| Objective: To evaluate the biomechanical influence of the different placements and base widths of macro-retentions on custom-made root analogue implants(RAI)under immediate loading by means of 3-dimensional(3D)finite elements analysis,exploring the best placements and base width of macro-retention and providing a reference for the design of RAI.Methods: 3D FE models of mandible containing mandibular first premolar RAI were constructed by means of computer aided design(CAD)software.The macro-retentions were designed in the interdental space of RAI root,and the models were divided into two groups according to different placements of the macro-retentions.Group 1: the macro-retentions were placed at the junctions between root neck 1/3,root middle 1/3 and root apex 1/3,respectively.Group 2: macro-retentions were designed in the middle line of trisections of root.All of the protruding heights were 0.2mm.In each group,7experimental models(M1-M7)were established according to diverse base widths of the macro-retentions(M1=0.8mm,M2=1.0mm,M3=1.2mm,M4=1.4mm,M5=1.6mm,M6=1.8mm,M7=2.0mm).The standard RAI without macro-retention was set as a blank control and recorded as M0.An average force of 129 N was applied under immediate loading vertically and buccolingually inclined 30° with the axis of the RAI,respectively.The maximum von Mises stress and stress distribution of bone tissues surrounding RAI and the maximum displacement,resonance frequency of the implants were analysed using CAD software.Results: 3D FE models of the mandible with mandibular first premolar RAI were constructed efficiently and accurately.Under the same loading,the maximum displacements of group 1 were higher than that of M0,and the maximum displacements of group 2 except M1 were less than that of M0.Under the same loading and with same base width,the maximum displacement of group 1 was greater than that of group 2,and the resonance frequency of group 1 was much lower than that of group 2.When the base width of RAI macro-retention was 0.8mm(M1),The maximum von Mises stress of cancellous bone and cortical bone as well as the maximum displacements of RAI increased significantly,while the resonance frequency of RAI decreased significantly.The stress concentration of the cancellous bone was observed around the macro-retention,which made the maximum stress value of cancellous bone exceeded the cortical bone,especially under oblique loading.When the base width was less than 1.4mm,the maximum von Mises of the bone tissues around the RAI and the maximum displacement of RAI decreased as the base width increased.When the base width was more than1.4mm,as base width increased,the maximum displacement of RAI under both loading increased,the peak stress of peri-implant bone decreases slowly under oblique loading while under vertical loading it was hardly affected by base width.When the base width was less than 1.2mm,the resonance frequency of RAI increases as base width increased,and reached its peak at 1.2mm,and then decreases while base width increased.Conclusions: Based on the results of this study and within the limitations,it can be concluded that adding macro-retention to RAI interdental space can reduce the maximum von Mises stress of peri-implant bone tissues and improve the initial stability of RAI under immediate loading.Designing macro-retention in the middle line of trisections of RAI is more beneficial to reduce the maximum displacement of the implant and increase the resonance frequency,improving the initial stability.Too small base width(less than1.0mm)is more likely to cause stress concentration of peri-implant bone tissues and decrease initial stability of RAI.It is most beneficial to improve the stress distribution of bone tissue and increase the initial stability of the RAI when the base width of macro-retention is 1.4mm. |
PDF Full Text Request