Journal of Dental Implant Research 2022; 41(3): 50-63  https://doi.org/10.54527/jdir.2022.41.3.50
Review on finite element analysis of dental implants
Fatma Nur Büyük, Efe Savran , Fatih Karpat
Department of Mechanical Engineering, Bursa Uludag University, Bursa, Turkey
Correspondence to: Fatih Karpat, https://orcid.org/0000-0001-8474-7328
Department of Mechanical Engineering, Bursa Uludag University, Bursa 16059, Turkey. Tel: +90-0224-294-1951, E-mail: karpat@uludag.edu.tr

Throughout this study, Tubitak 2244 program scholar Efe Savran with project code 119C154 would like to thank the institution received partial support from.
Received: July 25, 2022; Revised: August 14, 2022; Accepted: August 16, 2022; Published online: September 30, 2022.
© The Korean Academy of Implant Dentistry. All rights reserved.

This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Dental implants are structures of high importance, as in other implant studies used in the biomedical field. The jawbone is a structure of such importance that it affects the nutritional functions of the living thing with which it is integrated. Therefore, intervention in this structure is of high importance. Parts for use in the biomedical field can be produced using numerical analysis, thus saving time and cost. In addition, the level of trust increases in the living being where the dental implant is applied. This paper reviews studies using the finite element method for the numerical analysis of dental implants. The analysis revealed important conditions, such as groove type, material, osseointegration status, splinting, dimensions, neck region, and fatigue strength of the dental implant.
Keywords: Dental implant, Finite element analysis, Material, Groove type, Dental neck, Fatigue of dental implant
INTRODUCTION

From an engineering point of view, implants can be thought as the addition of parts to a structure for various reasons. Causes here may include factors such as malfunction or deterioration. In the machinery sector, a part is replaced or a part is added for a new function, as well as in the biomechanics field, a similar attitude is carried out for the function that needs to be fulfilled. The loss of some limbs in living things affects the static and dynamic endurance of the skeletal system, as well as indirectly affecting vital functions. One of these limbs is the jawbone, which houses the teeth. Any damage to the jawbone joints will cause the mouth part, which is the basic feeding organ of the creature, to not be able to perform its function. for this reason, he will suffer from a lack of live nutrition and will be in danger of losing his life, even if it is possible.

Teeth located in the jawbone are the elements that perform the function of making food smaller and grinding in living things. As mentioned before, these elements can also deteriorate over time. This deterioration or dysfunction is corrected with dental implants. In this process, a tooth-shaped structure is placed on the upper part and a cylindrical piece with a screw on the outside is placed on the bone in the area where there is a lack of teeth, and a bolt-nut relationship is formed in that area. At the same time, this structure is faced with negative conditions such as stability, loosening, insufficient osseointegration, and nonunion1). All these negative results can effect the patient comfort and health of implants. In order to prevent these discomforts, the reasons must be known beforehand. Analyzing the implant area in terms of the amount of stress and deformation can provide information about the condition of the area and make an estimate about the health of the implant. Finite element analysis is preferred in most of the studies to obtain stress and deformation values.

In this review, the finite element method solutions related to dental implants were examined and the findings were shared.

MATERIALS AND METHODS

In this review, the studies that are published in international journals between 2018 and 2022 were examined in view of finite element methods application to dental implants. Appropriate keywords related to the subject were searched through google scholar, scopus and science direct, 8, 5, 11, 9 and 2 publications were determined between 2018 and 2022, respectively. After a detailed examination, the properties of dental implants analyzed by the finite element method were shared. A review table has been prepared considering simplicity and easy accessibility to the results. In addition to finite element methods, the reviewed publications also refer to the effects of mechanical strength, material properties, implant size, tooth geometry and experimental data on dental implants.

RESULT

In this study, articles on the analysis of dental implants with the finite element method, which were made between 2018 and 2022, were examined and explained. In the studies examined, it was seen that there were validations with the finite element method, material comparison and experimental studies. Considering the results in the reference studies, evaluations were made on the basis of engineering. For the finite element method, the results of the applied force on the dental implant and the boundary conditions were investigated. It should be increased to support the analyzes carried out with the finite element method with experimental studies. As stated in a reference, conducting experimental studies on different materials (such as plexiglass) will also encourage the creation of new engineering materials. When the finite element method is considered, it is seen that the load applications that will cause compression, bending and shear stresses. In order to examine more realistic conditions, the torsional stress that will occur in the screw during implant installation should also be included in the studies. Titanium, ziconium and polymers, which have general use on the material side, have been encountered. In this regard, magnesium should also be among the studies due to its lightness and relatively sufficient mechanical strength. Magnesium, which has positive properties such as biocompatibility and biodegradation, also has negative properties such as ignition during additive manufacturing. Therefore, these conditions should be taken into account in researchs.

DISCUSSION

In this section, the publications mentioned in the material and method section will be explained. The reviewed publications will be grouped according to the effect of tooth type, material, loading type, and implant geometry using finite element analysis. After the publication of the reviewed publications, all of the reviewed publications will be displayed in tabular form.

1. Thread type effect on the dental implants

In a study in which the effect of different groove geometries on the structure was desired to be revealed, rectangular, buttressed, reverse buttressed, and symmetrical profiles were used for evaluation. 4 different groove geometries can be seen in Fig. 1 below. During the finite element analysis, the length of the cortical layer of the sample was defined as 2 mm, and the length of the trabecular layer was defined as 25 mm. FEA studies were conducted via ANSYS® 16.1 software and boundary conditions were assessed on sample of the cortical-trabecular couple and threaded part. In view of boundary conditions, fixed support was assessed to the outer surface of the trabecular layer and several vertical loadings were applied respectively. As a result, rectangular profile groove geometry was found as the lowest stress producer, while the other profiles showed that optimum stresses that promote bone regeneration in the peripheral bone reach the surrounding bone and reduce the negative stress shielding effects. According to this study, buttressed groove was defined as the most suitable profile for small diameter conical implants. By this study, proper Groove geometry might promote the osseointegration and patient comfort. Beside the biomedical side, it would be useful that findings from this study be used for bolt assemblies in the industry2).

Figure 1. Four different groove geometries2).

The finite element method was used in a study to analyze the effect of different implant designs on stress and strain distribution on implants and surrounding bone. 3 different implant samples as narrow pitch, large pitch and grooved on vertical arc were used for the finite element studies. Displacement and stress results for bone and dental implants were obtained from the analyzes. All implants showed good force distribution for non-axial loads at the bone-implant interface but groveed type implant has more distributed strain. This result is related to thread geometry and dimensions but also grove type and it’s location are among the factors3).

According to the results of the study, which aimed to determine the effect on stress transfer to the surrounding bone by changing the microgroove profile on an implant, implants with a square groove profile outperformed V-shaped grooves in terms of long-term implant stabilization. This result states that geometric integration of thread profiles has critical place. Normal force of square profile corresponds to normal force of contact surface but V profile’s normal force does not correspond to contact surface directly. Resultant force and friction force come into play. Force from tissue splits into forces that they have 0° and 90° to the thread surface. Force with 90° has less magnitude than the normal force. Fig. 2 states of load application and parts of dental implant below. It was stated that these threads are applicable to dental implants for long-term use of the implant4).

Figure 2. Load application points and assembly parts of a dental implant29).

A study using finite element analysis aimed at optimizing length and thread pitch found that length and pitch can dominate in dental implants. This study used the visualization method of the photoelasticity test. Observed stress areas on plexiglass were seen in the finite element analysis results similarly. In this way, a study that was validated both numerically and experimentally was obtained. It is also worth noting that the length of the implants varied between 8.5 mm and 13 mm during this study5).

A study aimed both numerical stress distribution and experimental verification to see the implant – tissue contact area stress model. In order to see shear stress, statical occlusal load was applied during finite element analyzes. Araldite resin and hardener were used as materials for experimental verification. From this verification, shear stress in sponge volume was predicted. In the results of the study, the top level of maximum stress was obtained with “reversed buttressed” thread model and opposite of this, the least level of maximum stress was obtained with “V” thread model6).

2. Material effect on the dental implants

For evaluating the micro-movement of dental implants, shock loading was applied in another study. Finite element analyzes were conducted on three structures that used Titanium (Ti) and Cobalt-Chromium (Co-Cr). Two working models, named A and B, were established. Model A and B are structures with titanium alloy and cobalt-chrome alloy respectively. Simulation of the shock-loading situations between the implant and the bone surface with friction coefficient of 0.71 were conducted. The result of this study is that the structures with Co-Cr alloy show higher micro-motion. FEA results are in Fig. 3 below. This study could enlarge the material usage to ensure the reliability of the study. Moreover, micromotion between the surfaces will be occurred definitely, but it can be managed in an appropriate tolerance. This study could include the tolerance calculation and can be directed to motion analysis for the future7).

Figure 3. FEA micro-strain result of dental implant7).

Another study that analyzing and comparing the stress distributions of different implants and materials, evaluated 12 different implant models were created in SolidWorks software. For finite element analyzes 118.2 N load was applied with 75.8° angle to the occlusal plane. As a result of this study, according to material comparison, the implant model with zirconia showed lower stress than titanium. Also, the same results showed 3.3 mm diameter implant with titanium-zirconium and 4.1 mm diameter implant with pure titanium have similar strength. This study achieved the material comparison in properly for dental implants. Titanium is well-known material for biomedical applications. Enough mechanical strength and biocompatible behaviour makes titanium frequently preferred material. This study highlighted zirconium provides more strength with titanium on smaller cross section of a dental implant. For instance, alloy with zirconium (ZrO2) has young’s modulus 2 times than Ti grade 4. This means that if the same stress value is considered, alloy with zirconium shows 2 time less displacement than only titanium structure under the same load8).

Another study compared the stress distribution patterns in view of the polymers and engineering materials. The materials that are the subject of this study are PEEK, PEKK, monolithic zirconia, and titanium. During finite element analyses axial and oblique 150 N loads were applied and analyzed. PEEK and PEKK showed the highest maximum principal stress and minimum principal stress values in cortical bone on oblique loading. Polymers such as PEEK and PEKK are the subject of various biomedical application. They have young’s modulus approximately 34 times less than zirconia and titanium. As poisson’s ratio, polymers have higher value so the change in area of section will be higher than zirconia and titanium with same length and under the same load9).

A study was conducted to evaluate the biomechanical behavior of bioglass and zirconia using the finite element methods. 3 different implant models as uncoated, 100 or 150-micron thick bioglass coated, and chemical mixed bioglass coated were used for analyzes. As result of the analyzes, the bioglass coating provided a 30% reduction in the stress value compared to the zirconia implant. therefore, bioglass-zirconia dental implants showed improved biomechanical behavior over Bioglass-coated or monolithic zirconia dental implants10).

In a study that aims to present a material selection strategy by utilizing finite element analysis in terms of reducing the possibility of adverse events in dental implants, stability, loosening, insufficient osseointegration, and nonunion are mentioned among the critical issues. As a thought, optimization that is the core of engineering, it appears in every stage of the processes. Thus, keeping the balance is keywords of this issue. Materials have different properties. If a feature is negative, there is definitely another feature that will be positive about it. The results of the study showed that zirconia abutment loosening performance was worse than Au83-88/Pt4-12/ Pd4.5-6. On the other hand, zirconia is the most promising material for dental crown stability. As such, it has the potential to perform best in clinical trials1).

3. Load type effect on the dental implants

Osseointegration based a study that evaluated strain and displacement. In finite element analyses applied force was approximately 150 N. With the aim of realistic conditions of the mouth, the applied force was separated in three directions. The first one is 150 N on the implant axis, the second one is 150 N at an angle of 45 degrees to the implant and the third one is 150 N in buccolingual order. This study mainly focused on osseointegration. Differences between partial and fully osseointegration were found. The conclusion of this study is limited osseointegration is critical for implants so if full and limited osseointegration is compared, limited osseointegration results in higher displacement. Therefore limited osseointegration has a negative effect on the lifetime of implants. Fig. 4 visualize the implant-tissue integration below. Some references were mentioned but frictional content could be more highlighted for this study due to osseointegration. Detailed modelled and meshed trabecular layer of mandibular and implant showed stress distribution very well11).

Figure 4. Osseointegration and implant-bone integration11).

In a study to obtain the fatigue curves of 5 different dental implants, the maximum value of the fracture load was obtained by simulating a compression test. After the breaking loads were found, the minimum number of cycles it had to support was calculated. In conclusion, this study found that the maximum number of cycles for implants with a fatigue limit of approximately 200 MPa is between 64,976 and 256,830. This finite element study proves the maximum load values for all implants subjected to loads between 100 and 80 N12).

In an article aiming to evaluate the effect of three different dental implant neck geometries under a combined compression/shear load using finite element analysis (FEA), three different models, 0°, 10°, and 20° were created with different implants. In conclusion, the configuration of the implant neck affected the stress distribution and size in cortical bone and cancellous bone tissues. According to the study, it is stated that implants with 10° and 20° neck configurations should be preferred rather than flat implant platforms to reduce the stress values in the bone tissue and improve the load distribution. Neck angle supports the attachment of implant to the surface of bone tissue. The reduction in thread angle provides an increase in magnitude of the force normal to the contact surface between thread and bone tissue13).

In another study to verify implant fatigue life, testing of implant specimens using the ISO specified apparatus accelerated life test method and revealing the fatigue life of a reduced diameter dental implant estimated by finite element analysis was performed. The lifetime value obtained from the finite element analysis was within the 95% confidence interval between the experimental results and the predicted lifetime values. The implant body root faced with the highest probability of failure14).

A study that stated that dental implants were applied to unilateral defects in the mandible aimed to evaluate the occlusal force distribution in the mandibular shortened dental arch (SDA). In the study, distribution of occlusal forces on the teeth and force – displacement graphic of teeth stated properly. It can be observed on the force distribution that the teeth close to the joint are exposed to greater forces due to the fundamental moment rule. It was revealed that reconstruction with the same number of implants as missing teeth will show almost symmetrical occlusal15).

In another study, which stated that screw loosening and fatigue damage are the most common problems, the effect of screw taper angle on the loosening performance and fatigue properties of dental implants was investigated. From 30°, screws with taper angles of 60°, 90°, and 180° were created and tested. Comparing the relaxation performance of the screws according to the initial and final loading conditions, measuring the fatigue properties, and observing the wear and fracture modes of the screws were carried out, respectively. At the same time, the damage locations were confirmed by finite element analysis. The results showed that screws with a 30° taper were better at preventing loosening and had less wear. Higher preload occurred in 180° tapered screws, resulting in longer fatigue life. At the same time, fatigue fracture of the screw occurred at the level of the first thread, similar to the finite element analysis results16).

Experimentally validated studies both ensure the reliability of the resulting product and increase the interest in the numerical studies. It is a great gain to be able to experimentally obtain the same results as obtained in the finite element method, but even if the same results are not obtained, it is also remarkable that the difference is small. In a study, bite forces as between 0 N and 100 N were measured by using MEMS. Beside this experimental study, a finite element analysis was concluded with comparison between numerical and experimental values. Fig. 5 states the parts of dental implant that was used in this study. Result of this study found that a sine function can define alveolar bone force-stress corelation17).

Figure 5. Parts of implant set17).

4. Geometry – Type effect on the dental implants

Due to Narrow-diameter implants (NDIs) suffering from higher defection than regular-diameter implants (RDIs) and wide-diameter implants (WDIs), a study aimed to evaluate potential risks related to narrow-diameter implants using finite element analysis (FEA) was conducted. After the simulation of biting forces, stress distribution around the implants was calculated. Results of this study showed the volume around splinted three-unit bridge was reduced when compared to nonsplinted type. It was confirmed that splinting has a beneficial effect on the mechanical side. Results were appeared as expected in the Fig. 6 below. Increased the cross sectional area that under the compression load makes stress reduce. This can be seen on splinted three-unit bridge. Also it can be mentioned that there is bending stress for tissues such as mandibular. Thus, increase in moment of inertia will result in more strength to bending stress18).

Figure 6. Stress-strain distribution on the dental implant18).

Another study that evaluated the bone density, cortical bone thickness, and bone type effect on the stresses was conducted. For this study, two implant geometries were obtained from Cone-beam computed tomography (CBCT). As boundary conditions, 400 N load was applied as compressive and 5 mm above the uppermost part of the implant with 15° angle. Eventually, it was found that M-12 implants show lower stress distribution in the cortical layer towards to Astra Tech. If the thread length was considered same, M12 has higher pitch and has supporter thread with smaller thread diameter when compared to Astra Tech. Astra Tech has relatively homogeneous thread geometry and was considered to possibly provides lower stress values to be achieved19).

Another evaluation study aimed the distribution and magnitude of stresses of the tissue that is surrounding Morse taper dental implants. 3D mandibular bone geometry was obtained computed tomography scan and this geometry was used for finite element analysis. During the periods of analysis, 150 N load were applied for both vertical and on the axis with 45°. As a result of loading parallel to the central axis, 6∼7 MPa maximum stress occurred in the trabecular layer while 73∼118 MPa maximum stress in the cortical layer. Meanwhile, stress results of loading with 45° were obtained as 15∼21 MPa for trabecular layer and 150 MPa for cortical layer. This study aimed the stress distribution around the dental implant. By this study, basic mechanical rules were reconfirmed. Thus, structure with vertical loaded has only compression pressure and analysis showed less stress value while the structure with oblique load applied which creates both compression, bending, and shear stress on the structure. Such that occurred stresses on the implants will be conducted to surrounding tissue20).

Surgical technique focused examination study aimed stress, strain, and displacement distribution. For implant volume, supporter tissue adding effects the mechanical strength significantly. The osseointegration process is facilitated simultaneously. General 4 different socket shield techniques were taken account for structures of implant. Structures varied according to supporter tissue adding and only implant-bone contact. If the effect of the socket shield technique on the dental implant is examined, it is observed that maximum stress, displacement, and strain occurred at higher values without a difference between the Socket-shield technique and conventional treatments. The result of this study showed that mechanical acting was not affected negatively by the use of the Socket-shield technique21).

Definition of length, diameter, and young modulus effect on the biomechanical behavior of dental implant study was benefited from finite element analysis model to simulate the situations. For this aim, 12 implant models and Abaqus software were used for analysis. In this study, the peri-implant trabecular layer showed the maximum strain value. Since the trabecular layer has a amount of porosity, its ability to absorb energy is higher than the full-filled structures due to bending of internal beams. Similar behavior can be seen in lattice structures that used for lightweight studies or biomedical implants. Fig. 7 shows the implant-bone integration, boundary conditions, stress – strain distribution. Results of this study included that the aforementioned three parameters affect both maximum stress and strain in von mises22).

Figure 7. (A) Implant-bone integration, (B) Boundary conditions, (C) Stress distribution, (D) strain distribution, (E) Stress distribution on the ver-tical axis22).

A study aimed section of cortical and spongy bone evaluation in terms of stress distribution used two dental implant models, named A and B, which have the same dimensions but different design and thread patterns. Model A is corresponding to a cylindric implant with a cylindric neck. Model B has reverse conical neck and stress distribution optimized. For finite element analyzes axial 100 N and oblique 223.6 N loads were used. Results of the study showed model with reverse conical neck has lower stress and strain values when compared to model with cylindric neck. When the thread geometries are observed, it will be seen that model B has a thread with larger side surface according to model A which has V-shaped thread with smaller side surface area. Thus both increased contact area and branches to improve the contact quality on the thread geometry23).

To evaluate the differences between the conventional and porous dental implants, a study examined maximum stress distributions based on finite element analyzes. 4 different porous implant designs with porosity in various regions and different amounts of porosity were included in this study. Static, dynamic, and impact loads were applied to obtained geometry on vertical and oblique axes for finite element analyses. On the vertical axis 300 N, and on the 45° angled axis 50 N load was applied. Impact load resulted in 1030 MPa so this value is higher than Ti-6Al-4V tensile strength. An optimization study should be conducted on porosity rate. In optimization study, porosity rate, beam thickness, and material properties (Density, Young’s Modulus, Possion’s Ratio etc.) show proper indications to obtain the reliable stuctures. According to results of this study, in view of stress distribution, porosity location plays more critical role than porosity rate24).

By using nonlinear finite element analysis, a study evaluated the effect of implant neck wall thickness and abutment screw size on alveolar bone. 12 implants with 3 different diameters were used for nonlinear analysis. 200 N load was applied with 30° angled to the center of a hemispherical load cap. Although some literatures prefer special metarials for nonlinear analysis but in this study materials that was used in this study were considered as isotropic, and linearly elastic. This issue can be checked with material library of a FEA software (Ansys, Abaqus etc.). From this study, it was concluded that implant neck wall thickness affects implants drastically and also it reduces implant, abutment, and abutment screw stresses and bone strain25).

In stress distribution assessed study found that transversal screw reduces the mechanical failure. This study, in finite element analyzes, applied 300 N load with different angles on assembled geometries. 15° angle was found as the lowest stress value on the transversal screw. Mechanical failure occurs because of high stress or fatigue generally. If the bending stress formula is considered, the stress value is directly proportional to the length between the point where the maximum stress occurs and the stress neutral axis. Thus, if the aforementioned length is increased, stress value goes up. That is why failure starts on out surface of the structure26).

The analysis results of a study evaluating 2 different types of implant models on the stress distribution in the jaws with finite element analysis showed that the stress distribution increased and the deformation decreased as the number of fences increased. Homogeneity of stress distribution provides more reliable structure. Otherwise load will be concentrated on a point. Shear stress increase as well27).

The external and internal threaded implant comparison study used the design of 2 different tooth–implant supported prostheses (TISPs). For this study, only compression load could be enough due to see the effect of thread location but authors preferred both axial and oblique loads in order to get more reliable results. When the strength of implant was taken into account, while the internal thread model showing lower maximum stress both in axial and oblique loading, it showed higher in abutment. As a result of this study, TISPs with internal threaded implants provide lower biomechanical failure risk28).

In a study in which fatigue and micro-void formation in screws were evaluated according to implant diameter, connection type, and bone density, 12 models were created using 2 different bone densities, 2 different connection types, and 3 different implant diameters. Each model consisted of cortical and spongy layer, nerve canal, and implant complex. In the finite element method studies, vertical (100 N) and inclined (200 N) loads were applied to the screws. The fatigue life of titanium alloy components was calculated based on repetitive chewing motion to simulate real conditions. The chewing motion can be simulated, but the actuality of the motion varies depending on the person and mouth structure. In this case, several different jaw movements should be examined and the average movement should be simulated and analyzed according to the worst-case scenario. According to the recommendation in the study, two-piece implants with a diameter of less than 3.5 mm should not be used in the posterior mandibular region29).

In a study to examine the effect of different occlusion conditions on dental implants in different positions and to create a biomechanical reference to this field, the effect of 4 common occlusion conditions on other dental implant classes was analyzed by using the finite element method. The indicators observed in the study are the reaction force and stress in the dental implant system. The results of the study showed that under occlusion, right unilateral molars, dental implant system and the entire mandible experienced higher stress, and the reaction force at the fixed upper end was higher. In addition, this study showed that the reaction forces in the posterior region were not superior to those in the anterior region30).

In a study conducted to investigate the stress distribution of tooth-implant-supported prosthesis (TISP) in different connectors and different implant abutments after load application, it is thought that the stress distribution in the TISP will be affected after loading. In the finite element study, a load of 50 N was applied at right angles on the 6 points of the occlusal surface. The study showed that by adding a flexible connector and 3-piece abutment design to the TISP, the occlusal load of the implant is distributed and stress can be gradually delivered to the strong implant abutment31).

In the study conducted to examine the biomechanical behavior of dental implants with 4 different neck designs in contact with the cortical layer, the results obtained from the finite element method were compared with the results obtained from an in vivo study. The neck designs discussed in this study can be grouped as flat surface, screw, three rings, and four rings. In the finite element method studies, it was observed that lower stress distribution values were achieved with the 3-ring design. Applied force and different geometries showed in Fig. 8 below. On the same design, it was observed that the highest bone-implant contact value was reached after a period of 3 and 6 weeks. Both numerical and experimental studies have shown that the best biomechanical and histological behavior in terms of new bone formation, mechanical stability, and optimum osseointegration is achieved with the implant with the three-ring neck design32).

Figure 8. 100 N load application on dental implant (left), 4 diffe-rent neck designs (right)32).

In a study aiming to evaluate the effect of bone reformation around a reduced diameter dental implant on the fatigue limit using finite element analysis, two setups were constructed remodeled bone (model 1) and remodeled spongy bone in regions adjacent to the implant screw threads (model 2). In model 1, Young's modulus is 20 GPa for the cortical layer and 14 GPa for the spongy bone layer. In model 2, Young's modulus of the spongy bone in contact with the implant screw threads was defined as 20 GPa. In the finite element study, the maximum stress was 439.9 MPa and the fatigue limit was 116.4 N for both models at 100 N load application. The study results show that the fatigue resistance of implants tested according to the ISO 14801 standard can be accurately estimated without simulating the bone-implant interface in the clinical case33).

Jafarian, Mirhashemi, and Emadi studied on maximum stress evaluations of different length and diamater by using finite element methods. With this propose, benefited from computed tomography for geometry visualization. While performing the finite element study, 200 N of vertical and 40 N of horizontal forces were applied to the middle point of abutment. What the obtained from this study is a decrase in mounted length of implant corresponds to increase in stress. This result can be stated by fundamental moment rule. The length of mounted implant is inversely proportional to the moment load on the implant. Also it can be observed that bone loss amount and stress have same beaviour34).

A research study was conducted in order to see the effect of diameter and bone quality to implant. By using finite element method, variable diameters with fixed length was considered for comparison. From bone quality side, 4 different quality levels were considered. During finite element analyzes, force applied as 200 N and diameter of 3.3 mm showed maximum stress with top level with bone quality IV. Contrary to maximum stress, diameter of 4.75 mm showed maximum stress with least level with bone quality 0-I. As expected, increase in bone quality resulted in decrease in maximum stress level35).

The general review of the publications shown as subtitles can be made through the Table 1 below.

Table 1 . Reviewed studies

Scope of the studyFindingsReference
Different groove geometry evaluation on stress and bone regenerationRectangular groove geometry is the lowest stress producer. Buttressed groove is the most suitable profile for small diameter conical implants.2
Micro-movement evaluation of dental implantsStructures with Co-Cr alloy show higher micro-motion.7
Strain and displacement evaluation on osseointegrationLimited osseointegration creates higher displacement. Therefore limited osseointegration has a negative effect on the lifetime of implants.11
Potential risk evaluation of narrow-diameter implantsSplinting has a positive effect on the mechanical behavior of dental implant.18
To reveal the effects of bone density, bone thickness and bone type on stressM-12 implant has mor emechanical strength than Astra Tech in the cortical layer.19
Effect of morse taper dental implants to surrounding tissueCompression stress is lower than bending and shear stresses on both tissue layer.20
Surgical technique focused stress, strain, and displacement distributionSocket-shield technique does not effect negatively the mechanical acting.21
Parameter effect on the biomechanical behavior of dental implantLength, diameter, and young modulus affect both maximum stress and strain in von mises.22
Stress distribution evaluation in bone tissue with 2 different thread geometryCylindrical neck model forces the bone tissue more than reverse conical neck model.23
Stress distribution evaluation on cortical and spongy bone tissuePorosity location is more critical than porosity rate in view of stress distribution.24
Implant neck wall thickness and abutment screw size effect evaluation on alveolar boneImplant neck wall thickness affects implants drastically.25
Stress distribution on dental implants with different materialsImplant with zirconia has more mechanical strength than titanium. Implant diameter with titanium-zirconium is smaller than pure titanium.8
Transversal screw effect on stress distributionLoad application angle of 15° has the lowest risk to failure on the implant.26
Effect of fence on stress distributionThe more fence number, the less stress on the tissue.27
Stress distribution evaluation in view of polymersPEEK and PEKK show the highest maximum stress values in cortical bone on oblique loading.9
External and internal threaded implant comparisonInternal threaded implant is more reliable according to external one.28
Biomechanical behavior evaluation of bioglass and zirconiaBioglass-zirconia dental implants showed improved biomechanical behavior over Bioglass-coated or monolithic zirconia dental implants.10
Stress – strain distribution with narrow pitch, large pitch and grooved on vertical arc implantsAll types shows good performance in view of stress distribution but grooved type implant has more homogeneous strain.3
Stress transfer to the surrounding bone tissue with different microgroove profiles on implantThreads with square profile are more stable than V profile.4
Fatigue and micro-void formation in evaluation with implant diameter, connection type, and bone densityImplants of 2-piece and diameter of less than 3.5 mm are critical for the posterior mandibular region.29
Effect of different occlusion conditions on dental implants in different positionsRight unilateral molars, dental implant system and the entire mandible tissue are faced with high stress under occlusion.30
Fatigue curve obtaining with 5 different dental implantsFatigue life cycle is between 64976 and 256830 at approximately 200 MPa.12
Implant neck geometry evaluationImplants with 10° and 20°neck configurations reduces the stress values in the bone tissue when compared to flat implant platforms.13
Implant neck geometry evaluationImplant neck affected the stress distribution and size in cortical bone and cancellous bone tissues.13
Investigation of stress distribution of tooth-implant-supported prosthesis in different connectors and different implant abutmentsAdding flexible connector and 3-piece abutment to the TISP makes the load is distributed and stress is transmitted.31
Implant fatigue life verificationThe implant body root faced with the highest probability of failure.14
Evaluation of the occlusal force distribution in the mandibular shortened dental arch (SDA)Same number of implant reconstructions as missing teeth show symmetrical occlusal feature.15
Loosening performance and fatigue properties of dental implantsFatigue fracture of the screw occurs at the level of the first thread.16
Experimental comparison of dental implants with 4 different neck designs3∼6 week period is proper to the highest implant-bone contact value and three-ring neck design provided the optimum osseointegration.32
Evaluation of the effect of bone reforming around a small diameter dental implant on the fatigue limit using finite element analysisISO 14801 validated and fatigue resistance can be predicted with high accuracy without the need for bone-implant interface simulation.33
Optimization of length and thread pitch by using photoelasticity testPlexiglass visualization is a good alternative to experimental studies. Results of experiment were similar to the finite element analysis results.5
Effect of diameter and lenght on dental implantsDecrease in length of implant equals to increase in stress.34
Stress monitoring and determination and control of bite forces using MEMS to prevent occlusal traumaThe relationship between loading forces and stresses on the alveolar bone and abutment can be described by sinus function.17
Effect of diameter and bone quality on the dental implantDiameter of 3.3 mm in bone of quality 4 is prone to failure in implant. Similarly, diameter of 4.75 mm has maximum stress with bone quality 0-I.35
To see and experimentally verify the implant-tissue contact area stress modelby numerical methodReversed buttressed thread created the maximum stress while V thread model has the least stress level.6

CONCLUSIONS

In this review, studies using finite element analysis for dental implants were subjected. Real-time experimental studies should be carried out in order to construct the correct structure, but this will cost a lot in terms of financial and time. For these two negative reasons, it will be a great advantage to perform numerical testing by creating a digital twin of the dental implant and the environment in which it will be mounted. When the previous studies are examined, it is seen that the finite element method is mostly used in numerical tests. For this, necessary structural and other analysis studies are carried out by using some software and possible negative situations can be determined in advance. Thanks to the early detection of negative results, a cost advantage is provided and at the same time a more comfortable use can be provided for the patient. Verification of the numerical analyzes performed with experimental studies also increases the reliability of the revealed product.

In the references, it is seen that reaching the finite element analysis supported results for dental implants reveals the accuracy of the structure. The results of studies that carried out according to various criteria such as stability, life, fatigue, and material are guiding the future dental implant studies. In the ideal implant design, besides static durability, biocompatibility, and osseointegration are also seen in critical phenomenons. From the material using side, there are various alternatives for this subject, as explained in the sections where the previous studies were examined and the results were shared. Among the all mentioned, materials that has proper mechanical property, good biocompatibility and promote osseointegration should be in the focus point of studies. Numerical finite element analysis has been used effectively in the studies examined to measure the biomechanical strength of the dental implant. These studies will also increase the reliability of dental implant studies.

CONFLICT OF INTEREST

We would like to submit the manuscript entitled “A review on finite element analysis of dental implants” for consideration for possible publication in scientific journal Journal of Dental Implant Research. The authors of this manuscript have directly participated in the planning, execution, or analysis of this study. The authors of the paper have read and approved the final version submitted. We declare that the paper is original, has not been submitted for publication in other journals and has not already been published. The authors declare that they have no known competing financial interest or personal relationships that could have appeared to influence the work reported in this paper.

Yours Sincerely.

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