Patient-specific numerical Finite Element models

Patient-specific numerical Finite Element models G. Boonena, G.Bekaert d , S. Debruyne e, JF Cuzinb and B. Vande Vannetc a Department of Orthodontics, Free University Brussels (VUB), Brussels, Belgium d KULeuven Campus Oostende Faculty of Engineering Technology , Belgium b Department of Orthodontics, Vrije Universiteit Brussel (VUB) Private Practice, Nancy, France and Luxembourg e KULeuven Campus Oostende Faculty of Engineering Technology , Belgium c Department of Orthodontics, Free University Brussels (VUB), Brussels, Belgium

INTRODUCTION In the past decades finite element models have been developped to study biomechanics in orthodontics. All of these lead to definitions of a standard model to study stresses of the different materials composing teeth and jaws. However customised appliances are delivered now. Recently in many today’s Orthodontic practices Intra Oral Cameras and 3 Dimensional X-ray procedures are used. What about creating a fully customised Finite Element Model? What about creating a patient-specific numerical Finite Element model coming from patient individual records ( CBCT, Intral Oral camera ) and even including his own appliance in order to have a really customised point of view on biomechanics. Aim Creating numerical models of anatomical areas to estimate the tissues adaptation processes and dental displacements induced by mechanical stimulus in lingual orthodontic custom appliances. These models simulate and predict the behaviour of biological tissues in order to evaluate the clinical and histological effects, and to realize new dental appliances or improve existing ones.

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Material and methods The general and diverse finite element (FE) method is used for analysis of coupled dental displacements. This method treats teeth, brackets, connection wire and cancellous bone as a set of structural components. Each of these is characterized by elastic properties such as Young’s modulus, shear modulus and Poisson’s ratio of its isotropically assumed material. By dividing each structural component into a coupled finite number of small elements, a numerical analysis of component stress or structural deformations. STL files obtained from intra-oral 3D Camera (Trios®, 3 shape, Denmark) and CBCT (Vatech, NJ, US) were converted to STEP files. Using Siemens NX software it was possible to convert the data to solid geometry. Non linear structures with contact points (unavoidable in that study) are defined. In a first approximation teeth are supposed to be infinitely stiff. This is allowed as teeth have a stiffness which is in orders of magnitude larger than stiffness of jaw bone. The outer surfaces of teeth are merely used to establish contact between teeth. Forces are transferred to dental root via RBE2 elements, which are of infinite stiffness. The lingual brackets were modelled with solid elements. This enabled their connection to the teeth and contact between lingual brackets and single bracket connection wire was established. The driving force which causes the teeth to move relative to jaw bone was modelled by a preload in the one-dimensional connection wire between brackets. Creep phenomenon is used to simulate growth and bone remodelling.

Intra Oral CAMERA

CBCT Cone Beam

STL Files

Results The different steps in setting up a finite element model suitable for an adequate numerical analysis of coupled dental deformations were performed. In detail important relevant numerical issues such as the optimal estimation of elastic properties of cancellous bone were incorporated. And this model is patient-specific.

Three alignment experiments were conducted. 1. The focus was placed on the cranial base and the acoustic meatus to visualize overall growth and treatment effects.

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DICOM Files 2. The palatum was focussed to study maxillar growth, changes in dentition, and orthodontic treatment.

Recent evolutions

3. The mandibular symphysis was chosen as focus to assess mandibular growth, changes in dentition, and orthodontic treatment.

This research demonstrates the possibilities of having a finite element method to be quickly created from imaging processes coming current in Orthodontic offices. In our “customised orthodontics” times, customised biomechanical studies are near to us.

After alignment the images were subtracted (Figs. 4, 9, and 14).

STEP Files

The pixels of the subtraction image were subdivided into three gray values bins of equal size. The pixels corresponding to the lowest bin (meaning more radiodensity in test than the reference image) were represented using shades of blue. Pixels with grey value in the middle bin (small or no difference between test and reference image) were represented using shades of green. Pixels with gray value in the higher bin (lower radiodensity compared to the reference image) were represented using shades of red (Figs. 5, 10, and 15).

Meshing

References Junning C. , Wei L. , MIichael V. , Swain M. , Ali D. , Qing L. A periodontal ligament driven remodeling algorithm for orthodontic tooth movement J. Biomech. 47 (2014) 1689-1695 Hussein H. Ammar, Peter Ngan, Richard J. Crout, Victor H. Mucino, Osama M. Mukdadi Three dimensional modeling and finite element analysis in treatment planning for orthodontic tooth movement Am J Orthod Dentofacial Orthop 2011;139:e59-e79 Xiulin Yan, Weijun He, Tao Lin, Jun Liu, Xiaofeng Bal, Guangqi Yan, Li Lu Three dimensional finite element analysis of the craniomaxillary complex during maxillary protraction with bone anchorage vs conventional dental anchorage Am J Orthod Dentofacial Orthop 2013; 143: 197-205 Andrew Boryor, Ansgar Hohmann, Martin Geiger, Uwe Wolfram, Christian sander, Franz Günter Sander A downloadable meshed human canine tooth model with PDL and bone for finite element stimulation Dental Materials 25 (2009) e57-e62

FEA Studies

Joanneke M. Plooij, Thomas J.J. Maal, Piet Haers, Wilfried A. Borstlap, Anne Marie Kuijpers-Jagtman, Stefaan J. Berge Digital three dimensional image fusion processes for planning and evaluating orthodontics and orthognatic surgery. A systematic review Int. J. Oral Maxillofac. Surg. 2011; 40 : 341-352 Cattaneo PM., Dalstra M., Melsen B., Strains in periodontal ligament and alveolar bone associated with tooth movement analyzed by finite element. Orthod. Craniofac. Res. 2009; 12: 120-8 Cattaneo PM., Dalstra M., Melsen B., The finite element method: a tool to study orthodontic tooth movement. J. Dent. Res. 2005;84:428-33 Fields C., Ichim I., Swain MV., Chan E., Darendeliler MA., Li W., et al. Mechanical responses to orthodontic loading: a 3-dimensional finite multi-tooth model. Am. J. Orthod. Dentofacial Orthop. 2009; 135:174-81

Vrije Universiteit Brussel Dr G. Boonen

KHBO Geert Bekaert

Laarbeeklaan 103, 1090 Brussel Belgium Tel. +32 2 477 49 08

Lecturer at KUL Campus of Technology Ostend Faculty of Industrial Sciences

Orthodontie.vub.ac.be

tel. +32 50 40 59 34 [email protected]

KHBO Stijn Debruyne KU Leuven | Campus Oostende (@KHBO) Faculty of Engineering Technology Cluster WIT Research Group Propolis Zeedijk 101 | B-8400 Ostend tel. +32 50 40 59 34 [email protected]

Dr J-F Cuzin Private offices in Nancy France and Luxembourg Tel. +33 3 83 25 22 50 [email protected]

Vrije Universiteit Brussel Prof. Dr. B. Vande Vannet Laarbeeklaan 103, 1090 Brussel, Belgium Tel. +32 2 477 49 08 Skype : bvandevannet [email protected] Orthodontie.vub.ac.be