| As C hina entered into the aging society rapidly,the number of the edentulous patients increased constantly.On this occasion,the implant supportedoverdenture(IPD)had become the best prosthetic method,because it not only could provide the reliable retention force and stabilization,but also hadslight surgical trauma and low cost.In the therapy,the patients not only need the implant could provide reliable retention force and stabilization,but also required the mandibular tissue stay healthy for long term to prolong the service time of the implant.The clinical practice proved that the inadequate stimulation would lead to the absorption of the bone tissue that around the implant and the remote alveolar ridge,and this is the main cause forthe shorter life of the IPD or even the failure restoration.The IPD is a mechanical system which contains bythe implant,the attachment,the denture and the bone tissue.Itgained the mechanical balance of the whole system through the movement of the denture on normal chewing process,and then finished the chewing movement.Onthisprocess,theocclusalforcewassendtothe mandibular bone through two ways which were the denture-attachment-implant and the denturebase-mocusa,the stimulated and maintained themandibular tissue's health and stabilization.As oneofthemost important department,the attachment influenced the movement,the retention and the stabilization of the supported overdenturedirectly,so itplayed an important role on the chewing process.Therefore,the study of the influence induced by different types of attachments to the IPD's movement pattern,occlusal characteristic,stress distribution inside ofthe mandibular bone and long-term reconstruction of the bone,and the analysis of eachelement'sinterrelationshiphad important guiding significance to choose the type of attachmentreasonablyonclinical practiceandforecast the situation of forward bone reconstruction scientifically.However,nowadays most of the studies of at tachment are focusing on the level of statics analyze.So far,there is no systematically research about the moving mode,occlusive characteristic,stress distribution or long-term bone reconstruction of the fournormal types of overdentures supported by different attachments.This research focused on theclinical practice of the IPD,andcollected Computed Tomography(CT)data of the patients,thenconstructedthebone reconstruction models of mandibular IPD supported by four types of attachments.The study tried to find the characteristics of four types of dentures' moving mode,stress distribution and bone tissue reconstruction through simulated the functional chewing process,and analyzed how the bone tissue reconstruction affected by the denture's movement pattern and occlusalforce distribution.Thus this research compared the results collected from the clinical practice with the numerical simulation analyze and verified the accuracy of the numerical simulation,and revealed the relationship between the atta chment type and the bone tissue reconstruction,then provided the theoretical basis for the reasonable choice of attachment on clinical practice.All the study can be divided into twodifferent parts:1.The study on clinical cases of IPD supported by different types of attachmentsThis part collected the clinical data ofthe patients who accepted normal operations of the mandibular IPD which were supported by different types of attachments at the same time nodes.The data included the patients' basic oral state,oral soft tissue and bone tissue around the implant.The study compared the occlusal characteristic of the IPD supported by different types of attachments which measured by the T-Scan?,and analyzed the related data that include the occlusive fo rce distribution state after the IPD,the change ofthe soft and hard tissue around the implant and the relationship between them,finallyafford theexperimental basis for the follow-up numerical simulation of the tissue reconstruction.The experimental results indicated that:(1)The soft tissue around the implant was health,and there was no evidence show that the types of attachment affected the health of the soft tissue around the implant;(2)The bone tissue's absorption ofall the control groups were large after a short time of the operation,and it mightcaused by the traumaofthe operation.(3)After a long period of the operation,the bone tissue's absorption ofall the control groups reduced,but the differences of theabsorption quantity were more significant.The comparison ofthe bone tissue's absorption of all the control groupswere: Around the implant: Group M(Magnetic)<Group E(ERA)<Group R(Ball-cap)<Group B(Bar-clip);The remote alveolar ridge: Group E<Group B<Group R<Group M.This phenomenon might causedby difference ofthe bone reconstruction results which induced by the different results of bone reconstruction.(4)The occlusal characteristics of the overdenturesupported by different types of attachments monitored by the T-Scan? indicated that: The COF Y wasconnectedwith the occlusal stress distribution'sdegree of the uniformity;the maximum of the occlusal force was connected with the retention force of the attachments.The occlusal force distribution of Group ERAwas larger and more homogeneous than other groups,and the COF Y was the lowest,meanwhile,its maximum of the occlusal force was the biggest,and the denture was more stable than other groups,too.Thus the ERA attachment is the prior choice on clinical practice.2.The numerical simulation study on the bone tissue reconstruction of the mandibular IPD supported by different types of attachments.This part of research based on the CT data collected from the clinical practice,constructed four bone reconstruction models of mandibular IPD supported by four types of attachments.The research simulated functional chewing process,and studied the features ofthe overdentures of different types of attachments that included the moving mode,the stress distribution and the bone tissue reconstruction,then compared the differences between groups and tried to explain the interrelationship of each factors,and provide the theoretical basis to choose the type of attachments reasonably.After this,the researchcomparedtheclinicalpractical results with the numerical simulated results,and testified the accuracy the numerical simulation then provide the clinical verification to numerical simulate and forecast scientifically the bone tissue reconstruction.The experimental results indicated that:The different attachments changed the occlusive characteristics of the denture by effected the moving mode of the dentures,then affected the stress distrib ution inside of the mandible and finally impressed the long-term functional reconstruction of the mandibularbone tissue.?The movement pattern,occlusal force distribution and bone tissue reconstruction state of the denture supported by the magnetic attachment.On thefunctional chewing process,the dentureof the magnetic group slid horizontally to the behind relative to the mandible,and the remote of the denture revolved slightly around theimplant which worked as the pivot line to the below and behind.In spite the magnetic attachment could buffer the lateral force,the implant still accepted large occlusive force in vertical direction on the chewing process,which lead to the stress concentrate on thecortical bone of the remotealveolar rid ge and the quantity of the bone absorption was large.?The movement pattern,occlusal force distribution and bone tissue reconstruction state of the denture supported by the clip-bar attachment.The movementof the denture supported by the clip-bar attachment mainly was the clip made by nylon which has buffer function rotated the bar to below and behind,sothe moving distance of the front denture which placed the nylon clip was notlong,butthe remote of the denturemovedobviouslyas the swirl of the clip and the bar.The occlusive force distribution was larger around the implant and smaller on the remote of the alveolar ridge.The high stress distribution range ofthebone andthe range of the bone absorption was consistent with the occlusal force distribution range.?The movement pattern,occlusal force distribution and bone tissue reconstruction state of the denture supported by the ball-cap and ERA attachment.The movement pattern of the denture supported by the ball-cap attachment was similar with the denture supported by the ERAattachment,because theyboth had the buffer function in vertical direction.The buffer gap in vertical direction reduced largely the fulcrum function of the implant on the moving process of the denture,which made the denture occlusal force distributed more large and more homogeneous.The stress force distribution of the bone tissue around the implant and on the remote alveolar ridge was more homogenous,and the bone absorption reduced less than other two types of attachments.The fulcrum function of ERA attachment worked less obviously than the ball-cap attachment,and the effect of buffer function on ERA group was better than the ball-cap group,so the stress concentration and the bone absorption was the least in all the groups.Conclusion:1.In this study,a bone remodeling model of mandibularoverdenture retained by two implants with four different types of attachments was established,in order to simulate and analyze movement patterns,occlusalforce distributions,stress distributions,and bone remodeling parameters.Results showed that data acquired from this study agreed to clinical findings,and has proved the feasibility and accuracy of the established model.And meanwhile,the simulative data could provide reliable reference for clinical implant-overdenture restoration.2.Different types of attachment contain units of varied cushioning directions and abilities,leading to different denture movement patterns and occlusion features,with varying implant fulcrum effects and elastic deformation of distal alveolar ridge.These factors will further impact the stress distribution within the alvealar bone,and finally determine the functional remodeling process and outcome of bone.On the clinical practice,by adjusting those influence factors,the bone remodeling outcome could be wel-controlled,and thus prolonged service time of denture could be achieved(Fig.1).3.Among the four types of attachment,the uniq ue cushion design of ERA has resulted in buffering movements in the vertical dimension,leading to reduced fulcrum phenomenon of the implants and more homogeneous occlusalforce distribution.Lower stress distribution around the implant and in the distal alveolar bone can ensure less bone resorption during the process of functional remodeling,and thus prolonging the service time of implants.To sum up,it is suggested that the ERA attachment could be the prior choice in the clinical practice. |
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