The Effect Of The Number And Distribution Of Implants On The Remodeling Of Mandible Induced By Implant Supported Overdenture

As China entered the aging society, the edentulous patients are also increased, andthe retention of conventional complete depends only on the base unable to meet therequirement of patients with heavy resorption of mandibular alveolar ridge. Implantsupported overdenture is to use the implants imbedded in bone to provide supportand retention, repair the missing teeth and morphological defects, also patients can removeit easily. Because of its good retention and stability as well as lower operation risks andcosts, Implant supported overdenture has become the best choice for these patients. Theimplant supported overdenture restoration aims to solve the issue of retention andsupport, and also to prevent obvious peri-implant and alveolar bone resorption. In order toachieve this purpose, in recent years, the study of implant supported overdenture mainlyconcentrated in the selection of different attachment system, implant number anddistribution. and also, the study of remodeling of mandibular alveolar bone under the long-term occlusal function.Alveolar bone can adapt to the external stimuli and eventually reached equilibrium statethrough the changes of bone density and morphology. This process is called boneremodeling. Biomechanical research for bone remodeling has experienced several stagessuch as animal experiment, molecular biology experiments and numericalsimulation research. After a series of research on animal and molecular biology, somescholars tried to quantify the bone remodeling process in order to establish boneremodeling constitutive equations, and associated with the finite element method, toachieve the numerical simulation of the bone remodeling process. The biomechanicalstudy of alveolar bone remodeling mainly concentred on bone remodeling around fixedimplant dentures and orthodontics, while few research is about the bone remodelingaffected by mandibular Implant supported overdenture.In this study, clinical data is collected to establish the finite element model for thepatient with implant supported overdenture restoration. Then analyses the effect of implantnumber and their distribution of bone remodeling under bite force，in order to providetheoretical guidance for clinicals.All the study can be divided into four parts：1.The bone remodeling model for implant supported overdenture was established.Clinical data is collected before patient is treated. Using reverse engineering softwaresuch as Mimics, Geo-magic, UG to rebuild solid models of mandible implant overdentureand mucous membrane. Then assemble them into the solid model of mandibularimplant supported overdenture. Imported this solid model and related mechanicalparameters into Abaqus to establish a three-dimensional finite element modelof mandibular implant overdenture. The strain energy density (SED) based onbone remodeling theory is combined in this software though user materialsubroutine (UMAT) by Fortran language. At last, the mandibular implant supportedoverdenture bone remodeling model is established.The experimental results show that: mandibular implant supported overdenture boneremodeling model established by this method can reflect the stress and bone density changes of mandible under bite force. This study prepared a reasonable model for furtherresearch.2.The effect of implant number for mandibular implant supported overdenture boneremodeling.Use the experimental technique mentioned above, established bone remodeling modelwith mandibular overdenture supported by2-,3-,4-implants.Under thesame bite force, calculating alveolar bone stress and observe bone remodeling trends.The results show that: two implants supported overdenture will not cause periimplant bone resorption, but the risk of bone resorption in distal mandible was higherbecause of the higher stress. When the overdenture was supported by4implants,occlusion force was mainly shared by implants. Bone density declined around the distalimplants. More attention should be paid on different A-P distance and well distribution ofstress. When the overdenture was supported by3implants, large scale of bone resorptionwill occur around the two distal implants, so this kind of restoration is not recommended.3.The effect of implant distribution for mandibular implant supported overdenturebone remodeling.Based on the experiments above, established bone remodeling models with differentimplants distribution of2-,4-implants supported mandibular overdenture to choose theoptimal implant site by the evaluation of mandibular bone remodeling.The results show that: For overdenture supported by2implants, whenthe implant located in the site of bilaterallateral incisor and canine,there is noobvious bone resorption in mandibular. For overdenture supported by4implants, whenthe implants located in the site of lateral incisor and first premolar, there is no boneresorption occur, when the implants located in the site of canine and first premolar, thesmall scale of bone resorption will occur around the distal implants.4.The validation of clinical data and numerical simulation results.Collect the clinical follow-up data and compare it with the numerical simulationresults, so as to evaluate the validation of numerical simulation results.The experimental results suggested that: the clinical follow-up data shows, bone level decrease around the left side of distal implant.It is in agreement with the numericalsimulation results. The results indicated that numerical simulation results can accuratelypredict the mandibular bone remodeling trends induced by implant supported overdenture.Conclusion:1. The mandibular implant supported overdenture biomechanical model established in thisexperiment can resonablely describe the geometry and tissue and functionalstatus, reflecting the stress distribution and bone density change.2. Implant number of mandibular overdenture have ignificantly influence on theremodeling of peri implant bone.2-,4-implant supported overdenture have smallerbone absorption area than the model with3implants. Considering the risk of bonerebsorption around implant,3implant restoration is not recommended.3. In2implants supported overdenture, when implant is located in lateral incisor andcanine, alveolar bone around implant and distal alveolar ridge showed no obvious boneresorption; in4implants supported overdenture, the two anterior implants located inthe bilateral lateral incisor, two posterior implants in the first premolar implant had noobvious bone resorption trend. But when the implants located in canine and thefirst premolar, bone resorption will easily occur around the distal implants.4. Numerical simulation model built in this study compared with clinical data, the resultshow the same remodeling trends. It indicated that the reliability of numericalsimulation experiment. through the verification and comparison of clinical data, thesame tendency of reconstruction and clinical case, to prove the reliability of numericalsimulation experiment, the numerical experiment results can providereliable theoretical guidance for clinical.