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| ORIGINAL ARTICLE |
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| Year : 2016 | Volume
: 5
| Issue : 1 | Page : 7-13 |
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Stress analysis in maxillary incisor following fragment reattachment: A finite element analysis
Attiguppe Ramasetty Prabhakar, Limaye Nandita Shrikant, Basappa Nadig
Department of Pedodontics and Preventive Dentistry, Bapuji Dental College and Hospital, Davangere, Karnataka, India
| Date of Web Publication | 1-Jul-2016 |
Correspondence Address:
Limaye Nandita Shrikant
Room No. 3, Department of Pedodontics and Preventive Dentistry, Bapuji Dental College and Hospital, Davangere - 577 004, Karnataka
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/2277-4696.185188
Objectives: To demonstrate stress propagation through three flowable composites used in fragment reattachment using finite element models. Study Design: It was a finite element analysis. Materials and Methods: Two permanent maxillary incisors were selected of which one was used as control. The test tooth was sectioned and reattached using simple reattachment technique. The groups were: Filtek Z350 (Group 1), G-aenial Universal Flo (Group 2), Esthet X-Flow (Group 3). Finite element models were created using cone beam computed tomography images of these teeth. Required physical properties of enamel, dentin, periodontal ligament (PDL), bone, flowable composites were fed into the software. Models were subjected to a load of 150N in a vertical direction. Analysis was done using ANSYS software wherein data were obtained in pictographic and numerical form (Von Mises' stresses [megapascal]). Results: Among flowable composites, maximum stress was created in Esthet X-Flow whereas least stress was observed in Filtek Z350. Maximum stress concentration occurred at the point of load application for flowable composite and enamel, at the point of load application directed in the cervical direction of the crown for dentin, in the apical region for PDL and the cervical bone area for bone.
Conclusion: The study revealed that Filtek Z350 had superior tested properties and showed the least stress propagation. Keywords: Finite element analysis, flowable composite, fragment reattachment
How to cite this article:
Prabhakar AR, Shrikant LN, Nadig B. Stress analysis in maxillary incisor following fragment reattachment: A finite element analysis. J Dent Allied Sci 2016;5:7-13 |
How to cite this URL:
Prabhakar AR, Shrikant LN, Nadig B. Stress analysis in maxillary incisor following fragment reattachment: A finite element analysis. J Dent Allied Sci [serial online] 2016 [cited 2023 Mar 27];5:7-13. Available from: https://www.jdas.in/text.asp?2016/5/1/7/185188 |
| Introduction | |  |
The incidence of dental trauma is on the rise as a result of greater involvement of children and teenagers in contact sports, automobile accidents, and outdoor activities.[1] Most common form of damage reported is the coronal fractures of anterior teeth representing 18-22% of all injuries to the dental hard tissues of which 96% involve the maxillary incisors alone.[2]
Numerous techniques have been put forth to reconstruct such traumatically injured teeth some of which include composite resin restorations with and without pins, use of resin crowns, stainless steel crowns, orthodontic bands, and ceramic crowns. However, all these interventions tend to sacrifice a lot of healthy natural tissue.[3] Hence with the advent of adhesive dentistry; fragment reattachment is increasingly being considered as a minimally invasive biological treatment option for managing such injuries.[4] This technique of fragment reattachment was first described by Chosack and Eidelman in 1964.[5]
Compared to conventional techniques, fragment reattachment offers several advantages the most predominant being-esthetics, as it makes it possible to preserve the original shape, color, brightness, and surface texture of enamel. In addition, incisal edges of re-attached fragments tend to wear at a much similar rate compared to adjacent natural teeth, unlike other restorative modalities. Furthermore, this technique can be less time-consuming and provide more predictable long-term results.[6]
However, the reattached fragments are prone to fracture, and their longevity depends on the firmness of its attachment to the tooth, the type of bonding material used and its fracture resistance to sustain the applied stress.[7]
Many in vitro studies have compared the efficacy of various bonding materials and have concluded that composite resin gave the best resistance to fracture.[8]
Finite element analysis (FEA) is a popular numerical method in stress analysis. FEA involves a series of computational procedures to calculate the stress and strain in each element. FEA is able to reveal the otherwise inaccessible stress distribution within the tooth-restoration complex, and it has proven to be a useful tool in the understanding of tooth biomechanics and the bio-mimetic approach in restorative dentistry. It was first used in dentistry in the 1970s.[9] FEA can help us create a virtual model of the natural tooth and simulate the natural conditions as close as possible to study the stress patterns through reattached fragments which otherwise would not be achievable.
With this background, this study, the first of its kind was designed to assess the pattern of stress propagation through three flowable composites used in fragment reattachment using finite element models wherein the Von Mises' stresses were evaluated.
| Materials and Methods | | |
Two permanent maxillary incisors with intact crown structure extracted due to therapeutic reasons were selected for the study. One tooth was considered as control. Data obtained for the FEA included the numerical values for physical properties namely modulus of elasticity and Poisson's ratio of enamel, dentin, periodontal ligament (PDL), bone and the three flowable composites. The three study groups were Group 1 Filtek Z350 flow-able (3M, ESPE), Group 2 G-aenial Universal Flo (GC), Group 3 Esthet X-Flow (Dentsply).
Preparation of the teeth before sample making procedure
The extracted teeth were cleaned and tissue remnants on the root surface of the teeth were removed using curettes and ultrasonic tips. The teeth were disinfected using 0.2% thymol. Teeth were stored in distilled water.
Preparation of the samples
Apart from the control tooth, the other tooth was cut using a low-speed diamond disk at the incisal third from the mesial side to the distal side horizontally [Figure 1].[10]
Application of 37% phosphoric acid to the fragment and the tooth remnant for 15 s was followed by rinsing for 10 s and air drying for 5 s to remove excess water. A bonding agent (Prime and Bond NT, Denstply) was applied in two consecutive coats. The surfaces were dried for 5 s using an air syringe to allow solvent evaporation, and then light cured for 20 s in the fragment and 20 s in the tooth remnant. A flowable composite was then applied on the surface of fragment and tooth remnant. The fragment was positioned back on the tooth remnant and light cured in four stages: 20 s mesiobuccal half, 20 s distobuccal half, 20 s mesiolingual half, and 20 s distolingual half.[3]
Cone beam computed tomography imaging of the prepared sample and control tooth
Both the teeth were then subjected for three-dimensional (3D)-cone beam computed tomography (CBCT) imaging (Planmeca Promax 3D) at Dental Digital Imaging CBCT Centre, Davangere, Karnataka, India for obtaining CBCT images of the same in Digital Imaging and Communications in Medicine format.
Conversion of cone beam computed tomography images to finite element models
The CBCT images were then imported into a computer program (MIMICS version 8.11). These images were then converted through sequential processing into solid models of the maxillary central incisors [Figure 2]. Computer-aided engineering software (Hypermesh version 11) was used for mesh generation of the solid models [Figure 3].[11] The hypermesh models of the sample tooth, control tooth, consisted of 12,854, 27,707 nodes and 68,319, 125,192 elements, respectively.
The hypermesh models were then subjected to a constant load of 150N which is the average force imposed on the anterior teeth.[12] The load was applied in a vertical direction on the incisal edge of the tooth [Figure 4].[13] Model of the sample tooth was subjected to this constant load with the numerical values of the physical properties of the materials being changed according to the three experimental groups. All materials were assumed to be homogeneous and isotropic. | Figure 4: Load application in vertical direction on the incisal edge of the tooth
Click here to view |
All the material properties used for the FEA are summarized in [Table 1] (G-aenial Universal Flo Technical Manual).[14],[15],[16],[17],[18],[19],[20],[21] Analysis of these finite element models was done using ANSYS software version 12.1. The Von Mises' stresses (in megapascal [MPa]) created in the enamel, dentin, PDL, bone, and the three flowable composites were obtained.[22]
| Results | | |
The results obtained were computed in tables. [Table 2] show the Von Mises' stress (MPa) created in the flowable composites, enamel, dentin, PDL, and bone, respectively in the sample tooth. [Table 3] represents Von Mises' stress values (MPa) obtained for the control tooth. As mathematical/numerical values are not subjective to statistical variation hence statistical analysis was not required in this scenario. | Table 2: Von Mises' stress (MPa) created in the flowable composites, enamel, dentin, periodontal ligament, and bone respectively in the sample tooth
Click here to view |
Among the flowable composites, maximum stress was created in Esthet X-flow (Group 3) whereas least stress was observed in Filtek Z350 flow-able (Group 1).
Irrespective of the material used the values of stress created in enamel, dentin, PDL, and bone individually did not differ much. However, maximum tensile stress was created in enamel followed by the bone, flowable composite, dentin, and PDL. Furthermore, in comparison to the control tooth, only the stress created in enamel for the sample tooth was more whereas the stress values for dentin, PDL and bone individually were almost similar.
The location and pattern of stress propagation have been represented with color mapping in pictographic form [Figure 5]. Red color indicates the maximum tensile stress that was created whereas the dark blue color indicates the least stress.
Additional finding noted was irrespective of the material used for fragment reattachment, it was evident from these finite element models that the pattern of stress propagation through the tooth structure was similar for the sample tooth as well as the control tooth [Table 4] and [Table 5]. For enamel and the flowable composite, maximum stress created was at the point of load application. In dentin, maximum stress created was at the point of load application extending further in the cervical direction of the crown. The maximum stress concentration in the PDL was seen in the apical region whereas for the bone the entire stress concentration occurred in the cervical bone area. | Table 4: Pictographic representation of stress propagation through the enamel, dentin, periodontal ligament, and bone for control tooth
Click here to view |
 | Table 5: Pictographic representation of stress propagation through the flowable composites, enamel, dentin, periodontal ligament, and bone for sample tooth
Click here to view |
| Discussion | | |
Episodes of dental trauma more commonly coronal fractures of anterior teeth are being increasingly reported due to the changing lifestyle of children and teenagers in the modern era.[1] The current generation of parents want a very esthetically pleasing and natural remedy for such traumatic injuries. Fragment reattachment can be considered as a biologically viable option which not just meets the current expectations but is minimally invasive as well. Even with multiple advantages, there have been incidences of failure of this modality reported in the literature.[23],[24]
As the literature quotes, 96% incidence of coronal fractures involving permanent maxillary incisors alone, these teeth were selected for the study.[2] The tooth was sectioned using a low-speed diamond disk to simulate the natural fracture.[4] Singhal and Pathak performed an in vitro study where they concluded that composite resin provided the highest fracture resistance for fragment reattachment when compared with resin-modified glass ionomer cement, compomer and dual cure resin cement.[8] As an exact approximation of the fragment with the remaining tooth structure is essential for fragment reattachment, as well as the space available, is minimal for the bonding material to sandwich between these two parts, flowable composite resins were chosen as the materials to be tested.[25],[26],[27]
Andreasen et al. found that fragments lost after reattachments were predominantly as a result of new trauma, nonphysiologic use of tooth and horizontal traction (i.e. biting into tough or chewy foods). Approximately, 1/4th of the fragment loss was attributed to unknown causes (e.g. spontaneous loss or loss during normal use).[23] Hence, for this study, a constant load of 150N corresponding to the normal anterior incising force was used.[12] Studying the response of the tooth after fragment reattachment for functional loading has never been studied in vivo as it would be unethical. Therefore, FEA was the technique of choice. This method allows researchers to overcome some ethical and methodological limitations and enables them to verify how the stresses are transferred throughout the materials.[28]
For quantitative stress analysis, the two-dimensional models overestimate stress magnitudes and do not represent the realistic model. Hence, 3D models were generated for our study as they provide more reliable data which is more accurate.[29] Although the stress distribution characteristics in the tooth-restorative complex were successfully evaluated in this study, there were certain limitations that were noted. Certain assumptions were made for this finite element study. All materials were assumed to be homogeneous, isotropic, and considered elastic throughout the entire deformation.[30]
According to this study, among the flowable composites, maximum stress was created in Esthet X-flow (Group 3) whereas least stress was observed in Filtek Z350 flow-able (Group 1). Stress created in G-aenial Universal Flo (Group 2) was more than Group 1. Filtek Z350 flowable composite has bisphenol-A-glycidyl methacrylate (Bis-GMA), Triethylene glycol dimethacrylate (TEGDMA), Bis-EMA (Ethoxylated bisphenol-A dimethacrylate), silane-treated ceramic, silica, zirconium oxide as its components. The filler content is 55 volume%/65 weight%.[31] G-aenial Universal Flo contains strontium glass urethane dimethacrylate (UDMA), (2,2-bis-[4-(methacryloxypolyethoxy)-phenyl]-propane, TEGDMA, silicon dioxide, pigment, and photoinitiator.[32] The filler content is 50 volume%/69 weight% (G-aenial Universal Flo Technical Manual). Esthet X-flow consists of Bis-GMA, Bis-EMA, TEGDMA, Ba–F–Al–B–Si–glass nanofiller silica. The filler content is 53 volume %/61 weight %.[33] The physical and mechanical properties of the composite are somewhat inferior when the filler content by weight is reduced.[34] Filtek Z350 is a nanocomposite and G-aenial Universal Flo is nanohybrid flowable composite (G-aenial Universal Flo Technical Manual) whereas Esthet X is a micro-hybrid varitety.[31],[33] The presence of nanofiller particles in resin based restorative materials produces superior performance compared to microparticles.[35] Both these facts justify our results of Esthet X-flow being the weakest among the tested materials. Composite resins containing high UDMA% have greater viscosity and increased shear bond strength.[36],[37] Incorporation of nano-sized strontium glass as filler particles reinforces the strength of the material.[38] This could be the potential cause for G-aenial Universal Flo being better than Esthet X-flow. However, it was not found to be better than Filtek Z350 flow-able. Composites containing 10 volume% zirconium oxide exhibit good hardness and fracture threshold.[39] It can be hypothesized that because of the content of zirconium oxide in Filtek Z350 it was found to be best among all the three flowable composites.
In our study, irrespective of the material used the values of stress created in enamel, dentin, PDL, and bone individually did not differ much for the sample tooth. However, maximum tensile stress was created in enamel followed by bone, flowable composite, dentin, and PDL. It is known that modulus of elasticity is directly proportional to tensile stress.[40] Enamel has the highest modulus of elasticity followed by bone, dentin, and the least value is for PDL (G-aenial Universal Flo Technical Manual).[15],[16],[19],[33] The results of our study are in accordance with these facts. Young's modulus value of pulp is negligibly small when compared with the other tissues, hence the effect of pulp on stress distribution was neglected, and the pulp was considered empty.[41]
The control tooth behaved in a similar manner to the sample tooth with respect to the values and pattern of stress propagation through dentin, PDL, bone except for enamel where higher stress values were created in the fractured teeth. This can be logically reasoned by the fact that a restored tooth is always weaker than a healthy natural tooth. Da Silva and his colleagues found that when a traumatic force of 2000N was applied on the incisal edge of the maxillary incisor in the cleidocranial direction harmful stresses were observed causing damage to both the tooth and adjacent tissue. However, the damage found in soft tissues such as PDL and dental pulp was negligible as compared to the integrity of the tooth and its associated hard tissue structures.[42] This is similar to our findings wherein PDL suffered the least and negligible trauma whereas comparatively large amounts of stress was created in enamel, dentin, the flowable composite, and bone.
The present study being the first of its' kind reveals the pattern of stress propagation through the tooth-restorative complex following fragment reattachment pattern while providing an understanding of failure sites in an attempt to improvise the prognostic value of this minimally invasive biological treatment modality.
| Conclusion | | |
The conclusions that can be made from this study are:
- Among the tested flowable composites, Filtek Z350 flow-able showed the least stress whereas Esthet X-flow was the weakest.
- Irrespective of the material used maximum stress concentration occurred as follows:
- For the flowable composite and enamel at the point of load application.
- For dentin at the point of load application extending further in the cervical direction of the crown.
- For PDL-in the apical region.
- For bone-in the cervical bone area. This pattern of stress propagation was similar to that of the control tooth.
- Among all the tissues, maximum stress concentration occurred in enamel.
- Stress concentration in control tooth was similar to the reattached tooth.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
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