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ORIGINAL RESEARCH |
https://doi.org/10.5005/djas-11014-0056 |
To Evaluate and Compare the Effect of Proximal Wall Height on Stress Distribution at Occlusal Surface of Tooth and Prosthesis Core in Porcelain Fused to Metal and Veneered Zirconia Crowns: A FEA Study
1–6Department of Prosthodontics, Bhojia Dental College and Hospital, Baddi, Himachal Pradesh, India
Corresponding Author: Manjit Kumar, Department of Prosthodontics, Bhojia Dental College and Hospital, Baddi, Himachal Pradesh, India, Phone: +91 9914640604, e-mail: manjitkiran@yahoo.co.in
How to cite this article: Sharma G, Kumar M, Kalra T, et al. To Evaluate and Compare the Effect of Proximal Wall Height on Stress Distribution at Occlusal Surface of Tooth and Prosthesis Core in Porcelain Fused to Metal and Veneered Zirconia Crowns: A FEA Study. Dent J Adv Stud 2024;12(3):130–136.
Source of support: Nil
Conflict of interest: Dr Tarun Kalra and Dr Abhishek Avasthi are associated as the Editorial board members of this journal and this manuscript was subjected to this journal’s standard review procedures, with this peer review handled independently of these Editorial board members and their research group.
Received on: 20 August 2024; Accepted on: 21 September 2024; Published on: 31 December 2024
ABSTRACT
Introduction: This study was undertaken to evaluate and compare stress distribution on tooth surface and core surface in porcelain fused to metal crown and veneered zirconia crown as a function of ratio of buccal axial length (BAL) to proximal axial length (PAL) with variations in loading condition and position using finite element analysis.
Materials and methods: The geometric models of the prepared mandibular first molar and prosthesis were generated. Total six models were generated in accordance with the needs of the study. Three models were generated for veneered zirconia and three for veneered porcelain fused to metal. The proximal wall height variations used in the study were 3.0, 3.2, and 3.4 mm. Combined forces of 200 N vertical and 100 N horizontal were applied to the central groove, mesial incline and cusp center over a 1 mm diameter surface area on the veneer layer.
Results: The maximum von Mises stress value was observed to be 39.691 MPa at the cusp center of the tooth with a veneered zirconia crown at proximal wall height of 3.0 mm. The maximum von Mises stress value was observed to be 34.916 MPa at the cusp center of a tooth with porcelain fused to a metal crown at proximal wall height of 3.0 mm. The maximum von Mises stress value was observed to be 34.214 MPa at the cusp center of the tooth with a veneered zirconia crown at a proximal wall height of 3.2 mm. The maximum von Mises stress value was observed to be 28.365 MPa at the cusp center of a tooth with porcelain fused to a metal crown at a proximal wall height of 3.2 mm. The maximum von Mises stress value was observed to be 29.729 MPa at the cusp center of the tooth with a veneered zirconia crown at a proximal wall height of 3.4 mm. The maximum von Mises stress value was observed to be 27.25 MPa at the cusp center of a tooth with porcelain fused to a metal crown at a proximal wall height of 3.4 mm. The maximum von Mises stress value was observed to be 59 MPa at the cusp center of zirconia coping with a veneered zirconia crown at a proximal wall height of 3.0 mm. The maximum von Mises stress value was observed to be 48.619 MPa at the cusp center of metal coping with porcelain fused to a metal crown at a proximal wall height of 3.0 mm. The maximum von Mises stress value was observed to be 57.516 MPa at the cusp center of zirconia coping with a veneered zirconia crown at a proximal wall height of 3.2 mm. The maximum von Mises stress value was observed to be 37.423 MPa at the cusp center of metal coping with porcelain fused to metal crown at proximal wall height of 3.2 mm. The maximum von Mises stress value was observed to be 54.694 MPa at the cusp center of zirconia coping with a veneered zirconia crown at a proximal wall height of 3.4 mm. The maximum von Mises stress value was observed to be 36.105 MPa at the cusp center of the metal coping with porcelain fused to the metal crown at a proximal wall height of 3.4 mm.
Conclusion: Maximum stresses were seen at the proximal wall height of 3.0 mm at the occlusal surface of the tooth in the veneered zirconia crown as compared to the proximal wall heights of 3.2 and 3.4 mm. Maximum stresses were seen at the proximal wall height of 3.0 mm at the occlusal surface of the zirconia coping in the veneered zirconia crown, as compared to the proximal wall heights of 3.2 and 3.4 mm. Maximum stresses were seen at the proximal wall height of 3.0 mm at the occlusal surface of a tooth in porcelain fused to a metal crown as compared to the proximal wall heights of 3.2 and 3.4 mm. Maximum stresses were seen at the proximal wall height of 3.0 mm at the occlusal surface of metal coping in porcelain fused to metal crown as compared to the proximal wall heights of 3.2 and 3.4 mm. When the proximal wall heights were compared maximum von Mises stresses were observed at the occlusal surface of the tooth with veneered zirconia crown as compared to the porcelain fused to metal prosthesis. When the proximal wall heights were compared maximum von Mises stresses were observed at the occlusal surface of zirconia coping in veneered zirconia crown as compared to the porcelain fused to metal prosthesis. The stresses increased as the proximal wall height was reduced. The maximum von Mises stresses were found at the cusp center, followed by mesial incline and central groove at all the variable proximal wall heights.
Keywords: Finite element analysis, Mandibular molar, PFM, Stress distribution, Veneered zirconia.
INTRODUCTION
Objectives of maintenance of oral health are that the patient should able to masticate for better digestion, speak with the prosthesis, be esthetically pleasant and psychological well-being.1 Under masticatory load, there will be inbuilt stresses in the tooth structure.2 The amount of remaining tooth structure, and systemic condition of the patient dictate the type of material and technique to be used. Small, mineralized tissue loss can be repaired with minimally adhesive procedures, more tissue damage require a full crown for proper function.3 The preservation of tooth become sometimes a challenge when tooth loss is more severe and require lifelike process like crown restoration.
The prognosis of crown restoration depends on the clinician as well as on the patient. The structural durability of the tooth depends on the material of the restoration, remaining hard tissue, luting cement as well as laboratory preparation. The biomechanical principles of tooth preparation have to be followed.4
There is continuous advancement in dental materials used in fixed partial dentures in terms of strength, marginal adaptation as well as color. These state of the art materials can be used as single restoration or multiple fixed partial dentures. There should be sufficient thickness of the material to withstand masticatory load. For this low fusing, feldspathic and glass ceramic materials are used. All ceramic materials are used to make the restoration translucent and it masks the metal. Tooth preparation, length, taper, resistance form and marginal geometry are the important factors for better prognosis of the restoration in term of strength, fit and life like restoration.5
Modulus of elasticity is the relationship between stress and strain, which is studied by 3D photoelasticity, 3D FEA, reflection microscopy and gauge technique. Widely used FEA studies are computerized numerical methods in which the deformation of the restoration is evaluated in a short time. The structure of the material is divided into tiny elements and nodes. A 3D model is generated by microcomputed tomography which saves time and reduces technique complexities.
In FEA study the removal of tooth structure is less, so thickness of restoration effects stress distribution. Solid model is made in place of clinical detailed tooth preparation.
The aim and objective of this study was to evaluate and compare the stress distribution on porcelain fused metal and zirconia crowns in relation to axial length in different loading conditions using FEA.
MATERIALS AND METHODS
The study was carried out in the Department of Prosthodontics Bhojia Dental College and CADD Centre, Chandigarh.
Models were made by Reverse Engineering Programme (I-deas Siemens, Germany). Surface data of the tooth was generated using SolidWorks software (Dassault System SolidWorks Corporation, Waltham, United States). Stress analysis was carried out using ANSYS 18.1 software (ANSYS 18.1, Inc, United States).
A pre-processing software, ANSYS version 18.1 was used to configure tooth model in the form of nodes and elements. Then six 3-D models of tooth and prosthesis Fig. 1) were generated. The three models for veneered zirconia crown had a proximal wall height variation of 3.0, 3.2 and 3.4 mm. For the porcelain fused to metal models also the same proximal wall height variations were used Fig. 2).
Fig. 1: Geometric model of prepared tooth (cyan) with cement layer (green), coping (purple) and veneer layer (pink)
Fig. 2: Proximal axial length variations
The models were entered into ANSYS software. The material properties of tooth, prosthesis and cement were then fed in the preprocessing stage Table 1) and 3D models were created. The entire assembly was then exported to ANSYS Workbench (ANSYS 18.1, Inc, USA) through an initial graphics exchange specification (IGES).
| Component | Material | Young’s modulus (E) (GPa) | Poisson’s ratio | Density (gm/mL) |
|---|---|---|---|---|
| Veneer | Porcelain | 70 | 0.19 | 2.40 |
| Ceramic core | Zirconia | 200 | 0.19 | 2.40 |
| Cement layer | Resin cement | 8 | 0.33 | 2.19 |
| Metal core | Nickel chromium | 206.6 | 0.33 | 8 |
| Tooth material | Dentin | 18 | 0.31 | 2.14 |
An assessment of the stress on the occlusal surface of the tooth and on the occlusal surface of zirconia/metal coping was performed on the central groove, the lingual slope incline of the buccal cusp and the buccal cusp at the maximum cuspal height was performed by using von Mises stress at the veneer layer. A color scale with stress values was used to quantitatively evaluate the stress distribution on the occlusal surface of the tooth and occlusal surface of zirconia/metal coping. The scale for stress runs from 0 MPa (blue) to the highest stress and strain values (red).
The models were meshed with Tetrahedral, Ten-Noded Elements. Models were composed of different numbers of nodes and elements.
Force Application
Loads of 100 and 200 N were applied to the central groove, the lingual slope incline of the buccal cusp and the buccal cusp at the maximum cuspal height of the mandibular first molar. The maximum Von Mises equivalent stresses were measured.
RESULTS
The present study evaluated and compared the stress distribution on tooth surface and core surface in porcelain fused to metal crowns and veneered zirconia crowns as a function of ratio of the buccal axial length (BAL) to proximal axial length (PAL) with variations in loading condition and position using finite element analysis under simulated combined loads of 100 and 200 N.
The maximum von Mises stress value was observed to be 39.691 MPa at the cusp center of tooth with veneered zirconia crown at proximal wall height of 3.0 mm Fig. 3 and Table 2), 34.916 MPa at the cusp center of tooth with porcelain fused to metal crown at proximal wall height of 3.0 mm Fig. 4 and Table 3), 34.214 MPa at the cusp center of tooth with veneered zirconia crown at proximal wall height of 3.2 mm Fig. 3 and Table 3), 28.365 MPa at the cusp center of tooth with porcelain fused to metal crown at proximal wall height of 3.2 mm Fig. 4 and Table 4), 29.729 MPa at the cusp center of tooth with veneered zirconia crown at proximal wall height of 3.4 mm Fig. 3 and Table 2), 27.25 MPa at the cusp center of tooth with porcelain fused to metal crown at proximal wall height of 3.4 mm Fig. 4 and Table 3).
Fig. 3: Stress distribution at the occlusal surface of tooth in veneered zirconia crown at different proximal wall heights
| Proximal wall height | Location | ||
|---|---|---|---|
| Cusp center | Mesial incline | Central groove | |
| 3.0 mm | 39.691 | 32.444 | 31.367 |
| 3.2 mm | 34.214 | 30.977 | 28.142 |
| 3.4 mm | 29.729 | 29.026 | 27.206 |
Fig. 4: Stress distribution at occlusal surface of tooth in porcelain fused to metal crown at different proximal wall heights
| Proximal wall height | Location | ||
|---|---|---|---|
| Cusp center | Mesial incline | Central groove | |
| 3.0 mm | 34.916 | 28.087 | 26.964 |
| 3.2 mm | 28.365 | 27.777 | 25.984 |
| 3.4 mm | 27.25 | 25.458 | 25.224 |
| Proximal wall height | Location | ||
|---|---|---|---|
| Cusp center | Mesial incline | Central groove | |
| 3.0 mm | 59 | 47.184 | 41.532 |
| 3.2 mm | 57.516 | 45.876 | 40.523 |
| 3.4 mm | 54.694 | 44.609 | 38.596 |
The maximum von Mises stress value was observed to be 59 MPa at the cusp center of zirconia coping with veneered zirconia crown at proximal wall height of 3.0 mm Fig. 5 and Table 4), 48.619 MPa at the cusp center of metal coping with porcelain fused to metal crown at proximal wall height of 3.0 mm Fig. 6 and Table 5), 57.516 MPa at the cusp center of zirconia coping with veneered zirconia crown at proximal wall height of 3.2 mm Fig. 5 and Table 4), 37.423 MPa at the cusp center of metal coping with porcelain fused to metal crown at proximal wall height of 3.2 mm Fig. 6 and Table 5), 54.694 at the cusp center of zirconia coping with veneered zirconia crown at proximal wall height of 3.4 mm Fig. 5 and Table 4), 36.105 MPa at the cusp center of metal coping with porcelain fused to metal crown at proximal wall height of 3.4 mm Fig. 6 and Table 5).
Fig. 5: Stress distribution at occlusal surface of zirconia core in veneered zirconia crown at different proximal wall heights
| Proximal wall height | Location | ||
|---|---|---|---|
| Cusp center | Mesial incline | Central groove | |
| 3.0 mm | 48.619 | 35.538 | 34.516 |
| 3.2 mm | 37.423 | 33.776 | 33.74 |
| 3.4 mm | 36.105 | 32.284 | 32.05 |
Fig. 6: Stress distribution at occlusal surface of metal coping in porcelain fused to metal crown at different proximal wall heights
DISCUSSION
Even with prevention of dental caries, there is requirement of prosthesis6 For single crowns mechanical properties like flexure strength, modulus of elasticity, and fracture toughness, marginal accuracy, and life like appearance are important.7 The clinical acumen and material properties had made advancements to restore decayed posterior teeth.8
Due to success rate, porcelain fused to metal restorations are routinely used.9,10 Biological failures are more common than technical failures.11
Due to the desirability of the patients, metal-free ceramics with more strength were the need of the hour. In cases of gingival recession, there is a possibility of metal grayish color visibility, which leads to a greater requirement of metal free ceramic having better look and biocompatibility.12–14
The selection of material is difficult due to availability, which is based on clinical requirement and material properties for esthetics and strength. The strength is important for posterior restoration as compare to esthetics for anterior restorations.15,16
Alsarani et al.17 in their study, reported that cuspal capping is less in metal-fused ceramics as compared to metal.
Rekow et al.18 had studied that cusp inclination, and crown thickness, luting cement and proximal margins are contributing factors to the success of restorations.
The present study used the finite element method to evaluate and compare the effect of proximal wall height on stress distribution at the occlusal surface of the tooth and prosthesis core in porcelain fused to metal and veneered zirconia crowns. Finite element analysis, originally used in solving engineering problems, is often used in dentistry to analyze stress distribution. Deformations can be evaluated at different parts of the restoration at the same time.
Computer model make complex clinical problems simple, but FEA has a demerit of sensitivity to material properties.
In the present study, a three-dimensional finite element analysis method was used to evaluate and compare the effect of proximal wall height on stress distribution at the occlusal surface of the tooth and prosthesis core in porcelain fused to metal and veneered zirconia crowns.
Comparison of the von Mises Stress Distribution at the Occlusal Surface of tooth with Porcelain Fused to Metal Crown and Veneered Zirconia Crown Fig. 7)
Fig. 7: Comparison of von Mises stress (MPa) values at occlusal surface of tooth with porcelain fused to metal crown and veneered zirconia crown at different proximal wall heights
The maximum von Mises stress value was observed to be 39.691 MPa at the cusp center of a tooth with veneered zirconia crown at proximal wall height of 3.0 mm Table 2). 34.916 MPa at the cusp center of tooth with porcelain fused to metal crown at proximal wall height of 3.0 mm Table 3). 34.214 MPa at the cusp center of tooth with veneered zirconia crown at proximal wall height of 3.2 mm Table 2). 28.365 MPa at the cusp center of tooth with porcelain fused to metal crown at proximal wall height of 3.2 mm Table 3). 29.729 MPa at the cusp center of tooth with veneered zirconia crown at proximal wall height of 3.4 mm Table 2). A total of 27.25 MPa at the cusp center of tooth with porcelain fused to metal crown at proximal wall height of 3.4 mm Table 3).
At all the proximal wall heights, it was found that maximum stress values in the porcelain fused to metal crown were lower than veneered zirconia crown.
The stress increased as the proximal wall height was reduced.
Comparison of the von Mises Stress Distribution at the Occlusal Surface of Metal/Zirconia Coping with Porcelain Fused to Metal Crown and Veneered Zirconia Crown Fig. 8)
Fig. 8: Comparison of von Mises stress (MPa) values at occlusal surface of metal/zirconia coping with porcelain fused to metal crown and veneered zirconia crown at different proximal wall heights
The maximum von Mises stress value was observed to be 59 MPa at the cusp center of zirconia coping with a veneered zirconia crown at a proximal wall height of 3.0 mm Table 5). A total of 48.619 MPa at the cusp center of the metal coping with porcelain fused to the metal crown at a proximal wall height of 3.0 mm Table 5). About 57.516 MPa at the cusp center of zirconia coping with a veneered zirconia crown at a proximal wall height of 3.2 mm Table 4). Of 37.423 MPa at the cusp center of metal coping with porcelain fused to the metal crown at a proximal wall height of 3.2 mm Table 5). About 54.694 at the cusp center of zirconia coping with a veneered zirconia crown at a proximal wall height of 3.4 mm Table 4) and 36.105 MPa at the cusp center of the metal coping with porcelain fused to the metal crown at a proximal wall height of 3.4 mm Table 5).
At all the proximal wall heights, it was found that maximum stress values in the porcelain fused to metal crown were lower than veneered zirconia crown.
The stress increased as the proximal wall height was reduced.
In the present study, stress distribution at the occlusal surface of teeth and at the occlusal surface of metal coping in porcelain fused to metal crowns was found to be lower than in veneered zirconia crowns. The result of this study was similar to the study by Silva et al.9 in which stress distribution on Y-TZP and MCR (metalloceramic) restorations were compared, and they found out that stresses were greater in the all-ceramic restoration at the core and veneer layers as compared to MCR. Silva et al.19 also conducted a study in 2010 and found that MCR is more reliable than all ceramic. As per the study conducted by Anusavice KJ and Hojjatie B in 1988, stresses were more at ceramic and cement layers.20 Campos et al.7 found that more fracture occurred in all ceramic restorations as compared to metal ceramic under compressive loads. Moris et al.21 in their study concluded that though less esthetics, for endodontically treated teeth is metal ceramics.
In the present study, in both the crown systems, the stress increased as the proximal wall height was reduced. The results of this study was also comparable to the findings of Paulo et al.3 in evaluating the effect of proximal wall height on all-ceramic crown core stress distribution, as they concluded that the maximum principal stress values increased in the proximal region as the proximal axial length of the preparation is reduced and the highest MPSs were located at the occlusal region and in the occlusogingival region of the ceramic core. Scherrer and de Rijik22 reported increase in fracture resistance with an increase of axial wall. A similar 3D finite element study was done by Maghami E et al.23 who found that stresses were less in the longer abutment than the shorter one, and their distribution was better than the convergence angle.
In the present study, the highest stress was seen at the cusp center, followed by the mesial incline, and the least was seen at the central groove. The results of the study were in accordance with the study by Rekow ED et al.18 found that stresses increased if the load changed from center to the tip of the cusp.
SUMMARY AND CONCLUSION
A three-dimensional finite element analysis was carried out to evaluate and compare the effect of proximal wall height on stress distribution at the occlusal surface of the tooth and prosthesis core in porcelain fused to metal and veneered zirconia crowns.
To conduct this study, three-dimensional geometry of the mandibular right first molar was generated, and three-dimensional numeric models were built up using SolidWorks software. Six models, i.e., 3 models of prepared teeth with porcelain fused to metal crowns and 3 models of prepared teeth with veneered zirconia crowns were generated. A combined axial load of 200 N and a horizontal load of 100 N were applied to the central groove, the lingual slope incline of the buccal cusp and the buccal cusp at the maximum cuspal height. Stress patterns were observed on the occlusal surface of the tooth and occlusal surface of the metal/zirconia coping.
At the occlusal surface of the tooth maximum von Mises stresses were observed with a veneered zirconia prosthesis at the cusp center at a proximal wall height of 3.0 mm. Maximum von Mises stresses were observed at the zirconia coping with veneered zirconia prosthesis at the cusp center at the proximal wall height of 3.0 mm as compared to porcelain fused to metal prosthesis.
Within the limitations of this study, the following conclusions were drawn:
Maximum stresses were seen at the proximal wall height of 3.0 mm at the occlusal surface of the tooth in veneered zirconia crown, as compared to the proximal wall heights of 3.2 and 3.4 mm.
Maximum stresses were seen at the proximal wall height of 3.0 mm at the occlusal surface of the zirconia coping in veneered zirconia crown, as compared to the proximal wall heights of 3.2 and 3.4 mm.
Maximum stresses were seen at the proximal wall height of 3.0 mm at the occlusal surface of the tooth in porcelain fused to metal crown, as compared to the proximal wall heights of 3.2 and 3.4 mm.
Maximum stresses were seen at the proximal wall height of 3.0 mm at the occlusal surface of metal coping in porcelain fused to metal crown as compared to the proximal wall heights of 3.2 and 3.4 mm.
When the proximal wall heights were compared, maximum von Mises stresses were observed at the occlusal surface of the tooth with veneered zirconia crown as compared to the porcelain fused to metal prosthesis.
When the proximal wall heights were compared, maximum von Mises stresses were observed at the occlusal surface of zirconia coping in veneered zirconia crown as compared to the porcelain fused to metal prosthesis.
The stresses increased as the proximal wall height was reduced.
The maximum von Mises stresses were found at the cusp center, followed by mesial incline and central groove at all the variable proximal wall heights.
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