Finite element method analysis of occlusal splint therapy in patients with bruxism

Abstract

Background

The prevalence of temporomandibular disorders is 25-50% in adults and, in particular, the prevalence of bruxism is 8-31.4% in adults [1,2]. In general, habits such as bruxism are contributory factors for temporomandibular joint (TMJ) disorders. From a biomechanical point of view, TMJ is the most complex joint in the human body. More than 2000 neuromuscular control signals are registered daily for normal performance of this joint [3]. The consequences of bruxism are mostly in form of wear and damage and are more prevalent in men than women [4]. Bruxism not only leads to wear, grinding, crushing, fracture and ultimately serious damage to teeth but also may cause hearing loss, maxillofacial problems and even facial deformation [5]. If bruxism is not treated, the teeth, bones and gum may be worn or fractured due to wear pressure [6]. Since bruxism is the most important risk factor for TMJ [7], the study of suitable strategies for treating this disorder is of great importance.

Previous studies related to the subject of this research can be divided into two main groups. The first group of studies has merely examined the changes in the biomechanical parameters in TMJ and mandible. Tanaka et al. examined in their study the effect of age on the manner of changes in the parameters affecting the TMJ disc displacement [8]. Hirose et al. investigated the destructive effects of prolonged jaw and teeth pressing on TMJ disc using finite element method (FEM) [9]. Donzelli et al. examined the kinematic and geometric changes in TMJ discs using FEM analysis [10]. Koolstra et al. showed with the help of FEM that the articular disk has the ability to distribute loads in a wide area [11]. Naeije et al. investigated in a biomechanical study the loads exerted on TMJ during chewing and chopping [12]. Del Palomar et al. examined the effective biomechanical parameters in lateral excursions of the mandible during chewing with the help of the FEM [13]. Commisso et al. examined the effect of pterygoid muscles on movement of the jaw during mastication using the FEM analysis [14]. Nishigawa et al. measured the maximum bite force in patients with sleep associated bruxism experimentally, however, they did not deal with the change of bite force during or after treatment [15]. Some studies focused solely on biomechanical parameters affecting implant insertion and filling teeth and dental pain [16-19].

The second group of studies has focused on the assessment of treatments of TMJ disorders. Ferreira et al. showed how the occlusal splint distributes stress in TMJ disc [20]. Salmi et al. found a new digital process to produce occlusal splints in a study using a laser scanner and evaluated the effectiveness of this new production method [21]. Kobayashi et al. examined the association between masticatory performance and bite force in children with bruxism [22].

The results of previous studies have shown that occlusal splint therapy can be a treatment option for patients suffering from bruxism [22-24]. These studies showed that biomechanical factors such as stress are associated with bruxism, however the exact contribution of these parameters is still unknown [22]. Therefore, it was tried in this research to perform a study with the aim of quantitative assessment of the effectiveness of occlusal splint for treating bruxism using in vivo image data of patients and control subjects. In the present study, the manner of changes in biomechanical parameters affecting this disease, such as stress and deformation, after occlusal splint therapy was also examined and more insight into the detail performance mechanism of this therapy was gained.

Methods

A total of 37 volunteer patients were selected from the 420 patients who had been referred to the Tehran Dental Hospital for 23 months. The patients included 19 women and 18 men aged between 21-49 years old and with a body mass index between 18.2-21.9 kg.m^-2. 5.5% of male and 10.5% of female patients had a history of tooth caries and tooth fracture for up to 3 teeth that did not result from jaw or mouth injury, and were previously treated and did not pose a particular problem during the study. Also 55.5% of male and 52.6% of female patients had a history of filled teeth for up to 2 teeth. All patients were evaluated first by the use of a questionnaire that identifies the main complaint, pain history and the bruxism. It should be noted that this research was approved by the Ethics Committee of North Tehran Branch, Islamic Azad University (No. 18245/86-2) which was confirmed with the 1964 Helsinki declaration. According to the ethical standard, all samples have provided informed consent in the study. For all patients before and after the occlusal splint therapy, we applied a diagnostic protocol which is standardized equally, by a professional dentist. It concludes interview and a systematic evaluation of dental, cranial, facial, cervical and other oral structures. The initial inclusion criteria includes, no craniofacial surgery, no use of any medication and no reported systemic disease. The basis of choosing the sleep bruxism patients was the below criteria mentioned by American Academy of Sleep Medicine [25]:

A. occurrence of tooth grinding at least 3/7 nights during 6 months, as approved by a sleep partner; B. clinical presence of tooth wear; C. hypertrophy of masseter muscle; and D. occurrence of the fatigue or tenderness of jaw muscle in the morning.

Among the patients referred to the Tehran Dental Hospital, 36 other volunteer patients included 18 women and 18 men aged between 26-52 years old and with a body mass index between 19.6-22.3 kg.m^-2 who had no history of disease or symptoms associated with bruxism or TMJ disorders, were selected as control subjects. They were completely healthy in concern with bruxism or TMJ disorders. But they had toothache with cracked and attrition tooth for up to 4 teeth (22.2% males and 16.6% female), tooth fracture and tooth carries for up to 4 teeth (27.8% males and 38.8% female) and 66.7% males and 77.8% female of control subjects need dental implant for up to 4 teeth which during the diagnosed and treating process, according to specialist’s diagnosis, CT scans were taken from them. Also 61.1% of male and 55.5% of female control subjects had a history of filled teeth for up to 3 teeth. It should be noted that all stages of diagnosis, informing about this study and provided informed consent for control subjects went through as the patients. For low cost, unique accessibility and low effective radiation dose, we use Cone-beam CT (CBCT) scanning for preparing the images. We use Newtom VG system (QR, Verona Italy) CBTC scan set. The scan setting includes: 3.6 mAs and 90 KV with radiation time of 15 seconds and field of view 20×19 inch. Furthermore, the position of samples during scanning was standing and Natural Head Position was the condition of their head. Swallow or breathe were prohibited for patients during image preparing. The voxel size and the slice thickness were 0.3×0.3×0.3 mm. and 0.3 mm, respectively. It should be noted that the jaw relation in providing images for all patients and control subjects was in the maximum intercuspation position.

Using the images obtained from the CT scan of the jaw and teeth of samples and importing DICOM files of these images into Mimics software version 13.1 (Materialise, Leuven, Belgium), the point cloud of the maxilla, mandible and teeth of each sample were produced as separate parts (Fig 1, a). In Mimics, the bony parts of the maxilla, mandible and teeth in image file were kept. After modifying the areas containing soft tissue in all image slices and repeating these modifications layer by layer, the spaces between layers were finally modified and differentiated and the point clouds of the teeth and jaw bone were extracted as the software output. Subsequently, the point clouds were transferred to the CATIA software version 5R21 (Dassault Systemes, Waltham, Mass., USA), and a three-dimensional model of the maxilla, mandible and teeth were built (Fig 1, b).

Fig. 1. (a) The point clouds of the maxilla, mandible and teeth. (b) 3D model. (c) Meshed model.

Three-dimensional models of the maxilla, mandible and teeth of all 37 patients and 36 control subjects were assembled in conditions of no contact pressure respect to each other. Six months after insertion of the occlusal splint, the process of preparing CT scan images, creating the point cloud, and building the three-dimensional models of jaws, teeth and splint were repeated for patients with the splint in their mouth. At this stage, the 3D models of used splints of the same patients were constructed from their CT scan images and the 3D splint models were inserted between the upper and lower teeth of patients. It should be noted that according to experienced dentist prescription, all patients were treated using occlusal splint therapy. However, a sleep hygiene measures combined with relaxation techniques was advised and prescribed for all patients. The material of splints was hard colorless acrylic resin which was polymerized using the method of conventional heat-curing. It is worth noting that due to personal limitations of the patients, there was only possible to create the 3D model of jaw, teeth and splint of 10 women and 11 men after 6 months of using splint. Since the analyses based on FEM are among the most familiar methods for biological simulation [26-39], the assembled models were transferred finally to ABAQUS software version 6.14 (Dassault Systemes) for FE analysis. Furthermore, for comparing the results of computer simulations between the patients and control subjects, and also for comparison of these results in patients before and after the occlusal splint therapy, three specific anatomical points in the skull of the samples were used as set points to synchronize procedures and standardize the samples head position. Also, in order to ensure the correct loading distribution for comparing the biomechanical parameters of the models with each other, the 3D models of the samples were standardized in terms of the definition of the x, y, and z axis relative to one same reference.

Table 1 shows the material properties considered for jaw bones, teeth, and splints [20, 40]. One of the most important points in FE analysis is how different parts of the model interact with each other. In this study, these interactions and constraints were defined based on the actual anatomical function of these components in the human body. The constraint considered for the contact between the inserted teeth on the upper and lower jaws with splint was a surface-to-surface constraint with a friction coefficient of 0.5 [20]. The degree of freedom of the upper surface of maxilla was considered to be zero at all three directions of x, y and z, i.e., the surface was considered to be fixed. Other degrees of freedom were considered in accordance with the real performance of TMJ, so that the necessary degrees of freedom for opening and closing movements of jaw (rotational degree of freedom) as well as the translation and lateral displacement of jaws over each other (translational degree of freedom) were considered (Fig 2, a). According to previous study, a first order Ogden hyperelastic model was used for defining the periodontal ligament with poisson's ratio of 0.45 and material parameter  MPa [41]. The average amount of force exerted by the medial pterigoid muscle and masseter muscle for both left and right muscles was assumed to be 50 N [20, 40]. It should be noted that, according to previous studies, the force of these muscles should be applied under a particular angle to the model, as shown in Fig 2, a. One of the most important issues in numerical computer simulations is to ensure the mesh independence of responses [42-46], The tetrahedral element was used for meshing the models (Fig 1, c). The results showed that the maximum difference between the stress values in the medium and fine meshes in all three groups of patients, control subjects and patients after 6 months of using the occlusal splint was less than 1.8%. Therefore, the convergence of responses from the grid and time step was ensured (Fig 2, b).

Table 1. Material properties of jaw bone, teeth and occlusal splint [20, 40].

Fig. 2. (a) Degree of freedom, interactions and constraints between parts. (b) Diagram of maximum stress in head of mandible - number of elements for grid independence study.

Statistical analyses

The mean value, standard deviation (SD) and coefficient of variation (CV) for maximum stress and maximum deformity were calculated in all three groups of patients, control subjects and patients after 6 months of using the occlusal splint using SPSS version 22 (IBM Corp., Armonk , New York, USA).

Results

Data validation is one of the most important concerns in computer simulations. Therefore, it was necessary to verify the correctness of the simulation results in order to assure the accuracy of the assumptions and the modeling and analysis processes. For data validation, the maximum bite force was measured experimentally in control subjects and patients (before using the splint) and was compared with the similar results calculated in the simulation process. For this goal, a miniature strain-gauge transducer (LM-50- KAM186, Kyowa Electronic Instruments Co., Tokyo, Japan) was mounted in the right and left first molar regions in all samples and the average value of maximum bite forces was recorded after 30 records for each sample and was compared with the similar parameter calculated by FEM simulation. Fig 3 shows that the maximum difference between the computer simulation and experimental results of the maximum bite forces in all patients and control subjects was less than 3.9%. Therefore, the validity of the simulation process is confirmed. Then, the correctness of the statistical analysis of the main results of this study, i.e. the maximum stress and maximum deformation, should be assured for each of the three groups of patients, control subjects and patients after 6 months of using splint. The results of the statistical analysis showed that the highest amount of CV in all three groups of samples was less than 3.1% for both maximum stress and maximum deformation (Table 2). The results in Table 2 showed that SD and CV values were acceptable for all parameters in all three groups of samples. It should be noted that the reported values for maximum stress and maximum deformation in the rest of the paper are the average values of these parameters for each of the three groups of patients, control subjects and patients after 6 months of using splint.

Table 2. Stress and deformation values in jaw bone and head of mandible.

SD: standard deviation; CV: coefficient of variation.

Fig. 3. The maximum difference between the computer simulation and experimental results of the maximum bite forces in control subjects (a) and patients (b).

According to Fig 4, a and Table 2, the maximum stress in the jaw bone of control subjects and patients was 4.82 and 21.10 MPa, respectively. Results of analysis of patients 6 months after using splint showed that the maximum stress was 6.12 MPa. The maximum stress produced in the head of mandible of control subjects and patients was 6.91 and 28.26 MPa, respectively. The respective value of this parameter in patients 6 months after using splint was 7.68 MPa.

Fig 4, b shows the manner of changes in deformation values. The results showed that the maximum deformation in jaw bone of control subjects and patients was 63.91×10^-4 and 368.10×10^-4 mm (Fig 4, c and Table 2). Similarly, for patients six months after using the splint the result was 71.10×10^-4 mm. The maximum deformation in the head of mandible of control subjects and patients was 9.40×10^-4 mm and 437.20×10^-4 mm, respectively. This value decreased in patients 6 months after using splint down to 93.11×10^-4 mm (Table 2).

Fig. 4. (a) Stress distribution of the jaw bone for a control subject (b) the manner of changes in deformation values in the upper and lower jaws. (c) deformation distribution of the jaw bone for a control subject. (d) The location of maximum stress.

Discussion

The main objectives of this study were the numerical examination of the manner of changes in effective parameters in occlusal splint therapy during bruxism treatment as well as the assessment of the effectiveness of using occlusal splint for treating this disease. Stress and deformation are the most important biomechanical indices for assessing TMJ disorders and are usually used for quantitative examination of these disorders [14, 47]. However, the bite force, as mentioned earlier, was used for data validation in the present study due to the fact that the experimental measurement of stress and deformation is very difficult [14] and experimental measurement of the distribution of these parameters in jaw bone is impossible. Therefore, the bite force parameter, which can be obtained both experimentally and using FEM simulation, was used in this study for data validation. The values of von Mises stress and deformation in jaw bone were also calculated using FE method for patients, control subjects and patients after 6 months of using splint in order to assess the disease. The results showed that the maximum stress in jaw bone of patients was 4.4 times the maximum stress in control subjects. After using the splint, the maximum stress decreased by 71.0% (Table 2). However, based on the results, the maximum stress in patients after using splint did not return exactly to the range of maximum stress in control subjects and there was a difference of 26.9% between the values of maximum stress in control subjects and patients after splint treatment. The contact surfaces opposite to the jaw bone are not exactly parallel to it and there are various geometric complexities in this area. Also, with regard to the jaw anatomy, the muscular forces exerted to it are not exactly perpendicular to the surface and are exerted in a particular orientation. Therefore, the von Mises stress calculated by computer simulation presented shear stress, in addition to compressive stress. Consequently, all areas undergoing deformation are not in the same direction and this can also lead to local shear stress. Hence, the lateral walls of splint can play an effective role in confrontation with these shear stresses and this is an important issue in designing the splint. Regarding the large difference between the elastic modules of splint material and jawbone and teeth materials (Table 1), a large contribution to load absorbing and damping can be attributed to the splint due to the softness and flexibility of its material. Therefore, the splint acts as an absorber and dissipater of the generated stress and can help reduce stress and somehow relax stress. If this additional loading due to the bruxism is not damped by splint, a reaction force and consequently an additional reaction stress will be generated in TMJ, which will damage the joints, muscles and ligaments associated with TMJ. Therefore, splint creates a biomechanical equilibrium between the physiological loading and the generated stress through stress relaxation. The imbalance between the input physiological loading and the generated stress can be one of the biomechanical causes of bruxism and the splint can contribute to the neuromuscular reflex and to reduce the stresses on ligaments and joints associated with the TMJ by helping to achieve this balance. As shown in Fig 4, d, the maximum stress in the total jaw bone is generated in the TMJ and, in particular, in the head of mandible. Its biomechanical cause can be the stress concentration, since the head of mandible, considering the jaw bone anatomy, has the most complex and limited cross sections in the entire mandible. The maximum stress in the head of the mandible in patients was 4.1 times that of control subjects but reduced by 72.8% after using the splint. The difference between this stress and the similar parameter in control subjects was 11.1%. The important point is that 6 months after using splint, the difference between the maximum stress in the head of the mandible and the other parts of the jaw bone was closer to the similar values in control subjects. This means that the effectiveness of the occlusal splint in patients suffering from bruxism in reducing the stress in the head of mandible is higher than other locations of mandible. It should be noted that the location of generation of the maximum stress after using the splint did not change and maximum stress always occurred in the head of mandible. The results showed that like the maximum stress, the highest deformation was located in the head of the mandible. According to Table 2, the maximum deformation in jaw bone and head of mandible of patients was, respectively, 5.8 and 4.9 times that in control subjects and decreased by 80.7% and 78.7%, six months after using splint. The difference between the maximum deformation in jaw bone and head of mandible of patients who used splint for six months and control subjects was 11.3% and 4.1%, respectively. The results in Table 3 show that the maximum stress and deformation in all samples were greater in the upper jaw than in the lower jaw. Similar to the reported results for patient No. 1, the greatest effectiveness of splint in the jaw bone was related to the areas adjacent to the first, second and third molar teeth in all patients (Table 3). The results also showed that the stresses in the left and right mandible of patients are not necessarily balanced and uniform. However, due to the flexibility of the splint material, the bilateral and simultaneous loading becomes possible, which can also be useful in the treatment of bruxism.

It should be noted that the minimal effectiveness of the splint for damping of stress and deformation was related to the canine teeth. The results showed that occlusal splint therapy was effective in reducing stress and deformation, especially in the head of mandible. It should be noted that following occlusal splint therapy, the maximum deformation approached almost 2.6 times the maximum stress to the respective values in control subjects. Thus, the effectiveness of splint was higher in reducing deformation than stress. In fact, the design of the occlusal splint therapy is not based on the prevention of bruxism, but the results of this study show that the occlusal splint can help treat this disease, by reducing stress and correcting deformations and deviations, especially in the head of mandible, and eventually reducing the additional support reaction due to bruxism in TMJ. It is suggested that the future studies record and compare the stimulation of TMJ-related muscles affecting bruxism before and after using splint by patients, so that the effect of splint on muscle stimulation and bruxism frequency is also examined as the main focus of the present study was on intensity not frequency.

Conclusions

The results showed that the occlusal splint creates a biomechanical equilibrium between the physiological loading and the generated stress by stress relaxation. The splint also provides the possibility for making the asymmetric and non-uniform loading due to bruxism bilateral and simultaneous. Thus, the occlusal splint can lead to regulation of bruxism by reducing stresses, and in particular, by reducing deformations and deviations in TMJ and consequently can help treat this disease. The results of this study can be useful in quantitative evaluation of the changes in stress and deformation before and after treatment of bruxism as well as in development of a biomechanical approach for assessing the effectiveness of occlusal splint therapy.

Abbreviations

SD: standard deviation; CV: coefficient of variation; TMJ: temporomandibular joint; FEM: finite element method.

Declarations

Ethics approval and consent to participate:

All procedures performed in studies involving human participants were in accordance with the ethical standards of North Tehran Branch, Islamic Azad University, Tehran, Iran, (Ethics committee of biomedical research center, No. 18245/86-2) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Furthermore, this article does not contain any studies with animals performed by any of the authors. It is noteworthy that according to ethical standards, all patients and control subjects provided verbal informed consent.

Consent for publication: The authors accept to publish all information of the article freely by the Journal of BMC Oral Health and its publisher.

Availability of data and material: Not applicable

Competing interests: The authors declare that they have no competing interests.

Funding: Not applicable

Authors’ contributions: S.G designed the study, collected and analyzed the data. H.G and HK wrote the manuscript. S.G, H.G and HK interpreted of data and provided critical input and revisions. All authors read and approved the final version of the manuscript.

Acknowledgements: Not applicable

Authors' information: ¹ Department of Biomedical Engineering, Islamic Azad University-North Tehran Branch, Tehran, Iran. ² Department of Electrical and Computer Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.

References

1. Manfredini D, Winocur E, Guarda-Nardini L, Paesani D, Lobbezoo F. Epidemiology of bruxism in adults: a systematic review of the literature. J Orofac Pain. 2013 Mar 1;27(2):99-110.
2. Kuttila M, Niemi PM, Kuttila S, Alanen P, Le Bell Y. TMD treatment need in relation to age, gender, stress, and diagnostic subgroup. Journal of orofacial pain. 1998 Jan 1;12(1).
3. Pizolato RA, Gavião MB, Berretin-Felix G, Sampaio AC, Trindade Junior AS. Maximal bite force in young adults with temporomandibular disorders and bruxism. Brazilian oral research. 2007 Sep;21(3):278-83.
4. Alkhiary YM, Nassef TM, Yassine IA, Tayel SB, Ezzat AE. A new numerical model to analyze stress distribution of TMJ disc from 2-D MRI scans. Advances in Computing. 2012 Dec;2(05):66-77.
5. Kitsoulis P, Marini A, Iliou K, Galani V, Zimpis A, Kanavaros P, Paraskevas G. Signs and symptoms of temporomandibular joint disorders related to the degree of mouth opening and hearing loss. BMC Ear, Nose and Throat Disorders. 2011 Dec;11(1):5.
6. Reichardt G, Miyakawa Y, Otsuka T, Sato S. The mandibular response to occlusal relief using a flat guidance splint. International journal of stomatology & occlusion medicine. 2013 Dec 1;6(4):134-9.
7. Pereira LJ, Costa RC, França JP, Pereira SM, Castelo PM. Risk indicators for signs and symptoms of temporomandibular dysfunction in children. Journal of clinical pediatric dentistry. 2009 Sep 1;34(1):81-6.
8. Tanaka E, Hirose M, Yamano E, Dalla‐Bona DA, Fujita R, Tanaka M, Van Eijden T, Tanne K. Age‐associated changes in viscoelastic properties of the bovine temporomandibular joint disc. European Journal of Oral Sciences. 2006 Feb;114(1):70-3.
9. Hirose M, Tanaka E, Tanaka M, Fujita R, Kuroda Y, Yamano E, Van Eijden TM, Tanne K. Three‐dimensional finite‐element model of the human temporomandibular joint disc during prolonged clenching. European journal of oral sciences. 2006 Oct;114(5):441-8.
10. Donzelli PS, Gallo LM, Spilker RL, Palla S. Biphasic finite element simulation of the TMJ disc from in vivo kinematic and geometric measurements. Journal of biomechanics. 2004 Nov 1;37(11):1787-91.
11. Koolstra JH, Van Eijden TM. Combined finite-element and rigid-body analysis of human jaw joint dynamics. Journal of biomechanics. 2005 Dec 1;38(12):2431-9.
12. Naeije M, Hofman N. Biomechanics of the human temporomandibular joint during chewing. Journal of dental research. 2003 Jul;82(7):528-31.
13. Del Palomar AP, Doblaré M. Finite element analysis of the temporomandibular joint during lateral excursions of the mandible. Journal of biomechanics. 2006 Jan 1;39(12):2153-63.
14. Commisso MS, Martínez-Reina J, Ojeda J, Mayo J. Finite element analysis of the human mastication cycle. Journal of the mechanical behavior of biomedical materials. 2015 Jan 1;41:23-35.
15. Nishigawa K, Bando E, Nakano M. Quantitative study of bite force during sleep associated bruxism. Journal of oral rehabilitation. 2001 May;28(5):485-91.
16. Rubo JH, Capello Souza EA. Finite‐element analysis of stress on dental implant prosthesis. Clinical implant dentistry and related research. 2010 Jun;12(2):105-13.
17. Svensson P, Jadidi F, Arima T, BAAD‐HANSEN L, Sessle BJ. Relationships between craniofacial pain and bruxism. Journal of oral rehabilitation. 2008 Jul;35(7):524-47.
18. Gholampour S, Jalali A. Thermal analysis of the dentine tubule under hot and cold stimuli using fluid–structure interaction simulation. Biomechanics and modeling in mechanobiology. 2018 Dec 1;17(6):1599-610.
19. Gholampour S, Zoorazma G, Shakouri E. Evaluating the effect of dental filling material and filling depth on the strength and deformation of filled teeth. Journal of Dental Materials and Techniques. 2016 Dec 1;5(4):172-80.
20. Ferreira FM, Cézar Simamoto-Júnior P, Soares CJ, Ramos AM, Fernandes-Neto AJ. Effect of Occlusal Splints on the Stress Distribution on the Temporomandibular Joint Disc. Brazilian dental journal. 2017 Jun;28(3):324-9.
21. Salmi M, Paloheimo KS, Tuomi J, Ingman T, Mäkitie A. A digital process for additive manufacturing of occlusal splints: a clinical pilot study. Journal of the Royal Society Interface. 2013 Jul 6;10(84):20130203.
22. Kobayashi FY, Furlan NF, Barbosa TS, Castelo PM, Gaviao MB. Evaluation of masticatory performance and bite force in children with sleep bruxism. Journal of oral rehabilitation. 2012 Oct;39(10):776-84.
23. Lee HS, Baek HS, Song DS, Kim HC, Kim HG, Kim BJ, Kim MS, Shin SH, Jung SH, Kim CH. Effect of simultaneous therapy of arthrocentesis and occlusal splints on temporomandibular disorders: anterior disc displacement without reduction. Journal of the Korean Association of Oral and Maxillofacial Surgeons. 2013 Feb 1;39(1):14-20.
24. Nitzan DW. Intraarticular pressure in the functioning human temporomandibular joint and its alteration by uniform elevation of the occlusal plane. Journal of Oral and Maxillofacial Surgery. 1994 Jul 1;52(7):671-9.
25. American Academy of Sleep Medicine: International Classification of Sleep Disorders: Diagnostic and Coding Classification of Sleep Disorders 697 Manual, 2nd ed. Westchester: American Academy of Sleep Medicine, 2005.
26. Gholampour S, Soleimani N, Zalii AR, Seddighi A. Numerical simulation of the cervical spine in a normal subject and a patient with intervertebral cage under various loadings and in various positions. International Clinical Neuroscience Journal. 2016 Sep 22;3(2):92-8.
27. Gholampour - S, Hajirayat K, Erfanian A, Zali AR, Shakouri E. Investigating the Role of Helmet Layers in Reducing the Stress Applied During Head Injury Using FEM. International Clinical Neuroscience Journal. 2017 Apr 15;4(1):4-11.
28. Gholampour S, Soleimani N, Karizi FZ, Zalii AR, Masoudian N, Seddighi AS. Biomechanical Assessment of Cervical Spine with Artificial Disc during Axial Rotation, Flexion and Extension. International Clinical Neuroscience Journal. 2016 Sep 22;3(2):113-9.
29. Gholampour S, Fatouraee N, Seddighi AS, Yazdani SO. A Hydrodynamical Study to propose a numerical Index for evaluating the CSF conditions in cerebralventricular system. International Clinical Neuroscience Journal. 2014 Aug 5;1(1):1-9.
30. Shakouri E, Haghighi Hassanalideh H, Gholampour S. Experimental investigation of temperature rise in bone drilling with cooling: a comparison between modes of without cooling, internal gas cooling, and external liquid cooling. Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine. 2018 Jan;232(1):45-53.
31. Hajirayat K, Gholampour S, Seddighi AS, Fatouraee N. Evaluation of blood hemodynamics in patients with cerebral aneurysm. International Clinical Neuroscience Journal. 2016 Jul 9;3(1):44-50.
32. Gholampour S, Seddighi A, Fatouraee N. Relationship between Spinal fluid and Cerebrospinal fluid as an index for assessment of non-communicating hydrocephalus. Modares Mechanical Engineering. 2015 Mar 11;14(13).
33. Khademi M, Mohammadi Y, Gholampour S, Fatouraee N. The nucleus pulpous of intervertebral disc effect on finite element modeling of spine. International Clinical Neuroscience Journal. 2016 Dec 7;3(3):150-7.
34. Gholampour S, Shakouri E, Deh HH. Effect of drilling direction and depth on thermal necrosis during tibia drilling: an in vitro study. Technology and Health Care. 2018 Jan 1;26(4):687-697
35. Vahdat I, TabatabaiGhomsheh F, Gholampour S, Rostami M, Khorramymehr S. Biomechanical evaluation of passive resistive torque structure of elbow joint and its application in rehabilitation and practical equipment. Journal of Modern Rehabilitation. 2015 Nov 15;9(4):16-24.
36. Gholampour S, Bahmani M, Shariati A. Comparing the efficiency of two treatment methods of hydrocephalus: shunt implantation and endoscopic third ventriculostomy. Basic and Clinical Neuroscience. 2019 May 15;10(3):185-98.
37. Gholampour S, Fatouraee N. The impact of the model boundary conditions on computer simulation of hydrocephalus patients. PloS one. 2018 [in press].
38. Gholampour S, Hajirayat K. Minimizing thermal damage to vascular nerves while drilling of calcified plaque. BMC research notes. 2019 Dec;12(1):338.
39. Gholampour S, Deh HH. The effect of spatial distances between holes and time delays between bone drillings based on examination of heat accumulation and risk of bone thermal necrosis. Biomedical engineering online. 2019 Dec;18(1):65.
40. dos Santos Marsico V, Lehmann RB, de Assis Claro CA, Amaral M, Vitti RP, Neves AC, da Silva Concilio LR. Three-dimensional finite element analysis of occlusal splint and implant connection on stress distribution in implant–supported fixed dental prosthesis and peri-implantal bone. Materials Science and Engineering: C. 2017 Nov 1;80:141-8.
41. Martinez S, Lenz J, Schweizerhof K, Schindler HJ. A Variable Finite Element Model of the Overall Human Masticatory System for Evaluation of Stress Distributions during Biting and Bruxism. In10th European LS-DYNA Conference, Würzburg, Germany 2015.
42. Gholampour S. FSI simulation of CSF hydrodynamic changes in a large population of non-communicating hydrocephalus patients during treatment process with regard to their clinical symptoms. PloS one. 2018 Apr 30;13(4):e0196216.
43. Gholampour S, Taher M. Relationship of Morphologic Changes in the Brain and Spinal Cord and Disease Symptoms with Cerebrospinal Fluid Hydrodynamic Changes in Patients with Chiari Malformation Type I. World neurosurgery. 2018 Aug 1;12(5):8.
44. Hajirayat K, Gholampour S, Sharifi I, Bizari D. Biomechanical Simulation to Compare the Blood Hemodynamics and Cerebral Aneurysm Rupture Risk in Patients with Different Aneurysm Necks. Journal of Applied Mechanics and Technical Physics. 2017 Nov 1;58(6):968-74.
45. Gholampour S, Fatouraee N, Seddighi AS, Seddighi A. Numerical simulation of cerebrospinal fluid hydrodynamics in the healing process of hydrocephalus patients. Journal of Applied Mechanics and Technical Physics. 2017 May 1;58(3):386-91.
46. Gholampour S, Fatouraee N, Seddighi AS, Seddighi A. Evaluating the effect of hydrocephalus cause on the manner of changes in the effective parameters and clinical symptoms of the disease. Journal of Clinical Neuroscience. 2017 Jan 1;35:50-5.
47. Chen-Tin L, Chou YR, Chao-Chia W, Chia-Yu W, Keng-Liang O, Han-Yi C. Research of Oral Remodeling on Mandible with Ameloblast. Journal of Biomedical Sciences. 2015 Jan 1;4(1).

Table 3

Table 3. Stress and deformation values in upper and lower teeth of patient No. 1 and patient No. 1 after using splint.