Experimental Study Of Muscle Flap For The Reconstruction Of The Oral Soft-Tissue Defects

Objective:The oral soft-tissue defects were usually reconstructed with skin flaps or composite grafts with skin.The muscle-only flaps were transferred in this experiment to repair oral mucosal defects, and the epithelialization process of the superficial lining were observed.The morphology and electromyo-physiology of the innervated and denervated muscle were studied An order to find a better way to reconstruct the oral tissue and organ defects. Materials and Metbods:Forteen New Zealand white rabbits ,weighing from 2.0 2.5kg and aged 68 months ,were used. In the oral cavity ,a mucoperiosteal defect approximately 1.2cm X 1.2cm was made on the superior and buccal aspect of the mandible in the edentulous region. The sternomastoid muscle flap was tunneled into the oral cavity without tension and sutured to the surrounding oral mucosa with 3/0 to cover the bony exposure.All the operations were done on the right side ,and half of the muscles were denervated.Clinic observation were made after operation.The transplanted muscle flaps were tested by stimulating electrodes after periods of 1,2,3,4,8,1 2,and 20 weeks.The specimens in the oral cavity were harvested and prepared ,and then observed with light microscopy and scanning electron niicroscopy(SEM) aiming at :( I )the healing process of the surface of the muscle flap and (2) the characteristics of the muscle flap ,innervated or denervated, histologically and ultrastructurilly compared with the opposite normal muscle. Results:The wound of the operation healed smoothly and all rabbits lived actively after the operation.Light Microscopic observation showed that the uncovered steronmastoid muscle flap in the mouth underwent eventual epithelialization by oral mucosa.On week F-2, the flap was infiltrated by abundant inflammatory cells.Vascular sprouts were seen and epithelial cell derived from the oral mucosa. On week 3,stratified squamous epithelium covered the surface of the granulating flap. On week 8-- 12, parakeratinized stratified squamous epithelium completely covered the surface of the granulating flap.The repaired submucosa had maturated into fibrous tissue. On week 20,the papillary layer was absent and without rete pegs and gland.Scanning Electron Microscopy resulted: 1 week:the surface of the muscle was covered by fibrinous substance;2 weeks:the wound margins were seen the epithelium;4 weeks:the surfaces of the muscle were completely covered by squamous epithelium; 1 2-20 weeks:keratinized epithelia were seen on the flaps. This showed that the healing process was the same as LM.Therefore,we can guess that the healing process of the uncovered muscle flap should be divided into :( 1) inflammatory cell infiltration,(2) granulation tissue formation, (3) epithelial migration,(4) fibrosis. The innervated muscle showed better integrality compared with the denervated muscle,and the latter had greater atrophy and abundant fat and connective tissue and loss of function .Electromyo-physiology showed the innervated muscle contract even normally on electronic stimulation.Within the period of 8 weeks of postoperation,there was slight difference in the values of contractility between the innervated muscle and the normal unoperated muscle.But little difference was found after 8 weeks(p>0.05).By 20 weeks postoperation,the innervated muscle flaps were observed through TEM ,and the characteristics were similar. Conclusions:The uncovere...