Key Biomechanical Study Of Materials And Structures In Oral And Maxillofacial Prosthesis And Orthodontics

Advanced therapeutic methods for oral diseases involve many fields including materials, biology and mechanics. Especially, mechanics often plays a major role. For example, oral and maxillofacial defects can be caused by congenital defects, tumor, trauma, and so on. Maxillofacial repair and orthodontic treatment need scaffold materials with good biocompatibility and antibacterial properties meanwhile mechanical structure coupling with maxillofacial tissue. It is necessary to understand the interaction between cells and interface of biomaterials at micro- and nano-scale, and study large-deformation flexible structure(such as orthodontic archwire) at the macro-scale, coupling with maxillofacial tissue, which has a complex biological structure in growth and change. Therefore, the research on the biomechanics of stomatology is often faced with more challenge. This thesis mainly focused on the material for scaffolds in tissue engineering and the design of orthodontic device which involve maxillofacial repair and orthodontics. Using theories and methods in solid mechanics, cell biology, nano materials science and other fields, we studied the size effect of graphene’s cytotoxicity, discovered and made a new scaffold material with good performance. We also quantitatively analyzed the interaction between archwire and teeth, put forward a way to realize en-masse retraction of anterior tooth in orthodontic treatment, and invented a computer assisted technology for generation of individual dental arch. A computer software was compiled and acquired the copyright. The creative results of this paper are as follows:(1) The effects of different sizes and concentrations of GO on cell activity, cell morphology, cytoskeleton structure and mechanical properties of normal cells, and two kinds of cancer cells were studied by laser confocal microscopy, AFM and other advanced cell biomechanics laboratory equipments. The results showed that the effects of different sizes of GO on cell viability were significantly different and the small size nanoparticles had a strong cytotoxicity. The effects of GO on the morphology and mechanical properties of cells were as follows: cell surface roughness of all kinds of cells decreased under the action of nano-particles and the size-dependent effect was related to the type of cells. Young’s modulus of different kind of cells increased with sizes of nano-particles decreasing meanwhile the concentration of nano-particles also had a great influence on the survival rate of cells.(2) Polylactic acid(PLA) and polyurethane(PU) have a good prospect in the field of tissue engineering because of good mechanical properties and biocompatibility. However, scaffold materials demand good biocompatibility and excellent antibacterial properties. In order to make up for the deficiency of PLA/PU, we take advantage of the finding which micron-sized GO is no toxic to tissue cells, but toxic to bacterias. In this paper, ternary PLA/PU/GO composite fibrous paper was fabricated by electrospinning, which exhibits good biocompatibility and antibacterial activity against the Gram-positive Staphylococcus aureus and the Gram-negative Escherichia coli.(3) In orthodontic clinic,prognathism or maxillary protrusion need to be treated with en-masse retraction of anterior teeth, which is difficult to achieve. This study presented a three-dimensional elastic finite element model of maxillary dentition, periodontal ligament, alveolar bone coupling with archwire. Using emulational calculation and analysis, we obtained conditions of achieving en-masse retraction of anterior teeth and designed a new orthodontic device, which can realize en-masse retraction of a group of teeth more easily.(4) In orthodontics, force values loaded on the teeth by archwire will affect treatment directly. Doctors always estimate force values based on their understanding of archwire material and experiences. False estimations caused by lack of experience will lead to serious side effects such as root resorption. In order to solve this problem and obtain the precise force values loaded on teeth, we got the quantitative function relationship among the material, structure and force values by assuming the archwire as an elastic curved beam. We made the clinical application forms by calculating the data. A software generating individual arch form for orthodontic patients was developed, which can help clinicians acquire images of dental arch form efficiently and conveniently.