A Study Of Controlling Mandible Growth By Animal Experiments

Mandibular prognathism(MP) or mandibular excess is defined as one of the mostsevere malocclusion caused by forward over-growth of mandible, characterized byconcave facial deformity, mesio-occlusion, anterior teeth overbite, etc. It has been afocus in orthodontics for a longtime and attracted more attention of orthodontists.However,recent orthodontic therapies are not much efficient for treating it.Orthodontists always do not satisfy with the result of treatment because of the relapsecaused by continued mandible growth. Patients with severe mandibular prognathismneed orthognathous surgery when they are grown up. Orthodontists seem to have nogood idea on how to control the growth of mandible. Mandibular prognathism hasbecome a worldwide problem.Chin-cup and function regulators are the main appliances for children andteenagers with mandibular prognathism. Adult patients could choose to be cured by orthognathous surgery. Chin-cup is effective to control mandible growth in animalexperiments, but not so good in clinic treatment for human. The results always makeorthodontists disappointed. The two most commonly applied surgical procedures tocorrect MP are sagittal split ramus osteotomy (SSRO) and intraoral vertical ramusosteotomy(IVRO). Both are suitable for patients in whom a desirable occlusalrelationship can be obtained with setback of the mandible, each having its ownadvantages and disadvantages. It seems that orthognathous surgery can solve theproblem once for all, but the complication of surgery and relapse make it not as perfectas it looks. So,orthodontist once again come back to the way of pursuing simple andefficient treatment measures.This study is to observe the influences of mechanical baffle on mandibledevelopment and growth in childhood minipigs with the of T-shape plates made bypure-Ti implanted in posterior of mandibular ramus by operation with the hope ofcontrolling the mandible growth.The study consists of two parts:1.To establish animal model of mandibular asymmetry by unilateral T-shape Tiplate implanted.Eight childhood minipigs of four-months old were selected as the experimentanimals. T-shaped plates made by pure Ti were implanted to one lateral posterior ofmandibular ramus by surgery,and the other side was taken a sham operation as control.Observe the growth of animals to detect weather mandible deviation occurred. Lateraldeviation occlusion was found in all animals several months later of operation.2. Measure the experiment animal mandible and analyze the reason of influenceThe changes of mandibular modality and occlusion relationship as well as the CTscan, Micro-CT scan, histological changes and scanning electron microscope (SEM)changes were studied24weeks after operation．There were obvious differencescompared with the control side in the breadth of the mandibular ramus and the length of the mandibular. There were significant influences on the growth of mandibular boneafter implanted mechanical baffle in posterior of mandibular ramus by operation inchildhood minipig,which caused the mandibular asymmetry.The results of our study demonstrate that the method of implanting mechanicalplates can effectively control the mandibular growth, which are mainly inhibiting bonedeposition of the ramus postirior surface. Growth of condyle was also influencedindirectly. When the local enviroment include muscles, periosteum, ect, was changedby operation process, the load of condyle was changed too. Load changing leaded thechange of condyle growth.