A Study Of Rigid Internal Fixation And Periosteal Injury Impacting Mandibular Growth

The majority of the pediatric maxillofacial fractures are situated in the mandible. The attitude to treat mandibular fractures with conservative or surgical treatment has been kept controversial in a long term, and the key point is the relationship of therapy and growth. Some experts argue that stress shielding of rigid internal fixation would restrict the growth of bones. Furthermore, periosteal injury, which disturb both the capacity of ossification and the blood supply of the mandible, would retard the growth of mandible,because the mandibular growth is mainly through intramembranous ossification at the periosteum; Some others consider that the effect of the clinically surgical management is certain with non-restrictive effect on the growth of mandible. Moreover, rigid internal fixation and early exercise functionnel could compensate the restriction of bone. Our study bases on this clinical question. Twenty 70-day-old white New Zealand rabbits are randomly divided into two groups. Each group contain ten animals. Build the models of mandibular fracture which is treated with rigid internal fixation and periosteal injury. The purpose of the experiment is to find how rigid internal fixation and periosteal injury affect the growing mandible and guide the clinical therapy of pediatric mandibular fractures.To build the model of mandibular facture treated with rigid internal fixation, fractures are created in all of the right mandibles and fixed with titanium microplates and screws. The contralateral side is employed as control group.To build the model of periosteal injury, periosteum is peel off in the right mandiblular body. The left side is served as control group.General observation, Micro-CT scanning and Histological observation of HE are conducted 3 months after surgery.Results:1) No obvious restrictive effect is observed on both rigid internal fixation and periosteal injury model. Occlusion disorder, mandibular asymmetry and midline shift were not found 3 month postoperatively.2) Rigid internal fixation can decline the quality of ossification. The cortical wall thickness and bone volume fraction of the area where plates and screws are fixed are smaller than the that of control group(P<0.05). The cortical density is decreased ,but this difference is not significant(P>0.05).3) Periosteal injury can decrease the cortical density, cortical wall thickness and bone volume fraction(P<0.05).4) The implants impact the bone formation. Superficial bone pores are found in the mandible where the plates and screws are inserted. The cortexofbone is discontinuous. The absorption of bone is so much in some regions so that the tooth root was exposed. Conclusion:Rigid internal fixation and periosteal injury do not restrict mandibular growth, but can affect the quality of bone formation. The cortical wall thickness and bone volume fraction are decreased, and the periosteal injury also makes the cortical density declined. But further research is needed to fathom its clinical significance.