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ORIGINAL ARTICLE
Year : 2021  |  Volume : 39  |  Issue : 2  |  Page : 178-182
 

Evaluation of stress in three different fiber posts with two-dimensional finite element analysis


1 Department of Pedodontics, Guru Gobind Singh Dental College and Research Center, Burhanpur, Madhya Pradesh, India
2 Department of Pedodontics, Kamineni Institute of Dental Sciences, Nalgonda, Telangana, India
3 Department of Pedodontics, HKDET Dental College and Hospital, Humnabad, Karnataka, India
4 General Dentistry, Denta Care Superspecialty Dental Clinic, Gulbarga, Karnataka, India
5 Department of Oral Medicine and Radiology, SB Patil Dental College, Bidar, Karnataka, India

Date of Submission29-Sep-2020
Date of Decision03-Dec-2020
Date of Acceptance09-Feb-2021
Date of Web Publication29-Jul-2021

Correspondence Address:
Dr. Dharmaraj Basavaraj Patil
Plot No 60 and 77, Swastik Nagar, Sedam Road, Gulbarga, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/JISPPD.JISPPD_240_20

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   Abstract 


Introduction: The primary function of corono-radicular post is to provide retention for the core and to reinforce and to replace the remaining coronal tooth structure. There is considerable controversy regarding optimal choice of the material. An ideal post system should exhibit fracture resistance higher than the average masticatory forces. Finite elemental analysis (FEA) method facilitates precise analysis of the distribution and magnitude of stresses at any point of complex and irregular structures. Thus, this FEA study has been undertaken to evaluate the fracture stress distribution patterns in three fiber posts, viz., carbon, glass fiber, and everStick with an FEA. Materials and Methods: The FE stress analysis was performed with the FE software program (CATIA). Three two-dimensional FEA models of central incisor were simulated, and elastic moduli and Poisson's ratio of all the materials were fed to the software. For all the models, a 200 N vertical force was applied on the lingual surface of the tooth at an angle of 45°. Stress concentration and distribution were evaluated and noted down for all the models. To evaluate the stresses within the restored tooth, the modified von Mises failure criterion was used. The equivalent stresses found in the tested models were compared with the tensile strength of the respective materials. Contact stresses in the luting cement–dentin interface were calculated. Results: Finite element method revealed that maximum stress concentration was at the point of stress application. The stress value was highest in carbon fiber post followed by glass fiber post and least stresses found in everStick post. Maximum stress was observed at the labial surfaces of crown. However, the stress values and distribution were more homogenous in everStick post. Conclusion: The present findings suggest that everStick post has uniform stress distribution within tooth structure.


Keywords: Carbon fiber post, everStick post, finite element analysis, glass fiber post


How to cite this article:
Patil DB, Reddy E R, Rani S T, Kadge SS, Patil SD, Madki P. Evaluation of stress in three different fiber posts with two-dimensional finite element analysis. J Indian Soc Pedod Prev Dent 2021;39:178-82

How to cite this URL:
Patil DB, Reddy E R, Rani S T, Kadge SS, Patil SD, Madki P. Evaluation of stress in three different fiber posts with two-dimensional finite element analysis. J Indian Soc Pedod Prev Dent [serial online] 2021 [cited 2022 Aug 11];39:178-82. Available from: http://www.jisppd.com/text.asp?2021/39/2/178/322499





   Introduction Top


An endodontically treated tooth has limited tooth structure to provide retention for definitive restoration, and the loss of coronal and radicular dentin makes it more prone for fracture.[1] The primary function of corono-radicular post is to provide retention for the core and to reinforce and to replace the remaining coronal tooth structure.[2]

There is considerable controversy regarding optimal choice of the material. Nowadays, prefabricated esthetic posts have gained popularity because of their easy handling, minimum fabrication, and low cost. Some manufacturers of glass and carbon fiber (CF) post purport that it has elastic modulus smaller than the dentine and hence less damaging to the teeth. An ideal post system should exhibit fracture resistance higher than the average masticatory forces.[3]

The finite elemental analysis (FEA) has been used effectively in dental mechanics in recent years and has been proved to be a powerful and popular method. The FEA is based on a mathematical model which approximates the geometry and the loading conditions of the structure to be analyzed. FEA method facilitates precise analysis of the distribution and magnitude of stresses at any point of complex and irregular structures. Thus, this FEA study has been undertaken to evaluate the fracture stress distribution patterns in three fiber posts, viz., carbon, glass fiber, and everStick with an FEA.


   Materials and Methods Top


The finite elemental (FE) stress analysis was performed with the FE software program (CATIA) [Figure 1]. The elastic constants used in this study were obtained from the literature[3],[4],[5],[6],[7] [Table 1]. A two-dimensional (2-D) FE model was fabricated to simulate an endodontically treated maxillary central incisor restored with porcelain crown restoration. The model of tooth and supporting structures had basic features identical or close to those used in previous studies.[8] On the basis of root form and geometry of teeth, approximately 5 mm gutta percha apical seal was developed. A total of three such separate models were generated to compare the properties of three different fiber posts, viz., carbon, glass fiber, and everStick™, keeping all the other parameters unchanged. All the materials were assumed to be isotropic except for the glass fiber post because it has different modulus and Poisson's ratio in two different directions.
Figure 1: Two-dimensional mesh model prepared using CATIA software

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Table 1: Isotropic material properties

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It is usually suggested that, when comparing the qualitative results of one case with respect to another, a 2-D model is efficient and just as accurate as a 3-D model. Hence, a 2-D model was generated as the study involves only qualitative comparison. As the model was supposed to be 2-D, the z axis (3-D) was specified to have a plane–strain condition. Later, each model was divided into small elements, and a mesh with predetermined dimensions was superimposed on the prepared model with software HyperMesh (9.0). The mesh consisted of 4-noded rectangular and 3-noded triangular shell–plane 42 ANYSYS plane element with 2° of freedom per node, which finally resulted in a model with 29,932 elements and 15,339 nodes. The interface between any two materials was considered to be continuous. The maximum displacement limit was fixed at the alveolar bone through the surrounding root. Once this was done, the model prepared was considered ready to be loaded. A static load of 200 N was applied at the node No. 29,959 above the cingulum on the palatal surface of all the three maxillary central incisor models at an angle of 45° to the long axis of the tooth.[4]

Stress representation criterion was selected based on an evaluation of the failure predictive potential of the analysis. The Von Mises (equivalent stress) energetic criterion was then chosen as a better representative of a multiaxial stress state. The Von Mises criterion is a formula for combining three principal stresses into an equivalent stress, which is then compared to the yield stress of the material. Von Mises stress is considered as a parameter of comparison to areas of stress concentration in various components of the generated FE model after application of the load. The desired values were later tabulated for comparison.


   Results Top


The results were represented in the form of Von Mises stress values, and the likelihood of failure was decided by accepting the fact that higher Von Mises stress value is a strong indication of a great possibility of failure. Assessments were made based on color patterns in models no. 2, 3, and 4 [Figure 2], [Figure 3], [Figure 4] where warm color plots denote higher stresses. The Von Mises stresses of all models are noted as shown in [Table 2].
Figure 2: The color plot of the Von Mises stresses for model 1 (glass fiber post, composite core, and porcelain crown)

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Figure 3: The color plot of the Von Mises stresses for model 1 (glass fiber post, composite core, and porcelain crown)

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Figure 4: The color plot of the Von Mises stresses for model 3 (chairside fabricated fiber-reinforced composite post, composite core, and porcelain crown)

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Table 2: Maximum von Mises stresses in the individual's components of crown, core, dentin, post, cement layer at the root interface and cement layer at the crown interface

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  1. Model 1 (prefabricated glass fiber post): The highest magnitudes of stresses were concentrated in the crown (722.38 MPa) followed by dentin (361 MPa), post (270 MPa), and post–cement interface (180 MPa) with maximum of labial distribution. The stresses were least distributed to the core (90.2 MPa)
  2. Model 2 (prefabricated CF post): Similar to the Model 1, maximum stresses were concentrated in the crown (721.45 MPa) followed by dentin (450 MPa), post (360 MPa) and post–cement interface (360 MPa) with maximum of labial distribution
  3. Model 3 (chair-side fabricated fiber composite post): A homogenous distribution of von Mises stresses was observed in the post, root dentin, and post–cement interface (271.2 MPa, 271 MPa, and 271 MPa, respectively) and 90.4 MPa in the core. Highest stresses were evident in labial portion of the middle one-third of the root.



   Discussion Top


Restoring these mutilated with the “post systems” strengthens and reinforces the damaged tooth, reduces stresses in the cervical area, and facilitates the distribution of stresses over a wide area and on to the radicular dentin. Multifarious post systems exist for the restoration of endodontically treated teeth that have inadequate tooth structure to support the final restoration.[9]

Posts can be broadly categorized as custom made and prefabricated. Prefabricated esthetic posts are again classified into ceramic and fiber-reinforced resin (carbon, graphite, glass, and quartz) posts. Ceramic posts have much higher modulus of elasticity than dentin. This mismatch in the moduli could result in maximum stress concentration, leading to its failure and nonrestorable tooth fractures.[10] To circumvent these problems, a variety of prefabricated fiber-reinforced composite (FRC) posts containing a high volume percentage of continuous reinforcing fibers in epoxy polymers were developed. These polymers have a high degree of conversion and a highly cross-linked structure. FRC posts have many advantages of being highly esthetic, less incidence of post or root fractures, and better retention as these are actually bonded to the tooth structure rather than cemented to it. In addition, these posts are biocompatible, ready to use, easy to place, and retrieve (when endodontic retreatment is required), and save the productive chair-side time.[11] Multitudinous biomechanical advantages such as good fatigue strength, potential to reinforce a compromised root, modulus of elasticity closer to dentin, leading to uniform stress distribution, property to yield to root fracture,[12] resistance to corrosion,[13] and reduced incidence of nonretrievable root fractures made these posts a material of choice.[3] Duret et al. first developed Composipost™ made of carbon/graphite fibers embedded in epoxy resin.[14] However, they are black and lack cosmetic qualities. In 1992, esthetic (white or translucent) fiber posts (glass or quartz) were introduced without compromising the modulus of elasticity and biocompatibility. Glass fiber posts can be made of electrical (E-glass), S-glass (high strength glass), and quartz fibers (pure silica).[14] everStick, a new post system containing unidirectional silanized E-glass fibers (60% vol) in light polymerizable dimethacrylate-polymethyl methacrylate matrix, has been developed. Stress formation in the fiber–matrix interface during deflection is reduced by plasticization of cross-linked BISGMA matrix, which in turn contributes to the higher flexural strength. In addition, pliability of the material enables easy adaptability in eccentricities of the canal morphology.[15]

In the present study, the ferrule was taken into consideration with a length of 1.5 mm,[16] which resulted in excessive stress concentration at the labial aspect of cervical one-third of the root. Various studies have demonstrated that ferrule with 1–2 mm of vertical tooth structure doubles the resistance to fracture;[17] however, few researches did not show additional resistance to fracture.

From the analysis of the stress plots obtained from three FE models, all the three models exhibited similar stress distribution patterns which are more seen in middle one-third, cervical one-third, and no stress was seen in apical one-third. This was in accordance with the study done by Yaman et al.[18] The difference in the stress values was better appreciable in the middle third and was clearly defined in the apical one-third of the post. This exemplifies the “wedging effect” seen in the dentin adjacent to the apex of the tapered post, a finding consistent with the existing literature. The “wedging effect” is due to the reduction in the dimensions of the tapered post near the apical portion.[19]

Glass fiber post (Model 1) showed less Von misses stress distribution into the dentin when compared to carbon post (Model 2). Similarly, Pegoretti et al. used the finite element method in a study and observed that glass fiber posts restored tooth showed a low stress concentration inside the root, in comparison with metal and CF posts. Greater the difference between the Young's modulus of the dentin and the post, lesser homogenous the stress distribution on the dental surfaces, and thus stress concentration are produced into the dentin.[20]

With everStick, a homogeneous distribution of Von Mises stress was observed into the post, dentin, and post–cement interface when compared to carbon and glass fiber post in accordance with the study done by Toparli et al. and Toparli.[21] Since the CF-FRC post has similar Young modulus of elasticity to dentin, there is approximately equal distribution of stresses within the post as well as dentin.

FEA is a powerful tool in analyzing stresses without variations. Validity of the results depends upon the model which approaches reality. The model in this study may deviate from reality in several aspects. In spite of these limitations, the study may be considered to provide relative values that are meaningful representation of qualitative trends. Further in vivo studies and fracture resistance studies of everStick should be conducted to correlate these findings with the clinical results.


   Conclusion Top


Within the limitations of this study, it can be concluded that everStick fiber post has shown more homogeneous distribution of Von Mises stresses in the core, post, root dentin, and post–dentin interface as compared to carbon and glass fiber post.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Freedman G. The carbon fibre post: Metal-free, post-endodontic rehabilitation. Oral Health 1996;86:23-6, 29-30.  Back to cited text no. 1
    
2.
Hegde MA, Sureshchandra B. Esthetic posts – An update. Endodontology 2010;22:100-7.  Back to cited text no. 2
    
3.
Ahangari AH, Geramy A, Valian A. Ferrule designs and stress distribution in endodontically treated upper central incisors: 3D finite element analysis. J Dent Tehran Univ Med Sci 2008;5:105-10.  Back to cited text no. 3
    
4.
Farah JW, Craig RG. Distribution of stresses in porcelain-fused-to-metal and porcelain jacket crowns. J Dent Res 1975;54:255-61.  Back to cited text no. 4
    
5.
Vasconcellos WA, Cimini CJ, Albuquerque RC. Effect of the post geometry and material on the stress distribution of restored upper central incisors using 3D finite element models. Stress distribution on incisors with posts. J Indian Prosthodont Soc 2006;6:139.  Back to cited text no. 5
  [Full text]  
6.
Eskitaşcioğlu G, Belli S, Kalkan M. Evaluation of two post core systems using two different methods (fracture strength test and a finite elemental stress analysis). J Endod 2002;28:629-33.  Back to cited text no. 6
    
7.
Holmes DC, Diaz-Arnold AM, Leary JM. Influence of post dimension on stress distribution in dentin. J Prosthet Dent 1996;75:140-7.  Back to cited text no. 7
    
8.
Wheelers RC. Wheelers Dental Anatomy, Physiology and Occlusion. 8th ed. St. Louis: Saunders; 2003. p. 154.  Back to cited text no. 8
    
9.
Strassler HE. Fiber posts: A clinical update. Inside Dent 2007;3:70-7.  Back to cited text no. 9
    
10.
Trope M, Maltz DO, Tronstad L. Resistance to fracture of restored endodontically treated teeth. Endod Dent Traumatol 1985;1:108-11.  Back to cited text no. 10
    
11.
Hattori M, Takemoto S, Yoshinari M, Kawada E, Oda Y. Durability of fiber-post and resin core build-up systems. Dent Mater J 2010;29:224-8.  Back to cited text no. 11
    
12.
Singh A, Logani A, Shah N. An ex vivo comparative study on the retention of custom and prefabricated posts. J Conserv Dent 2012;15:183-6.  Back to cited text no. 12
[PUBMED]  [Full text]  
13.
Güler AU, Kurt M, Duran I, Uludamar A, Inan O. Effects of different acids and etching times on the bond strength of glass fiber-reinforced composite root canal posts to composite core material. Quintessence Int 2012;43:e1-8.  Back to cited text no. 13
    
14.
Duret B, Reynaud M, Duret F. New concept of coronoradicular reconstruction: The Composipost (1). Chir Dent Fr 1990;60:131-41.  Back to cited text no. 14
    
15.
Davis P, Melo LS, Foxton RM, Sherriff M, Pilecki P, Mannocci F, et al. Flexural strength of glass fiber-reinforced posts bonded to dual-cure composite resin cements. Eur J Oral Sci 2010;118:197-201.  Back to cited text no. 15
    
16.
Al-Hazaimeh N, Gutteridge DL. An in vitro study into the effect of the ferrule preparation on the fracture resistance of crowned teeth incorporating prefabricated post and composite core restorations. Int Endod J 2001;34:40-6.  Back to cited text no. 16
    
17.
Stankiewicz NR, Wilson PR. The ferrule effect: A literature review. Int Endod J 2002;35:575-81.  Back to cited text no. 17
    
18.
Yaman SD, Alaçam T, Yaman Y. Analysis of stress distribution in a maxillary central incisor subjected to various post and core applications. J Endod 1998;24:107-11.  Back to cited text no. 18
    
19.
Cooney JP, Caputo AA, Trabert KC. Retention and stress distribution of tapered-end endodontic posts. J Prosthet Dent 1986;55:540-6.  Back to cited text no. 19
    
20.
Pegoretti A, Fambri L, Zappini G, Bianchetti M. Finite element analysis of a glass fiber reinforced composite endodontic post. Biomaterials 2002;23:2667-82.  Back to cited text no. 20
    
21.
Toparli M. Stress analysis in a post-restored tooth utilizing the finite element method. J Oral Rehabil 2003;30:470-6.  Back to cited text no. 21
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2]


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