An Experimental Study On Biomechanical Property And Injury Characteristics Of Mandible And TMJ In Maxillofacial Blast Injury

Spherical explosive was used to wound maxillofacial region of dogs at different distances, the pressure on tissue at different levels, the variation of horizontal acceleration and strain of the mandible and temporal bone were dynamically measured at the same time to study the biomechanical property.Another type of spherical explosive was used to wound maxillofacial region of rabbits at different distances to establish another animal model of maxillofacial blast injury. After gross observation of rabbits after trauma was done, bone tissue specimens were collected respectively from areas 0.5, 1.0cm outside the wound area at 6 hours, 3 and 7 days after wounding, the samples were prepared and stained with HE and modified Mallory 's trichrome staining and observed under light microscope to study mandibular pathology. The results of ink injection were also observed in bone grinding sections to study the changes of mandibular microcirculation ; and the specimens of disc and condyle were dissected out for light and electron microscopic observations right after trauma, 6 hours and 24 hours after trauma respectively to study the pathomorphological and ultrastructural changes.The animal model shows good stability and has most characteristics of injuries in war. The phenomenon that shock wave damps when spreading in body wasstudied and considered needing further study. No changes were found in mandible at 6 hours,but inflammatory infiltration was found at 3 days. It was at 7 days that osteonecrosis was apparent, the structure of bone beyond 0.1 cm was nearly normal and restoration of bone was seen. The disc of the wounded side became disorder right after trauma; edematous and degradation existed in collagenous fiber 6 hours after trauma while chondrocyte were edematous or even necrotic. It was 24 hours after trauma that the pathomorphological changes of collagenous fiber and chondrocyte were more apparent. The surface of disc and condyle was destroyed. and the underlaying collagenous fiber was exposed.The animal model is typical and can be used widely; The pressure and response of head and mandible acceleration are important signs of wounding energy of blast injury, and the strain is an important biomechanical parameter measuring the transfiguring severity of bone and wounding effect of blast injury. Pathological changes of mandible injured by explosive are similar to usual fracture except that the wound of blast injury is seriously polluted. TMJ has a great cushion effect on protecting the brain from injury to some extent, but indirect trauma on the TMJ can cause some TMJ diseases.