title: Hertzian contact response of dentin with loading rate and orientation.
abstract: OBJECTIVE
  To test the hypothesis that dentin Hertzian contact response varies with loading rate and tubule orientation.
  
  
  METHODS
  Sound teeth (n=12) were cut either parallel or perpendicular to the axial direction to expose dentin (n=6 each). The cut specimens were embedded (poly-methyl-methacrylate (PMMA) and divided into two groups: (GL) load applied parallel to dentin tubule direction and (GP) load applied perpendicular to tubule direction. A 1.5mm diameter tungsten-carbide ball was used for Hertzian contact testing with a maximum load of 150 N load and loading rates of 0.1, 1, 100, and 1000 N/s on each specimen. Indented specimens were observed microscopically and photomicrographs acquired. Hertzian contact diameter and modulus were analysed (p<0.05) by one-way ANOVA and Tukey test.
  
  
  RESULTS
  There were significant differences (p<0.05) in Hertzian response with respect to loading rate for GL (0.1N/s versus 1000 N/s, 0.1N/s versus 100 N/s, 1N/s versus 1000 N/s, and 1N/s versus 100 N/s), and GP (0.1N/s versus 1000 N/s, 0.1N/s versus 100 N/s, and 1N/s versus 1000 N/s). Contact modulus was higher for GL compared to GP at all loading rates (p<0.05).
  
  
  CONCLUSIONS
  The results suggest that dentin contact modulus is loading rate dependent. Tubule orientation of dentin did not influence contact modulus values (p>0.05).
authors.affiliation: Department of Prosthodontics, New York University College of Dentistry, NY, USA. nrd1@nyu.edu
authors.forename: Nelson Renato Franca Alves
authors.initials: NR
authors.lastname: da Silva
authors.forename: F
authors.initials: F
authors.lastname: Lalani
authors.forename: Paulo G
authors.initials: PG
authors.lastname: Coelho
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Clark
authors.forename: Carlos Augusto de Oliveira
authors.initials: CA
authors.lastname: Fernandes
authors.forename: Van P
authors.initials: VP
authors.lastname: Thompson
mesh_terms: D003799:Dental Stress Analysis / Q000379:methods; D003804:Dentin / Q000648:ultrastructure*; D006801:Humans; D021621:Imaging, Three-Dimensional; D009949:Orientation; D013314:Stress, Mechanical