The Effect Of Microthread Neck Design On Stress Distribution And Marginal Bone Loss Around Dental Implants

PARTI The study on stress distribution of dental implants with microthread neck design in alveolar bone of differenttype:a finite element analysisObjective:Whether microthreads in the crestal portion can reduce the amount of marginal bone loss(MBL)around implants has not yet been determined.The purpose of this studywas to investigate the stress distribution of microthread neck design dental implants.Methods:A patient with mandibular edentulous jaw was selected and scaned by the cone beam CT.The DICOM image data of the patients were imported into MIMICS.The model got form MIMICS was imported into CREO Elements/Pro.The implant position was cutted to get the intersecting surface and the solid model were established.According to the proportion of dense bone/cancellous bone and the density of cancellous bone,the mandibular bone model was defined to four types.An implant system with microthread neck design was selected and the solid model of the microthread implant was established exactly(Mi model).Acroding to Mi,a regular macrothread implant model(Ma model)was established.Mi and Ma were different only in neck design.The superstructure of the implant was simplified as a cone with a diameter of 3.84mm on the lower surface,a maximum diameter of 5.42mm in the middle and a diameter of 2.96mm on the upper surface.The implant model and superstructure were assembled and formeda composite structure of implant abutment crowns.The composite structure was then assembled with bone model of different types.A total of 8 models were obtained,and the assembled models in CREO Elements/Pro were imported into ANSYS to establish three-dimensional finite element models.The distal,medial,buccal and lingual position of the bone model was given rigid constraint.To mimictheocclusalforce,a vertical force of 100N and a 45 obliqueforce of 30 N were applied ontop ofthecrown.Stressesandstrainsaroundthecorticalbone-implantinterfaces were analysedusing ANSYSsoftware.Von-Mises force peak and shear stress peak were calculated.Results:1.Overall characteristics of stress distributionThe largest von-mises stress and shear stress were found in the cortical bone region of the neck of the implant in all models.At vertical loading,the maximum stress mainly existed in the cortical bone around the implant neck.When oblique loading,the maximum stress mainly existed in the lingual cortical bone of the neck.The maximum stress of cancellous bonemainly concentrated at the end of the implant while the minimum stress mainly distributed in lower 1/3 of the groove of the implant.2.Stress changes according to different implant neck designs in the same bone type models.In type ?,?,? bone models,Von Mises-force and shear force peak value of implant-cortical bone interface in Mi group were significantly less than in Ma Group.In type IV bone models,Von Mises-force and shear force peak of implant-cortical bone interface in Mi group were less than in Ma Group,but the difference is relatively small.In ?,?,IV bone,there was not significant differenceinVon Mises-force and shear stress peak value of implant-cancellous bone interface between Mi group and Ma group,which suggested that the microthreadsdesign show no obvious advantage in cancellous bone.3.The stress changes according to different bone types in the same neck design group.3.1 Mi group,vertical loading.The order of bone type according to the Von Mises-forcepeak value in implant-cortical bone interfacewas as follow:Type ?<Type ?<Type?<Type?.The order of bone type according to the shear stress peak value in implant-cortical bone interface is as follow:Type ?<Type ?<Type?<Type IV.The peak value are significantly different between Type? and Type IV.The order of bone type according to the Von Mises-forcestrength peak value in implant-cancellous bone interface is as follow:Type ?<TypeIV<Type?.The difference between Type? and Type IV were small.3.2 Mi group,Oblique loading.The order of bone type according to the Von Mises-force strength and the shear stress peak value in implant-cortical bone interface is as follow:Type ?<Type ?<Type?<Type ?.The difference among different bone type models was not asobvious as vertical loading.The difference between Type ? and Type IV was especially small.the order of bone type according to the Von Mises-force strength and the shear stress peak value in implant-cancellous bone interface was as follow:TypeIV<Type?<Type ?.The stress in Type ? was obviously large than Type?and Type?,but the difference between Type ? and Type ? were small.3.3 Ma group,vertical loading.The order of bone type according to the Von Mises-force strength and the shear stress peak value in implant-cortical bone interface is as follow:Type ?<Type ?<Type?<Type ?.The differences among different bone type models were not as obvious as Mi group.The order of bone type according to the Von Mises-force strength and the shear stress peak value in implant-cancellous bone interface is as follow:Type ?<TypeIV<Type?.The difference between Type ? and Type ? was small.3.4 Ma group,oblique loading.The order of bone type according to the Von Mises-force strength and the shear stress peak value in implant-cortical bone interface is as follow:Type?<Type?<Type ?<Type ?.The difference among different bone type models was small.The order of bone type according to the Von Mises-force strength and the shear stress peak value in implant-cancellous bone interface is as follow:TypeIV<TypeIII<Type ?.The difference among different bone type models was small.Conclusions:1.Relative to the Ma group,Mi implant is more suitable for ?,?,? bone2.The differences between Ma group and Mi group is least in type IV bone model.3.The stress in cortical bone around implant is large in Type IV bone no matter which kind of implant(Mi or Ma)were selected.PART ? Marginal bone loss around dental implants with and without microthreads in the neck:A systematic review andmeta-analysisObjective:Threaded dental implantis the main type of dental implant used in clinic.The design of implant surface threads affects the biomechanical behavior of the implant and is of great significance to the study of implant.Studies have confirmed that the cortical bone region is the main part that bears the loading.When the implant is underfunctional loading,the stress concentration mainly occurs in the cortical bone region around the neck of the implant,and so,the neck design of the implant has an important influence on the stress distribution.lt is a reliable method to improve the implant neck design and evenly distribute the implant neck stress.Hansson proposed the concept of microthread in 1999 and claimed that microthreads in the crestal portion could reduceshear forces at the implant-bone interfaceand the amountof marginal bone loss(MBL)around the implants.Some clinical studies show that roughsurfaced implants with microthreads at the neck could maintain the marginal bone level during healing period and cause significantly less MBL underlongtermfunctionalloading.On the contrary,some scholars have different opinions that microthreadscan not improve marginal bone preservation,and there is no significant difference between implants with macrothread and microthread in terms of MBL after loading(1yearor 12 years)with good oral hygiene and a stable periodontal condition.Whether microthreads in the crestal portion are able to reduce the amount of marginal bone loss(MBL)around implants has not been determined yet.The purpose of this review was to investigate the marginal bone loss around dental implants with and without microthreads in the neck through searching published randomized controlled clinical studies and a systematic evaluation and meta-analysis.Methods:This review was based on the PRISMA guidelines.An electronic search from inception to Aug 19,2015 without any restrictions on language was performed in PubMed,Cochrane Central Register ofControlled Trials,EMBASE,Web of Sciences,and AMED(Ovid)databases.A manualsearchwas performed.Randomized clinical trials(RCTs)compared the MBL between implants with and without microthreads in the neck were included.A detailed search strategy was preparedfor each databaseusing the followingMeSHTermsexploded:'Dental implant','Dental implantation',in combination with the following Text Words:'dental implant*','oral implant*','tooth implant*','teeth implant*','osseointegrated AND implant*' and 'microthread*'.The exclusion criteria contained the following:case report,review,animal studies,finite element analysis(FEA),in vitro studies;studies compared not only the microthreads design but also other mixed design;studies with a follow up period of less than 1 year.Two reviewers read the titles and abstracts of the studies independently to decide whether the studies met the inclusion criteriaor not.Twoinvestigatorsperformed the quality assessment independentlyby using The Cochrane Collaboration tool for assessing risk of bias.Date were extracted by two reviewers independently using a designed form and included the followinginformation:year of publication,characteristics of Participants,duration of follow-up,implant brand,implant surface(with microthreads at the neck or not,rough or machined),data on dental implant failure,data on marginal bone loss.Software(ReviewManagerversion 5.3)was used for meta-analysis.Results:1.Fivearticles 339 implants were included in qualitative synthesis.Each study studied two groups of implants,which had the same brand,dimensions,surface,andimplant-abutment connection type,only differ in the design of the neck.The followup time ranged from 1 to 5 years.All the implants survived.Four studies found that a microthreads design in the implant neck can significantly reduce the amount of MBL under functional loading,whereas 1 study found no significant differencebetween implants with macroneck and microneck threadsin terms of MBL after 1 year of loading.2.These studies can be divided into 2 subgroups:2 studiescompared the effects of implantswith a roughened microthreaded neckor a polished neck(the first subgroup),3 other studiescompare the effects of implants included a roughened neck with or without microthreads(the second subgroup).3.Two studies in the first subgroup had different baseline of MBL,and were thus excluded from meta-anlysis.Three studies in the second group were included in the Meta-analysis.The homogeneity test confirmed thatthere was acceptable heterogeneityamong the 3 studies(12=0.49).A random-effects model was used.The result show that the mean difference were-0.09(95%Cl-0.18 to-0.01).This means that MBL was significantly less inroughened implants with microthreads thanwithoutmicrothreads.Conclusions:Within the limitations of this systematic review andmeta-analysis,the following conclusions were drawn:1.A microthread design in the implant neck cansignificantly reduce the amount ofMBL underfunctional loading.2.The amount of MBL around implants with aroughened neck is less than with a polished neck.3.Because of the limited number of RCTs included inthe review,the evidence was insufficient to draw adefinite conclusion on the effect of the microthreaddesign.4.Further RCTs are needed,with longer follow-upperiods,larger patient samples,and adequate controlfor confounding factors.