Research For The Biomechanical Of Periodontal Ligament And Orthodontics Application In Simulation

With the development of society and the improvement of people's living standard,people pay more attention to their own profile.Orthodontics receive more and more people's attention.However,orthodontic treatment is a long-term process with repeated and even side effects,the main reason is the mechanism of tooth movement have not been clarified.As a soft tissue that connects the teeth and alveolar bone,the periodontal ligament(PDL)plays a key role during orthodontic treatment.The PDL can first feeling the orthodontic force and delivering it to surrounding bone tissue,bone remodeling occurs that cause tooth movement.Furthermore,during orthodontic treatment,the ratio of force/moment(F/M)that apply to the crown through appliance is a major factor that lead to the tooth moving in different ways.Therefore,studying the biomechanical properties of PDL and realizing the relationship between force system and tooth movement is great significant for improving orthodontic treatment efficiency.This paper uses experiments,theoretical model and finite element analysis(FEA)to research deeply for PDL's mechanical properties from the macroscopic and microcosmic angle.As a research object,the beagle's slice samples with the thickness of 0.2mm was made in cervical margin,midroot and apex areas(each area have 3 samples).By means of universal testing machine,each group samples were stretched at different rates,and the test date of every sample were achieved.As a certain sample's tension test curve,the average value of every sample date was calculate.Billinear model was adopted to fit the tension curve,and the curve of each section was obtained.Based on the results,the difference of elastic modulus for different rate and position of the PDL was evaluated by the statistical analysis software.Meanwhile,the mechanical properties of PDL can be regards as a superposition of instantaneous hyperelastic and time-dependent elastic behavior.For that reason,an extended Mooney-Rivlin model was established to describe the mechanical properties of PDL for different tension rates.The parameters of elastic and viscosity part was estimated by fitting the experiment curve of different rates.In order to investigate the difference of elastic modulus along longitudinal and circumference directions for the PDL,the nano-indentation tests were performed in cervical margin,midroot,apex(along longitudinal directions)and lingual-labial,mesial-distal(along circumference direction).The average elastic modulus in each region was calculated by Oliver-Pharr method,and analysis of whether there is statistical difference in these regions.The results show that there have no statistical difference along circumference direction,but there are obvious difference along longitudinal directions,and the average elastic modulus is lowest in midroot region,followed by cervical margin,apex.In order to study the viscosity behavior of the PDL in nanoscales,the nano-indentation tests were performed in various loading rates,Maxwell element,Kelvin element,standard Maxwell element and Kelvin element model were used to fit the test curves,and the parameters of model were obtained.The better fitting model parameters are regarded as the initial parameter for the finite element simulation.The results show that the effect of the substrate on the indentation experiments makes the large different between finite element and experiments results,but there exists ratios to the two parameters.Finite element simulation is widely used in orthodontics.In order to gain accurate finite element results,a high-precision tooth model and accurate element model of the PDL are necessary.The date of dental organizations can be obtain by CT scanning,entity models include teeth,PDL and alveolar bone are build via reverse engineering method.Based on the continuous medium mechanics theory,the hyperelastic part of the extended Mooney-Rivlin model above and elasticity tensor are deduced,on this foundation,the model subroutine was developed end embedded in ABAQUS.Simulation of the tension experiment,the fitted parameters are regarded as the initial parameter for the finite element simulation,and the experiment curves are considered as the objective function,the optimal value of the model can be obtained by iteration.The human teeth have a variety of ways to move during orthodontic treatment,various types of tooth movement can be divided into four types: tipping,translation,rotation and root movement.Each is comprehensive effect of orthodontic force and moment applied to the tooth(including the value,direction and the position of the force),the ratio of force and moment(M/F)determine the types of tooth movement.The combination of three-dimensional kinematics and non-linear constitutive model investigate the center of resistance position.The position have slight changes with the different directions of the moments applied to the tooth.Several types of tooth movement corresponding to the precise M/F value in buccal-lingual and distal-desial directions,including canine,incisor,and molar get by application of various moments.The results show that the canine required largest M/F ratio,followed by incisor,molar for the same tooth movement.For the different directions,the value of M/F ratio is larger in buccal-lingual than distal-desial direction.In order to investigate the effect of piles on tooth restoration and their service life.A three-dimensional finite element model of first maxillary canines for pile restoration was established.The stress distributions after tooth restoration with different pile materials were analyzed using 100 N bite force.The S-N fatigue characteristic curve of zirconia material was obtained using experimental data.The static analysis results demonstrate that when fiber piles are used to study the service life of zirconia piles in teeth.The static analysis results demonstrate that when fiber piles are used to repair,the stress from the dentin neck is larger than that by zirconia piles,but the stress from the apical of the dentin is smaller than that by zirconia piles.Besides,the stress exerted by fiber piles is lower than that by zirconia piles.Furthermore,the fatigue analysis results indicate that under normal conditions,zirconia piles results indicate that under normal conditions,zirconia piles can be used in teeth for over 20 years.Compared with firber piles,zirconia piles have a better effect on the repair of tooth defects.