|Year : 2016 | Volume
| Issue : 2 | Page : 49-52
The effect of implant and abutment diameter on peri-implant bone stress: A three-dimensional finite element analysis
Helen Mary Abraham1, Jacob Mathew Philip2, Ashish R Jain3, CJ Venkatakrishnan2
1 Department of Prosthodontics, Tagore Dental College, Chennai, Tamil Nadu, India
2 Department of Dentistry, Bharath University, Chennai, Tamil Nadu, India
3 Department of Prosthodontics, Saveetha University, Chennai, Tamil Nadu, India
|Date of Web Publication||13-Oct-2016|
Jacob Mathew Philip
Ph.D Scholar, Bharath University, Chennai 600 059, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Introduction: Load transfer mechanisms from the implant to surrounding bone and failure of osseointegrated implants are affected by implant geometry and mechanical properties of the site of placement as well as crestal bone resorption. Estimation of such effects allows for a correct design of implant geometry to minimize crestal bone loss and implant failure.
Objectives: To evaluate the effect of implant and abutment diameter on stress distribution in the peri-implant area.
Materials and Methods: Three-dimensional finite element models created to replicate completely osseointegrated endosseous titanium implants and were used for the purpose of stress analysis. Two study groups that consisting of a regular platform (RP) group and narrow platform (NP) group were used with a standard bone density and loaded using the ANSYS Workbench software to calculate the von Mises and Principal (maximum tensile and minimum compressive) stress.
Results: The von Mises, compressive, and tensile stresses in the peri-implant bone were lower in the RP model compared to the NP model.
Conclusion: RP model yielded a positive result with regard to lowering of peri-implant bone stress levels, in healthy as well as compromised bone qualities when compared to NP designs.
Keywords: Abutment diameter, bone stress, implant diameter
|How to cite this article:|
Abraham HM, Philip JM, Jain AR, Venkatakrishnan C J. The effect of implant and abutment diameter on peri-implant bone stress: A three-dimensional finite element analysis. J Oral Res Rev 2016;8:49-52
|How to cite this URL:|
Abraham HM, Philip JM, Jain AR, Venkatakrishnan C J. The effect of implant and abutment diameter on peri-implant bone stress: A three-dimensional finite element analysis. J Oral Res Rev [serial online] 2016 [cited 2019 Mar 20];8:49-52. Available from: http://www.jorr.org/text.asp?2016/8/2/49/192136
| Introduction|| |
Implant design (material, structure, and dimensions) is an important factor affecting the implant stability and the stresses generated in its surrounding bone. Variations in implant designs have been investigated aiming to achieve better stability to diminish the effect of shear forces on its interface so that marginal bone is preserved and to enhance osseointegration process. 
Implant diameter was reported to be more important than implant length in distributing stresses to the surrounding bone in the case of two stage implantation.  Implant taper also plays a role in stress transmission. It was reported that under immediate loading conditions, minimally tapered implants generated the most favorable stress distribution patterns.  Using wider implants may allow the engagement of extra surrounding amount of bone, and hence improves both structure stability and induced stress distribution pattern. 
The aim of this study was to investigate the effect of implant and abutment diameter on peri-implant bone stress.
| Materials and Methods|| |
Three-dimensional (3D) finite element models created to replicate completely osseointegrated endosseous titanium implants were used for the purpose of stress analysis. The models were constructed using measurements and geometries similar to previous studies, with isotropic material properties [Table 1] and [Figure 1] and [Figure 2]. An isotropic material is deﬁned as having identical physical properties in all directions; therefore, only two independent material constants exist.
A computer aided design package called Pro Engineer Wildfire (Parametric Technology Corporation, Waltham, MA, USA) was used to generate the models in a .prt file format. Using the Pro/E feature and parameteric-based design capability, the implant critical dimensions, such as the height and diameter, were defined to create a virtual assembly in a mesh form.
Three 3D finite element models were created to replicate an implant (13 mm in length with 0.375 mm V thread depth and 0.6 mm pitch) and abutment (6.5 mm in length) with peri-implant bone tissue, in which two different implant-abutment configurations were represented. Two study groups consisting of a regular platform (RP) group where a regular 4.3 mm diameter abutment was connected to regular 4.3 mm diameter implant and a narrow platform (NP) group where a 3.5 mm diameter abutment was connected to a 3.5 mm diameter implant was used. A three dimensionally generated finite element model of a Ni-Cr restoration of 8 mm height, 8 mm in maximum diameter, and with an occlusal thickness of 1.5 mm was designed over the abutment.
Complete osseointegration at the implant-bone interface was simulated by combining the nodes of the implant and bone models. Similar integration of the abutment and implant body was adopted to be a single unit. The same type of contact was also provided at the prosthesis-abutment interface. This eliminated any potential inﬂuence from the micromovement between components.
Each of the models was tested in a standard bone density environment [Table 1], assumed to be homogeneous, isotropic, and linearly elastic. A three dimensionally generated FE model of bone tissue, in which the two implant-abutment configurations, RP and NP with the prosthesis are embedded was designed to be a block 16 mm in height, 11 mm in width, and 11 mm in breadth. Oblique load of 90N was applied on the flat surface of the restoration on the abutment of the 3D finite element analysis (FEA) models [Color plate 1 [Additional file 1]] and [Color plate 2 [Additional file 2]]. The oblique loading angle of 35.6° imitated the chewing pattern recorded with a jaw tracking device by Ishigaki et al.
The finite element mesh was generated with the following nodes and elements. The final models had a total of 139,334 nodes and 74,324 elements for the NP model, 113,596 nodes and 65,897 elements for the PS model, and 120,703 nodes and 607,536 elements for the RP model.
The implant geometries were digitally imported into ANSYS Workbench software (Swanson Analysis System, Houston, PA) after converting into .iges file format and used to calculate the von Mises and Principal (Maximum tensile and Minimum compressive) stress ranges for the bone on implant loading.
The von Mises stresses were obtained, when each of the implant-abutment models RP and NP along with the restoration, were embedded in bone and subjected to oblique loading.
| Results|| |
The data obtained from the three dimensionally generated models created using finite element software, makes it possible to compare the stress distribution in the bone of the two models for oblique loading situations. The positive values of the maximum principal stress and the negative values of the minimum principal stress were taken to indicate maximum tensile stress and maximum compressive stress, respectively. To enable comprehension of the effect of the implant diameter and prosthetic platform configuration, the percentage differences in stress values among the groups are shown in [Table 2] and [Figure 3].
|Table 2: Effect of platform configuration on von Mises, maximum, and minimum principal stress concentrations (in MPa) in the models under oblique loading|
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|Figure 3: Effect of Implant and abutment diameters on von Mises, maximum, and minimum principal stress concentrations (in MPa). NP: Narrow platform; RP: Regular platform|
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It was clearly observed that the RP model reduced von Mises stress values for oblique load. Compressive stress was higher than tensile stress, and RP reduced both compressive and tensile stresses. The increase in implant diameter played a role in stress reduction.
The percentage of decrease of von Mises, maximum, and minimum principal stresses between NP and RP configurations under oblique loading conditions were compared in [Table 2] and [Figure 3].
| Discussion|| |
Studies have looked into the failure of small diameter implants showing higher implant fracture rates,  even at clinical loads.  Petrie and Williams  showed that crestal bone stresses were dependent on three interrelated parameters: Diameter, length, and taper. According to them, diameter had the single most influence on crestal bone stresses. This fact was reinforced in other studies.  Previous FEA studies have shown that a decrease in diameter increases the stress transferred to crestal bone. 
This study indicated that the maximum von Mises stress in both models was lower in the RP than the NP model under both loading conditions. Since compression may compromise in vivo the periosteal blood supply and lead to necrosis, high compressive stress may increase the risk of bone loss; extensive tensile stress has also been reported to cause bone resorption. Similarly, this study revealed higher compressive and tensile stresses in NP model when compared to the RP model under oblique loading condition. The possible reason may be attributed to the different implant and abutment diameters. The use of a wider implant reduced stress concentrations, probably as the result of a larger contact surface between the bone and the implant.  Data from a study conducted by Schrotenboer et al.  suggested that when the abutment diameter was reduced by 10% or 20%, it resulted in less stress transferred to the crestal bone, regardless of the type of thread pattern (microthread or smooth) or direction of force (vertical or oblique).
Studies by Himmlovα et al.,  Holmgren et al.,  and Bozkaya et al.  show that maximum implant diameter seems to affect stress peaks at the cortical bone but not at the trabecular region, whereas stress values and distribution at the cancellous bone-implant interface are primarily influenced by implant length. To control the risk of bone overload and to improve implant biomechanical stress-based performance, numerical results from a study by Baggi et al.  suggest that implant diameter can be considered to be a more effective design parameter than implant length. This study can be considered to be complementary to similar, previously published studies.  Due to the simplified and different geometrical models usually used in these studies, quantitative comparisons cannot be made.
| Conclusion|| |
Within the limitations of this study, stresses in the peri-implant bone were lower in the RP model compared to the NP model. The reduction of the stress concentration at the implant-bone interface area is a favorable development to ensure the continuity of osseointegration.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]