Effect Of Mandible Forward Resulted From Functional Therapy On Mandibular Bone

Objective: The incidence of Angle II malocclusion accounts for 15-20% of people and 49% of the patients who received orthodontic therapy. The main features of Angle II are retrusive or deficient mandible. The clinical appearance showed short upper lip, protrusive maxilla, retrusive and short mandible. These usually gave patients some bad psychological effects. Right now, early functional treatment to reduce the mandible forward was adopted to treat Angle II malocclusion. Since the functional appliance (FA) designed by Andresen in 1910 had been used, although many scholars in the world made a lot of studies, the exact mechanism and effect involved are unclear. Some studies showed that FA could promote or the mandible growth and remodel soft and hard tissue to a new balance, so that the treatment of malocclusion was performed. Other studies showed that FA might play a few roles in the jaw growth or only for a short time. Some reported that FA placed a "mortgage" on mandibular growth, and did not result in mandibular length increased.In this study, we applied bio-mechanics, animal model and clinical assays to analyze the mechanism of FA involved in mandibular protraction, and to know the effect on the growth of the mandible forwarded. We intended to provide an experimental basis for the early treatment to Angle II malocclusion.Method:1 A three-dimensional finite element analysis of mandibular stress distribution on a state of mandibular protractionPatients with typical Angle II malocclusion in a period of peak were entered into this study. All the children were of normal development and had not received orthodontic therapy.Transverse sections of mandible were taken by means of CT: Transverse sections of mandible below the FH plane were scanned by means of CT.The three-dimensional geometric model of mandible was re-established in CAD software.Three-dimensional finite element model was constructed in MSC.PATRAN software. Six thousand one hundred and forty-eight 8-point hexahedron and 6-point three-square entity units were set off and 7646 points were produced. Thin-shell unit was used in muscles and 888 4-point were set off and 1032 points were produced.The results were treated and analyzed by MSC.NASTRAN and MSC.PATRAN software.2 The effect of mandible forward on mandibular shapes of the growing ratsThe design of the appliance: the appliance was consisted of the upper crown and the inclined plane. Before surgery the upper incisor moulages and the lead molds were got, then bands (alloy flake with 0.25mm thick) jointed inclined plane lingually by 25?were made. On adhering, the lower incisor was just on the labial inclined plane and the mandible was in an edge-to-edge or even cross-bite position when the rats bit. In order to remodel mandible, the inclined plane was designed to ensure the mandible on a forward position and molars untouched.Forty 4-week-old male SD rats were selected and divided into four groups randomly (2 groups were the experiments and 2 groups were the controls), each group included 10 rats. The experimental group animals wore protrusive-type appliances for four weeks, while the control animals did not wear appliances. The mandibular condyles (from both experimental group 1 and control group 1) were observed by scanning electron microscope (SEM).The experimental rats (from both experimental group 2 and control group 2) at 7th day and 1st day before killed were injected tetracycline25mg/ per kg in abdominal cavity (tetracycline was provided by Chinese Medical and Biological Production Institute). The samples of left mandible were used for fluorescent observation and the samples of right mandible were used for the morphologic measurement. The control rats were observed comparatively. 3 Cephalometric analysis of Angle II malocclusion by FAEleven patients with Class II malocclusion at the stage of mixed dentition were selected. All patients showed retrusive mandible and normal maxilla by X-ray cephalometric measurement and the ANB angle was 5? They were...