/home/opencode/cpanel/stomaeduj_hacked/uploads/art-4-Stanusi-1-2020-1.pdf www.stomaeduj.com OCCLUSION AND TMJ ANALYSIS OF STRESS GENERATED IN THE ENAMEL OF Original Articles AN UPPER FIRST PREMOLAR: A FINITE ELEMENT STUDY Andreea Stănuşi1a , Veronica Mercuţ1b , Monica Scrieciu1c , Sanda Mihaela Popescu2d , Monica Mihaela Iacov Crăiţoiu1e , Luminiţa Dăguci1f , Ştefan Castravete3g, Marina Olimpia Amărăscu1h 1 Department of Proshodontics, Faculty of Dentistry, University of Medicine and Pharmacy of Craiova, Craiova, Romania 2 Department of Oral Rehabilitation, Faculty of Dentistry, University of Medicine and Pharmacy of Craiova, Craiova, Romania 3 Caelynx Europe SRL, Craiova, Romania a DMD, PhD Student; e-mail: andreeacazan22@yahoo.com; ORCIDiD: https://orcid.org/0000-0003-2520-7967 b DDS, PhD, Professor; e-mail: veronica.mercut@yahoo.com; ORCIDiD: https://orcid.org/0000-0003-3573-7128 c DMD, PhD, Professor; e-mail: scrieciu_monica@yahoo.com; ORCIDiD: https://orcid.org/0000-0003-0696-7100 d DMD, PhD, Professor; e-mail: sm_popescu@hotmail.com; ORCIDiD: https://orcid.org/0000-0003-3011-6322 e DMD, PhD, Professor; e-mail: mcraitoiu@yahoo.com; ORCIDiD: https://orcid.org/0000-0003-4998-8198 f DMD, PhD, Professor; e-mail: daguciluminita@yahoo.com; ORCIDiD: https://orcid.org/0000-0003-4327-2738 g Eng; e-mail: scastravete@caelynx.ro h DMD, PhD; e-mail: marinaamarascu@yahoo.com; ORCIDiD: https://orcid.org/0000-0002-3394-1486 ABSTRACT https://doi.org/10.25241/stomaeduj.2020.7(1).art.4 Introduction This study investigated the distribution and magnitude of stress generated in the enamel of an upper first premolar, after applying normal and excessive occlusal loads in a vertical and horizontal direction, using Finite Element Analysis (FEA). Methodology A 3D virtual model of an upper first premolar was analyzed. The CT images of the tooth were converted into 3D data using the program MIMICS and Finite Element Analysis (FEA) was used for the stress study. To better understand the distribution of stress generated by occlusal loading, the situation of the enamel in various 3D virtual models was presented. 14 scenarios for the occlusal loading of the virtual models of the upper first premolar were obtained and the areas with the highest concentration of stress were emphasized. Results In the model with the tooth intact, stress values were higher than the admissible ones in the simulation of the excessive vertical loading, normal horizontal loading and excessive horizontal loading. Stress was found in the buccal cusp area and in the cervical area, mainly on the buccal side of the tooth. In the models with horizontal occlusal tooth wear, stress values were higher than the admissible ones in the simulation of the excessive vertical loading. Stress was found in the cervical area. In the models with oblique occlusal tooth wear, stress values were higher than the admissible ones in the simulation of the normal and excessive horizontal loading. Stress was found mainly in cervical area, on the buccal side of the tooth. Conclusions The most harmful loads were the heavy vertical ones and the horizontal ones, no matter the magnitude. KEYWORDS Tooth Wear; Finite Element Analysis; Stress, Non-Carious Cervical Lesions. 1. INTRODUCTION [3], and in an advanced stage they can determine endodontic pathology and even the fracture of Non-carious cervical lesions involve the loss of hard the teeth involved [4]. Furthermore, non-carious dental tissues in the cervical areas of the teeth, cervical lesions are important because of their high without carious activity [1,2]. These lesions are prevalence (5-85%) [5]. Initially, the toothbrush/ important because, in a first stage, they can produce dentifrice abrasion was considered to be the cause gingival retractions associated with teeth sensitivity for the loss of dental tissues in the cervical area, as OPEN ACCESS This is an Open Access article under the CC BY-NC 4.0 license. Peer-Reviewed Article Citation: Stănuşi A, Mercuţ V, Scrieciu M, Popescu SM, Iacov Crăiţoiu MM, Dăguci L, Castravete Ş., Amărăscu MO. Analysis of stress generated in the enamel of an upper first premolar: a finite element study. Stoma Edu J. 2020;7(1):28-34. Received: February 20, 2020; Revised: February 26, 2020; Accepted: March 16, 2020; Published: March 18, 2020 *Corresponding author: Prof. Veronica Mercuţ; Prof. Sanda Mihaela Popescu, Faculty of Dentistry, University of Medicine and Pharmacy of Craiova Craiova, Romania Tel./Fax: +40/0251 - 524 442 e-mail: veronica.mercut@yahoo.com; e-mail: sm_popescu@hotmail.com Copyright: © 2020 the Editorial Council for the Stomatology Edu Journal. 28 Stoma Edu J. 2020;7(1):28-34 pISSN 2360-2406; eISSN 2502-0285 Stress analysis in upper premolar enamel – FEA Study www.stomaeduj.com Original Articles Table 1. Dental materials properties. Properties Enamel Dentin Pulp Periodontal ligament Elastic Modulus of Young (GPa) 80.35[32-34] 19.89 [22,23] 0.002 [22] 0.069 [22,23] Poisson Ratio 0.33[32-34] 0.31 [22,23] 0.45 [22] 0.45 [22,23] Table 2. Ultimate tensile and compressive strength of dental enamel. Ultimate Properties Enamel Tensile Strength (MPa) 24 [8] Compressive Strength (MPa) 62 [13] Figure 1. Von Mises Stress in enamel: a) intact premolar; b) horizontal tooth wear version 1; c) horizontal tooth wear version 2. Figure 2. Von Mises Stress in enamel: a) intact premolar; b) horizontal tooth wear version 1; c) horizontal tooth wear version 2. stated by Zsigmondy in 1894 [6]. He described these the non-carious cervical lesions, away from that lesions as being wedge-shaped and distributed point [12]. The effects of stress in teeth depend on on the buccal surface of the upper frontal teeth. the magnitude, direction, frequency, point of force In 1991, Grippo named the non-carious cervical application, but also on the axis of the teeth, their lesions produced by the mechanism of occlusal form, structure and mobility [12,17]. loads as “abfraction lesions”, so that they could be The areas most affected by abfraction lesions are easily differentiated from the erosion and abrasion located on the buccal surfaces of teeth, in the cervical lesions [7]. Recently, a series of studies [7-16] claim zone, with the highest prevalence amongst upper that many factors are involved in the genesis of and lower premolars [8,15,16,18]. Initially, abfraction non-carious cervical lesions: heavy occlusal loads, lesions appear at the enamel-cement junction in the biocorrosion, and abrasion. enamel structure, as a result of reduced thickness of These factors could be encountered individually enamel in that area, the absence of enamel rods and or in association. It was suggested that heavy low frequency of Hunter Schreger Bands [19]. occlusal loads from mastication, swallowing and The aim of this study was to investigate the parafunctional movements determine tooth flexure distribution and magnitude of stress generated and high stress concentration in the cervical area by normal and heavy occlusal loads, which were with the development of enamel cracks. In 2012 directed vertically and horizontally in the enamel of Grippo et al. described the mechanism via which an upper first premolar, using Finite Element Analysis heavy occlusal loads generate stress in the cervical (FEA) and the virtual model from a previous study area [12]. [20]. Finite Element Analysis (FEA) is a numerical Depending on the direction of forces, in the tooth procedure used in dentistry for the simulation of structure there appear forces of compression, various clinical situations, in order to study the tension, flexion and shear, all known as stress, which distribution of stress in the tooth structure and the generate fatigue at the enamel-dentine junction restorative materials, as a result of occlusal loading at the point of force application, and in the case of [21]. Stoma Edu J. 2020;7(1): 28-34 pISSN 2360-2406; eISSN 2502-0285 29 Stănuşi A. et al. www.stomaeduj.com Original Articles Figure 3. Tensile stress in enamel: a) intact premolar; b) lateral tooth wear version 1; c) lateral tooth wear version 2; d) lateral tooth wear version 3. Figure 4. Compressive stress in enamel: a) intact premolar; b) lateral tooth wear version 1; c) lateral tooth wear version 2; d) lateral tooth wear version 3. 2. MATERIAL AND METHODS normal horizontal load (F=180 N) and an excessive horizontal load (F=532 N) [35] were applied on the The 3D virtual model of the upper first premolar was virtual model with the intact premolar and on the made using the CT images of a 14 year-old patient three models with oblique occlusal tooth wear, [20]. The CT images were converted into 3D data there resulting eight scenarios for the horizontal using the MIMICS program (Materialise NV, Leuven, occlusal loading. The study was approved by the Belgium, 1992) and the 3D virtual model obtained Ethics Committee of the Faculty of Dental Medicine was analysed using Finite Element Analysis (FEA) of University of Medicine and Pharmacy of Craiova and the Abaqus/CAE program (ABAQUS Software, (no. 257/12.10.2019). An informed consent for using S.A.R.L., Versailles, France, 1994). The 3D virtual model the CT was obtained from the patient. consisted of all the tissues of the given premolar: enamel, dentine, pulp and periodontal ligament. The 3. RESULTS alveolar bone was reconstructed as a parallelepiped, to which the tooth was not rigidly fixed, and between In the simulations with horizontal occlusal tooth these two structures the periodontal ligament wear the Von Mises Stress, which is a combination was simulated. The finite element model was a 3D of compressive, tensile and shear stress, the model with tetrahedral elements resulting in 47548 compressive stress was dominant. In the simulations elements and 68504 nodes. The average size of an with oblique occlusal tooth wear, the dominant element was approximately 0.5 mm per surface. stress was both compressive (Min Principal Stress, For the elastic modulus of Young and Poisson’s ratio the maximum values are negative) and tensile (Max of the dental tissues, data from the literature were Principal Stress, the maximum values are negative). used as shown in Table 1. The values obtained for the tensions generated in enamel were compared to the a - Simulation of normal vertical load, F=180 N ultimate values of tensile and compressive strength In the simulation of a normal vertical loading for enamel used in other studies (Table 2) [8,13]. (F=180 N), in the model with the intact premolar, a To better understand the distribution of stress compressive stress higher than 62 MPa, located in generated by occlusal loading, the situation of the superficial layer of enamel, at the buccal cusp enamel in various 3D virtual models was presented. was observed (Fig. 1a). In the models with horizontal A virtual model of the upper first premolar with no occlusal tooth wear, the values of compressive stress lesion was used to create five more models with were lower. The highest ones were found in the different degrees of occlusal tooth wear. T palatal cervical area, but they did not exceed 62MPa he occlusal tooth wear models used in this study (Fig. 1 b, c). represent simulations of some clinical conditions encountered in clinical practice as a consequence b - Simulation of excessive vertical load, F=532 N of the occlusal load in static mandibular position In the simulation of an excessive vertical loading (occlusal horizontal tooth wear) - 2 models, and (F=532 N), in all models, the compressive stress was the occlusal load in lateral movements of the jaw higher than 62 MPa (Fig. 2 a, b, c), the maximum (oblique occlusal tooth wear) -3 models. Using these value being found in the model with the intact models, various scenarios emerged for the occlusal premolar (Fig. 2a). Regarding the distribution of the loading applied as a flat surface of a block, in a compressive stress in enamel, in the model with the vertical and horizontal direction. A normal vertical intact premolar, it was located at the buccal cusp load (F=180 N) and an excessive vertical load (F=532 affecting the whole enamel layer and in the cervical N) [24] were applied on the virtual model with area (Fig. 2a). In the models with horizontal occlusal the intact premolar and on the two models with tooth wear, the maximum values for the compressive horizontal occlusal tooth wear, there resulting six stress were located in the cervical area of the enamel scenarios for the vertical occlusal loading. Also, a (Fig. 2 b, c). 30 Stoma Edu J. 2020;7(1):28-34 pISSN 2360-2406; eISSN 2502-0285 Stress analysis in upper premolar enamel – FEA Study www.stomaeduj.com Original Articles Figure 5. Tensile stress in enamel: a) intact premolar; b) lateral tooth wear version 1; c) lateral tooth wear version 2; d) lateral tooth wear version 3. Figure 6. Compressive stress in enamel: a) intact premolar; b) lateral tooth wear version 1; c) lateral tooth wear version 2; d) lateral tooth wear version 3. c - Simulation of normal horizontal load, F=180 N occlusal tooth wear, the stress values were higher In the simulation of normal horizontal loading than the admissible ones in the simulation of the (F=180 N), in the model with the intact premolar, the normal and excessive horizontal loading. The stress tensile stress (Max Principal Stress) exceeded 24 MPa was found mainly in cervical area, on the buccal in the occlusal area and in the cervical lingual distal side of the tooth. The most harmful forces were the area (Fig. 3a). In the models with oblique occlusal excessive vertical ones and the horizontal ones, no tooth wear, the highest values for the tensile stress matter the magnitude. were found at the palatal cusp (Fig. 3 b, c, d). 4. DISCUSSIONS The values for the compressive stress generated exceeded 62 MPa in the buccal cervical area and in the This study aimed to analyse the distribution and occlusal area in the model with the intact premolar magnitude of stress generated by normal (F=180 (Fig. 4a). In the models with oblique occlusal tooth N) and excessive (F=532 N) occlusal loads, directed wear, these small values for the compressive stress vertically and horizontally. The stress obtained repre- were found at the palatal cusp and in the cervical sents the effect of the cumulative action of the palate-distal area (Fig. 4 b, c, d). compressive and tensile stress in the dental tissues. For this study, a 3D virtual model of an upper first d - Simulation of excessive horizontal load, F=532 N premolar was used. Clinical experience and data from In the simulation of an excessive horizontal loading the literature [8,16,18] showed that the upper first (F=532 N) in the model with the intact premolar, the premolar had a great susceptibility towards abfra- tensile stress (Max Principal Stress) exceeded 24 MPa ction lesions. Meanwhile, its form and the way the in the occlusal area and in the cervical disto- linguo- occlusal forces are distributed in its structure make mesial area (Fig. 5a). In the models with oblique it liable for fractures. For the conversion of the CT occlusal tooth wear, these high values for the tensile images into 3D data the MIMICS program (Materialise stress were found in the occlusal and palatal area NV, Leuven, Belgium, 1992) was used as it was used in and less in the cervical area (Fig. 5 b, c, d). The values prior studies [20, 25-27]. For the stress analysis Finite for the compressive stress (Min Principal Stress) Element Analysis (FEA) was applied as it was used in generated exceeded 62 MPa in the occlusal area and prior studies [28-39]. A similar study was performed in the cervical buccal area in the model with the intact by Lee et al. in 2002 [8], also using the Finite Element premolar (Fig. 6a). In the models with oblique occlusal Analysis (FEA) in which a normal vertical force (F=170 tooth wear, these small values for the compressive N) was applied at the buccal cusp of an upper second stress were found in the occlusal and palatal area, premolar. The highest value of the tensile stress was towards the distal part of the tooth (Fig. 6 b, c, d). observed in the cervical area, namely 13.55 MPa [8]. 14 scenarios for the occlusal loading of the virtual In our study, for the normal vertical force of 180 N, models of the upper first premolar were obtained the values for the Von Mises Stress in the cervical and the areas with the highest concentration of area were around 10-15 MPa. The results of our stress were enhanced. In the model with the tooth study are similar to those found by Lee et al in their intact, the stress values were higher than the admi- study in 2002 [8]. In both studies the value of the ssible ones in the simulation of the excessive vertical tensile stress obtained in the cervical area was lower loading, normal horizontal loading and exce- than the admissible one. In 2003, Rees and Jagger ssive horizontal loading. Stress was found in the [5] performed a study using the Finite Element buccal cusp area and in the cervical area, mainly Analysis (FEA) in order to find an explanation for on the buccal side of the tooth. In the models with the high prevalence of non-carious cervical lesions horizontal occlusal tooth wear, the stress values were in maxillary teeth. In that study they used three 2D higher than the admissible ones in the simulation of models, representing an upper incisive, upper canine the excessive vertical loading. The stress was found and upper premolar and through the Finite Element in the cervical area. In the models with oblique Analysis (FEA) recorded the magnitude of stress in Stoma Edu J. 2020;7(1): 28-34 pISSN 2360-2406; eISSN 2502-0285 31 Stănuşi A. et al. www.stomaeduj.com the cervical area, obtained after applying a force of between bruxism and non-carious cervical lesions Original Articles 500 N. In the case of the upper premolar, force was [42]. In 2017, Duangthip et al. [47] performed a applied at the buccal cusp and angulated 45 degrees review to search for correlations between excessive in a buccal and apical direction. They recorded the occlusal loads and abfraction lesions and found such tensile stress and compared the values obtained on an association in 81% of cases. the buccal surfaces with the ones obtained on the palatal surfaces. The values obtained were similar. 5. CONCLUSIONS Our study had results in accordance with the results obtained in the Rees and Jagger study. However, This study showed the distribution and magnitude practice has proven that abfraction lesions were of stress obtained in the virtual 3D model of an upper rarely found on the palatal surfaces of the teeth first premolar, after applying normal and excessive, [5] and this phenomenon could be correlated with vertical and horizontal forces. The most harmful stress corrosion, meaning that the association forces were the excessive vertical ones and the between stress and acidic substances cause more horizontal ones, no matter the magnitude. Regarding lesions than if these factors act alone. Acidic the tooth morphology, the least favourable models substances are removed by saliva from the palatal for the distribution of stress were the ones with the surfaces of teeth 6 times more rapidly than the ones intact premolar and with lateral tooth wear. located on the buccal surfaces [5]. Furthermore, the In current practice, these situations are found in the enamel affected by demineralization can regain its case of occlusal interferences, parafunctions and mechanical resistance as a result of the action of bruxism. different substances and even saliva [14]. Clinically, these excessive forces or the ones with a horizontal CONFLICT OF INTEREST direction can be identified in the case of occlusal interferences [39-41], any other clinical situation The authors declare no conflict of interest. that modifies occlusion, such as parafunctions, bruxism [42,43] and treatment procedures [44,45]. AUTHOR CONTRIBUTIONS Other studies have tried to find evidence for the AS, VM: Concept, protocol, manuscript writing; causal relationship between occlusion and non- MS, SMP, MMIC, LD, AMO: Manuscript writing, critical review of carious cervical lesions [41,46]. In these studies, manuscript; SC: concept, data entry, data analysis, critical review the presence of non-carious cervical lesions was of manuscript. associated with the presence of occlusal wear ACKNOWLEDGMENTS facets. If excessive occlusal forces can cause non- carious cervical lesions, it would be expected that Acknowledge persons who have made substan- parafunctional habits such as bruxism and clenching tive contributions to the study. Specify grant or other financial support, citing the name of the supporting organization would increase the progression of non-carious and grant number. cervical lesions. Two studies reported a correlation REFERENCES 1. LittleStar ML, Summit JB. Non-carious cervical lesions: 8. Lee HE, Lin CL, Wang CH, et al. Stresses at the cervical lesion an evidence-based approach to their diagnosis. Tex Dent J. of maxillary premolar--a finite element investigation. J Dent. 2003;120(10):972-980. 2002;30(7-8):283-290. [PubMed] Google Scholar Scopus [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus 2. Michael JA, Townsend GC, Greenwood LF, Kaidonis JA. 9. Grippo JO, Simring M, Schreiner S. Attrition, abrasion, corrosion Abfraction: separating fact from fiction. Aust Dent J. 2009;54(1):2-8. and abfraction revisited: a new perspective on tooth surface [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus lesions [published correction appears in J Am Dent Assoc. 2004 3. Lafzi A, Abolfazli N, Eskandari A. Assessment of the etiologic Oct;135(10):1376]. J Am Dent Assoc. 2004;135(8):1109–1165. factors of gingival recession in a group of patients in Northwest [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus Iran. J Dent Res Dent Clin Dent Prospects. 2009;3(3):90-93. 10. Addy M, Shellis RP. Interaction between attrition, abrasion and doi:10.5681/joddd.2009.023. erosion in tooth wear. Monogr Oral Sci. 2006;20:17-31. [Full text links] [PubMed] Google Scholar [Full text links] [CrossRef ] Google Scholar Scopus 4. Pereira FA, Zeola LF, de Almeida Milito G, et al. Restorative 11. Borcić J, Antonić R, Urek MM, et al. 3-D stress analysis in first material and loading type influence on the biomechanical maxillary premolar. Coll Antropol. 2007;31(4):1025-1029. behavior of wedge shaped cervical lesions. Clin Oral Investig. [Full text links] [PubMed] Google Scholar Scopus 2016;20(3):433-441. 12. Grippo JO, Simring M, Coleman TA. Abfraction, abrasion, [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus biocorrosion, and the enigma of noncarious cervical lesions: a 20- 5. Rees JS, Jagger DC. Abfraction lesions: myth or reality? J Esthet year perspective. J Esthet Restor Dent. 2012;24(1):10-23. Restor Dent. 2003;15(5):263-271. [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus [Full text link] [CrossRef ] [PubMed] Google Scholar Scopus 13. Chun K, Choi H, Lee J. Comparison of mechanical property 6. Zsigmondy U. [About the wedge-shaped defects on the facial and role between enamel and dentin in the human teeth. J Dent surfaces of the Zajn necks]. [Article in German]. Österr Ungar Biomech. 2014;5:1758736014520809. Vjhrschr Zahnärzte. 1894;1:439-442. [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus [Full text links] 14. Shellis RP, Addy M. The interactions between attrition, abrasion 7. Konagala RK, Mandava J, Anupreeta A, et al. The “Abfraction and erosion in tooth wear. Monogr Oral Sci. 2014;25:32-45. - Paradox” - A literature review on biomechanics, diagnosis and [CrossRef ] [PubMed] Google Scholar Scopus management. Int J Sci Res (Ahmedabad). 2018;7(6):46-49. 15. Nascimento MM, Dilbone DA, Pereira PN, et al. Abfraction [Full text links] lesions: etiology, diagnosis, and treatment options. Clin Cosmet 32 Stoma Edu J. 2020;7(1):28-34 pISSN 2360-2406; eISSN 2502-0285 Stress analysis in upper premolar enamel – FEA Study www.stomaeduj.com Investig Dent. 2016;8:79-87. 32. De Jager N, de Kler M, van der Zel JM. The influence of different Original Articles [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus core material on the FEA-determined stress distribution in dental 16. El-Marakby AM, Al-Sabri FA, Alharbi SA, et al. Noncarious crowns. Dent Mater. 2006;22(3):234-242. cervical lesions as abfraction: etiology, diagnosis, and treatment [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus modalities of lesions: a review article. Dentistry. 2017;7(6):438. 33. Ateş M, Cilingir A, Sülün T, et al. The effect of occlusal contact [CrossRef ] Google Scholar localization on the stress distribution in complete maxillary 17. Kuroe T, Caputo AA, Ohata N, Itoh H. Biomechanical effects of denture. J Oral Rehabil. 2006;33(7):509-513. cervical lesions and restoration on periodontally compromised [Full text links] [CrossRef ] Google Scholar Scopus teeth. Quintessence Int. 2001;32(2):111-118. 34. Hattori Y, Satoh C, Kunieda T, et al. Bite forces and their [PubMed] Google Scholar Scopus resultants during forceful intercuspal clenching in humans. J 18. Bader ID, Shugars DA. Variation in clinical decision making Biomech. 2009;42(10):1533-1538. related to caries. In: Fejerskov O, Kidd EAM, editors. Dental caries: [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus the disease and its clinical management. 2nd ed. Oxford, UK: Blackwell Munksgaard Ltd; 2008. 35. Coelho PG, Silva NR, Thompson VP, et al. Effect of proximal 19. Lynch CD, O’Sullivan VR, Dockery P, et al. Hunter-Schreger Band wall height on all-ceramic crown core stress distribution: a finite patterns in human tooth enamel. J Anat. 2010;217(2):106-115. element analysis study. Int J Prosthodont. 2009;22(1):78-86. [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus [PubMed] Google Scholar Scopus 20. Stănuşi A, Mercuţ V, Scrieciu M, et al. Effects of occlusal loads 36. Fu G, Deng F, Wang L, Ren A. The three-dimension finite in the genesis of non-carious cervical lesions – a finite element element analysis of stress in posterior tooth residual root restored study. Romanian Journal of Oral Rehabilitation. 2019;11(1):73-81. with postcore crown. Dent Traumatol. 2010;26(1):64-69. Google Scholar [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus 21. Zeola LF, Pereira FA, Galvão AdaM, et al. Influence of non 37. Jiang W, Bo H, Yongchun G, LongXing N. Stress distribution in carious cervical lesions depth, loading point application and molars restored with inlays or onlays with or without endodontic restoration on stress distribution pattern in lower premolars: a 2D treatment: a three-dimensional finite element analysis. J Prosthet finite element analysis. Biosci J. 2015;31(2):648-656. Dent. 2010;103(1):6-12. Google Scholar Scopus [CrossRef ] Google Scholar Scopus 22. Gurbuz T, Sengul F, Altun C. Finite element stress analysis of 38. Hasegawa A, Shinya A, Nakasone Y, et al. Development short-post core and over restorations prepared with different of 3D CAD/FEM analysis system for natural teeth and jaw restorative materials. Dent Mater J. 2008;27(4):499-507. bone constructed from X-Ray CT images. Int J Biomater. [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus 2010;2010:659802. 23. Munari LS, Cornacchia TP, Moreira AN, et al. Stress distribution [Full text links] [CrossRef ] Google Scholar in a premolar 3D model with anisotropic and isotropic enamel. 39. Brandini DA, Trevisan CL, Panzarini SR, Pedrini D. Clinical Med Biol Eng Comput. 2015;53(8):751-758. evaluation of the association between noncarious cervical lesions [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus and occlusal forces. J Prosthet Dent. 2012;108(5):298-303. 24. Larson TD. The effect of occlusal forces on restorations. J Mich [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus Dent Assoc. 2014;96(9):38-47. 40. Brandini DA, Pedrini D, Panzarini SR, et al. Clinical evaluation [PubMed] Google Scholar of the association of noncarious cervical lesions, parafunctional 25. Huang Z, Chen Z. Three-dimensional finite element modeling habits, and TMD diagnosis. Quintessence Int. 2012;43(3):255-262. of a maxillary premolar tooth based on the micro-CT scanning: [Full text links] [PubMed] Google Scholar Scopus a detailed description. J Huazhong Univ Sci Technolog Med Sci. 41. Wood ID, Kassir AS, Brunton PA. Effect of lateral excursive 2013;33(5):775-779. movements on the progression of abfraction lesions. Oper Dent. [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus 2009;34(3):273-279. 26. Sang YH, Hu HC, Lu SH, et al. Accuracy assessment of [FullTextLink] [CrossRef ] [PubMed] Google Scholar Scopus three-dimensional surface reconstructions of in vivo teeth 42. Ommerborn MA, Schneider C, Giraki M, et al. In vivo evaluation from cone-beam computed tomography. Chin Med J (Engl). of noncarious cervical lesions in sleep bruxism subjects. J Prosthet 2016;129(12):1464-1470. Dent. 2007;98(2):150-158. [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus 27. Vătu M, Crăițoiu MM, Vintilă D, et al. Determination of 43. Antonelli JR, Hottel TL, Garcia-Godoy F. Abfraction lesions-- resistance forces from mandibular movements through where do they come from? A review of the literature. J Tenn Dent dynamic simulation using kinematic analysis and finite Assoc. 2013;93(1):14-21. elements method. Romanian Journal of Oral Rehabilitation. [PubMed] Google Scholar 2018;10(1):20-28. 44. Bernhardt O, Gesch D, Schwahn C, et al. Epidemiological Google Scholar evaluation of the multifactorial aetiology of abfractions. J Oral 28. Palamara JE, Palamara D, Messer HH. Strains in the marginal Rehabil. 2006;33(1):17-25. ridge during occlusal loading. Aust Dent J. 2002;47(3):218-222. [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus 45. Vasudeva G, Bogra P. The effect of occlusal restoration and 29. Nishigawa G, Matsunaga T, Maruo Y, et al. Finite element loading on the development of abfraction lesions: A finite analysis of the effect of the bucco-lingual position of artificial element study. J Conserv Dent. 2008;11(3):117-120. posterior teeth under occlusal force on the denture supporting [Full text links] [CrossRef ] [PubMed] Google Scholar bone of the edentulous patient. J Oral Rehabil. 2003;30(6):646- 46. Telles D, Pegoraro LF, Pereira JC. Incidence of noncarious 652. cervical lesions and their relation to the presence of wear facets. J [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus Esthet Restor Dent. 2006;18(4):178-184. 30. Dejak B, Młotkowski A, Romanowicz M. Finite element analysis [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus of stresses in molars during clenching and mastication. J Prosthet 47. Duangthip D, Man A, Poon PH, et al. Occlusal stress is involved Dent. 2003;90(6):591-597. in the formation of non-carious cervical lesions. A systematic [Full text links] [CrossRef ] [PubMed] Google Scholar review of abfraction. Am J Dent. 2017;30(4):212-220. 31. De Jager N, Pallav P, Feilzer AJ. The influence of design [Full text links] [PubMed] Google Scholar Scopus parameters on the FEA-determined stress distribution in CAD- CAM produced all-ceramic dental crowns. Dent Mater. 2005;21(3):242-251. [Full text links] [CrossRef ] [PubMed] Google Scholar Scopus Stoma Edu J. 2020;7(1): 28-34 pISSN 2360-2406; eISSN 2502-0285 33 Stănuşi A. et al. www.stomaeduj.com Original Articles Andreea STĂNUŞI DMD, PhD Student, Prosthodontic Medical Resident Department of Proshodontics Faculty of Dentistry University of Medicine and Pharmacy of Craiova Craiova, Romania CV Andreea Stănuşi (DOB: September 22, 1992) graduated from the Faculty of Dentistry, University of Medicine and Pharmacy of Craiova in 2017 and became Medical Resident in Prosthodontics. As a student, she held various positions: President of the Craiova Stomatology Students Society (2013-2014), Member of the Faculty Council (2016-2017), Member of the University Senate (2016-2017). As a postgraduate her activity is still connected with the academic life. In 2017 she became a PhD student under the guidance of University Professor Veronica Mercuț, her research interest being the etiology and treatment of tooth wear. In 2019 she published the results of an experiment in which the stress involved in the etiology of tooth wear was examined (“Effects of occlusal loads in the genesis of non-carious cervical lesions – a Finite Element Study”). Questions 1. Non-carious cervical lesions can produce in a first stage: qa. endodontic pathology; qb. gingival retractions associated with teeth sensitivity; qc. fracture of the teeth involved; qd. periodontal pockets. 2. The areas most affected by abfraction lesions are located on: qa. enhanced thickness of enamel in that area; qb. reduced thickness of dentine in that area; qc. the high frequency of Hunter Schreger Bands; qd. the low frequency of Hunter Schreger Bands. 3. Abfraction lesions appear at the enamel-cement junction in the enamel structure, as a result of: qa. less than 20% in the three groups with no statistical difference among groups; qb. over 10% in the three groups with no statistical difference among groups; qc. over 80% in the three groups with no statistical difference among groups; qd. less than 10% in the three groups with no statistical difference among groups. 4. The excessive forces or the ones with a horizontal direction involved in the etiology of NCCL, can be identified in the following clinical situations apart from: qa.occlusal interferences; qb. parafunctions; qc. bruxism; qd. procedures that do not modify occlusion. 34 Stoma Edu J. 2020;7(1):28-34 pISSN 2360-2406; eISSN 2502-0285