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Int Poster J Dent Oral Med 8 (2006), No. 4     15. Dec. 2006

Int Poster J Dent Oral Med 2006, Vol 8 No 04, Poster 334

Finite Element Simulation of the Human Mandible: The Influence of the PDL on its Structural Behaviour

Language: English

Authors:
Prof. Dr. Cornelia Kober, Ph.D.
  Faculty of Engineering and Computer Science, University of Applied Science Osnabrueck
Dr. Stefan Stübinger
  Department of Maxillofacial and Facial Plastic Surgery, Johann Wolfgang Goethe-University Medical School, Frankfurt
Bodo Erdmann,
  Zuse Institute Berlin
Prof. Dr. Christian Hellmich
  Institute for Mechanics of Materials and Structures, Vienna University of Technology (TU Wien)
Dr. Thomas Radtke
  Faculty of Engineering and Computer Science, University of Applied Science Osnabrueck
Prof. Dr. Dr. Robert Sader
  Department of Maxillofacial and Facial Plastic Surgery , Johann Wolfgang Goethe-University Medical School, Frankfurt
Prof. Dr. Dr. Hans-Florian Zeilhofer
  University Clinic for Reconstructive Surgery, Departement of Cranio- and Maxillofacial Surgery, University Hospital Basel

Date/Event/Venue:
4./5. November 2005
Das Mundhöhlenkarzinom. Bewährte Konzepte - Moderne Strategien.
20. Jahrestagung der Schweizerischen Gesellschaft für Kiefer- und Gesichtschirurgie
Le carcinome de la cavité buccale. Conceptions eprouvées - Stratégies modernes
Basel, Switzerland


DGZMK-Poster-Award 2007 für das beste Poster in 2006

Introduction

This paper refers to a detailed research project concerning the structural mechanics of a human mandible dedicated to a stepwise refinement of the simulation model towards the anatomical reality. For its common pathological condition, the partially edentuluous mandible of the female Visible Human [8], characterized by beginning atrophy of the alveolar ridge, was chosen as simulation example. The "periodontal ligament" (PDL) is a thin fibrous connective tissue of a thickness of about 0.2 mm present at the interface between teeth and the mandibular corpus (Figure 1). It surrounds the root of a tooth, separating it from and attaching it to the alveolar bone.

Micro-CT slice of a human premolar in vitro, resolution 160 μm x 160 μm x 320 μm [7]. FEA Model with integrated PDL and simplifid temporomandibular joint capsules, transparent rendering of the cortical bone, altogether about 400.000 tetrahdra.

Objectives

The article is dedicated to an analysis of the influence of the PDL on the structural behaviour of human jaw bone by means of finite element simulation of an entire mandibular model (Figure 2).

Material and Methods

In general, the preprocessing of the simulation consists in reconstruction of the individual anatomy, implementation of the inhomogeneous and anisotropic material law of bone, and realization of the load case due to teeth, muscle and joint forces (Figure 3). For the sake of the stepwise refinement towards anatomical reality being a key feature of the project, the mandible was modelled as inhomogeneous and anisotropic [4]. Further, individual muscular lines of action and simplified TMJ capsules were introduced [5,6].

Due to strongly varying dimensions, the PDL was reconstructed by a special semiautomatic procedure. As regards its adaptive viscoelastic material properties, during static biting, a reference to the higher Young's modulus within a "bilinear material approach" was chosen [2].
In order to guarantee reliability and efficiency of the simulation we applied the adaptive Finite Element code KASKADE [3,10]. The geometry reconstruction from 3D image data and all visualizations were performed with Amira 4.1. [1,9].

Prerequisites of the simulation.

Results

The simulation results proved remarkable force absorption due to the PDL (Figure 4) as well as qualitative changes of the stress/strain profiles of the alveolar ridge.
Concerning the simulation without PDL, observed high compressive strain at the adjacent bone were in agreement with regions of frequent implant failure (Figure 5).

Simulated volumetric strain due to an intrusion on the leftmost premolar (force: 5N), remarkable force absoption on behalf of the PDL can be stated.

Volumetric strain due to a bite on all teeth (a) without integrated PDL (b) with integrated PDL, view into the alveolar bone, teeth omitted.

Conclusions

The simulation results confirmed that the PDL is essential for the structural behaviour of the human mandible. Based on the mechanical adaptation of bone, the comparison of the simulation with and without PDL provides special insight to the changes due to dental implants, in particular implant loss and bone resorption. Finally, the simulation will serve as virtual platform for evaluation (a) of implant design (b) of implant placement.

Literature

  1. Amira User\'s Guide and Amira Reference Manual, www.amiravis.com
  2. Dorow C, Krstin N, Sander FG, Determination of the Mechanical Properties of the Periodontal Ligament in a Uniaxial Tensional Experiment. Orofac Orthop, 64, 2003: 100-7.
  3. Erdmann B, Lang J, Roitzsch R, KASKADE Manual. Technical Report TR 93-05, Konrad-Zuse-Zentrum Berlin (ZIB), 1993.
  4. Kober C, Erdmann B, Hellmich C, Sader R, Zeilhofer HF. Consideration of anisotropic elasticity minimizes volumetric rather than shear deformation in human mandible. Comp Meth Biomech Biomed Eng April 2006; 9(2): 91-101.
  5. Kober C, Erdmann B, Lang J, Sader R, Zeilhofer HF. Adaptive Finite Element Simulation of the Human Mandible Using a New Physiological Model of the Masticatory Muscles. PAMM 2004; 4: 332-3.
  6. Kober C, Erdmann B, Lang J, Sader R, Zeilhofer HF. Sensitivity of the Temporomandibular Joint Capsule for the Structural Behaviour of the Human Mandible. Biomed Tech - Biomed Eng 2004; 49 Suppl 2: 372-3.
  7. Kober C, Dorow C, Geiger M, Sader R, Zeilhofer HF, Sander FG. An interdisciplinary project on a fresh cadaver mandible. In: The Finite Element Method in Biomedical Engineering, Biomechanics and Related Fields. Proceedings of the 10th Workshop [CD-ROM]; 2003 July 17-18; Ulm, Germany. University of Ulm.
  8. National Library of Medicine, The Visible Human Project, www.nlm.nih.gov/research/visible/visible_human.html, 1995.
  9. Stalling D, Westerhoff M, Hege HC, Amira: A Highly Interactive System for Visual Data Analysis. In: The Visualization Handbook, No. 38 (ed. Hansen CD, Johnson CR), Elsevier 2005, pp. 749-767.
  10. www.zib.de/Numerik/numsoft/kaskade/

This Poster was submitted by Prof. Dr. Cornelia Kober.

Correspondence address:
Prof. Dr. Cornelia Kober, Ph.D.
Faculty of Engineering and Computer Science
Univ. of Appl. Sc. Osnabrueck
Albrechtstr. 30
P.O. Box 19 40
D-49009 Osnabrueck
Germany