|Year : 2020 | Volume
| Issue : 5 | Page : 491-497
Investigation of the effects of cement in different thicknesses and mechanical properties on implant with zirconia crown: A finite element analysis
Mahmut Sertac Ozdogan1, Harun Gokce2
1 Department of Prosthodontics, Faculty of Dentistry, Ankara Yildirim Beyazit University, Ankara, Turkey
2 TUBITAK Defence Industries Research and Development Institute, Ankara, Turkey
|Date of Submission||22-Dec-2019|
|Date of Decision||24-Apr-2020|
|Date of Acceptance||24-Apr-2020|
|Date of Web Publication||21-Oct-2020|
Dr. Mahmut Sertac Ozdogan
Department of Prosthodontics, Faculty of Dentistry, Ankara Yildirim Beyazit University, Ayvalı Mah. 150. Sk. Etlik-Keçiören, Ankara.
Source of Support: None, Conflict of Interest: None
Aim: To evaluate the stress distribution in the implant-supported mandibular premolar monolithic zirconia crowns with different cement types and thicknesses under constant masticatory force using three-dimensional (3D) finite element analysis (FEA). Materials and Methods: The 3D models of monolithic zirconia crowns, which were cemented on abutment, were generated. Nine numerical models were fabricated by applying different cement thicknesses (0.02, 0.05, and 0.10 mm). The solid models were imported into the FEA software and meshed into tetrahedral elements. All models were simulated under masticatory force loads of 100N at two points, respectively. Results: Stress distribution was affected by cement thickness. When the solutions of total deformation on crown were examined, it was observed that Cement-1 with a thickness of 0.02 mm showed the lowest value (0.07 mm). It was shown that the use of Cement-2 material with a thickness of 0.02 mm provides the lowest maximum principle stress on abutment (4.90MPa). When the stresses on the implant were examined, it was determined that the lowest stress values were again formed in cements with a thickness of 0.02 mm (130MPa). The results showed that 0.05 mm thick High Modulus Resin Adhesive Cement (Panavia, Kuraray, Tokyo, Japan) gave the lowest strain values. Conclusion: It was observed that the different resin and cement thicknesses played an important role in the stresses on the zirconia crown, abutment, and implant. Cement thickness has also been evaluated as an important factor, affecting the material life and leading to the preservation of recovery.
Keywords: Ceramics, Dental Implants, Dental Porcelain, Finite Element Analysis, Resin Cements
|How to cite this article:|
Ozdogan MS, Gokce H. Investigation of the effects of cement in different thicknesses and mechanical properties on implant with zirconia crown: A finite element analysis. J Int Oral Health 2020;12:491-7
|How to cite this URL:|
Ozdogan MS, Gokce H. Investigation of the effects of cement in different thicknesses and mechanical properties on implant with zirconia crown: A finite element analysis. J Int Oral Health [serial online] 2020 [cited 2020 Nov 29];12:491-7. Available from: https://www.jioh.org/text.asp?2020/12/5/491/298797
| Introduction|| |
Over the past 20 years, dental implants have revolutionized the compensation of missing teeth and the practice of dentistry. They have emerged as a good alternative to the treatment of fixed and removable prosthesis due to the fact that they can overcome many shortcomings in traditional approaches. Cement and screw-type fixing applications are used for dental implant implementation. Application of the restoration is selected taking into account the advantages and disadvantages, depending on the clinical experience or preferences of the dentist. Nowadays, cement-type implant-supported prostheses are widely used in dentistry. Zirconium restorations have become popular as dental restorative materials in implant dentistry due to their superior aesthetics, strength, and biocompatibility properties.
When the literature is examined, there are several studies analyzing the thickness and type of cement.,, In their study, in which they analyzed the conditions and cement thicknesses, May et al. stated that feldspathic porcelain crown bonding could withstand higher loads than the nonbonded feldspathic crown; however, the bonding effect decreases as the cement thickness increases. In another study, Soliman et al. investigated the effects of the metal-supported ceramic crown as well as cement and cement thickness using three-dimensional (3D) finite element analysis (FEA) package programs. They stated that the prosthetic material was minimally affected by the type and thickness of cement in the study. In another study, Liu et al. generated eight 3D FEA models for two adhesive cements with 60, 90, 120 and 150 μm thickness with a full ceramic crown on the first mandibular molar. It showed that the tensile stress in the crown with large cement thicknesses had increased in two-resin cement.
FEA has become an increasingly useful tool for estimating the effects of stress on the implant and surrounding gingiva. It is used as an effective method to evaluate the importance of the thickness of the cement, and the basic behavior of the cement on stress distribution developing under oral operations. In this study, stress and strain values on the implant, abutment, and crown with different three-resin cement in various thicknesses were evaluated through the finite element method (FEM) by evaluating the literature. In the literature, there are no FEA studies evaluating zirconia crowns fixed on mandibular premolar titanium implants with resin cement in different thicknesses and types. The null hypotheses tested in this study were that different thicknesses and types of cement do not cause different stress accumulations on zirconia crowns and implants.
| Materials and Methods|| |
In this study, FEA is used to find different stresses and strains caused by different cement materials and thicknesses of an implant prosthesis, which is subjected to constant load. For all models, stress and strain values were calculated at a constant load. The 3D model of an implant prosthesis, which was used in place of a tooth, was generated by means of reverse engineering methods. The shape of the mandible was produced in a plaster replica and was transferred into a point cloud data using a 3D laser scanner. The 3D laser scanner (AICON Smart Scan brand scanner, Hexagon Manufacturing Intelligence, RI, USA) with the LED (light-emitting diode) light source (red, blue, white, and green), working in miniature projection technique, having 30 mm small and 1500 mm large field of vision, can be adjusted to five different resolutions ranging from 0.8 to 8.0 megapixels. The scanner with exposure time less than 1 s supports the Breuckmann Scanner File (BRE), stereolithography (STL), Python Lex-Yacc (PLY), and Virtual Reality Modeling Language (VRML) data formats [Figure 1].
To create a precise model of the plaster replica on a computer, it is necessary to take an image of the part in the finest detail. Reflections during scanning of objects may result in missing data in some areas of the objects. To prevent this, parts may be stained using anti-reflection spray (BT-70 Developer; Beta Kimya, Tekirdag, Turkey). Ratios of materials are scaled 1:1. It has a convergent value as 99%. The accuracy of the scanner is 0.01 mm. After completing the scan, the voids that the scanner did not detect were filled by the software, starting from the smallest space. After filling was completed, the image was saved in STL format. To obtain a 3D solid model of plaster replica, whose point cloud data were generated, Quick Surface Reconstruction and Digitized Shape Editor modules of CATIA V5 software (Dassault Systèmes, Villacoublay Cedex, France) were used. Point cloud data transferred to the CATIA V5 software are in STL format. The number of points generated is 230,077. A mesh model needs to be created between points for a remodeling over the point cloud. For this purpose, the mesh model is generated, with the help of the Mesh Building Wizard, based on the maximum and minimum length data between the dimensions of the mesh and the points. The structure of the mesh was designed so that the maximum dimension of the mesh was 1.5 mm and the maximum distance between the points was 0.1 mm [Figure 2].
|Figure 2: Point cloud data and network geometry for mandibular jaw model|
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It is very important to minimize the amount of deviation between the 3D model generated and the point cloud data. For this purpose, a deviation analysis needs to be conducted for all surfaces generated through zone definitions. The deviation analysis is studied taking into account the dimension of the part, running accuracy, and regional stability variables. The maximum allowable deviation for this model is 0.05 mm. For this reason, an analysis was performed on every surface generated. The implant, abutment, and crown models, of which cross sections are presented in [Figure 3], were added on the solid model generated and a whole was formed.
A FEA software (ANSYS version 17.2, Ansys Inc., Canonsburg, PA, USA) was used for the identification of the distribution of the stress formed on the installation. The 3D solid model generated on CATIA V5 was transferred onto ANSYS Design Model, and a 3D mesh was created on Mesh Generation. FEM is a numerical method that allows us to get information on a mold by dividing the mold into a finite number of small elements and by solving a finite number of equations instead of an infinite number of equations. Therefore, the mesh generated is vital for the calculation result. An adaptive mesh was applied in the FEM generated. The connection types of all parts are defined as bonded. The dimensions of the mesh used for the constituent parts are given in [Table 1].
In this study, three dual-cure resin cements (High Modulus Resin Adhesive Cement [Panavia; Kuraray Japan, Tokyo, Japan], Cement Plus Handmix [Panavia], and RelyX ARC) were used for luting zirconia crown. The cement thicknesses were 0.02, 0.05, and 0.10 mm, respectively. Stress and strain values of cements, zirconia crown, implants, and abutments were evaluated through FEM by evaluating the literature. Nine different FEAs were carried out for three different cement materials at three different thicknesses. The same limiting conditions were designated for all solutions, and two forces on buccal cusp tip and central fossa were applied in the direction of the vertical and oblique axis through the coating material as 100N forces. However, the surface of the bone was fixed in all directions through the base. It was considered that there was a 100% bone-implant contact. [Figure 4] shows the limiting conditions used in the linear static analysis.
| Results|| |
Linear static results were obtained through modeling of the crown-cement-abutment model by using the ANSYS and performing a stress analysis in FEM. In the generation of the model, the lengths were given in units of μm, and the modulus of elasticity was given in units of N/μm2 [Table 2]. In the model of the crown, the height of the crown was considered as 7000 μm, the width of the crown was considered as 5000 μm, the thicknesses of the adhesive agent were 20, 50, and 100 μm, and the height of the crown was 4950 μm. The usability of the model was checked by ensuring that some of the forces were equal to zero (where resultant force was equal to zero), which is a condition of static equilibrium. In [Figure 5], a 100N force was applied in the direction of the axes Y and Z, and total deformations that formed on the crown were shown. When the solutions of total deformation were examined, it was observed that Cement-1 with a thickness of 0.02 mm showed the lowest values [Figure 5].
In [Figure 6], the highest and lowest stresses acting on the abutment are analyzed. It was observed that lowest stresses on the abutment were formed on the axial seat, and the highest stresses were formed on the top of the groove, which is the surface of connection with the implant. In all solutions carried out, the highest and the lowest stress zones were identified to be at the same points. It was shown that the use of Cement-2 material with a thickness of 0.02 mm provides the lowest stresses [Figure 6].
|Figure 6: Principle stress (MPa)—Distribution in abutment. (A) Maximum principle stress in abutment (MPa). (B) Minimum principle stress in abutment (MPa)|
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In [Figure 7], the highest and lowest stresses acting on the implant were analyzed. It was observed that the lowest stresses on the implant were formed on the axial seat, and the highest stresses were formed on the top of the groove, which is the surface of connection with the abutment. In all solutions carried out, the highest and the lowest stress zones were identified to be at the same points. It was shown that the use of Cement-1 material with a thickness of 0.10 mm provides a contribution for getting lowest stresses [Figure 7].
|Figure 7: Principle stress (MPa)—Distribution in implant. (A) Maximum principle stress in implant (MPa). (B) Minimum principle stress in implant (MPa)|
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When the von Mises stress distribution in[Figure 8] was analyzed, the highest stresses were stated in the connection point of the abutment and on the outer surface of the implant. Considering the properties of the material, this stress distribution and the general crack formation in the model and the separation between the layers can be estimated. When von Mises stresses were considered, it was identified that the use of Cement-1 material with a thickness of 0.02 mm had shown better results than other applications [Figure 8].
|Figure 8: Principle stress (MPa)—Distribution in implants. (A) von Mises equivalent stress (MPa)—Distribution in abutment. (B) von Mises equivalent stress (MPa)—Distribution in implants|
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| Discussion|| |
Implant-retained zirconia crowns are widely used today because of its desirable aesthetic, biocompatibility, and strength. All ceramic restorations are applied to the aesthetic area. The adhesive and/or cohesive failures in adhesive cement are an important factor in the formation of microleakage. If breakage occurred in the adhesive agent, the connection between the abutment and crown would be weakened, and the retention would be affected. In addition, it was stated that microleakage could be seen on the tooth-cement-restoration interfaces if breakage occurred in the cement. It was assumed, in this study, that the geometry of the model remained fixed, and that there were no faults, which might originate from the production in the interfaces of the tooth crown (crown-adhesive and adhesive-abutment) made using adhesive cement without the properties of the crown being altered.
Three cement thickness (20, 50, and 100 μm) were used according to several investigations., In this study, the use of different cement materials in various thicknesses changed the load transmission resistance of the whole system. Also, Ha et al. found that the thickness of cement plays a significant part in the effectiveness of zirconia restorations. In an another study, Tribst et al. examined the stresses in implants and stated that monolithic zirconia crown does not increase the peri-implant strain under axial loads. On the basis of the results, the hypothesis that the thickness of the crown and the type of cementation influenced the in vitro survival and fracture resistance of zirconia crowns could be approved.
Cement thickness should be as small as possible so that it does not affect the success of the restoration in case of water absorption.
When the literature is analyzed, it is seen that the use of metal abutments made a significant contribution to the retention strength of the cement, andthere is no common approach to use adhesive cement with cement-retained prosthetic implants. Adhesive agents are generally arbitrarily selected in clinical operations. This is due to the familiarity with natural dental cementation procedures in clinical practice.
One of the basic parameters for the evaluation of the mechanical properties of dental materials is the modulus of elasticity. The high modulus of elasticity of the supporting structures such as implants and abutments has caused an increase in the mechanical-bearing capacities expected from ceramic materials used in coating. For this reason, substrate with a higher energy absorption capacity would be suitable for the stability of ceramic restorations and the stress strains on the crowns with no cement would be inadequate in terms of durability.,[15-20] The adhesive cement should be sufficiently strong in mechanical strength to protect the restorations and should possess characteristics for easily removing the restorations from the abutment when necessary. The limitation of the research was the lack of assessment of mechanical cycling that simulates the dynamic loading during mastication with a mixture of compressive and tensile pressures on the reconstruction; only a tensile force was applied for study. Another limitation was that one form of luting cement was being used. Had specific cements been used, various findings would have been obtained.
The results of this study showed that different resin and cement thicknesses played an important role in the stresses on the zirconia crown, abutment, and implant. Cement thickness has also been evaluated as an important factor affecting the material life and leading to the preservation of recovery.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
Both authors contributed equally and finally approved for the publication.
Ethical policy and Institutional Review board statement
Patient declaration of consent
Data availability statement
Data can be available on valid request on contacting to corresponding author mail.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2]