| ClassⅡdivision 1 malocclusion is the most common malocclusion in clinic.It is difficult for treatment,especially for severe mandibular retrusion. Because of mandible moving backward passively,musclar position,occlusion and joint position is not consistent in action,which affects maxillofacial function and profile.The development of tooth,occlusion,jaws and face can be promoted with the use of functional corrector early.This study is to explore the clinical effects and mechanisms of action of fixed inclined bite-plate used in children who are in puberty or pre-puberty and have ClassⅡdivision 1 malocclusion with mandibular retrusion.The purpose is to provide principle basis and clinical guide for orthodontists.Objective:1.To study the remodeling of condyle process and glenoid fossa and the change of position of condyle process in glenoid fossa under the action of fixed inclined bite-plate by MRI.2.To evaluate the treatment effects on mandible and dentition of juveniles with ClassⅡdivision 1 malocclusion under the action of fixed inclined bite-plate by roentgenographic cephalometry.Methods: Thirteen children who are in puberty or pre-puberty and have ClassⅡdivision 1 malocclusion with mandibular retrusion were selected in random and were treated with fixed inclined bite-plate for 7.3-month on the average.The remodeling of condyle process,glenoid fossa and the tissue profile are detected. Ten children with similar malocclusion were selected as the controlled group and were treated only first for teeth alignment without any functional corrector.Results:1.After 3-month treatment with fixed inclined bite-plate for mandibular retrusion,MRI shows that the cartilage on condyle process of 13 children in experimental group is hyperplastic.The left hyperplasia is 0.86±0.19mm,and the right one is 0.83±0.20mm.And there is no statistical significance between them. It is indicated that the both condyle process have adaptive remodeling.As a whole condyle process both have the similar remodeling.2.The remodeling of glenoid fossa shows large inter-individual differences. There are 4 images in 13 experimental groups showing fresh bone formation on the anterior of the post-glenoid spine,which is the evidence of the remodeling of glenoid fossa.The MRIs of glenoid fossa remodeling in other cases is not significant.3.In T1 stage,the front joint space decreases while the post-joint space increases and joint space index increases significantly.The position of condyle process moves forward significantly(P < 0.01).In T2 stage,the joint space index decreases gradually.And the condyle process remains back to glenoid fossa.There is no statistical significance between space index of T3 and T0 stage(P>0.05).There is no significant position change between condyle process and glenoid fossa.And the relationship between them comes back to the normal. 4.After the average 7.3-month treatment with fixed inclined bite-plate,the overbite,overjet and molar relationship get to the normal. Decrement of overjet is about 6.12mm, of which osteal factors cause 2.81mm(45.92﹪) and teeth factors cause 3.31mm(54.08﹪). Variety of molar relationship is about 5.03mm,of which osteal factors cause 2.81mm(55.86﹪) and teeth factors cause 2.22mm(44.14﹪).5. The fixed inclined-bite plate may make the mandible develop,and the angle of SNB,the distance of Pg-OLP and length of body of mandible increase obviousely.There is no statistical significance between the controlled and experimental group of angle of SNA and distance of A-OLP.However,the fixed inclined bite-plate is inhibitory to development of the maxilla through the result of pre- and post-treatment.6.It is significant that the fixed inclined bite-plate makes condyle process improve vertically,and the actual increment of condyle process is three times of that of the controlled group,which makes the height of mandiblar ramus and length of mandible increase remarkablely.The fixed inclined bite-plate has no effect on sagittal increasement of condyle process.7.After fixed inclined bite-plate treatment,anterior facial height,posterior facial height and anterior-inferior facial height are increased and the proportion of face gets to harmony and the profile with ClassⅡmalocclusion is improved. Conclusions: The mandible of children who are in puberty or pre-puberty and have ClassⅡdivision 1 malocclusion with mandibular retrusion is protracted passively by using fixed inclined bite-plate.And the force of masticatory muscles are activated by the fixed inclined bite-plate.The height and length of mandible are increased through founctional orthopedic action.The sagittal and vertical developments of mandible are stimulated,and the profile with ClassⅡmalocclusion is improved,which are related with adaptive remodeling of condyle process,but the remodeling of glenoid fossa shows large inter-individual differences.The physiology relationship of condyle process and glenoid fossa is recovered after treatment. And the position of condyle process in glenoid fossa has no significant change compared with pre-treatment. |
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