title: Interfacial sliding properties of bone screw materials and their effect on screw fixation strength.
abstract: BACKGROUND
  This study examined the effect of interfacial sliding and test material properties on the fixation strength and insertional properties of self-tapping bone screws. Various substitute materials (polyacetal [POM], poly(methyl methacrylate) [PMMA] and E-glass-filled Epoxy [Sawbones®]) for human bone were evaluated, and the results were compared with the findings for cadaver bone.
  
  
  METHODS
  Initial coefficient of friction (CoF) of the screw material stainless steel AISI316 was tested using a pin-on-disk apparatus, and the screws were exposed to pullout tests after insertion torque tests. The effect of a smooth diamond-like carbon (DLC) coating was studied by applying the coating on both CoF test balls and bone screws.
  
  
  RESULTS
  Mechanical properties of test blocks strongly correlated to both pullout strength and insertion torque of the screws: for noncoated 2.7-mm screws, tensile strength correlated to pullout strength and insertion torque, with Pearson correlation coefficients r=0.977 and r=0.738, respectively. In contrast, CoF correlated strongly to screw insertion torque but not to pullout strength in bone substitute materials (for noncoated 2.7-mm screws, r=0.652 and r=0.248, respectively). There were no significant differences in CoF using noncoated and DLC-coated screw materials against bone substitutes.
  
  
  CONCLUSIONS
  Proper materials for in vitro testing help in evaluating the biomechanics of the implants in advance. However, choosing the material needs attention, as their ability to model human bone depends on test type.
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio - Finland and SIB Labs, University of Eastern Finland, Kuopio - Finland.
authors.forename: Arto P
authors.initials: AP
authors.lastname: Koistinen
authors.forename: Hannu
authors.initials: H
authors.lastname: Korhonen
authors.forename: Heikki
authors.initials: H
authors.lastname: Kröger
authors.forename: Reijo
authors.initials: R
authors.lastname: Lappalainen
mesh_terms: D015519:Bone Density; D001863:Bone Screws; D001842:Bone and Bones / Q000737:chemistry / Q000502:physiology*; D055119:Elastic Modulus; D006801:Humans; D019904:Polymethyl Methacrylate / Q000737:chemistry; D013314:Stress, Mechanical; D013718:Tensile Strength
chemical_list: D019904:Polymethyl Methacrylate