_Applied_  
_sciences_  
Comparison of the Effects Caused by Three Different Mandibular Advancement Devices on the Periodontal Ligaments and Teeth for the Treatment of Osa:  
A Finite Element Model Study  
**[PERSON] 1,*()**, **[PERSON] 1,*()**, **[PERSON] 2**, [PERSON] 1**,  
**[PERSON] 3**, **[PERSON] 2**, **[PERSON] 2** and **[PERSON] 1**  
1 Department of Neuroscience, Section of Dentistry, University of Padua, 35100 Padua, Italy; [EMAIL_ADDRESS] (F.Z.); [EMAIL_ADDRESS] (A.G.)  
2 Department of Industrial Engineering and Mathematical Sciences, Universita Politecnica delle Marche, 60131 Ancona, Italy; [EMAIL_ADDRESS] (M.C.); [EMAIL_ADDRESS] (D.L.); [EMAIL_ADDRESS] (M.M.)  
3 Department of Materials, Environmental Sciences and Urban Planning, Universita Politecnica delle Marche, via Brecce Bianche 12, 60131 Ancona, Italy; [EMAIL_ADDRESS]  
* Correspondence: [EMAIL_ADDRESS] (G.B); [EMAIL_ADDRESS] (A.G.S.)  
Received: 29 July 2020; Accepted: 27 September 2020; Published: 3 October 2020  
**Abstract: AIM: The purpose of this study is to compare the stress effects developed on the periodontal ligaments and teeth by three different types of mandibular advancement devices (MADs) using a finite element method (FEM) analysis. Introduction: Obstructive sleep apnea (OSA) is a disease with a high prevalence and, in recent years, the use of MADs as an alternative or support treatment to the continuous positive airway pressure (CPAP) has spread. Their use finds relative contraindications in the case of partial dentulism and severe periodontal disease. Given the widespread of periodontal problems, it is essential to know the effects that these devices cause on the periodontal ligament of the teeth. Materials and methods: Starting from the computed tomography (CT) scan of a patient's skull, 3D reconstructions of the maxilla and mandible were implemented. Three different MADs were prepared for the patient, then 3D scanned, and lastly, coupled with the 3D models of the jaws. The devices have two different mechanics: One has a front reverse connecting rod (Orthoapnea(tm)), and two have lateral propulsion (Somnodent(tm) and Herbst(tm)). A FEM analysis was performed to calculate the stress applied on periodontal ligaments, on every single tooth and the displacement vectors that are generated by applying an advancement force on the mandible. Results: Herbst(tm) and Somnodent(tm) devices present very similar stress values, mainly concentrated on lateral teeth, but in general, the forces are very mild and distributed. The maximum stresses values are 3.27 kPa on periodontal ligaments and 287 kPa on teeth for Somnodent(tm) and 3.56 kPa on periodontal ligaments and 302 kPa on teeth for Herbst(tm). Orthoapnea(tm) has, instead, higher and concentrated stress values, especially in the anterior maxillary and mandibular area with 4.26 kPa and 600 kPa as maximum stress values, respectively, on periodontal ligaments and teeth. Conclusions: From the results, it is concluded that devices with a bilateral mechanism generate less and more distributed stress than an anterior connecting rod mechanism. Therefore, they may be advisable to patients with compromised periodontal conditions in the anterior area.  
**Keywords:** dental materials; orthodontics; obstructive sleep apnea; mandibular advancement device; finite element method