title: Material assignment in finite element modeling: heterogeneous properties of the mandibular bone.
abstract: OBJECTIVE
  The properties of the biomaterial are normally characterized by heterogeneity on all scales influencing the function and biomechanics. Elastic modulus (EM), which is one of the most important mechanical properties of material, is necessary for finite element modeling and needed to be determined by some methods. The aim of this study is to demonstrate the feasibility of assessment of EM from GrayValue (GV) of computed tomographic image and assignment of material properties in heterogeneous finite element modeling for studying the performance of the mandibular bones.
  
  
  METHODS
  Three mandibles obtained from fresh human cadavers were used in this study. All mandibular bones were scanned using computed tomography, and the original data were stored in optical disks. The finite element modeling of the 3 mandibles was meshed using Materialise Mimics 10.01 and Abaqus 6.10 software. Using the empirical expression on relationship between GV and EM, the empirical EM of the meshed mandibular elements were calculated. To verify the empirical EM, actual EM of the three was determined by nanoindentation test using Oliver and Pharr method. The dependence of EM on test regions and loading directions were also discussed.
  
  
  RESULTS
  The empirical EM of the mandible element is in the range of 3.7 to 23.4 Gpa, and EM of the cortical element is in the range of 8.6 to 13.6 Gpa. In comparison, the actual EM of cortical bone tested by nanoindentation method is in the range of 10.0 to 22.0 Gpa. The tested EM is varied with the test regions and loading directions. The difference in the values of EM determined by the empirical analysis and by the nanoindentation test is approximately 5.0 Gpa.
  
  
  CONCLUSIONS
  A mandibular finite element model with heterogeneous material properties is built. By analyzing the EM value of this model, it is concluded that the actual EM in anterior-posterior direction in mandibular ramus and EM in superior-inferior direction in mandibular body match the empirical EM better than the other directions.
authors.affiliation: Department of Oral and Craniomaxillofacial Surgery, Ninth People's Hospital, College of Stomatology, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, People's Republic of China.
authors.forename: Pengfei
authors.initials: P
authors.lastname: Xin
authors.forename: Pulin
authors.initials: P
authors.lastname: Nie
authors.forename: Bin
authors.initials: B
authors.lastname: Jiang
authors.forename: Simin
authors.initials: S
authors.lastname: Deng
authors.forename: Guanghong
authors.initials: G
authors.lastname: Hu
authors.forename: Steve G F
authors.initials: SG
authors.lastname: Shen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D055119:Elastic Modulus; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D008297:Male; D008334:Mandible / Q000000981:diagnostic imaging / Q000502:physiology*; D008875:Middle Aged; D012984:Software; D014057:Tomography, X-Ray Computed