Simulation Of Rat Molar Periodontal Microstructure In Orthodontic Tooth Movement

Orthodontic force acts on periodontal structures through teeth crown androots, during which induces a series of biomechanical and molecular biologicalchanges through local stress stimuli and deformation. Tooth movement is theresult of bone resorption on the pressure side as well as bone osteogenesis on thetension side. The macroscopic biomechanics of teeth, periodontal membrane andalveolar bone has been investigated thoroughly. However, researchers treatedalveolar bone as isotropic and homogeneous material and ignored the fact thatperiodontal microstructure around roots is highly complex and inhomogeneous.After the development and application of high-resolution Micro-CT, moreaccurate three-dimensional photograph of periodontal membrane, lamina duraand trabecular net structure can be achieved, which make researchers realizedthat how little we know about the biomechanics of periodontal microstructuresin this level. Different kind of alveolar, especially alveolar under osteoporosis,has different reactions towards orthodontic treatment, by learning which willhelp clinical practitioners a lot. Thus, we establish a finite elemental model tosimulate microstructure around molar root of rat. My research consists of5steps:1. Morphological analysis of alveolar bone of SD rats through Micro-CT scanningArchive bone feature parameters of maxillary alveolar bone around firstmolar roots and cervical vertebra by female SD rats Micro-CT scanning toperform alveolar bone morphological analysis, especially osteoporotic alveolarbone.2. An in vivo Micro-CT observation of molar movement under orthodontictreatment in healthy SD ratsBuild healthy rats molar mesial movement model (30g VS.100g). Throughin vivo Micro-CT scanning at0d,1d,2d,3d,5d and7d, periodontal ligamentthickness, molar displacement and angular changes were recorded, throughwhich molar movement pattern can be learnt.3. An in vivo Micro-CT observation of molar movement under orthodontictreatment in OVX ratsBuild osteoporotic rats molar mesial movement model (30g). Use in vivoMicro-CT scanning at0d,1d,2d,3d,5d and7d to register periodontal ligamentthickness and molar movement pattern.4. Establishment of periodontal microstructure simulation model around ratmolarBuild trabecular unit model according to bone feature parameters achievedin step1. Establish trabecular tetrakaidecahedral unit to simulate individualcancellous bone net structure. Then assemble molar root, periodontal membrane,lamina dura and trabecular net structure together; construct simulation modelworking condition on the basis of molar stress distribution and movementdiscipline in step2to observe model stress distribution and mechanicaldeformation under orthodontic force load.5. Orthodontic simulation model verification of healthy rats Build20individual simulation models according to20healthy female SDrats maxillary alveolar bone feature parameters. Then load30g and100gorthodontic force to rats and models respectively. Observe rats bone featureparameters longitudinal changes at0d,1d,2d,3d,5d and7d, then compare withmodels parameters at the same time points. Analyze the difference between ratsand models to testify the simulation degrees.6. Orthodontic simulation model verification of OVX ratsBuild20osteoporotic simulation models according to20osteoporoticfemale SD rats maxillary alveolar bone feature parameters.30g force wasloaded on rats and models to compare the difference. Analyze the differencebetween osteoporotic rats and models to testify the simulation degrees.Results:1. BV/TV, Tb.N and SMI in healthy rat maxillary alveolar bone are higher thanin cervical vertebra, while Tb.Th and Tb.Sp are lower than in cervicalvertebra. BV/TV, Tb.Th and Tb.N of OVX rats alveolar bone decreasedsignificantly comparing with healthy rats while Tb.Sp and SMI increasedobviously. In OVX group, cervical vertebra bone volume fraction decreased50.5%compare with healthy rats, while alveolar bone volume fractiondecreased only29.8%.2. PDL thickness changes can be observed immediately after force loading,however, there are difference between light and heavy force. The100g forcecan cause PDL thickness changes in a shorter time. Molar mesial movementcan be observed in both groups.100g force induced more movement than30g and followed by a longer lag period.30g force has shorter lag periodand molar continues to move forward after day5. Healthy rats molar has abodily movement pattern and no obvious rotation and inclination. 3. PDL width change in OVX rats is similar to healthy rats. However, OVX ratPDL width doesn’t has recover trend like healthy rats. We can observe moremolar mesial movement in OVX rats than in healthy rats. OVX rats molarhas a bodily movement pattern.4. Simulation model can represent the morphological characteristics of healthyand osteoporotic alveolar bone. Then the simulation of orthodontic force(30g and100g) on normal model shows characteristic stress distribution andmechanical deformation.5. Simulation models kept good consistency with healthy rats during0-5daysafter loading. On day7, every features simulation decreased obviously. Thesimulation degree is lower under100g force than30g force.6. The results are similar with healthy rats simulation. OVX models have goodconsistency with rats suffering osteoporosis during0-5days after forceloading (30g). On day7, features are obvious different between OVX ratsand models. The simulation degree is lower in OVX models than in controlgroups.Conclusions:1. Alveolar bone features in rats has its own characteristics comparing withvertebra bone: trabecular around molar roots are mixture of both plate-likeand rod-like trabecular and cervical vertebra trabecular are mainly plate-like.Bone volume fraction in OVX rat alveolar bone decreased significantly,however, the decreasing degree is not as much as the one in cervicalvertebra.2. The upper first molar of healthy rats moves bodily during0-7days afterorthodontic force loading.30g force can induce PDL width recoveringduring5d-7d.100g force can induce more obvious molar mesial movement. 3. Molar movement pattern in OVX rats are similar to health rats. OVX ratsdoesn’t have PDL width recover trend and have more obvious molarmovement than healthy rats.4. The simulation model shows similar micro structure with rats alveolararound molar roots. The model has infinite deformation trend after forceloading compared with rats actual measurement. The model morphology canbe transferred to cancellous bone parameter in math language.5. Results show that the consistence is high during0-5days then decreasedalong with the bone remodeling activation. On day7, the consistencedecreased significantly both in light force groups and heavy force ones,which indicates models lack of biological analogue couldn’t simulate thecomplicated alveolar bone changes under long-term orthodontic forceloading. The simulation degree is higher under30g force than100g force.6. Similar to healthy rats simulation, osteoporotic model can analogue themechanical deformation under short-term force loading. However,osteoporotic alveolar bone is usually more sensitive to force loading,especially the heavy one. So simulation model could only analogueosteoporotic rats under short-term orthodontic force loading.