title: Effect of microthreads and platform switching on crestal bone stress levels: a finite element analysis.
abstract: BACKGROUND
  The aims of this study were to investigate the effects of implant microthreads on crestal bone stress compared to a standard smooth implant collar and to analyze how different abutment diameters influenced the crestal bone stress level.
  
  
  METHODS
  Two-dimensional finite element imaging was used to create a cross-sectional model of an implant (5-mm platform and 13 mm in length) placed in the premolar region of the mandible. The two tapered implant models consisted of one with microthreads at the crestal portion and the other with a smooth neck. The implant model was reverse-engineered to resemble a commercially available microthread implant. Abutments of different diameters (4.0 mm: 20% platform switching; 4.5 mm: 10% platform switching; and 5.0 mm: standard) were loaded with a force of 100 N at 90 degrees vertical and 15 degrees oblique angles. Finite element analysis was used to analyze the stress patterns in bone, especially in the crestal region.
  
  
  RESULTS
  Upon loading, the microthread implant model had 29% greater stress (31.61 MPa in oblique and 9.31 MPa in vertical) at the crestal bone adjacent to the implant than the smooth-neck implant (24.51 and 7.20 MPa, respectively). When the abutment diameter decreased from 5.0 to 4.5 mm and then to 4.0 mm, the microthread model showed a reduction of stress at the crestal bone level from 6.3% to 5.4% after vertical loading and from 4.2% to 3.3% after oblique loading. The smooth-neck model showed a reduction of stress from 5.6% to 4.9% after vertical loading and from 3.7% to 2.9% after oblique loading.
  
  
  CONCLUSIONS
  Microthreads increased crestal stress upon loading. Reduced abutment diameter (i.e., platform switching) resulted in less stress translated to the crestal bone in the microthread and smooth-neck groups.
authors.affiliation: School of Dentistry, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Schrotenboer
authors.forename: Yi-Pin
authors.initials: YP
authors.lastname: Tsao
authors.forename: Vipul
authors.initials: V
authors.lastname: Kinariwala
authors.forename: Hom-Lay
authors.initials: HL
authors.lastname: Wang
mesh_terms: D000539:Alveolar Process; D003198:Computer Simulation; D003758:Dental Implantation, Endosseous / Q000295:instrumentation*; D019250:Dental Implants, Single-Tooth; D017267:Dental Prosthesis Design; D003799:Dental Stress Analysis; D020342:Finite Element Analysis; D006801:Humans; D008334:Mandible; D013314:Stress, Mechanical