|Year : 2019 | Volume
| Issue : 9 | Page : 1252-1258
Evaluation of the use of PEEK material in implant-supported fixed restorations by finite element analysis
S Tekin1, Y Değer2, F Demirci3
1 Department of Prosthodontics, Faculty of Dentistry, Firat University, Elazig, Turkey
2 Department of Prosthodontics, Faculty of Dentistry, Dicle University, Diyarbakir, Turkey
3 Department of Prosthodontics, Faculty of Dentistry, Adiyaman University, Adiyaman, Turkey
|Date of Acceptance||28-Apr-2019|
|Date of Web Publication||6-Sep-2019|
Dr. F Demirci
Department of Prosthodontics, Faculty of Dentistry, Adiyaman University, Adiyaman, Turkey, 02200
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Aims: The purpose of this study is to compare the stresses occurring in the peri-implant bones, implants, crowns, abutments, and screws after loading through finite element analysis by using the poly-ether-ether-ketone (PEEK) materials, which are alternative to titanium abutment and metal supported restorations and to try to reduce the level of neck resorption. Materials and Methods: In our study, three-dimensional modeling of 2 PEEK and titanium abutments, metal-ceramic, and monolithic PEEK upper central dental restorations were made on four titanium implants (Biohorizons® Implant Systems Ins., Birmingham, AL, USA) with diameters of 3.8 mm and 10.5 mm and four groups were obtained. Then, a stress analysis of the finite element was performed by applying a 178 N oblique force of 45° to the long axis of the tooth 2 mm below the incisal edge of the model's palatal surface. Results: It has been observed that the PEEK material reduces the stresses caused by the force applied on itself during all tests. In all groups, PEEK abutments and PEEK crowns have reduced stress on the abutment. The most significant difference is observed in the stresses on the crowns and screws. When the stresses on the crown are examined, the use of PEEK crown reduces the stresses on itself and the use of PEEK abutment increases the stresses on the crown. Conclusions: The stress on the implant system can be changed through the usage of different prosthetic materials.
Keywords: Dental implant, finite element analysis, poly-ether-ether-ketone
|How to cite this article:|
Tekin S, Değer Y, Demirci F. Evaluation of the use of PEEK material in implant-supported fixed restorations by finite element analysis. Niger J Clin Pract 2019;22:1252-8
|How to cite this URL:|
Tekin S, Değer Y, Demirci F. Evaluation of the use of PEEK material in implant-supported fixed restorations by finite element analysis. Niger J Clin Pract [serial online] 2019 [cited 2020 Aug 3];22:1252-8. Available from: http://www.njcponline.com/text.asp?2019/22/9/1252/266155
| Introduction|| |
Nowadays, dental implants are needed partially or completely as well as classical prosthetic applications, in order to regulate the chewing systems of patients suffering tooth loss. Since there is no periodontal ligament around the implant, the forces on the implants are transmitted directly to the jawbone. The lack of periodontal ligaments at the implant bone interface causes a decrease in the proprioception, which can sometimes cause excessive stress in the restoration and breakage of the porcelain restoration. The occlusal forces are transmitted to the prosthesis, implant, and the bone around the implant, respectively. Therefore, the direction and amount of the load; the prosthetic material; the design of the prosthesis; the implant material; the design of the implant; the number of implants; and the mechanism of bone implant interface, bone type, and bone characteristics can be listed as factors affecting the load on the bone., Prosthetic design and material selection affect the distribution of stress on prosthetic structures, implants, and bones. These stresses can lead to bone resorption around the implant and loss of implants.,,
The poly-ether-ether-ketone (PEEK) material is a synthetic thermoplastic polymer exhibiting high mechanical performance.,, PEEK was developed in 1978 and began to be used in industrial applications in 1980s and in the medical field in the late 1990s., PEEK, which has become widely used in the medical field, has shown excellent results as an alternative to titanium material. Due to its high biocompatibility, PEEK has been used to make implants, provisional abutments, healing abutments, and implant-supported hybrid prostheses in dental implantology.
The PEEK material is a biologically inert material. In the conducted studies, there was no evidence of the effects of the material on cytotoxicity, mutagenicity, carcinogenicity, and immune system. It is resistant to hydrolysis and shows good mechanical and thermal resistance. It is also quite resistant to chemical abrasions. It is a degradation-resistant material during various sterilization processes. Moreover, PEEK material allows magnetic resonance imaging (MRI). One of the most important features of PEEK material is low elastic modulus like the bone. Due to this feature, the material is considered to be used in fixed prosthetic treatments. PEEK is a very light, flexible, and hard to break material. The PEEK material's cost-efficiency and its feature of easy to be processed in the mouth also support its use. In addition, PEEK can be modified with various materials.
Finite element analysis (FEA) is simply based on mathematical modeling of the complex structure by dividing it into smaller pieces or elements. By this way, FEA allows numerical analysis. Thanks to FEA, it is possible to imitate and evaluate behaviors at the interfaces of bones, implants, and prosthetic parts, which cannot be evaluated as in vivo and in vitro.
The bones, implants, and implant-mounted structures can be modeled with FEA in a similar way to clinical conditions. In this way, it becomes possible to fully monitor the amount of stress on implants and surroundings of bone, shape change, and amount of displacement and their localization under the applied forces. In several studies, in which the FEA was used, the effect of using different prosthetic materials and abutment materials on stress distribution after implant therapy was evaluated.,
| Materials and Methods|| |
In our study, an original maxilla model, previously obtained by computer tomography (CT), and transferred to the computer environment with a 3D image, was used. Four dental implants, abutments, and screws of the same size (3.8 × 10.5 mm) of the company Biohorizons (Biohorizons ® Implant Systems Ins., Birmingham, AL, USA) were used as the implant system.
Equal sized implants, abutments, and screws were scanned in macro mode in 3D with a laser scanner device NextEngine 3D (NextEngine, Inc. 401 Wilshire Blvd., Ninth Floor Santa Monica, California, 90401, USA). With the ScanStudio program provided with the machine, the data obtained after cleaning, aligning, and merging are recorded in 'stl' format. The files have been transferred to the Rhinoceros 4.0 (3670 Woodland Park Ave N, Seattle, WA 98103, USA) software.
Three-dimensional (3D) solid modeling of images obtained by CT was performed through Rhinoceros 4.0 software program. Type 3 spongious bone was modeled as being surrounded by 1 mm cortical bone in the bone model through the same software., Subsequently, the cortical bone was separated from the spongious bone. As a result, modeling and integration of the bone-implant system was completed.
In metal-supported ceramic restorations, the metal thickness was set to be at least 0.5 mm and the porcelain thickness was customized with a maximum thickness of 2 mm. The sizes and images of upper left central tooth No. 21 taken from the Wheeler's Dental Anatomy Atlas More Details were transferred to the Rhinoceros 4.0 software and the model of the crown was obtained and assembled with the abutment underneath. The compatibility of the restoration with the abutment was determined using Rhinoceros 4.0 software. The cement layer between the crown and the abutment was ignored because of the thinness of the layer and the low value of the materials, which would have a minimal impact on the analysis. The abutment and implant angles were determined as 0° in all the obtained models. All models were considered to be in continuous contact with each other before the analysis and the friction coefficient was set at 0.5. Implants were accepted as 100% osseointegrated to the bones. In addition, all models used were considered as homogeneous, isotropic, and linear elastic structures.
The elastic modulus and Poisson's ratios of all the materials (cortical bone, spongious bone, titanium implant, chromium-cobalt alloy, feldspathic porcelain, PEEK) to be used in our study were planned to be entered into the computer system to obtain the analysis results [Table 1].,,, The physical properties of each structure forming the model were defined in this way. In our study, four analysis groups were obtained as a result. The analysis groups are shown in [Table 2]. In this study, the meshing with the highest quality was tried to be formed by the elements with the highest nodes. In this context, a total of 48,900 nodes and 224,145 elements were used for each model [Figure 1]. The obtained models were fixed in such a way that at each DOF (degree of freedom) from the lower and side regions of the cortical and spongious bone has '0' motion. In the last stage, 3D solid models were analyzed by applying a force of 178 N at 45° oblique to the palatinal surface at 2 mm below the crown incisal.
The models made in Rhinoceros 4.0 are transferred to ANSYS software for the analysis in “igs” format by preserving 3D coordinates. After analysis, von Mises equivalent strain values of the peri-implant bone, implant, abutment, screw, and crown were examined by using the method of finite element stress analysis. In addition, analysis results obtained from four models were transformed into graphics and contributed to the interpretation of findings [Table 3].
|Table 3: Grafik veri aralığının boyutunu değiştirmek için aralığın sağ alt köşesini sürükleyin|
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| Results|| |
Comparison of von Mises stress values of the implants
In all groups, stresses on the implants were observed to be concentrated in the neck of the implants [Figure 2]a, [Figure 2]b, [Figure 2]c, [Figure 2]d. When the stresses on the implant were examined in all groups, they were not significantly affected by the change in the crown material. As a result of the change of the abutment material, it was observed that the use of titanium abutments with more elastic modulus reduced the stresses that occurred on the implant.
|Figure 2: (a): von Mises stress values of the implant group I. (b): von Mises stress values of the implant group II. (c): von Mises stress values of the implant group III. (d): von Mises stress values of the implant group IV|
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Comparison of von Mises stress values of the abutments
It was observed in all groups that the stress on the abutments occurred in the implant junctions of the abutments [Figure 3]a, [Figure 3]b, [Figure 3]c, [Figure 3]d. When stress on the abutment was examined in all groups, it was more affected by the change of abutment material than the change of crown material, and with the use of PEEK abutments with low-elasticity modulus, PEEK provides less stress on abutment by transmitting the stress to implant and screw. In the groups using PEEK crown as a crown material, it was observed that the stress on the abutment was decreased.
|Figure 3: (a) von Mises stress values of the abutment group I. (b): von Mises stress values of the abutment group II. (c): von Mises stress values of the abutment group III. (d): von Mises stress values of the abutment group IV|
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Comparison of von Mises stress values of the bones
When all groups were examined, it was observed that the von Mises stresses on the bone occurred in the cortical bone and adjacent to the neck of the implant [Figure 4]a, [Figure 4]b, [Figure 4]c, [Figure 4]d. In the presence of cortical bone, most of the loads transferred by the implant to the bones were met by the cortical bone itself, leading to a much lower amount of stress being transmitted to the trabecular bone. In all groups, von Mises stresses on the bones were found to be very close to each other and no significant difference was observed. However, when stress values on bone are examined, lower stress values were measured after the use of PEEK abutment as abutment material and the use of metal-supported porcelain as crown material.
|Figure 4: (a): von Mises stress values of the bone group I. (b): von Mises stress values of the bone group II. (c): von Mises stress values of the bone group III. (d): von Mises stress values of the bone group IV|
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Comparison of von Mises stress values of the crowns
When all the groups were examined, it was observed that the highest von Mises stress values on the crown were concentrated on the marginal finish line [Figure 5]a, [Figure 5]b, [Figure 5]c, [Figure 5]d. The stresses on the crown were observed to be lower in the groups using titanium abutment than the groups using PEEK abutment. As the superstructure, the stresses in the groups using PEEK material were found to be lower than the groups using metal-supported porcelain.
|Figure 5: (a): von Mises stress values of the crown group I. (b): von Mises stress values of the crown group II. (c): von Mises stress values of the crown group III. (d): von Mises stress values of the crown group IV|
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Comparison of von Mises stress values of the screws
When all groups were examined, it was observed that the highest von Mises stress values on the screw was concentrated in the middle of the screw in the groups where PEEK abutment was used and was concentrated in the middle part of the screw close to the apical in the groups where titanium abutment was used [Figure 6]a, [Figure 6]b, [Figure 6]c, [Figure 6]d. The von Mises stresses on the screw were observed to be much lower in the titanium abutment groups than in the PEEK abutment groups. As regards to the crown material, von Mises stress values of the screws are lower in the titanium abutment used groups with a model made up of PEEK crown and in the PEEK abutment used groups with a model made up of metal-supported porcelain.
|Figure 6: (a): von Mises stress values of the screw group I. (b): von Mises stress values of the screw group II. (c): von Mises stress values of the screw group III. (d): von Mises stress values of the screw group IV|
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| Discussion|| |
Titanium implants used in dentistry with the definition of osseointegration concept are used with high success rates. In our study, titanium implants were used in all groups. Biomechanics has a significant role in the long- and short-term clinical success of dental implants. In unsuccessful implant procedures, bone destruction is usually reported around the implant neck region. Numerous experimental and clinical studies have been conducted to explain these destructions.,
There are several stress analysis methods used in dentistry. Recently, two-dimensional and 3D finite element stress analysis methods have been used to investigate how prosthetic restorations over implants affect the stress distribution in the bones. FEA is regarded as the most ideal technique for the detailed evaluation of the dental implant-bone system, and the most common technique used for evaluation of the implant and peripheral bone stress is the finite element stress analysis. Recently, 3D finite element stress analysis method has been used to investigate how prosthetic restorations on implant affect the stress distribution in the bones. Natural teeth do not have a plain or symmetrical structure. For this reason, it is more appropriate to make a 3D model showing geometry closer to the actual dimensions of object in order to perform a more reliable analysis. Thanks to the technology and its facilities; our study models are prepared in three dimensions, in a detailed and meticulous manner, in the most appropriate way for the real anatomy.
All models used in this study are considered to be homogeneous, isotropic, and linear elastic. Actually, there is no 100% homogeneous and isotropic material in nature. In this case, assuming that the material is homogeneous and isotropic, the use of mean values does not preclude the in vitro test results to be close to the original. In this study, it is also assumed that the connection between implants and bone is 100%. It is a known fact that there is never 100% connection between bone and implant. These factors are limitations of our study. For this reason, it is necessary to take into account the limitations of the finite element stress analysis method when evaluating the results of our study.
CT, MRI, and laser scanning methods can be used as monitoring methods in the finite element stress analysis technique. Among these techniques, CT images are reported to provide the most detailed 3D image. Maxilla model obtained by CT was used in our study.
Since Type 3 bone is mostly found in maxillary anterior region, a trabecular bone conforming to Type 3 bone feature and 1 mm cortical bone surrounding this bone were modeled in this study., In our study, the highest stress values in the bone were detected in areas where the implant first contacted the cortical bone in the neck region. In the presence of cortical bone, most of the loads transferred by the implant to the bones were met by the cortical bone itself, leading to a much lower amount of stress being transmitted to the trabecular bone.
In the literature, forces at different values and at different angles were applied to the upper central tooth., The oblique force applied to our study was 178 N and the angle of application was 45°. The same angle degree and force amount were also used in similar studies.,,, The force was applied to 2 mm below the incisal edge of palatinal. A homogeneous distribution of stress to the bone is required for maintaining the implant-bone combination for a long time. Appropriate dental implants and prosthetic components should be selected to meet these requirements., It has been suggested that PEEK can solve stress-related problems  and it has been stated that it can be used both as an abutment and as a prosthetic material due to its high mechanical properties.
PEEK is more biocompatible than the metal-supported ceramics used in dentistry. However, since it does not have sufficient transparency, it may require improvements such as veneer application., Since PEEK is lighter, it may be a suitable alternative to metal supported ceramics. They also do not cause galvanic elements (corrosion) when they contact with other metals in the mouth. It has been suggested that PEEK material alleviates the forces generated during chewing due to its elasticity.
When all groups are examined in accordance with the results obtained in this study, it was observed that the use of PEEK crowns instead of metal-supported ceramics did not make a significant difference in terms of stresses on bones and implants. The use of PEEK crowns reduced the stress on itself and abutments. When the PEEK crown was used on titanium abutments, the stress on screw was decreased and when it was used on PEEK abutment, the stress was increased. It was observed in all tests that the use of PEEK material in this study reduced the stresses resulting from the applied forces on itself. Because of its low solubility in water and low reactivity with other substances, PEEK may also be suitable for patients with metal allergy or susceptibility to metallic taste.
Many materials have been used in the production of implant abutments. The abutments made up titanium, gold, zirconium are among these materials. Although the use of titanium is controversial in terms of its susceptibility to corrosion and the hypersensitivity to it, titanium is the first preferred material in implantology and it is the gold standard. The desired results cannot be obtained in cases where the aesthetic is of top priority. Especially in the presence of thin gingival biotype, it creates esthetic problems.
It has been suggested that PEEK material may promote the remodeling process of the bone and it has been stated that PEEK material may be an appropriate alternative to titanium in abutment construction. Since they have a high elastic modulus of titanium, they do not have the ability to absorb the shock during chewing loads. Since the elastic modulus of the PEEK material is very close to the bone, it has been suggested that it absorbs the incoming forces and minimizes the stresses on the bone. As a rigid structure can transmit the loads exposed by implant to the bone, it causes bone resorption. At this point, it has been stated that PEEK material has the advantage of protecting the bone structure by absorbing some of the stresses. When the stresses on bones occurred as a result of PEEK abutment use in our study were examined in all groups, the stress levels of the groups are very close to each other. However, the use of PEEK abutments resulted in less stress. The result we obtained is parallel to this suggested view. In addition, the use of PEEK abutment decreased the stress on itself by spreading the incoming forces to the implant, crowns, and screws and increased the stresses on the implant, the crowns, and the screw as compared with the titanium abutments. Stresses reached very high levels in all crowns and screws, especially with the use of PEEK abutments.
PEEK can be coated with veneer materials as well as it can be produced with monolithic materials and this process increases aesthetics. Before the coating process, alumina powders are applied under pressure to the outer surface of the material. It has been reported that PEEK's low elasticity modulus is advantageous over metal-supported ceramics in reducing the occlusal forces and decreasing the separation rates with the use of composite resin polymerized by indirect light as the veneer material. Either coated with monolithic or veneer material, PEEK material can be used for final restorations. PEEK can be a material with high strength and hardness with its improved abrasion resistance reinforced with carbon and glass fiber., Furthermore, it can be provided to monitor PEEK on image easily, particularly in traumas, by increasing its radiopacity with adding barium sulfate. PEEK, which is normally in tan color, transforms into black color by the addition of carbon.
| Conclusion|| |
The use of titanium abutments with more elastic modulus after replacement of implant abutment material reduced the stress on the implant. The stresses on the abutment were more affected by the change of the abutment material than the change of the crown material and PEEK abutments and PEEK crowns reduced stress on the abutment in all groups. When the stress that occurred on crown has been examined, we think that the use of PEEK crown can increase the life span by decreasing the stress on itself. It was observed that the use of PEEK abutment increased the stress on the crown. We are of the opinion that complications such as screw loosening and screw fracture may be caused by excessive increase of the stresses on screw with PEEK abutment use. It is seen at the end of this study that the use of different prosthetic materials can change the stresses in the implant system. The results of our study should be supported by long-term in vitro and in vivo researches. We think that the clinical dentistry applications of PEEK material can be increased by improving the modifications and material features.
The authors thank Dr. Emre Ari (Dicle University, Department of Mechanical Engineering) for their helpful advices on the FE analysis.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2], [Table 3]