| Summary: | 碩士 === 國立成功大學 === 生物醫學工程學系 === 104 === Rapid maxillary expansion is an orthodontic method to correct skeletal Class III, posterior cross-bite, narrow nasal cavity and maxillary width deficiency. Increasing maxillary arch circumference and posterior cross-bite may improve nasal respiration as well. The procedure produces forces to disrupt connective tissue and cause suture separation. There are few reports on evaluation of the effects of bone-borne expanders with or without surgical assistance rapid maxillary expansion. None of them was focused on the effects of bone-borne expanders with different position of mini-screws.
The purpose of this study is to study the mechanical effects of nonsurgical rapid maxillary expansion with different locations of mini-screws. It is using a finite difference model to study the applied incremental displacements and stress distribution of the craniofacial structures.
The study includes clinical follow up, finite element simulation and 3D printing model experiment. In this study, the patient is a 15-year old girl with maxillary transverse deficiency. She was subjected to the Bone-borne expander treatment from September, 2014 to March, 2015 in the Division of Orthodontics, Department of Stomatology of the National Cheng Kung University Hospital in Tainan, Taiwan.
The finite element model is based on the digitized geometry of the cone-bean computer tomography scan. It includes teeth, alveolar bone, maxillary plane, mini-screws and mid-palatal suture. Four mini-screws are symmetrically implanted at the maxillary. The boundary condition is mini-screws displacement and the foramen magnum is fixed. The 3D co-ordinates origin point is on the end of suture. All materials were considered to be linearly elastic, homogeneous and isotropic.
In the results, the mini-screws implanted near tooth significant influence the tooth displacement; The screws implanted near suture, the suture have expanded a partial. However, the whole suture expanding and tooth expanding is inconsistent. Screws implant near tooth, the type B, recommended for clinical application. In the experiment, we find the displacement of screw close to the expander when the screws and the expander are approaching separation. The material of mid-palatal suture is an important parameter; the suture is complex connective tissue and it cannot be simplified to a gap.
This research provides the framework of maxillary expansion for future study. It uses computer-aided engineering to analysis the mechanical effect of the expander, mid-palatal suture and mini-screws, and also gives suggestion of mini-screws position to the dentist.
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