|Year : 2022 | Volume
| Issue : 3 | Page : 302-310
A comparative study of conventional and Hall techniques of crown placement using finite element stress analysis
Pawan Pramodrao Herkar, A Anantharaj, P Praveen, Prathibha Rani Shankarappa, R Sudhir
Department of Paediatric and Preventive Dentistry, D. A. Pandu Memorial R. V. Dental College, Bengaluru, Karnataka, India
|Date of Submission||08-Apr-2022|
|Date of Decision||19-May-2022|
|Date of Acceptance||24-May-2022|
|Date of Web Publication||18-Oct-2022|
Pawan Pramodrao Herkar
Department of Paediatric and Preventive Dentistry, D. A. Pandu Memorial R. V. Dental College, Bengaluru - 560 078, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: Hall technique of crown placement causes the changes in vertical occlusal dimension; the mode of settlement of which needs to be explored. Aim: To assess and compare the changing patterns of stress distribution following placement of stainless steel crowns on primary teeth by Hall and conventional techniques using a finite element model analysis. Materials and Methods: The clinical crown heights of primary molars restored with Hall and conventional techniques and opposing teeth in contact, vertical dimension changes in the primary canine area were measured using intraoral digital scan. T-scan was used to measure the changes in bite force while the finite element analysis was used to assess deformative changes on the 2nd, 5th, 10th, and 15th days. Results: The Hall technique of crown placement caused more stress distribution in the tooth supporting tissues that settled in 2 weeks as compared with conventional technique of crown placement in which settlement occurred in 2 days. Conclusion: The settling of vertical occlusal dimension as well as stress distribution in Hall technique probably takes place by intrusion of crowned tooth and opposing teeth in contact.
Keywords: Bite force, finite element analysis, Hall technique, Intraoral Digital Scan, occlusal vertical dimension, T scan
|How to cite this article:|
Herkar PP, Anantharaj A, Praveen P, Shankarappa PR, Sudhir R. A comparative study of conventional and Hall techniques of crown placement using finite element stress analysis. J Indian Soc Pedod Prev Dent 2022;40:302-10
|How to cite this URL:|
Herkar PP, Anantharaj A, Praveen P, Shankarappa PR, Sudhir R. A comparative study of conventional and Hall techniques of crown placement using finite element stress analysis. J Indian Soc Pedod Prev Dent [serial online] 2022 [cited 2022 Nov 29];40:302-10. Available from: http://www.jisppd.com/text.asp?2022/40/3/302/358842
| Introduction|| |
The Hall technique of stainless steel crown placement was proposed by Dr. Norna Hall and involves the placement of a stainless steel crown on an unprepared tooth, without local anesthesia or caries removal. The stainless steel crown is cemented using glass ionomer luting cement. This is in contrast with the conventional method of stainless steel crown placement which requires local anesthesia, removal of caries as well as tooth preparation.
As there is no tooth reduction in Hall technique of preformed stainless steel crown placement, the occlusion can be expected to be “propped open” following placement of the crown. There is an obvious increase in occlusal vertical dimension (OVD) by 1–2 mm. However, several studies have indicated that occlusal re-equilibration occurs within 2–4 weeks.,, It has been hypothesized that this equilibration occurs because of a wider periodontal ligament (PDL) space in primary teeth, by intrusion of opposing teeth as well as changes in the morphology of the stainless steel crown and/or tooth in occlusion. However, these changes are not traceable with conventional methods of investigation and very few studies have documented this process of occlusal equilibration.
Therefore, this methodological study seeks to investigate the use of finite element model (FEM) analysis, in conjunction with T-scan mapping and intraoral digital scan (IODS) to assess and compare the patterns of stress distribution in the supporting tissues and the consequent changes in occlusal forces that ultimately contribute to the equilibration process following conventional and Hall techniques of crown placement in primary teeth.
| Materials and Methods|| |
Source of data
The physical properties of enamel, dentin, PDL, supporting alveolar bone, stainless steel crown, and luting GIC from the previous studies published in PubMed index journals/textbooks were used as input for the finite element study [Table 1].
|Table 1: Material properties of structures used in the finite element model(s)|
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- Two mandibular second primary molars in two patients with untreated single surface or multi-surface cavitated carious lesion extending to dentine with or without marginal ridge breakdown; i.e., ICDAS 4 and 5.
Children were excluded if they:
- Had chronic medical conditions requiring long-term specialist care, e.g., immuno-compromised, cardiovascular and bleeding disorders
- Had teeth with pain or sepsis
- Had teeth with carious lesion extending into pulp clinically or on radiographic examinations
- Had traumatic tooth involving dental pulp
- Any supra-erupted tooth.
Flow chart of methodology [Figure 1]
T-Scan occlusal analysis
- The digital analysis of occlusion was done using Tekscan III version 9
- Once the sensor was prepared to be placed in the child's mouth, the software was calibrated for the mixed dentition by incorporating the mesiodistal widths of teeth present in the oral cavity into the software window
- The sensor was calibrated for both children by taking three measurements of the bite at Maximum Intercuspal Position (MIP)
- A single examiner recorded three MIP readings. Each time child was asked to bite on a sensor. The single closure that contained the maximum recorded occlusal force was selected for analysis.
Intra-oral digital scanner
- Digital intraoral scanning was done with Intra oral digital scanner by CareStream Dental version CS3600
- It has ground-breaking Intelligent Matching System eliminates need for light guidance with dedicated restorative, orthodontic, and implant-borne restorative workflows
- To gather surface data points, energy from either laser light or white light is projected from the wand onto an object and reflected back to a sensor or camera within the wand
- Based on algorithms, tens or hundreds of thousands of measurements are taken per inch, resulting in a 3D representation of the object's shape
- This procedure was performed first on occlusal surface then on buccal and lingual/palatal surface in both arches to record all possible images
- These all images are automatically combined in the software to form a single 3D image of both the jaws intraorally including the occlusion.
Finite element analysis
Planning of analysis
In this stage, the material properties are assigned.
| Setting the type of analysis|| |
In the present study, a structural analysis was done.
| Creating the model|| |
A 3D Model with Proper dimensions in mm was created from the cone-beam computed tomography images of the patient.
| Applying a mesh|| |
Mesh generation is the process of dividing the analysis continuum into a number of discrete parts or finite elements. The finer the mesh, the better is the result but longer the analysis time. In this study a tetrahedral mesh network was used to create the model [Table 2] and [Figure 11].
| Assigning properties material properties|| |
Young's modulus and Poisson's ratios are defined in this step [Table 1].
| Applying loads|| |
Since patient had only primary teeth in occlusion, constant Biting force of 172.2 N was used as a baseline input for the analysis. Depending on the T-scan values, input values were also adjusted and load was applied on areas, as shown in [Figure 11].
|Figure 11: Mesh plot of tooth model and surrounding structures and force application areas in FEA|
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| Applying boundary conditions|| |
When applying a load to the model, in order to stop accelerating infinitely through the computer's virtual ether, at least one constraint or boundary condition must be applied. For this study boundary conditions were applied to cortical bone.
This part is fully automatic and results of analysis are prepared in this step.
Here, the results of the analysis are read and interpreted. They can be presented in the form of a contour plot, a table, deformed shape of the component or the mode shapes and natural frequencies.,
Sample size estimation
- The study design was a finite element analysis (FEA) requiring only a model on which all parameters were assessed
- The required sample size 2 was used to create the model and obtain inputs for FEA.
- FEA is a qualitative analysis and results obtained through this method are pictographic and self-explanatory
- Therefore, there is no need for sample size estimation and statistical analysis.
| Results|| |
- This study was done to compare and evaluate stress distribution pattern and deformative changes in supporting structures after placement of crown by conventional technique and hall technique through FEA. Along with that change in occlusal vertical dimensions (OVD) and clinical crown height of crowned tooth and opposing teeth in contact were measured with IODS and maximum bite force on crowned tooth with the help of T-scan for both the techniques of crown placement [Table 3] and [Table 4] [Graph 1], [Graph 2], [Graph 3], [Graph 4]
- Follow-up period for conventional technique was only 2 days as occlusion reequilibration observed within these days, whereas for hall technique, 15 days follow-up was done.
|Table 3: Master chart table for conventional technique of crown placement|
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| Discussion|| |
With the Hall Technique, the process of fitting the crown is quick and noninvasive. But a Propped open occlusion can be seen as there is no tooth reduction used to place SS crown. According to an observational study of 10 children who had crowns fixed using Hall technique were analysed over time with serial study models using digital scanning and subtraction technology, they found that by around 2–4 weeks, the children's occlusions had returned to full balance across the arches, the OVD returned to previous values (for some of the children this was sooner). It seems that the occlusion resolves mainly through intrusion of the crowned tooth and slight intrusion of the opposing teeth.
In present study the OVD returned to previous values in about 2 weeks. The OVD was continuously decreasing over a period of 15 days. For evaluating this OVD two methods were used:
- Change in OVD in canine area
- Clinical crown height of crowned tooth and opposing teeth in contact.
In the present study, there was an increase in OVD of about 0.62 mm. which decreased to baseline value in 2 weeks [Figure 2], [Figure 3], [Figure 4]. The OVD decreased rapidly till 2nd day after placement of crown and from 2nd to 5th day follow up, and same also observed in between 10 and 15 day. But there was minimal decrease during 5th–10th day. Closer values to baseline were observed after 2 weeks of follow up. Almost identical results were observed in literature where the occlusion came back to normal in 2–4 weeks. Even though there was increased overbite, these studies also support the above results with no reports of pain and TMDs.,,
|Figure 2: Baseline and last day follow-up for canine relationship in millimeters with conventional technique|
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|Figure 3: Baseline and 15th-day follow-up for canine relationship in millimeters with Hall technique|
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|Figure 4: Tissue landmarks used for measurement of clinical crown height|
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According to a study in which the landmarks used for measurement are tip of nose to vermilion border of upper lip and chin to lower lip vermilion border, the post treatment values with the baseline, was statistically significant difference until the 2nd week. In the 3rd week, the OVD values did not show significant difference when compared to the baseline indicating that the OVD had been restored. At the 4th week, the OVD value decreased further compared to the baseline value; though the difference was statistically insignificant. This study failed to answer whether, only the restored tooth intruded or the antagonist also intruded. Another limitation in this study was the use of soft tissue land marks for measuring the OVD. Making use of hard tissue landmarks with the help of radiographs for this purpose would have been a more standardized approach.
In the present study, clinical crown height of crowned tooth as well as opposing teeth in contact were measured; it showed that there was almost 0.68 mm increase in clinical crown height of crowned tooth, but net decrease was about 0.37 mm. The remaining occlusal settlement occurred because of intrusion of opposing teeth in contact which is almost 0.14 mm. Remaining 0.17 mm might have settled because of occlusal deformation on stainless steel crown surface or might be because of supra-eruption of opposite side teeth [Graph 2] and [Graph 3].
In the present study when a tooth is subjected to crown placement by Hall technique, it appears as a supra erupted tooth among the arch which results in more bite force on that particular tooth as well as antagonist teeth in contact. Through follow up values of T scan, it was observed that the dento-alveolar compensation also takes place due to the equilibration of the bite force that was attained after 2 weeks in our study and achieved a balanced occlusion on the tooth subjected for treatment.
But this equilibration process was not uniform. Immediately after placement of crown the bite force increased by almost 36 percentile on the Hall crown. On 2nd day follow up, it was reduced by 15 percentile. Maximum reduction was seen between 2nd and 5th day i.e., almost 25 percentile causing reduction in the bite force below base line value. In spite of repeated assessment with T scan [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10] and [Graph 4]. This can be because child might have developed an altered path of occlusion to avoid pain due to premature contact on crowned tooth. But in subsequent follow up, the bite force showed gradual increment and it subsequently came back to close to the baseline value. This can be because of child's altered path of occlusion gradually shifted to physiological path of occlusion due to settlement of OVD with intrusion of crowned and opposing teeth.
|Figure 5: Baseline T-scan data for conventional technique on crowned tooth|
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|Figure 6: T-scan data for conventional technique on crowned tooth immediately after placement of crown|
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|Figure 7: T-scan data for conventional technique on crowned tooth on the 2nd day follow-up|
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|Figure 9: T-scan data for Hall technique on crowned tooth immediately after placement of crown|
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|Figure 10: T-scan data for Hall technique on crowned tooth on the 15th day follow-up|
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According to a study done by Nair et al. the mean values of the Bite force percentage on the left side of the arch were 46.11 at the baseline, 60.39 immediately after placing the SSC and 46.73 after 1 month. The mean total bite force on the right side was 54.91 at the baseline, 46.07 immediately postinsertion of SSC and 51.46 as the values recorded after 1 months. It was observed that on the crowned tooth, the mean bite force at baseline was 7.52, immediately after placement of SSC the bite was drastically increased to 46.87 and after 1 month it decreased to 11.20. There was statistically significant difference baseline and immediate force values on crowned tooth whereas no significant difference was seen between baseline value and 1 month follow up value.
The FEM analysis helps in understanding the effect of masticatory force applied on dental restorative materials like restorations, crowns, implant, and removable appliances on human living tissue. Compared with actual model research, FEM has various advantages. By using FEM, the researcher can conduct many simulations without needing patients or carrying out human experiments, which is an effective way to improve load management in order to reduce discomfort for patients and achieve long-term clinical performance.,,
In the present study FEA was used to assess stress distribution pattern after placement of crown by Hall technique and Conventional technique. In Hall technique, overall more stresses were developed and more deformative/deflective changes observed immediately after placement of crown compared with Conventional technique. But these stresses and deformative changes slightly reduced on 2nd day follow up more during 5th day follow up i.e., below base line value in Hall Technique due to altered path of occlusion by child to avoid premature contact on crowned tooth. But this temporary provision gradually shifted to baseline physiological path of occlusion due to intrusion of crowned tooth and opposing teeth in contact which resulted in gradual increase in stress distribution till it returned to baseline values citation as [Figure 12], [Figure 13] and [Graph 5] and [Graph 6].
|Figure 12: FEA for Hall Technique (a) Overall stress for baseline bite force (Maximum stress: 75.6176 Mpa), Vonmises stress in the (b) cortical bone (Maximum stress: 10.5519 MPa), (c) cancellous bone (Maximum stress: 5.7956 Mpa), (d) PDL (Maximum stress: 2.22013 MPa), (e) dentine (Maximum stress: 38.4348 Mpa) (f) Enamel (Maximum stress: 75.6176 MPa) in FEA. FEA: Finite element analysis, PDL: Periodontal ligament|
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|Figure 13: FEA for Hall Technique (a) Overall deflection in the model at Baseline biting forces in FEA (Maximum deformation: 0.006725 mm), Deflection in the (b) cortical bone (Maximum deflection: 0.002989 mm), (c) cancellous bone (Maximum deflection: 0.04679 mm), (d) PDL (Maximum deflection: 0.006502 mm), (e) Dentine (Maximum deflection: 0.006502mm), (f) Enamel (Maximum deflection: 0.006725 mm) in FEA. FEA: Finite element analysis, PDL: Periodontal ligament|
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Limitations of this study includes its sample size, though single sample is enough for FEA, other supporting investigations like IODS and T scan could have given better results with a larger statistically approved sample size. Also during the follow up period, T scan value showed sudden decrease in bite force below baseline value in Hall technique on the 5th day follow-up and then gradual increase till baseline value. This finding can be better explained with larger sample size and more research. In the FEA, the analysis static loads were applied which showed minute changes in deformation and stress in supporting tissues but rather a creep model of FEA could have given better understanding as occlusion is a dynamic process.
| Conclusion|| |
The following conclusions can be drawn from this study:
- In Hall technique, magnitude of increased stresses on PDL and supporting alveolar bone settles within a period of 2 weeks, whereas for conventional technique, it settles in 2 days
- This increased stress distribution causes more intrusion of crowned tooth and slight intrusion of opposing teeth in contact till the occlusal settlement occurs in Hall technique. There are no such changes observed with Conventional technique of crown placement as there was minimal increase in OVDs.
However, it is recommended to carry out similar studies on larger sample size, with more extensive follow-up.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13]
[Table 1], [Table 2], [Table 3], [Table 4]