title: Clinical and Radiographic Evaluation of Marginal Bone Changes around Platform-Switching Implants Placed in Crestal or Subcrestal Positions: A Randomized Controlled Clinical Trial.
abstract: BACKGROUND
  It has been reported in many articles that marginal bone resorptions are prevented by platform-switching design. However, what occurs when these implants are placed in the apical position is not completely known.
  
  
  OBJECTIVE
  This report describes a randomized controlled clinical trial study that aims to test the hypothesis that less resorption will occur when platform-switching implants are placed 1 mm below bone level.
  
  
  METHODS
  A total of 56 randomly selected implants were inserted bilaterally, either 1 mm below bone level (test group, 28 implants) or at bone level (control group, 28 implants) of the patients' posterior regions. Marginal bone resorptions were examined through periapical radiographies taken with the parallel technique at the time of crown cementation and the third, sixth, 12th, and 36th months after prosthetic loading. The modified plaque index, gingival index, bleeding on probing, and probing depths were used for follow-up periodontal care of the implants.
  
  
  RESULTS
  After 3 years, the mean radiographic vertical bone loss in the control group was significantly lower than in the test group (0.56 ± 0.35 mm and 1.21 ± 1.05 mm, respectively) (p < .01). In terms of periodontal indexes, there were no statistically significant differences between the two groups (p > .05). No peri-implantitis or peri-implant mucositis was observed around the test or control implants.
  
  
  CONCLUSIONS
  More marginal bone resorptions occurred after the third year of loading in implants placed 1 mm below bone level. However, the resorptions did not reach the implants thread. In the control group, the first bone implant contact was placed under the level of the first threads. Therefore, the present randomized clinical trial confirmed the hypothesis that placing platform-switching implants 1 mm below bone level reduced marginal bone loss. It can be noted that to reduce resorption, platform-switching implants should be placed below bone level.
authors.affiliation: Department of Oral Implantology, Faculty of Dentistry, Yeditepe University, Istanbul Turkey.
authors.forename: Esma
authors.initials: E
authors.lastname: Kütan
authors.affiliation: Department of Oral Implantology, Faculty of Dentistry, Istanbul University, Istanbul, Turkey.
authors.forename: Nilufer
authors.initials: N
authors.lastname: Bolukbasi
authors.affiliation: Department of Oral Implantology, Faculty of Dentistry, Istanbul University, Istanbul, Turkey.
authors.forename: Esra
authors.initials: E
authors.lastname: Yildirim-Ondur
authors.affiliation: Department of Oral Implantology, Faculty of Dentistry, Istanbul University, Istanbul, Turkey.
authors.forename: Tayfun
authors.initials: T
authors.lastname: Ozdemir
mesh_terms: D000328:Adult; D000368:Aged; D016301:Alveolar Bone Loss / Q000000981:diagnostic imaging / Q000209:etiology*; D059605:Dental Implant-Abutment Design / Q000009:adverse effects* / Q000379:methods; D003758:Dental Implantation, Endosseous / Q000009:adverse effects* / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011861:Radiography, Dental
keywords: marginal bone loss; platform switching; submerged healing