A Novel Mandibular Advancement Device for Treatment of Sleep-Disordered Breathing: Evaluation of Its Biomechanical Eﬀects Using Finite Element Analysis

applied sciences

Article A Novel Mandibular Advancement Device for Treatment of Sleep-Disordered Breathing: Evaluation of Its Biomechanical Eﬀects Using Finite Element Analysis

Jonghun Yoon 1, Sang Hwa Lee 2, Yuhyeong Jeong 3, Dong-Hyun Kim 4,* , Hyun-Il Shin 4 and So Yun Lim 4

1 Department of Mechanical Engineering, Hanyang University, 55 Hanyangdaehak-ro, Sangnok-gu, Ansan-si, Gyeonggi-do 15588, Korea; [email protected] 2 Department of Dentistry, Eunpyeong St. Mary’s Hospital, College of medicine, the Catholic University of Korea, 1021 Tongil-ro, Eunpyeong-gu, Seoul 03312, Korea; [email protected] 3 Department of Mechanical Design Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Korea; [email protected] 4 Department of Otorhinolaryngology-Head and Neck Surgery, Incheon St. Mary’s Hospital, College of medicine, the Catholic University of Korea, Incheon 21431, Korea; [email protected] (H.-I.S.); [email protected] (S.Y.L.) * Correspondence: [email protected]; Tel.: +82-32-280-5151

Received: 2 June 2020; Accepted: 24 June 2020; Published: 27 June 2020

Abstract: Stress or pressure induced by the use of a mandibular advancement device (MAD) to treat sleep-disordered breathing can cause side effects including occlusal changes, pain, and discomfort. In this paper, we describe and use finite element (FE) analysis to evaluate a novel MAD that can reduce the stress and side effects associated with these devices. The MAD includes a protruding part that enables rostral movement of the lower tray, providing a wider upper airway and a supporting shield that helps uniformly distribute the concentrated stress. After assembling the three-dimensional model for the MAD and the upper oral structures, a designated force was applied to evaluate the stress distributions of a conventional MAD and the proposed design. FE analysis showed that the stress applied to the upper front teeth and the gingival area near the upper incisors differed between the newly developed and conventional MAD. Concentrated stress was relieved by inserting such a shield, helping to distribute the stress from the front teeth to the gingival area. Our proposed MAD reduced the concentrated stress on the front teeth by distributing it over the gingival area.

Keywords: ﬁnite element analysis; mandibular advancement device; sleep-disordered breathing

1. Introduction Sleep-disordered breathing (SDB), including snoring and sleep apnea, tends to be induced by narrow upper airways and collapse of the throat. It results in daytime sleepiness, neurocognitive impairment, cardiovascular and metabolic disorders, and severe functional impairment that can even cause traffic accidents [1,2]. Although continuous positive airway pressure (CPAP) therapy devices are highly effective for treating SDB by utilizing air pressure to maintain the upper airway, there are several issues such as adaptation and compliance problems as well as the risk of iatrogenic pneumothorax [3]. A mandibular advancement device (MAD) is a superior alternative to CPAPs for patients suffering from SDB because they mainly act by expanding the upper airway. MADs push the mandible forward, which pulls up the oropharyngeal wall and keeps the airway open, thereby making breathing easier while

Appl. Sci. 2020, 10, 4430; doi:10.3390/app10134430 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, 4430 2 of 7 asleep. Cephalometric and radiographic analysis revealed that the retropharyngeal air space increased after MAD use [4].MADs are also effective in increasing the tension around the oropharyngeal area, which reduces its collapsibility [5,6]. MADs are simple, easy to use, and convenient because they do not require surgery and thus eliminate the need to control postoperative pain and surgical side effects. However, the patient must wear the MAD every night to reduce the symptoms of SDB. According to previous studies [3,7,8], pain in the teeth and gingiva is one of the main factors in patient unwillingness to continue using an MAD. In addition, one of the most important side effects of MAD use are occlusal change following long-term treatment [9–11]. Therefore, to improve patient compliance, it is important to design an MAD that minimizes discomfort or pain by avoiding such side effects [12]. Stress analysis can provide useful information to control MAD-induced discomfort and prevent occlusal or mandibular changes after long-term treatments. Finite element (FE) analysis is a mathematical method that uses computation to predict approximate values in a physical system that is highly susceptible to external factors. Recent studies have reported the use of FE analysis for dental braces, but such use for the evaluation of MAD-induced stress has yet to be explored [13,14]. Therefore, the purpose of this study was to propose a novel MAD design to distribute stress among the teeth and gingiva and to use FE analysis to show positive outcomes such as a reduced risk of occlusal change and relief from discomfort. To carry out the optimized design, FE analysis was adopted to analyze the modeled stress distribution between a conventional MAD and the newly proposed design.

2. Materials and Methods

2.1. Proposal for a New Mandibular Advancement Device Figure1a demonstrates a conventional MAD design consisting of upper and lower trays with an elastic strap connecting the two [15]. When a patient wears this device, the elastic strap obliquely connects the upper and lower trays, resulting in lower tray protrusion to prevent airway closure. Although conventional MADs have their merits, such as low cost and easy attachment, they tend to concentrate stress on the upper dentition. Because of this design, orthodontic side eﬀects such as occlusal changes have been reported [7,9,16]. Furthermore, once the MAD is installed, the patient tends to feel discomfort because it does not allow even the slightest of movements. To resolve these disadvantages, we propose a new type of MAD (Figure1b) that consists of new components for the upper tray: a supporting shield, which helps to distribute the stress along the upper dentition, and a protruding part to maintain the lower tray in the protruded position (Figure2). In addition, the supporting shield made of a soft biocompatible material diﬀerent from the hard tray materials serves to minimize damage to the upper gingiva. The trays are connected with several elastic springs through hooks (Figure1b). Because the upper and lower trays are installed separately and then connected with springs, the patient is more likely to experience comfort during attachment and detachment. Furthermore, with the proposed MAD in place, the specially designed springs allow slight movements,

Appl.providing Sci. 2020 more, 10, x FOR comfort PEER andREVIEW guaranteeing a superior compliance rate. 3 of 7

FigureFigure 1. MandibularMandibular advanced advanced device device (MAD): (MAD): (a (a) )conventional conventional type type and and ( (bb)) prototype prototype of of the the proposed MAD.

Figure 2. Mechanism of the proposed MAD: (a) initial state and (b) mechanism blocking protrusion.

2.2. Finite Element Analysis for the Newly Proposed Mandibular Advancement Device To validate the stress distribution induced by the proposed MAD, FE analysis was conducted using the commercial FE package, ABAQUS/Explicit [17]. Based on laser scanning data, three- dimensional modeling for the upper dentition and MAD was conducted using HyperMesh (Figure 3a and Figure 3b) [18]. The material properties of the upper dentition, including the gingival area, were assumed to have the average physical properties of teeth and gingiva, and the MAD was assumed to have the properties of standard plastic [19–21]. Table 1 summarizes the material properties for the FE analysis. Because the MAD is assumed to maintain the mandible at 60–70% of the maximal advancement position, the mandible protruded by the MAD is subjected to an external force for returning to the original position (Figure 3c) [22]. To analyze the stress at the upper tooth and gingival area caused by this external force, a force boundary condition of 2.5 N was applied along the Z-direction [23]. The FE analysis results between the conventional and the newly proposed MAD were compared in terms of stress distribution to ensure the effect of the supporting shield on the upper dentition and gingival area.

Figure 3. Finite element (FE) modeling of MAD with upper dentition: (a) conventional, (b) proposed, and (c) boundary condition.

Table 1. Material properties of MAD, upper dentition, and gingiva.

Number of Young’s Modulus Poisson’s Part Element Type Elements (MPa) Ratio MAD Tetrahedron 169,624 700,000 0.30 Upper dentition Tetrahedron 38,660 18,000 0.30 Gingiva Tetrahedron 130,964 9,009 0.03

Appl. Sci. 2020, 10, x; doi: FOR PEER REVIEW www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, x FOR PEER REVIEW 3 of 7 Appl. Sci. 2020, 10, x FOR PEER REVIEW 3 of 7

Figure 1. Mandibular advanced device (MAD): (a) conventional type and (b) prototype of the Appl. Sci.Figureproposed2020 ,1.10 MAD.,Mandibular 4430 advanced device (MAD): (a) conventional type and (b) prototype of the 3 of 7 proposed MAD.

Figure 2. Mechanism of the proposed MAD: (a) initial state and (b) mechanism blocking protrusion. FigureFigure 2. 2. MechanismMechanism of of the the proposed proposed MAD: MAD: ( (aa)) initial initial state state and and ( (b)) mechanism mechanism blocking blocking protrusion. protrusion. 2.2. Finite Element Analysis for the Newly Proposed Mandibular Advancement Device 2.2. Finite Element Analysis for the Newly Proposed Mandibular Advancement Device 2.2. FiniteTo validate Element the Analysis stress fordistribution the Newly Proposedinduced Mandibularby the proposed Advancement MAD, FEDevice analysis was conducted To validate the stress distribution induced by the proposed MAD, FE analysis was conducted using usingTo the validate commercial the stress FE distributionpackage, ABAQUS/Explicit induced by the proposed[17]. Based MAD, on laserFE analysis scanning was data, conducted three- the commercial FE package, ABAQUS/Explicit [17]. Based on laser scanning data, three-dimensional usingdimensional the commercial modeling forFE thepackage, upper ABAQUS/Explicitdentition and MAD [17]. was Based conducted on laser using scanning HyperMesh data, (Figure three- modeling for the upper dentition and MAD was conducted using HyperMesh (Figure3a,b) [ 18]. dimensional3a and Figure modeling 3b) [18]. forThe the material upper propertiesdentition and of theMAD upper was dentition, conducted including using HyperMesh the gingival (Figure area, The material properties of the upper dentition, including the gingival area, were assumed to have the 3awere and assumed Figure 3b) to [18].have Thethe materialaverage propertiesphysical prop of theerties upper of teethdentition, and gingiva,including and the the gingival MAD area,was average physical properties of teeth and gingiva, and the MAD was assumed to have the properties wereassumed assumed to have to havethe propertiesthe average of physicalstandard prop plasticerties [19–21]. of teeth Table and gingiva,1 summarizes and the the MAD material was of standard plastic [19–21]. Table1 summarizes the material properties for the FE analysis. Because assumedproperties to for have the FEthe analysis. properties Because of standard the MAD plastic is assumed [19–21]. to maintainTable 1 thesummarizes mandible theat 60–70% material of the MAD is assumed to maintain the mandible at 60–70% of the maximal advancement position, propertiesthe maximal for advancement the FE analysis. position, Because the the mandible MAD is prot assumedruded toby maintainthe MAD the is subjected mandible to at an 60–70% external of the mandible protruded by the MAD is subjected to an external force for returning to the original theforce maximal for returning advancement to the original position, position the mandible (Figure prot 3c) ruded[22]. To by analyze the MAD the is stress subjected at the to upper an external tooth position (Figure3c) [ 22]. To analyze the stress at the upper tooth and gingival area caused by this forceand gingival for returning area caused to the by original this external position force, (Figure a force 3c) boundary [22]. To analyze condition the of stress 2.5 N atwas the applied upper alongtooth external force, a force boundary condition of 2.5 N was applied along the Z-direction [23]. The FE andthe Z-direction gingival area [23]. caused The FEby analysisthis external results force, betw a forceeen the boundary conventional condition and ofthe 2.5 newly N was proposed applied alongMAD analysis results between the conventional and the newly proposed MAD were compared in terms of thewere Z-direction compared [23]. in terms The FE of analysis stress distribution results betw toeen ensure the conventional the effect of and the the supporting newly proposed shield on MAD the stress distribution to ensure the eﬀect of the supporting shield on the upper dentition and gingival area. wereupper compared dentition andin terms gingival of stress area. distribution to ensure the effect of the supporting shield on the upper dentition and gingival area.

Figure 3. Finite element (FE) modeling of MAD with upper dentition: (a) conventional, (b) proposed, Figure 3. Finite element (FE) modeling of MAD with upper dentition: (a) conventional, (b) proposed, and (c) boundary condition. Figureand (c) 3.boundary Finite element condition. (FE) modeling of MAD with upper dentition: (a) conventional, (b) proposed, and (c) boundaryTable condition. 1. Material properties of MAD, upper dentition, and gingiva. Table 1. Material properties of MAD, upper dentition, and gingiva. Number of Young’s Modulus PartTable 1. Element Material Type properties of MAD, upper dentition, and gingiva.Poisson’s Ratio ElementsNumber of (MPa)Young’s Modulus Poisson’s Part Element Type MAD Tetrahedron 169,624NumberElements of 700,000Young’s(MPa) Modulus 0.30 Poisson’sRatio Part Element Type MADUpper dentitionTetrahedron Tetrahedron 38,660Elements169,624 18,000700,000(MPa) 0.30 Ratio 0.30 UpperMAD dentitionGingiva Tetrahedron Tetrahedron 130,964169,624 38,660 9,009700,000 18,000 0.03 0.30 6 UpperGingiva dentitionMAD: mandibular Tetrahedronadvancement device; MPa: megapascal,130,964 38,660 unit of pressure 18,000 9,009 equal to 10 pascals. 0.300.03 Gingiva Tetrahedron 130,964 9,009 0.03 Appl.3. Results Sci. 2020, 10, x; doi: FOR PEER REVIEW www.mdpi.com/journal/applsci Appl. Sci.The 2020 stress, 10, x; distribution doi: FOR PEERof REVIEW the FE analysis comparing the conventional www.mdpi.com/journal/applsci and proposed MAD is shown in Figure4. We used FE analysis based on four data points over the front teeth (a–d) and two data points over the gingiva (e and f) to compare the stress distribution (Figure5). The mean stress and standard deviation of the proposed MAD were lower than in the conventional MAD. The stress level at points “a” to “e” in the proposed MAD decreased substantially to 17% from 53% in the conventional MAD. However, stress distribution induced by the proposed MAD around the gingival area increased to 173% compared with the conventional MAD at point “f” because the supporting shield tended to distribute the concentrated force to the gingival area (Table2). Appl. Sci. 2020, 10, x FOR PEER REVIEW 4 of 7 Appl. Sci. 2020, 10, x FOR PEER REVIEW 4 of 7 MAD: mandibular advancement device; MPa: megapascal, unit of pressure equal to 106 pascals. MAD: mandibular advancement device; MPa: megapascal, unit of pressure equal to 106 pascals. 3. Results 3. Results The stress distribution of the FE analysis comparing the conventional and proposed MAD is shownThe in Figurestress distribution4. We used FEof theanalysis FE analysis based onco mparingfour data the points conventional over the frontand proposedteeth (a–d) MAD and twois datashown points in Figure over the4. We gingiva used FE(e andanalysis f) to based compare on four the datastress points distribution over the (Figure front teeth 5). The (a–d) mean and twostress anddata standard points over deviation the gingiva of the (e prop andosed f) to MADcompare were the lower stress than distribution in the conventional (Figure 5). The MAD. mean The stress stress leveland standardat points deviation “a” to “e” of thein the prop proposedosed MAD MAD were decreased lower than substantially in the conventional to 17% MAD. from The53% stress in the conventionallevel at points MAD. “a” However,to “e” in the stre proposedss distribution MAD induced decreased by thesubstantially proposed toMAD 17% around from 53% the gingivalin the areaconventional increased MAD. to 173% However, compared stre sswith distribution the conventional induced byMAD the proposedat point “f”MAD because around the the supporting gingival Appl.area Sci. increased2020 10 to 173% compared with the conventional MAD at point “f” because the supporting shield tended, , to 4430 distribute the concentrated force to the gingival area (Table 2). 4 of 7 shield tended to distribute the concentrated force to the gingival area (Table 2).

FigureFigureFigure 4. 4. 4.Stress StressStress distribution distributiondistribution fromfrom FE FE analysis: analysis:analysis: ((aa)) conventional conventional and andand ( ( b(bb)) )proposed proposed proposed MAD. MAD. MAD.

FigureFigureFigure 5. 5. 5. ComparativeComparative Comparative analyzed analyzedanalyzed points points of of stressstress distribution: distribution: ( a(a)) )conventional conventionalconventional and and and (b ( (b)b )proposed) proposed proposed MAD. MAD. MAD.

Table 2. Comparison of stresses between the conventional and proposed MAD. TableTable 2.2. ComparisonComparison of stresses betweenbetween thethe conventional conventional and and proposed proposed MAD. MAD. Position (MPa) Stress PositionPosition (MPa) (MPa) Stress Stress MAD MAD MAD a a b cc dd ee f Meanf STDMean ± STD a b c d e f ± Mean ± STD ConventionalConventionalConventional 0.0800.080 0.102 0.0700.0700.070 0.1120.1120.112 0.040 0.0400.040 0.023 0.0230.023 0.071 0.034 0.071 0.071 ± 0.034± 0.034 (Figure(Figure (Figure5a) 5a) 5a) ± Proposed Proposed 0.063 0.048 0.058 0.065 0.023 0.040 0.050 0.016 Proposed(Figure 5b) 0.063 0.048 0.058 0.065 0.023 0.040 0.050 ± 0.016 (Figure 5b) 0.063 0.048 0.058 0.065 0.023 0.040 ± 0.050 ± 0.016 (FigureProposed 5b)/Conventional 0.79 0.47 0.83 0.58 0.58 1.73 0.70 Proposed/Conventional 0.79 0.47 0.83 0.58 0.58 1.73 0.70 Proposed/ConventionalSTD, standard deviation; 0.79 MPa,0.47 megapascal; 0.83 unit of pressure0.58 equal0.58 to 10 6 pascals.1.73 0.70 STD, standard deviation; MPa, megapascal; unit of pressure equal to 106 pascals. STD, standard deviation; MPa, megapascal; unit of pressure equal to 106 pascals. 4. Discussion 4. Discussion 4. Discussion OurOur proposed proposed novel novel MAD MAD design design notnot onlyonly maintainedmaintained a wide upper upper airway, airway, but but also also controlled controlled Our proposed novel MAD design not only maintained a wide upper airway, but also controlled thethe induced induced force. force. The The presence presence of aof supporting a supporting shield shield in the in newly the newly proposed proposed MAD MAD produced produced a change a the induced force. The presence of a supporting shield in the newly proposed MAD produced a inchange the contact in the area contact between area the between device and the oral device structures, and oral causing structures, a different causing stress a distribution different stress on the change in the contact area between the device and oral structures, causing a different stress frontdistribution teeth and on gingival the front area. teeth This and was gingival confirmed area. This by FE was analysis. confirmed by FE analysis. distribution on the front teeth and gingival area. This was confirmed by FE analysis. FactorsFactors that that influenceinfluence patientpatient compliance with with th thee use use of of an an MAD MAD include include side side effects effects such such as Factors that influence patient compliance with the use of an MAD include side effects such as asdiscomfort, discomfort, mouth mouth dryness, dryness, gum gum irritation, irritation, excessive excessive salivation, salivation, and pain. and Additionally, pain. Additionally, side effects side discomfort, mouth dryness, gum irritation, excessive salivation, and pain. Additionally, side effects effassociatedects associated with occlusal with occlusal changes, changes, such as such overjet, as overjet, overbite, overbite, and incisor and incisor inclination inclination in occlusion, in occlusion, have haveassociatedbeen been reported reported with occlusalfor forlong-term long-term changes, use usesuch [7,9,16]. [7 as,9, 16overjet, Larger]. Larger overbite, forces forces produce and produce incisor larger larger inclination occlusal occlusal inchanges, changes, occlusion, which which have progressivelybeen reported decrease for long-term the advancement use [7,9,16]. of the Larger lower forces jaw, resulting produce in larger a reduced occlusal therapeutic changes, eff ectwhich on SDB.Appl. In Sci. addition, 2020, 10, x; excessive doi: FOR PEER overstretching REVIEW can adversely affect the shape of the www.mdpi.com/journal/applsci soft tissue structures in Appl. Sci. 2020, 10, x; doi: FOR PEER REVIEW www.mdpi.com/journal/applsci the upper airway and the tension of the muscles involved [4]. A device that can minimize occlusal changes would lead to a reduced risk of having to keep the mandible continuously advanced [24]. A device that can be more easily adaptable with an appropriate anatomic fit would also provide more comfort to patients, resulting in increased compliance. FE analysis is an interpretation program that provides the researcher with flexibility in options. It can predict stress values and their distribution while handling external forces at any level. It also provides accurate analyses before and after specific modifications. In addition, there are no limitations to the materials that can be used for testing, which makes it more cost-effective and time-efficient than animal experiments [13,14,25]. FE analysis is used in the analysis and design of medical devices, including dental braces [13,14,26]. Moreover, the computational mechanobiological algorithms for developing a suitable and optimized design Appl. Sci. 2020, 10, 4430 5 of 7 of medical devices are currently being tried in many clinical applications [26,27]. Here we have demonstrated that quantitative visual analysis can be applied to MADs using FE analysis and that there are advantages to this method. A novel simulation program using FE analysis and computational mechanobiological algorithms will be valuable in minimizing the side effects and developing advanced MADs for patients with skeletal deformities, such as a retrognathic mandible and constricted maxilla. Close collaboration between clinicians and mechanical engineers is essential. Our novel MAD design can enhance comfort in attachment and detachment because the upper and lower trays can be inserted separately, controlling tension through the springs. However, further studies including clinical trials are needed to confirm these points. There were some limitations to our study because the force boundary conditions in the FE analysis applied to the upper tray were simplified in terms of patient anatomy, such as oral structure and the shape of the upper dentition. Simplifying the model could reduce the cost, but the conditions of analysis must be set carefully to consider these neglected parts. Additionally, this study restricted the movement of mandible to only anterior and posterior directions. Considering the diverse range of movement of the mandible, further studies are needed to measure the actual stress induced by wearing an MAD on the entire mouth, maxilla, mandible, and temporomandibular joint. In scanning for this study, we had difficulty distinguishing the upper dentition from the upper gingival area; therefore, we used the average physical properties for the dentin and gingiva as parts of the same structure. Further studies are needed to assess the stress on the dentition and gingiva separately. Advanced technologies such as three-dimensional printing will be possible to create more realistic models that reflect individual patient characteristics and complex head structures [27]. The relationship between the results of FE analysis and clinical side effects should also be verified in clinical studies. Despite these limitations, we hope that this study will facilitate further research into MAD design.

5. Conclusions A proposed novel MAD design with a supporting shield reduced concentrated stress levels at the front teeth by distributing it into the gingival area, according to the FE analysis. Simulation models using biomechanics such as FE analysis, which help to evaluate differences in stress induced by different MAD devices, will be needed in the future to control or reduce the side effects of MADs such as occlusal change, discomfort, and pain.

Author Contributions: Conceptualization, J.Y., S.H.L. and D.-H.K.; Data curation, S.H.L. and S.Y.L.; Formal analysis, J.Y., Y.J. and H.-I.S.; Project administration, D.-H.K.; Validation, J.Y., S.H.L. and D.-H.K.; Writing—original draft, S.H.L. and D.-H.K.; Writing—review & editing, J.Y., Y.J., D.-H.K., H.-I.S. and S.Y.L. All authors have read and agreed to the published version of the manuscript. Funding: Support for this study was provided by the Alumni of Department of Otorhinolaryngology, the Catholic University of Korea, College of Medicine, and the Catholic Medical Center Research Foundation made in the program year of 2014 (grant number, 52016B000100026). Conﬂicts of Interest: The authors declare no conﬂict of interest.

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