title: Quantifying the influence of bone density and thickness on resonance frequency analysis: an in vitro study of biomechanical test materials.
abstract: OBJECTIVE
  Resonance frequency analysis (RFA) offers the opportunity to monitor the osseointegration of an implant in a simple, noninvasive way. A better comprehension of the relationship between RFA and parameters related to bone quality would therefore help clinicians improve diagnoses. In this study, a bone analog made from polyurethane foam was used to isolate the influences of bone density and cortical thickness in RFA.
  
  
  METHODS
  Straumann standard implants were inserted in polyurethane foam blocks, and primary implant stability was measured with RFA. The blocks were composed of two superimposed layers with different densities. The top layer was dense to mimic cortical bone, whereas the bottom layer had a lower density to represent trabecular bone. Different densities for both layers and different thicknesses for the simulated cortical layer were tested, resulting in eight different block combinations. RFA was compared with two other mechanical evaluations of primary stability: removal torque and axial loading response.
  
  
  RESULTS
  The primary stability measured with RFA did not correlate with the two other methods, but there was a significant correlation between removal torque and the axial loading response (P < .005). Statistical analysis revealed that each method was sensitive to different aspects of bone quality. RFA was the only method able to detect changes in both bone density and cortical thickness. However, changes in trabecular bone density were easier to distinguish with removal torque and axial loading than with RFA.
  
  
  CONCLUSIONS
  This study shows that RFA, removal torque, and axial loading are sensitive to different aspects of the bone-implant interface. This explains the absence of correlation among the methods and proves that no standard procedure exists for the evaluation of primary stability.
authors.affiliation: Institute for Surgical Technology and Biomechanics, University of Bern, Bern, Switzerland. thibaut.bardyn@istb.unibe.ch
authors.forename: Thibaut
authors.initials: T
authors.lastname: Bardyn
authors.forename: Philippe
authors.initials: P
authors.lastname: Gédet
authors.forename: Wock
authors.initials: W
authors.lastname: Hallermann
authors.forename: Philippe
authors.initials: P
authors.lastname: Büchler
mesh_terms: D015519:Bone Density; D001842:Bone and Bones / Q000033:anatomy & histology; D003758:Dental Implantation, Endosseous; D015921:Dental Implants; D017268:Dental Prosthesis Retention; D003799:Dental Stress Analysis / Q000295:instrumentation / Q000379:methods*; D020878:Device Removal; D006801:Humans; D008422:Materials Testing / Q000295:instrumentation / Q000379:methods*; D008953:Models, Anatomic; D016348:Osseointegration; D015203:Reproducibility of Results; D019415:Torque; D014732:Vibration
chemical_list: D015921:Dental Implants