|Year : 2014 | Volume
| Issue : 3 | Page : 109-114
Stress analysis of different prosthesis materials in implant-supported fixed dental prosthesis using 3D finite element method
Pedram Iranmanesh1, Alireza Abedian2, Naeimeh Nasri1, Ehsan Ghasemi1, Saber Khazaei3
1 Department of Prosthodontics and Dental Students' Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran
2 Department of Mechanical Engineering, Daneshpajoohan Higher Education Institute, Isfahan, Iran
3 Department of Research, School of Dentistry, Kermanshah University of Medical Sciences, Kermanshah; Department of Prosthodontics and Dental Students' Research Center, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran
|Date of Web Publication||15-Jul-2014|
Department of Research, School of Dentistry, Kermanshah University of Medical Sciences, Shariati St., Kermanshah and Dental Students' Research Center, Isfahan University of Medical Sciences, Isfahan
Source of Support: This project was fi nancially supported by Vice Chancellery
for Research and Technology, Isfahan University of Medical Sciences,
Isfahan, Iran (Grant#189089). The results of present study also have been
presented at 9th Iranian and 13th Kuwaiti Division of International Association
for Dental Research, Tehran, Iran (December 2013) as poster presentation, Conflict of Interest: None
Introduction: In the present study, the finite element method (FEM) was used to investigate the effects of prosthesis material types on stress distribution of the bone surrounding implants and to evaluate stress distribution in three-unit implant-supported fixed dental prosthesis (FDP). Materials and Methods: A three-dimensional (3D) finite element FDP model of the maxillary second premolar to the second molar was designed. Three load conditions were statically applied on the functional cusps in horizontal (57.0 N), vertical (200.0 N), and oblique (400.0 N, θ = 120°) directions. Four standard framework materials were evaluated: Polymethyl methacrylate (PMMA), base-metal, porcelain fused to metal, andporcelain. Results: The maximum of von Mises stress in the oblique direction was higher than the vertical and horizontal directions in all conditions. In the bone-crestal section, the maximum von Mises stress (53.78 MPa) was observed in PMMA within oblique load. In FDPs, the maximum stress was generated at the connector region in all conditions. Conclusion: A noticeable difference was not observed in the bone stress distribution pattern with different prosthetic materials. Although, higher stress value could be seen in polymethyl methacrylate, all types of prosthesis yielded the same stress distribution pattern in FDP. More clinical studies are needed to evaluate the survival rate of these materials.
Keywords: Dental prosthesis, dental implant, finite element analysis
|How to cite this article:|
Iranmanesh P, Abedian A, Nasri N, Ghasemi E, Khazaei S. Stress analysis of different prosthesis materials in implant-supported fixed dental prosthesis using 3D finite element method. Dent Hypotheses 2014;5:109-14
|How to cite this URL:|
Iranmanesh P, Abedian A, Nasri N, Ghasemi E, Khazaei S. Stress analysis of different prosthesis materials in implant-supported fixed dental prosthesis using 3D finite element method. Dent Hypotheses [serial online] 2014 [cited 2019 Nov 12];5:109-14. Available from: http://www.dentalhypotheses.com/text.asp?2014/5/3/109/136757
| Introduction|| |
Tooth loss, particularly posterior teeth loss, causes insufficient and poor masticatory performance.  Masticatory function is an important factor for general health and also can directly affectthe nutritional status, quality of life, and overall health, especially in the elderly. , Several prosthetic treatments could be used to replace the missing dentition. One of these techniques for replacing the missing or more posterior teeth is implant-supported fixed dental prosthesis (FDP). 
The type and direction of loads,  the quantity and quality of the supporting bone,  dental implant, and typesof prostheticmaterial  are the most important factors that can affect the osseointegration and prognosis of implant-supported FDPs. ,
The type of prosthetic material influences stress distribution in dental implants and consequently affects morphology of the surrounding bone, which may lead to the loss of osseointegration. Based on the present evidence, polymethyl methacrylate, base-metal alloy, and porcelain are well-known prosthetic materials.  Currently, porcelain has presented an accepted level of fracture resistance, fit and aesthetics, so that most clinicians recommend it. ,
Motta et al. in a comparative study showed that the stress distribution of FDP is changed by applying load in different directions. Kamposiora et al. utilized FEM to investigate the stress distribution of three-unit FDPs constructed with different connector heights. The highest von Mises stresses were identified in the apical section of connectors, particularly in gold materials. Also, the effects of loading at one to three locations on stress distributions in an implant-supported FDP and surrounding bone have been evaluated indicating maximum stresses concentrated on the framework and occlusal surface. 
Given the significant role of prosthetic materials and their different physical and mechanical properties, it is necessary to figure outtheir role and produced stress pattern through mastication. Hence, the aim of the present study was to analyze stress distribution inboth bone and FDP when occlusal loads were applied to an implant-supported three-unit FDP with different framework materials.
| Materials and Methods|| |
In the present study, a three-dimensional (3D) finite elementmodel of three-unit implant-supported FDP was designed for the maxillary second premolar to the second molar. This model was designed with CATIA V5 R18 software (Dassault System, Suresnes Cedex, France)  based on Wheeler's dental anatomy textbook.  [Figure 1] shows the geometry of modeled FDP.
The maxillary second premolar and maxillary second molar were supported by two standard-plus screw-shaped implants (4.1 diameter, 043.152S for premolar and 4.8 diameter, 043.252S for second molar; Straumann AG, Waldenburg, Switzerland) with regular neck solid abutments (048.541, Straumann AG) with 5.5 height and 6° tapered tightened on the implants. A sanitary pontic was considered to replace the missing maxillary first molar. All superstructure materials used in this study had two connectors with dimensions of 4-6 mm 2 occlusogingivally.
Four types of framework materials were examined: Polymethyl methacrylate (PMMA), base-metal alloy, porcelain fused to metal (PFM), and porcelain. The base-metal and PMMA frameworks were designed with a thickness of 2.5 mm. Porcelain and PFM frameworks with a porcelain veneer layer of 1-mm thicknessand a substructure with maximum thickness of 1.5 mm were established for each framework. In all case studies, the luting agent was Panavia [Table 1] with a thickness of 25 μm.
The FDP model was designed by CATIA software and meshed using ABAQUSCAE, version 6.6 (Hibbitt, Karlsson and Sorensen Inc., Providence, Rhode Island, USA). The commercial package ABAQUS was also used to carry out finite element analysis (FEA) calculations. The entire model was meshed with C3D4 elements (4-node linear tetrahedron). The model consisted of 465108 nodes and 86296 elements [Figure 1].
To simulate the model during mastication movements, three types of load were considered in oblique, vertical, and horizontal directions. The 400.0 N oblique, 200.0 N vertical, and 57.0 N horizontal loads were applied statically on the functional cusps of FDP. The oblique load was applied with θ = 120° withrespect to the horizontal plane [Figure 2]. Each load case was carried out separately on 8 points of each unit.  To apply the boundary condition, all nodes in the y-z plane at the end of the x-axis in both directions were fixed; no translation was allowed in any direction. All materials were assumed to be linear elastic, homogeneous, time-independent,and isotropic. , [Table 1] and [Table 2].
| Results|| |
The stress levels were calculated using the von Mises stress value, which is an appropriate criterion for stress evaluation of ductile materials.
The maximum stress on the occlusal surface was found by oblique loads (535 MPa) in the porcelain material. The stress distribution patterns of occlusal surface were similar in all materials. Maximum stress was located on the buccal ridge of each functional cusp. [Figure 3] shows von Mises stress on the occlusal surface with different load directions in the porcelain prosthesis.
|Figure 3: Stress distribution on the occlusal surface (a) Horizontal, (b) Oblique, (c) Vertical|
Click here to view
The stress distribution patterns of the framework were similar within all materials. The maximum stress in the framework was concentrated on the inferior of one-third of the connectors' region, especially in the oblique load case and in the porcelain framework. Furthermore, there was no significant difference between the stress distribution pattern of mesial and distal connectors [Figure 4].
|Figure 4: Stress distribution in the connectors' region (a) Horizontal, (b) Oblique, (c) Vertical|
Click here to view
The neck area of implants, particularly the interface of implants with surrounding bone, showed the maximum stress within the porcelain framework. Additionally, the stress distribution patterns were similar in all frameworks. Thus, there was no noticeable difference between the premolar and molar implants in this respect [Figure 5]. The maximum von Mises stress of implant and abutment was obtained in the oblique load direction.
|Figure 5: Stress distribution in implant and abutment regions (a) Horizontal, (b) Oblique, (c) Vertical|
Click here to view
The stress distribution pattern was almost uniform inthe cortical bone surrounding both implants. Maximum von Mises stress values were localized in the palatal side of the second premolar supporting bone, particularly the area of the cortical bone that interacts with the implant. Minimum von Mises stress values occurred in the spongy bone, the areas far from the implants. Maximum stress occurred at oblique load cases within PMMA (53 MPa) [Figure 6]. However, maximum stress at oblique loads was 48 MPa in the other prostheses.
| Discussion|| |
Many factors can affect stress distribution such as the direction and magnitude of the applied load and physical properties of the material.  The results of this study showed that oblique loads were the most destructive as they could influence FDP and subsequently cause fracture and failure. Similarly, Motta et al. demonstrated that stress distributes differently depending on the load direction. Occlusal loads more than 1000 N will overload the compact bone and change its geometric shape.  In this study, the maximum mastication load was 400.0 N obliquely, 200.0 N vertically,and 57.0 N horizontally. 
In this study, loads were applied on 8 points of each functional cusp. It has been discussed that applying loads at more than one location produces higher stresses on the framework and occlusal surface of the implant-supported FDP and lesser stress is distributed to the bone. 
The results of this study showed that maximum stress was greater in the framework and occlusal surface than on the bone. In the framework, maximum stress was found in the connector region. According to the results of different studies, the connector is the weakest region of FDP regardless of the connectors' material type. ,, Kamposiora et al. studied the stress concentration in all-ceramic posterior FDP with different connector heights. They concluded that stress level washigher in 3-mm connector heights than in 4-mm connector heights. Within the 3-mm connector height, the apical region revealed the highest stress; the lowest stress occurred in the middle portion of the connectors.
Stresses were concentrated at the neck of the implants. The maximum stress value was identified in the oblique loads. According to the rigid connection between implant and bone, stress was generated in the neck of the implant  and was similar to previous studies. ,
In the implant-supported FDP, the periodontal ligaments are absent. The stress induced directly to the supporting bone is the result of transmitted functional forces. The influence of excessive load on the bone has been well-demonstrated in several studies. , As bone density declines, crater-like defects arise and bone resorption increases as a result of excessive loads. The result of the present study showed that maximum von Mises stress of the cortical bone was at the palatal side of the second premolar. The modulus of elasticity of the cortical bone is higher than that of the spongy bone, and for this reason, the cortical bone is stronger and more resistant to deformation. Hence, higher stress values can be noted in the cortical bone compared to the spongy bone.  Additionally, the results of this study showed that there were no noticeable changes in the cortical bone stress distribution pattern for different prosthetic materials. Therefore, the prosthetic materials may only play the role of transferring the load to the cortical bone, and different material types do not affect the load transferred to the cortical bone.
The PMMA model showed the greatest maximum stress values in both horizontal and oblique loads, which may increase the risk of osseointegration; therefore, PMMA is not recommended to be used in FDPs for a long term.
Ciftci et al. established a 3D FEA to study four different veneering materials. Acrylic resin showed greater displacement than porcelain due to its lower modulus of elasticity. Another study indicated that using different veneering materials has no significant effect on the stress levels or distribution at the bone-implant interface.  It is important to realize the physical features of these materials that may have clinical effects. The results of the present study would be beneficial to select an appropriate material for implant-supported prostheses.
In the present study, all luting agents were not observed and only well-known luting agents were evaluated. In addition, due to high calculation cost for simulation of whole jaw bone, the model of jaw bone was simplified. In the current study, the numerical results were achieved considering some assumptions for material properties in each layer of the FE model and were compared qualitatively with each other. Therefore, stress distribution patterns may have been different depending on the material properties assigned to each layer of the FE model and the model used in the experiments. Thus, as with many in vitro studies, it is difficult to extrapolate the results of this study directly to the clinical situation, and the inherent limitations in this study should be considered.
| Conclusion|| |
A 3D FEA model was constructed to investigate the effect of different prosthetic materials on stress generation under different mastication load situations (horizontal, vertical, and oblique directions). Within the limitation of this study, the following conclusions could be obtained:
- The stress distribution pattern depends on the loading conditions.
- Highest stress values were observed at oblique loads condition.
- In the framework, maximum stress was concentrated on the inferior of one-third of the connectors' region.
- In the implant and abutment, the neck area of implant showed maximum stress in all case studies.
- Maximum von Misesstress at the cortical bone was in the palatal side between the cervical regions of the implant with the value of 48 MPa although, in the PMMA model, a higher value (53 MPa) was observed.
- Different prosthetic materials have no significant effect on the stress distribution pattern of the cortical bone. However, it seems that PMMA can increase the stress level.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2]