75 cm above the lower border of the mandible, midway between the intersection of the masseter muscle with the mandibular border and the midline.
- Lymph Nodes: Submandibular lymph nodes are palpable beneath the body of the mandible; submental lymph nodes are palpable in the midline region beneath the mandibular body.
Clinical Significance: Pathologies and Anesthesia
- Odontogenic Cysts: The growth of a radicular cyst causes resorption and remodeling of the surrounding bone, increasing the volume of the mandibular body. Thinned bone may spring upon palpation (Dupuytren's sign or parchment crackling). Large cysts pose a significant risk of pathological fracture of the mandibular body.
- Tumors: Over 80% of ameloblastomas (benign epithelial odontogenic tumors) are localized to the body of the mandible (molar, premolar, and angle regions). As they grow, they cause bone deformation and appear on radiographs as multilocular radiolucencies resembling "soap bubbles."
- Anesthesia: During inferior alveolar nerve block, the anesthesia zone encompasses the alveolar process, part of the body of the mandible, as well as the mucosa of the lower lip and the skin of the chin.