|Year : 2022 | Volume
| Issue : 1 | Page : 7-12
Comparison of magnitude and distribution of stress at implant-bone interface in carbon-fiber-reinforced-polyetheretherketone, zirconium, and titanium implant: A three-dimensional finite element study
Naveen Edavan Puliya Cheriyath, Natarajan Kalavathy, Mitha Shetty, P Roshan Kumar, Archana Sanketh, Anuradha Venkataramani, M Roopa
Department of Prosthodontics, Crown and Bridge and Implantology, DAPM RV Dental College, Bengaluru, Karnataka, India
|Date of Submission||20-Sep-2021|
|Date of Decision||09-Feb-2022|
|Date of Acceptance||14-Feb-2022|
|Date of Web Publication||14-Mar-2022|
Dr. Naveen Edavan Puliya Cheriyath
Navaneetham, Mavilachal PO Eachur, Kannur – 670 591, Kerala
Source of Support: None, Conflict of Interest: None
Background: Titanium and its alloys are used as implant materials for decades. Zirconium and carbon-fiber-reinforced-polyetheretherketone (CFR-PEEK) are newer materials available in implantology but long-term clinical studies are not yet available to prove their advantages over titanium implants. Aim: The objective of this study was to evaluate and compare the magnitude of stress distribution at implant-bone interface when using titanium, zirconium, and CFR-PEEK implants. Materials and Methods: Mandibular first molar was considered for the study along with surrounding bone structure. Implant of specific dimensions was constructed at the first molar region and then lithium disilicate crown was modeled on the abutment. Hypermesh 13.0 software was used for creating finite element models and then assign the material properties for each part. This model was exported to ANSYS 19.2 software for analysis. Loads and boundary conditions were applied to the model and then solved. Interpretation of results was done. Results: The results revealed that von Mises stress distribution on medullar bone under different loading conditions, model with zirconium implant with PEEK abutment (Model B) showed better performance compared to others. Von Mises stress distribution on abutment and implant showed that model with CFR-PEEK implant with PEEK abutment (Model C) had better performance compared with others under different loading conditions. Deformation of medullar bone and implant-abutment structure was more in model with CFR-PEEK implant when compared to others although this was within the acceptable limits. Conclusions: Within the limitation of the study, it was observed that the magnitude of von Mises stress for all the models was within the acceptable range and hence zirconium and CFR-PEEK can be a suitable alternative to conventional titanium implants.
Keywords: Carbon-fiber-reinforced-polyetheretherketone, crown, finite element analysis, implant-bone interface, stress distribution
|How to cite this article:|
Puliya Cheriyath NE, Kalavathy N, Shetty M, Kumar P R, Sanketh A, Venkataramani A, Roopa M. Comparison of magnitude and distribution of stress at implant-bone interface in carbon-fiber-reinforced-polyetheretherketone, zirconium, and titanium implant: A three-dimensional finite element study. SRM J Res Dent Sci 2022;13:7-12
|How to cite this URL:|
Puliya Cheriyath NE, Kalavathy N, Shetty M, Kumar P R, Sanketh A, Venkataramani A, Roopa M. Comparison of magnitude and distribution of stress at implant-bone interface in carbon-fiber-reinforced-polyetheretherketone, zirconium, and titanium implant: A three-dimensional finite element study. SRM J Res Dent Sci [serial online] 2022 [cited 2022 Dec 10];13:7-12. Available from: https://www.srmjrds.in/text.asp?2022/13/1/7/339637
| Introduction|| |
Implantology has experienced significant advancements that has revolutionized the field of fixed prosthodontics. The restoration of partially and completely edentulous patients using implants is a well-documented and scientifically accepted treatment modality. Implants made of polymer materials are latest trend in research. Titanium and its alloys are commonly used in manufacturing of implants and are considered gold standard in implantology. They are used due to their outstanding biocompatibility and well-documented results. On exposure to air, titanium instantly forms an oxide layer that is the foundation of its biocompatibility. The properties of oxide layer are significant for osseointegration. The major drawback of titanium implants was its gradient difference in elastic modulus (110 GPa) compared to its surrounding bone (14 GPa), that may lead to high stresses in the implant-bone interface during load transfer, resulting in peri-implant bone loss, that may lead to implant loosening and shedding. However, this situation can be overcome with carbon-fiber-reinforced-polyetheretherketone (CFR-PEEK) implants as they have elastic modulus of 18 Gpa which is similar to bone. Various studies have been done to find a suitable substitute for titanium implant to overcome the drawbacks of titanium.
The newer materials that are introduced into implantology are zirconium and PEEK. Zirconia was considered because of its color, biocompatibility, and radiopacity. Bacterial colonization around zirconia is less as compared to titanium. Some studies have reported that zirconia has more biocompatibility than titanium, as the latter produces corrosion products at the implant site. It has minimal ion release than metallic implants. Inflammatory reaction and bone resorption are comparatively less in ceramic materials. It also has high strength and fracture toughness.
PEEK is synthetic polymer material used in orthopedics. It exhibits excellent antioxidant property, high thermal stability, high strength, biocompatibility, good fatigue resistance, and excellent processing performance. The major beneficial property is its lower elastic modulus which is similar to bone (3–4 GPa). Incorporation of carbon fiber increases elastic modulus upto 18 GPa. The elastic modulus of CFR-PEEK is similar to those of cortical bone, and stress shielding is less. Other properties are also similar to those of bone, enamel, and dentin, making it suitable in implantology. It has more homogenous stress distribution.
Studies comparing these three implant materials together are very limited and hence the aim of this finite element method (FEM) study was to compare stress distribution at the peri-implant bone when using implants made of three different materials, namely CFR-PEEK, zirconium, and titanium.
| Subjects and Methods|| |
This study was conducted using finite element models to compare the stress distribution near the peri-implant bone in three distinct models composed of PEEK abutment with CFR-PEEK implant, PEEK abutment with zirconium implant, and PEEK abutment with titanium implant.
Modeling of specimens
Element used for modeling
SOLID 186 element was used for modeling. SOLID 186 is a higher-order 3-D 20-node element that exhibits quadratic displacement behavior. The element is defined by 20 nodes having three degrees of freedom per node: translations in the nodal x, y, and z directions. The element supports plasticity, hyperelasticity, creep, stress stiffening, large deflection, and large strain capabilities. It also has mixed formulation capability for simulating deformations of nearly incompressible elastoplastic materials and fully incompressible hyperelastic materials.
Methodology of the study
The mandibular first molar was considered for the study along with the surrounding bone structure. Implant of specific dimensions was constructed at the first molar region and then lithium disilicate crown was modeled on the abutment. Hypermesh 13.0 software was used for creating finite element models and then assign the material properties for each part. This model was exported to ANSYS 19.2 Software (USA) for analysis. Loads and boundary conditions were applied to the model and then solved. Interpretation of results were done.
All materials used in the model were considered to be homogenous, isotropic, and linear elastic. The Poisson's ratio (μ) and Young's modulus (E) of elasticity of the material were incorporated into the model as shown in [Table 1].
The finite element model was divided into small elements. Each element was considered to be interconnected at a number of discrete points called nodes. Each model was meshed by elements defined by ten nodes and three degrees of freedom in tetrahedral nodes. The displacement of each of these nodes was calculated to determine the maximum von Mises stresses throughout the structure.
Three distinct models composed of PEEK abutment with CFR-PEEK implant, PEEK abutment with zirconium implant, and PEEK abutment with titanium implant were used in this study. All three models were of the same dimensions with different implant materials as shown in [Table 2].
Finite element model
Graphic preprocessing software Hypermesh 13.0 was used for creating the geometric configuration of a section of an implant placed in the mandibular first molar region. Three 3D models of this section were created with three different implant materials, namely titanium, zirconium, and CFR-PEEK with all other components the same. These models were named Model A, Model B, and Model C. All three models were of the same dimensions. All the three implants were cylindrical in shape with a diameter of 4.1 mm and a length of 10 mm replacing mandibular first molar. Abutment height was 4 mm for the models. All three models had internal hex type connection and were placed at crest level. Cortical bone of 2 mm thick surrounds the implants at bone crest and trabecular bone covering the inner portion. Cementation of the crowns was done with zinc phosphate cement. The mesiodistal diameter of crown, mesiodistal diameter of crown at cervix, buccolingual diameter of crown, buccolingual diameter of crown at cervix, and cervico-occlusal height of crown were 11 mm, 9 mm, 10.5 mm, 9 mm, and 7.5 mm, respectively.
Models were created using ANSYS software. Meshing was done by the software automatically.
Loading and boundary conditions
The test setup was created. A refinement process was done to validate meshes, checking, and convergence of results were verified. Forces to be applied were axial and oblique forces. Two sets of each axial and oblique forces were applied on each model. One was normal functional and the second was parafunctional forces. Both functional and parafunctional loads were applied on each model for analysis. Functional loads with 400 N axial force and 240 N oblique force were applied. Parafunctional loads with 800 N axial force and 480 N oblique force were applied. The summary of loading details applied for each specimen is shown in [Table 3]. The stress concentration developed at the implant-bone interface for various types of loading were processed and compared with each other.
| Results|| |
In all the three models, the deformation and von Mises stress on medullar bone as well as implant and abutment for each specimen under four different loading conditions were illustrated and analyzed. The summary of all the values is depicted in [Table 4].
Under normal axial load of 400N, deformation and von Mises stress contour on medullar bone were highest for CFR-PEEK implant model, Model C1 (0.01633 mm and 17.51 MPa), and lowest for zirconium model, Model B1 (0.01002 mm and 8.71 MPa). On implant and abutment, the von Mises stress contour was least for Model C1 (0.02178 mm and 49.99 MPa) [Figure 1]. Under normal oblique load, 240 N deformation and von Mises stress contour were highest on medullar bone for Model C2 (0.04262 mm and 83.91 MPa), least for Model B2 (0.02458 mm and 47.04 MPa) and on implant and abutment, deformation and von Mises stress was Model C2 (0.14195 mm and 121.61 MPa) [Figure 2].
|Figure 1: Von Mises stress contours on Medullar bone with Normal Axial Load 400N|
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|Figure 2: Von Mises stress contours on Medullar bone with Normal Oblique load 240N|
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Under parafunctional loading with axial load of 800 N deformation and von Mises stress contours on medullar bone was also highest for CFR-PEEK implant model, Model C3 (0.03251 mm and 35.17 MPa), lowest for zirconium model, Model B3 (0.02005 mm and 18.07 MPa) and on implant and abutment, Model C3 had the least von Mises stress [Figure 3]. Under parafunctional loading with oblique, load of 480 N deformation and Von Mises stress contours were highest on medullar bone for CFR-PEEK implant model, Model C4 (0.09258 mm and 163.89 MPa). On implant and abutment Model C4 exhibited the least von Mises stress (154.40 MPa).
|Figure 3: Von Mises stress contours on Medullar bone with Parafunctional Axial Load 800N|
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| Discussion|| |
Three-dimensional finite element analysis (FEA) simulates stress behavior on the surrounding bone. Values which cause resorption and remodeling are not documented presently. Quantitative evaluation for this is not possible. The FEM is a numerical method introduced in orthopedics in 1970s. ANSYS 19.1 software was used for numerically solving a variety of problems in a FEA study.
In this study, three 3D models were created by incorporating modulus of elasticity and poisons ratios of different implant materials currently available. Standard dimensions were taken for each component and various loading conditions were applied and analyzed using FEA. Several studies have proved that FEA is similar to clinical study since clinical conditions can be simulated, hence, it is more reliable. Osseointegration and marginal bone height determine the success of implant. Marginal bone height depends on stress distribution and periodontal health. Osseointegrated and marginal bone resorption around implants are unavoidable. Strategies for the prevention of implant failure are crucial. Material, design, surface topography, bone quality, prosthesis used, and loading protocols along with oral microflora and parafunctional forces determine the success of treatment. Many implant designs have been introduced to improve primary implant stability, diminish the effect of shear forces on the interface, and also stimulate bone formation.
Available bone particularly is important in implantology that describes the external architecture or volume of the edentulous area. Internal structure of bone is described in terms of quality or density, which suggests the strength of the bone. According to Zarb and Schmitt, bone structure is the most important factor in outcome in implant dentistry. Bone density provides primary stability during healing and stresses distribution. The percentage of bone contact is significantly greater in cortical bone than in trabecular bone. Number of implants is increased or implant with greater surface area is used to decrease stress. Implant designs are different for different bone qualities. It is suggested that in D4 type of bone, the implant design should have the greatest surface area, whereas in D1 type of bone, the implant should be designed for easy surgical placement.
Different implant materials distribute stress differently in implant-bone interface. This study evaluates the amount of stress distribution and deformation of different implant materials in different loading conditions. According to Misch, 1998 mean maximum bite forces on dental implant in mandibular molar is from 50 to 400 N and parafunctional forces can be double of it. Masticatory forces in natural dentition are different from implants since periodontal ligaments are absent in case of implant, load transmission happens directly onto the surrounding bone. Parafunctional loads with 800 N axial force and 480 N oblique force were applied. Von Mises stress of each load on the cortical bone and on the implant and abutment was observed and analyzed. Von Mises stress was selected for the study since it gives a clear idea about the material strength and chances of failure or fracture when forces are applied.
In this study, von Mises stress on cortical bone was maximum in CFR-PEEK implant model least stress on cortical bone was seen with zirconium implant. For parafunctional oblique load, the least stress values were for titanium implant. The von Mises stress on implant and abutment was least in case of CFR-PEEK implants for parafunctional axial load. Based on the analysis results, the von Mises stress distribution on medullar bone under different loading conditions, model with zirconium implant with PEEK abutment (Model B) showed better performance compared to others. It showed lesser stress when subjected to loading.
The von Mises stress distribution on abutment and implant showed that model with CFR-PEEK implant with PEEK abutment (Model C) had better performance compared with others under different loading conditions. It possesses lesser stresses when subjected to loading.
The deformation contour of surrounding medullar bone and implant-abutment structure was more in case of CFR-PEEK implant when compared to other models. This can be because PEEK is a composite material which is less rigid when compared to titanium and zirconium hence more force is transmitted to the surrounding bone and chances of micromovements are more when compared to titanium and zirconium.
Bone becomes mildly overloaded which is compensated by forming more bone with increase in strain. Fatigue fracture can occur if it goes beyond its threshold. According to this hypothesis, all the stress values on the bone observed in our study were within the acceptable limit for normal and parafunctional axial loads. Whereas the stress values on the bone in case of normal oblique load were slightly higher for CFR-PEEK and parafunctional oblique load was slightly higher CFR-PEEK and zirconium.
Limitations of this study are that it has used only three types of models with standard implants of three available materials. More detailed analysis can be done using models created with different surface and material modifications to improve the stress distribution properties. Stress distribution while using different concepts like platform switching and the use of single-piece implants can also be checked. In this study, loading forces used were based on a reference range that can be varied in clinical conditions depending on age and sex of an individual, type of food intake, opposing dentition, etc. Although titanium and its alloys used in implantology have a variety of drawbacks, it is still the most common and proved material in use today. Zirconium and PEEK are newer materials in this field, hence, more long-term clinical research has to be done to understand the advantages and disadvantages of using these materials as implants. Different material modifications of zirconium and PEEK can be tried to improve its properties and to gain a more homogenous stress distribution, thereby reducing chances of implant failure.
| Conclusions|| |
According to this study, zirconium and CFR-PEEK implants can be a replacement for conventional titanium implants but long-term clinical research must be done to understand the actual prognosis of these newer materials.
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], [Table 3], [Table 4]