The Impact Of Condylar Cartilage Defect On Mandibular Growth And Development In Rat

Objective:The development of mandible is a complex process.Mandibular condyle is recognized important in the development and remodeling of the mandible,but its role is still unclear.This paper aims to establish models of partial and full mandibular condylar cartilage defect,and model of condylectomy in growing SD rat.And to discuss about the impact of condylar cartilage defect and condylectomy on mandible growth and development,as well as the ability of self-repair in mandibular condyle.Method:32 SD rats were randomly divided into 4 groups,with 8 rats in every group.Group A(sham):only expose the mandibular condyle;Group B(partial defect of mandibular condylar cartilage):excision of more than half the thickness of condylar cartilage with a scalpel;Group C(Full defect of mandibular condylar cartilage):excision of the full thickness of condylar cartilage with a scalpel;Group D(condylectomy):excision of the whole condylar head 3mm below the condylar cartilage surface with a scissors.Sacrifice the animals in 4 weeks and 8 weeks post-operation,and measure the body weight.The ramus length(Cor-GoT,Cond-GoT),corpus length(Go-Id))and corpus height(Ma-Me)were measured with vernier caliper to analyze the mandibular growth and development.The data were processed by SPSS 23 software with ANOVA and LSD methods,while statistical significance is recognized when p<0.05.Paraffin sections with HE staining and Safranin O staining of the condyle were made to observe the repair of condyle.Result:4 weeks post-operation,the result Cor-GoT and Ma-Me length showed no statistical difference between each groups.The Cond-GoT length of group B,C and D are shorter than that of group A(p<0.05),and the length of group D is shorter than that of group B and C(p<0.05).The Go-Id lengths of group B,C and D are shorter than that of group A(p<0.05),while there are no statistical difference between groups B,C and D(p>0.05).8 weeks post-operation,the length of Cor-GoT,Go-Id and Ma-Me showed no statistical difference between each groups(p>0.05).The histological observation showed that newly formed cartilage with presence of hypertrophic chondrocytes have been identified in all experimental groups at the sites of defects,indicating that the condylar is capable of self-repair with some extent of cartilage regeneration.Hypertrophy of fibrocartilage like tissue can be found on the surface of the condyles in group C and D.Conclusion:This research successfully established animal model of partial condylar cartilage defect,full condylar cartilage defect,and condylectomy in growing SD rat.Condylar cartilage defect and condylectomy can lead to some degree of hypodevelopment of condyle and mandible corpus in growing rat,but do not cause severe morphological and functional disturbance to mandible.It indicates that the condyle is not the only growth center in the mandible,as the mandibular development may be a result of combination of different ways of bone formation.The endochondral ossification of mandibular cartilage has regional effect on mandibular development during growth.The long-term self-repair and regeneration of condylar cartilage and condyle would need further studies.