title: Effect of double conical abutment screw on implant preload.
abstract: OBJECTIVE
  This study compared the loosening torque of experimental double conical abutment screws to that of conventional conical abutment screws and flat-head screws in implants with internal connections before and after mechanical loading.
  
  
  METHODS
  Eighty implant-screw-abutment assemblies were divided into four groups: flat-head screw (Xive S), conical screw (Straumann), conical screw (Nobel Biocare), and double conical screw (RTB). Abutments were tightened to a torque of 30 Ncm. After 10 min, they were retightened and loosening torque was measured. The same abutments were then retightened with new screws to a torque of 30 Ncm and, again, retightened after 10 min. They were then mechanically loaded for 3 000 000 cycles, and loosening torque was again measured. Data were collected, and an exploratory analysis was performed.
  
  
  RESULTS
  Comparisons before mechanical cycling showed significant differences between groups. After mechanical cycling, only the comparisons of Straumann and Nobel Biocare showed no significant differences. Considering the same group before and after mechanical cycling, all comparisons showed significant differences.
  
  
  CONCLUSIONS
  The shape of the abutment screw head significantly influenced loosening torque: Double conical-head screws showed significantly higher loosening torque values than conical-head screws. Conical-head screws showed higher loosening torque values than conventional flat-head screws before and after loading.
authors.affiliation: Austrian Society of Computerized Dentistry, Graz, Austria.
authors.forename: Gerwin Vincent
authors.initials: GV
authors.lastname: Arnetzl
authors.affiliation: Department of Oral Surgery and Radiology, School of Dentistry, Medical University Graz, Graz, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Payer
authors.affiliation: Department of Orthodontics, School of Dentistry, Medical University Vienna, Vienna, Austria.
authors.forename: Frank
authors.initials: F
authors.lastname: Falkensammer
authors.affiliation: Department of Prosthodontics, School of Dentistry, Medical University Graz, Graz, Austria.
authors.forename: Gerwin
authors.initials: G
authors.lastname: Arnetzl
mesh_terms: D001863:Bone Screws; D000044:Dental Abutments; D015921:Dental Implants; D003799:Dental Stress Analysis; D006801:Humans; D019415:Torque
chemical_list: D015921:Dental Implants
keywords: abutment screw design; implant abutments; implant preload