title: Radiological and micro-computed tomography analysis of the bone at dental implants inserted 2, 3 and 4 mm apart in a minipig model with platform switching incorporated.
abstract: BACKGROUND
  The purpose of this study was to assess the effect of inter-implant distance on interproximal bone utilizing platform switching. Analysis of interproximal bone usually depends on traditional two-dimensional radiographic assessment. Although there has been increased reliability of current techniques, there has been an inability to track bone level changes over time and in three dimensions. Micro-CT has provided three-dimensional imaging that can be used in conjunction with traditional two-dimensional radiographic techniques.
  
  
  METHODS
  This study was performed on 24 female minipigs. Twelve animals received three implants with an inter-implant distance of 3 mm on one side of the mandible and another three implants on the contra-lateral side, where the implants were placed 2 mm apart creating a split mouth design. Twelve other animals received three implants with an inter-implant distance of 3 mm on one side of the mandible and another three implants on the contra-lateral side, where the implants were placed 4 mm apart creating a split mouth design too. The quantitative evaluation was performed comparatively on radiographs taken at t 0 (immediately after implantation) and at t 8 weeks (after termination). The samples were scanned by micro-computed tomography (μCT) to quantify the first bone to implant contact (fBIC) and bone volume/total volume (BV/TV). Mixed model regressions using the nonparametric Brunner-Langer method were used to determine the effect of inter-implant distance on the measured outcomes.
  
  
  RESULTS
  The change in bone level was determined using radiography and its mean was 0.05 mm for an inter-implant distance of 3 and 0.00 mm for a 2 mm distance (P = 0.7268). The mean of this outcome was 0.18 mm for the 3 mm and for 4 mm inter-implant distance (P = 0.9500). Micro-computed tomography showed that the fBIC was always located above the reference, 0.27 and 0.20 mm for the comparison of 2-3 mm (P = 0.4622) and 0.49 and 0.34 mm for the inter-implant distance of 3 and 4 mm (P = 0.1699). BV/TV inside the defined parallelepipedic masks reached 82.38% for the 2 mm inter-implant distance and 85.00% for 3 mm, P = 0.8432. For the comparison of the 3-4 mm inter-implant distance, the means were 84.69% and 84.38%, respectively, P = 0.8401. Non-inferiority tests for the smaller inter-implant distances for both comparisons showed similar differences and similar tolerance ranges.
  
  
  CONCLUSIONS
  The effect of a smaller interproximal distances between implants on bone level, fBIC and BV/TV assessed by two convergent investigation methods, radiology and μCT, was similar to that of larger distances. Implants can potentially be placed 2 mm apart instead of 3 mm and 3 mm apart instead of 4 mm when platform switching is utilized. Further research with a conventional platform is warranted.
authors.affiliation: Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, NY, USA.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Elian
authors.forename: Mitchell
authors.initials: M
authors.lastname: Bloom
authors.forename: Michel
authors.initials: M
authors.lastname: Dard
authors.forename: Sang-Choon
authors.initials: SC
authors.lastname: Cho
authors.forename: Richard D
authors.initials: RD
authors.lastname: Trushkowsky
authors.forename: Dennis
authors.initials: D
authors.lastname: Tarnow
mesh_terms: D000818:Animals; D003758:Dental Implantation, Endosseous / Q000379:methods*; D015921:Dental Implants; D017267:Dental Prosthesis Design; D005260:Female; D021621:Imaging, Three-Dimensional; D020007:Implants, Experimental; D008334:Mandible / Q000000981:diagnostic imaging* / Q000601:surgery; D023421:Models, Animal; D013552:Swine; D013556:Swine, Miniature; D014945:Wound Healing; D055114:X-Ray Microtomography
chemical_list: D015921:Dental Implants