_Applied sciences_  
_Article_  
**Investigating the Ability of the Tooth and Surrounding Support Tissues to Absorb and Dissipate Orthodontic Loads during Periodantal Breakdown--Finite Elements Analysis**  
**[PERSON] 1,*\({}^{\text{*}}\)**\({}^{\text{*}}\)**, [PERSON] 2,* and [PERSON] 1  
1 Department of Cardiology, Endodontics and Oral Pathology, School of Dental Medicine, University of Medicine and Pharmacy [PERSON], Str. Morlicot 33, 400001 Cluj-Napoca, Romania; [EMAIL_ADDRESS]  
2 Department of Orthodontics, School of Dental Medicine, University of Medicine and Pharmacy [PERSON], Str. [PERSON] 33, 400001 Cluj-Napoca, Romania  
* Correspondence: [EMAIL_ADDRESS] (R-A.M.); [EMAIL_ADDRESS] (C.D.O.)  
**Featured Application: For an orthodontist practitioner, quantification of the absorption-dissipation ability of dental tissues is of extreme importance since there is a constant danger when applying loads to produce ischemia and further resorptive processes (e.g., 0.6-1.2 N vs. 2.4 N). Orthodontic treatment is not always performed in intact periodontium; thus, it must be emphasized that in reduced periodonotin, there are biomechanical changes that if not acknowledged could compromise treatment prognosis. The study is the first to analyze not only the absorption-dissipation issues, but also to investigate how the biomechanical behavior is affected by bone loss. For researchers, this study not only approaches the technical issues related to the numerical studies methodology, but also clears some aspects that could significantly influence the results accuracy. Herein, the analysis proves that the tooth absorbs and dissipates most of the stress due to applied forces (high percentage variability), in both intact and reduced periodontitis, acting as a single-stand continuum structure, with enamel having a similar absorption-dissipation ability as dentine (both behaving in a similar way to ductile materials). All other tissular components have a constant absorption-dissipation ability, that changes very little during periodontal breakdown. It has also been proven that some of the movements are more stressful (i.e., rotation and translation) than the others (tipping, intrusion, and extrusion). The analysis herein showed that the assumed boundary conditions (linear elasticity, isotropy, and homogeneity) widely used in dental studies, are correct up to 2.4 N of loads when Tresca failure criterion is employed.**  
Herein, the finite elements analysis (FEA) numerical study investigated the absorption-dissipation ability of dental tissues under orthodontic forces, during orthodontic movements and the periodontal breakdown process. Additionally, we investigated the correctness of FEA boundary assumptions up to 2.4 N of loads. Eighty-one models of the second lower premolar were subjected to 810 FEA numerical simulations using Tresca failure criterion under 0.6 N, 1.2 N, and 2.4 N and five movements: intrusion, extrusion, rotation, tipping, and translation. The results showed that both coronal dentine and enamel components had comparable high absorption-dissipation abilities, allowing for only a limited fraction of stresses to reach the circulatory sensitive tissues. Isotropy, linear elasticity, and homogeneity are correct when Tresca is employed up to 2.4 N. Forces of 0.6 N, 1.2 N, and 2.4 N displayed similar qualitative results for all movements and bone levels, while quantitative results doubled for 1.2 N and quadrupled for 2.4 N when compared with 0.6 N. FEA simulations showed 0.6-1.2 N to be safe for application in intact periodontium, while for reduced periodontium more than 0.6 N are prone to resorptive and ischemic risks. For reducing these risks, after 4 mm of bone loss, 0.2-0.6 N are recommended. Rotation and translation were the most stressful followed by tipping.**  
**Keywords: tooth; enamel; dentin; periodontal breakdown; finite elements analysis; failure criteria selection; orthodontic movements**