| Implantation has been a preferred method for restorations of missing teeth.Compared to traditional implants,custom-made root-analogue implants(RAIs),which have similar configurations with natural teeth,have some advantages,such as less traumatic procedures,shortening therapeutic course,uncomplicated operations,etc.Researches of clinical application of RAIs have drawn attentions in recent years.There are many factors which can affect the success of clinical application of RAIs.One of the most important factors is the configuration design of RAIs.Problems about whether a reduction design should be done in the labial neck area of RAIs and how to select the reduction amount before clinical application still remain controversial.Until now,researches comparing the influence of different configuration designs in the case reports of RAIs on stress distribution in peri-implant bone have been in blank.In addition,problems like if the thread design was applied to RAIs just like traditional implants,which kind of thread shapes should be used and whether the effect of the thread design would be affected by the sagittal root positions(buccolingual positions)of RAIs have not been studied so far.The clinical application of RAIs,which has potential value of development,is relatively easy in the single-root areas.Based on the previous researches of our group,the study was designed to explore the influence of different configuration designs of single-root RAIs on stress distribution in peri-implant bone,including different thread shapes,diameter reductions in the labial neck region and different retention designs,to provide experimental basis for the follow-up studies in vivo and to provide references for the clinical application of RAIs.Based on the analysis of the anatomical characteristics of healthy maxillary central incisor and congruent alveolar bone,four groups of one-stage RAI three-dimensional finite element(FE)models with different configuration designs and congruent bone models were created through the reverse engineering technology.Different RAI models are listed as follows:1.RAI models with different thread shapes(V-shaped design,square design,buttress design,reverse buttress design and none thread design).2.RAI models with reverse buttress thread design and none thread design on the condition that RAIs are in the Class 1,2,3 sagittal root position.3.RAI models with a reduction of the diameter(0-3 mm)of the implant neck next to the labial cortical bone.4.RAI models with different retention designs(reverse buttress thread design,raindrop shape design,round concave design and smooth design).At the same time,a traditional threaded implant and congruent bone model were created.A force of 100 N was applied parallelly and of 45° to the implant axis respectively to evaluate the von Mises stress distributions and the maximum von Mises stress at the peri-implant regions using the Ansys 16 software.Subsequently,part of the finite element analysis results was verified primarily through a short-term observation of 2 clinical application cases of RAIs,which was designed based on the previous finite element analysis.The results and conclusions of this study are as follows:1.Stress concentrations in peri-implant bone were lower for RAIs with thread design than that with none thread design.There was no obvious difference of stress distribution conditions among different thread shape designs.2.Stress distribution conditions were different when RAIs were in different sagittal root positions.Among the three sagittal root positions included in this study,the minimum stress concentration on the labial lamella and the cortical bone around implant neck region was found when RAIs were in the Class 2 position(the implant is centered in the middle of the alveolar housing without engaging either the labial or the palatal cortical plates at the apical third of the implant).Stress concentrations in peri-implant bone were lower for RAIs with thread design than that with none thread design,regardless of the sagittal root position.3.There were no obvious differences in stress distributions in the cortical bone around implant labial neck area,when the diameters of RAIs were reduced by no more than 2 mm on the labial neck area.Stress concentrations on the cancellous bone around RAIs transferred from the labial side to the palatal side gradually.When the diameter of the implant neck was reduced by 3 mm,there were obvious stress concentrations on RAI and bone around the implant.4.Stress was better dispersed in the bone around implant with retention designs than the smooth group.The thread design showed lower stress concentrations in bone around RAIs than the raindrop shape design and the round concave design.5.Stress concentrations on the bone around RAIs were obviously smaller than traditional implants.6.The primary stabilities in the clinical application of RAIs designed on the basis of previous research were good.Soft tissues around RAIs kept stable during the short-term clinical observation.And there was no obvious bone resorption around RAIs.It could be concluded that,adding retention designs to the surface of RAIs can help stress disperse in the peri-implant bone.Among these retention designs included in this study,the thread design showed the best effect of stress distribution.There was little difference of stress distributions in the peri-implant bone among RAIs with different thread shape designs.Adding thread design to the surface of RAIs can reduce the stress concentration in any sagittal root position(buccolingual position).The Class 2 sagittal root position(the implant is centered in the middle of the alveolar housing without engaging either the labial or the palatal cortical plates at the apical third of the implant)was found to be the most appropriate site for applying RAIs among these three sagittal root positions.In addition,the reduction of the diameter of the implant next to the labial cortical bone can help stress disperse but no more than 2 mm.RAIs were better for stress dispersion than traditional implants. |
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