title: Interfacial shear strength of endosseous implants.
abstract: OBJECTIVE
  Surface roughness is known to affect the load-bearing strength of implants. However, the underlying mechanisms are not completely understood. This study sought to investigate the potential effects of bone-to-implant contact (BIC) and mechanical interlocking on the stability of titanium implants using a newly established assessment system that combines nondestructive microcomputed tomography (ΜCT) and the biomechanical push-in test.
  
  
  METHODS
  Cylindric implants with a machined or a dual acid-etched (DAE) surface were placed into the distal femurs of Sprague-Dawley rats. At weeks 2 and 4, the femur-implant specimens were harvested and scanned in a desktop ΜCT device, and the BIC was calculated. The implants were then loaded axially using a universal mechanical testing machine and the breakage force was recorded as a push-in value. Machined and DAE implants were also embedded in histology-quality resin to serve as a nonbiologic reference. Two-way analysis of variance and the Mann-Whitney U test were used for statistical analysis.
  
  
  RESULTS
  BIC showed no surface- or time-dependent differences. The mean push-in value of DAE implants was four times greater at week 2 and three times greater at week 4 than that of machined implants. The shear strength at the interface (push-in value/BIC) was greater for DAE surfaces than for machined surfaces in a proportionate manner. When the implants were embedded in the resin with virtually 100% implant-resin contact, DAE implants showed 30% greater push-in values and shear strength than machined implants (P < .05).
  
  
  CONCLUSIONS
  These findings suggest that the percentage of BIC and mechanical interlocking cannot fully explain the surface roughness-related increase in osseointegration, as opposed to the common understanding of osseointegration. Further studies must include more details to discover the precise understanding of the physiology of osseointegration and the potential biologic mechanisms involved.
authors.affiliation: The Jane and Jerry Weintraub Center for Reconstructive Biotechnology, Division of Advanced Prosthodontics, Biomaterials and Hospital Dentistry, University of California at Los Angeles School of Dentistry, Los Angeles, California, USA. frank.butz@uniklinik-freiburg.de
authors.forename: Frank
authors.initials: F
authors.lastname: Butz
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ogawa
authors.forename: Ichiro
authors.initials: I
authors.lastname: Nishimura
mesh_terms: D000134:Acid Etching, Dental; D000818:Animals; D003758:Dental Implantation, Endosseous; D015921:Dental Implants; D003775:Dental Polishing; D003799:Dental Stress Analysis / Q000379:methods; D005269:Femur / Q000601:surgery; D020007:Implants, Experimental; D008297:Male; D016348:Osseointegration / Q000502:physiology*; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D033081:Shear Strength; D013499:Surface Properties; D014025:Titanium; D055114:X-Ray Microtomography
chemical_list: D015921:Dental Implants; D014025:Titanium