Three Dimensional Arrangement of Matrix Fibrils and Tendon Attachment of Mandible

To examine the three-dimensional arrangement of bone matrix fibrils at their attachment with Sharpey's fibers or muscle tendons, we observed the surface of the body of the mandible, the angle of the mandible, and the coronoid process with a scanning electron microscope. Materials were three male crab-eating macaques (three years old). The fibrous layers of the ectoperiosteum were dissected free. Specimens were incubated in 1% trypsin solution for 72 hours at 37°C to digest both osteoblasts and amorphous organic matrix. At the external and internal surfaces of the body of the mandible, collagen fibril bundles ran horizontally. Spindle-shaped openings were observed between collagen fibril bundles, and we believe that the Sharpey's fibers entered the spindle-shaped openings. At the uneven area of the body of the mandible, collagen fibril bundles crossed each other. Many openings into which tendons of the masseter muscle entered were observed at the external surface of the angle of the mandible. The collagen fibril bundles organizing the surface matrix surrounded the places where the tendons entered. At the external surface of the coronoid process, collagen fibril bundles ran up and down in parallel. Tendons of the temporal muscle entered between collagen fibril bundles.