Viscoelastic finite element analysis model of the mandible with Herbst appliance

Abstract

We read with great interest the manuscript titled “A clinically friendly viscoelastic finite element analysis model of the mandible with Herbst appliance” (Zadi ZH, Bidhendi AJ, Shariati A, Pae EK. A clinically friendly viscoelastic finite element analysis model of the mandible with Herbst appliance. Am J Orthod Dentofacial Orthop. Epub 2020 Aug 27). We appreciate and thank the authors for this interesting finite element method study highlighting the use of viscoelastic models over elastic models to accurately assess clinical outcomes of orthodontic appliances. However, we would like further clarification regarding some aspects of the study.(1)What was the element type used for the cortical bone model? It is known that tetrahedral elements and hexahedral elements can both significantly affect the simulation outcome while yielding different results.1Benzley S.E. Perry E. Merkley K. Clark B. Sjaardama G. A comparison of all hexagonal and all tetrahedral finite element meshes for elastic and elasto-plastic analysis. Proceedings of the 4th International Meshing Roundtable; 1995, Oct 16-17; Albuquerque, NM. Sandia National Laboratories, Albuquerque1995Google Scholar The choice of element may thus dilute the accuracy of simulation.(2)In previous finite element method studies,2Patil H.A. Tekale P.D. Kerudi V.V. Sharan J.S. Lohakpure R.A. Mude N.N. Assessment of stress changes in dentoalveolar and skeletal structures of the mandible with the miniplate anchored Forsus: a three-dimensional finite element stress analysis study.APOS Trends Orthod. 2017; 7: 87-93Crossref Google Scholar,3Panigrahi P. Vineeth V. Biomechanical effects of fixed functional appliance on craniofacial structures.Angle Orthod. 2009; 79: 668-675Crossref PubMed Scopus (13) Google Scholar significantly lower force values (2 N) have been used than that used in this study. The references quoted for the use of a static force (40 N in the vertical and 60 N in the horizontal direction) do not validate the magnitude of protraction force with a rigid fixed functional (Herbst) appliance. We would be grateful if the authors would further elaborate on this.(3)In this study, the boundary conditions were imposed as the translational lock in all the global directions on the condylar head. We believe that imposing boundary conditions in this area may lead to undermining the stress patterns generated at the condylar head, which is hypothesized to be the major area of remodeling in fixed functional appliance therapy.2Patil H.A. Tekale P.D. Kerudi V.V. Sharan J.S. Lohakpure R.A. Mude N.N. Assessment of stress changes in dentoalveolar and skeletal structures of the mandible with the miniplate anchored Forsus: a three-dimensional finite element stress analysis study.APOS Trends Orthod. 2017; 7: 87-93Crossref Google Scholar, 3Panigrahi P. Vineeth V. Biomechanical effects of fixed functional appliance on craniofacial structures.Angle Orthod. 2009; 79: 668-675Crossref PubMed Scopus (13) Google Scholar, 4Chaudhry A. Sidhu M.S. Chaudhary G. Grover S. Chaudhry N. Kaushik A. Evaluation of stress changes in the mandible with a fixed functional appliance: a finite element study.Am J Orthod Dentofacial Orthop. 2015; 147: 226-234Abstract Full Text Full Text PDF PubMed Scopus (12) Google Scholar, 5Shrivastava A. Hazarey P.V. Kharbanda O.P. Gupta A. Stress distribution in the temporomandibular joint after mandibular protraction: a three-dimensional finite element study.Angle Orthod. 2015; 85: 196-205Crossref PubMed Scopus (10) Google Scholar Therefore, we request that the authors kindly explain the same.(4)The simulation setup seems to be oversimplified. The articulation between the mandible and the cranium is missing because the skull, muscles, and articular ligaments were not considered. We believe that detailed modeling inclusive of all these as well as the teeth, periodontal ligament, and alveolar bone will enhance the confidence in results and give better clinical insight about material model comparison. A clinically friendly viscoelastic finite element analysis model of the mandible with Herbst applianceAmerican Journal of Orthodontics and Dentofacial OrthopedicsVol. 160Issue 2PreviewAs a powerful numerical approximation tool, finite element analysis (FEA) has been widely used to predict stress and strain distributions in facial bones generated by orthodontic appliances. Previous FEA models were constructed on the basis of a linear elastic phase of the bone response (eg, elastic bone strains to loading). However, what is more useful for clinical understanding would be predicting long-term strains and displacements of bone-segments responding to loading, yet tissue responses are (1) not promptly observable and (2) hard to predict in nature. Full-Text PDF Authors’ responseAmerican Journal of Orthodontics and Dentofacial OrthopedicsVol. 159Issue 2PreviewThank you for your interest in and your questions about our article. Full-Text PDF