Study On The Biomechanical Mechanism Of Personalized And Accurate Orthodontics And Its Realisation Based On SMP(Shape Memery Polymer Materials)

Orthodontics can adjust the balances and harmonizations among the facial skeleton,dental and maxillofacial muscle,which prompt treatment objects to get better appearances,establish positive and optimistic personal images and life attitudes,and improve self-confidence in social comunication at the same time.In orthodontic treatment,the corrections of dislocated teeth mainly depend on orthodontic forces loaded by treatment appliances on the crowns,and the magnitudes of the forces must be within a suitable range to motivate bone remodeling mechanism better and achieve ideal teeth movements.Therefore,it is significant to investigate the complex relationships of ‘orthocontic forces-parodontium stress/strain-alveolar bone remodeling-teeth movement' deeply.Currently,clinical experiences and subjective judgments of orthodontists are play dominant roles in clinical treatment,and the patient's regular return of visiting for treatment trial and error correction is still extensively adopted.Till now,the orthodontic fores exerted on teeth are rarely determined quantitativly by computer simulations or experimental measurements,which make orthodontic treatment often fall in the cycle of correction-adjustment-correction with a low efficiency.On the other side,the frequently-used orthodontic appliances in clinic include fixed appliances and invisible aligner at present.The metal nickel-titanium wire used in fixed appliance has potential threats to human body in the complex oral environment.Invisible aligner is a kind of personalized and customized appliances,but its limits include high cost,limited treat capacity and narrow indications.Shape memory polymer(SMP)such as shape memory polyurethane(SMPU),with good biocompatibility,low cost,easy forming and transparent color,had been proved by some scholars as a potential ideal material for orthodontic appliances.The aims of this study were to investigate the biomechanical mechanism during orthodontic treatment and construct a kind of integrated personalized appliance based on SMPU materials to promote the precision and individuation of clinical orthodontics.Firstly,a periodontal ligament(PDL)constitutive model that conforms to the biomechanical properties of human PDL was constructed,and then the optimal orthodontic force ranges under various tooth movements were studied and obtained,which offered a good biomechanical foundation for the design of personalized and accurate orthocontic planning,then verified the availability of design techniques on personalized orthodontic planning through a clinical case.On this basises,the personalized and accurate orthodontics based on SMPU was studied,the foundational thermodynamic responses of SMPU were analyzed,as well as the design and fabrication techniques of personalized SMPU appliance.At last,the mechanical responses of appliance were investigated by computer simulations and verified by experimental measurements.The main works and reaearch results are as follows:(1)Based on the experimental data of human PDL,a material constitutive model,which conformed to the biomechanical properties of PDL,was proposed by combining hyperelastic material model and viscoelastic material model,and the experimental processes were simulated by finite element software ABAQUS to verify the accuracy of the model.(2)Taked the maxillary canine as research object,considered the PDL hydrostatic stress and logarithmic strain as indicators,calculated and obtained the optimal orthodontic forces of tooth under various movements,offered a biomechanical foundation for the design of personalized and accurate orthocontic planning.(3)Based on orthocontic biomechanics,a design technique of personalized orthodontic planning on the basis of orthodontic force measurement and finite element simulation was proposed,and a clinical case from Zhejiang People's Hospital was considered as research object to verify the design methodology of personalized and accurate orthodontic planning.That is,we helped orthodontist formulated and implemented accurate and safe orthodontic planning by means of orthocontic forces measurement and finite element simulation,and the availability of planning was varied by clinical feedback during treatment process.(4)A three-dimensional thermodynamic constitutive model was constructed in order to describe the situation of SMPU material under complex stress,and its shape recovery effects under different loading conditions were investigated through finite element simulations in detail.(5)On the basises of SMPU thermodynamic material model and the design technology of personalized orthodontic planning,a design technique of integrated personalized SMPU appliance was proposed,then a integrated personalized SMPU appliance was designed and fabricated,and its shape recovery forces under different deformations were studied by finite element.Further,a three-dimensional orthodontic force dynamical measurement platform was built to measure the mechanical responses of the appliance during shape recovery process,the availability of integrated SMPU appliance was initially verified.