Optimal Design And Fabrication Of A Hybrid Structures Implant For Surgical Mandibular Reconstruction

Mandibular continuity defect is one of the common defects of the maxillofacial region,which usually resulted from trauma,infection and tumors resection.The defects severely affect facial disfigurement as well as physiological functions such as language,chewing,swallowing and breathing.The objective of surgical mandibular functional reconstruction of mandibular defects is to restore normal appearance,denture and occlusal function on the basis of ensuring the stability of the reconstruction system.At present,the reconstruction of mandibular defects using autogenous bone transplantation has a low success rate of dental prosthesis repair due to insufficient vertical height and volume of the autogenous bone.So it is difficult to restore the occlusal function.Reconstruction using metal implants can restore occlusal function by directly reserving the installation structure of the abutment at the corresponding crown restoration position.However,it may be defeated caused by the significant stiffness mismatch among the hardware,graft and the remaining host anatomy would create a stress shielding effect.Reconstruction using tissue-engineered bone transplantation,as one of the most potential methods,has not yet achieved routine clinical application in a short time because it can not effectively guarantee the bone healing between the tissueengineered scaffold and autogenous bone.Currently,the biomechanical problems in mandibular reconstruction are still unclear.None of the reconstruction methods could provide all of the functions required for mandibular repairing,including soft tissue shaping,initial stability,mastication force supporting and bone growing guidance.Especially,the accurate reconstruction of the ideal mechanical properties of the mandible can not be realized by the present methods.The objective of this dissertation is to study the biomechanical problems in the reconstruction of mandibular defects,to construct the biomechanical principles of mandibular reconstruction,to propose and design a personalized mandibular implant with hybrid structures(including units of plastic-type,fixation,supporting,occlusal and growth),which can improve the stability and success rate of mandibular defects reconstruction.Firstly,the biomechanical properties of the mandible reconstructed by fibula transplantation were evaluated,and the biomechanical principles of the design of mandibular implants were proposed.On this basis,a personalized mandibular implant with hybrid structures that meets the requirements of biomechanics was designed combining the theory of bone functional adaptability and the topological optimization technology.Thirdly,animal experiments were conducted to evaluate the feasibility of reconstruction of mandibular defects with titanium alloy hybrid structures implant in terms of structure,biology and mechanics.Finally,a new artificial mandibular bone analog with hybrid structures based on non-degradable parts(including units of plastictype,fixation,supporting and occlusal)of polyether ether ketone(PEEK)biopolymer and tissue-engineered scaffold(growing unit)of polylactic acid(PLA)was proposed and designed due to the shortcomings of metal hybrid structures implant.The mechanical properties of the bone analog that meet the requirements of human bone tissue implants were verified by finite element analysis and physical experiments.The main works and research results of this paper are concluded as follows:(1)The method of accurately constructing the finite element model of mandibular biomechanics from CBCT data was studied.The validity of the finite element model was verified by the biomechanical characteristics and stress distribution of mandible.(2)A fibular graft is commonly placed at the inferior border of the mandible because of surgeon preference,although it makes a later dental implant placement and tooth restoration more difficult.Finite element models of reconstructed mandibles with a fibular graft placed at three vertical positions were established.Finite element method was used as an analytic tool to study the mechanical behaviors of the reconstructed mandibles.The main problems of reconstruction using autogenous fibular bone were concluded.This research provided an important basis for future improvement of the surgical and supported efforts in developing novel ways of generating bone graft segments of the same size and shape of the original segment.(3)The relationship between strain energy of bone-scaffold system and time was constructed as the biomechanical mechanism for bone growth under the guidance of scaffold.The design strategy for hybrid structures implant was proposed and the implant that meets the requirements of biomechanics was designed by using topological optimization technology.(4)The feasibility of mandibular defects reconstruction with titanium alloy hybrid structures implant and fabrication by additive manufacturing technology was verified by taking canine mandibles as the case study.The main problems of reconstruction using metal implants were identified.(5)The mandibular biomechanical properties between reconstructed by bone analog with hybrid structures based on non-degradable parts of PEEK biopolymer and tissue-engineered scaffold of PLA and reconstructed by fibula with titanium fixation plate were compared and analyzed by using the finite element method and the biomechanical testing platform of the jaw bone.The validity of the finite element method results was verified.The satisfied potentiality of PEEK biopolymer as a mandibular implant has been preliminarily confirmed.