| Angle's Class ID malocclusion is one of common dentofacial deformities in orthodontic clinic, especially skeletal class â…¢ malocclusion, which severely influences the craniofacial growth, and development, oral function and facial aesthetics. It is very difficult to treat and should be pay more attention because of its complicated etiology. It is very important for orthodontists to use dentalfacial orthopedic therapy to treat skeletal class â…¢ patients as early as possible.The aim of this study was to investigate the changes in hard tissue profile in patients with early functional-skeletal Class â…¢ malocclusion are treated with Twin-block Magnetic Appliance (TMA).In this study, we chose 40 patients at random included 17 boys and 23 girls, aged from 4 - 145/12 years from Orthodontic Department of Dental School of Kunming Medical College, clinically diagnosed as Functional-skeletal Class â…¢ malocclusion with Class â…¢ molar relationship, at least four anterior teeth presented cross-bite during growing. Cephalometric radiographs showed Class in dentofacial characteristics. Facial profile appeared straight or concave. The patients were treated with a new magnetic dentofacial orthopedic appliance, TMA.40 cases, 80 sheets of pre-treatment and post-treatment lateral cephalograms were obtained. In order to evaluate its effect on the treatment of early skeletal Class in malocclusion, we used a computer cepholametric finite element analysis system developed ourselves. We selected 35 hard tissue landmarks to divide to 21 finite elements and six parameters were used to describe changes of finite elements.The results showed:1. The maximum strain of all finite elements exhibited elongated strain; the minimum strain exhibited compressed strain. The surface area of all finite elements increased.Shape had the larger increase than size. Most of the maxillary finite elements rotated upward and forward; the mandibular showed a downward and backward rotation.2. Anterior cranial base (element 1), posterior cranial base (element 2) had a mild increase in the surface area and rotated upward and forward. The smallest shape and size change in all elements.3. Hard palate (element 3, element 4). Element 3 had a 6.8% surface area increase Element 4 increased in the surface area (15.1%). Two elements showed an upward and forward rotation.4. Maxillary posterior face (element 5), maxillary upper face (element 6), maxillary anterior face(element 7) and maxillary sinus(element 8) had a downward and backward rotation. The surface area increased largely (11.3%, 8.4%, 14.1%, 5.9 %.)5. Condylar process (element 9), mandibular ramus (element 10), mandibular angle (element 11), mandibular body (element 12, 13, 14) and chin (element 15) rotated downward and backward. The shape and size change had a smaller increased than maxilla.6. Upper anterior teeth (element 16), upper molar (element 17), lower anterior teeth (element 18) and lower molar (element 19) had a downward and backward rotation. The shape and the size had a mild increase.7. Anterior face (element 20) and posterior face (element 21) rotated downward and backward. Element 20 increased more (4.6%) than element 21 (5.5%).The conclusion was:1. The main mechanism of treatment is to optimize growth guidance: (1) The growth of maxilla was stimulated. The length of maxilla increased and maxilla moved forward (2) On the contrary, the growth of mandible was restrained. The length of mandible had no significant change and the mandible showed a downward and backward rotation.2. TMA is a kind of very effective and safe appliance to treat early functional-skeletal Class HI malocclusion. |
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