title: Implant abutment screw rotations and preloads for four different screw materials and surfaces.
abstract: BACKGROUND
  Chronic implant screw loosening remains a problem in restorative practices. Some implant manufacturers have introduced abutment screws with treated surfaces in an effort to increase preload and reduce potential loosening. Purpose. This study evaluated the materials and surfaces of 4 commercially available abutment screws on preload generation.
  
  
  METHODS
  Twenty of each of the following abutment screws-Gold-Tite (Gt), TorqTite (Tt), gold alloy (Ga), and titanium alloy (Ta)-were divided into 2 groups. Measurements were recorded for each abutment screw on a mounted 3.75 x 18 mm external hex implant with a titanium abutment. Rotational angle measurements were conducted on the 4 abutment screws at 20 and 32 Ncm. Removal torque values were recorded and used to indirectly generate preload values. Random implant block specimens were sectioned and qualitatively evaluated with an SEM.
  
  
  RESULTS
  At 20 and 32 Ncm, the largest rotational angles were recorded for the Tt groups: 21.2 +/- 3.1 degrees and 38.1 +/- 8.7 degrees, respectively. The greatest preload values at 20 and 32 Ncm were calculated for the Gt groups: 596.8 +/- 101.2 N and 1015.3 +/- 191.2 N, respectively. SEM analysis of the 4 implant block specimens revealed mating thread contacts located in the middle portion of the superior surface of the abutment screw thread. The greatest number of mating thread contacts were seen in the Gt implant block specimen (14 of 20 possible thread contacts).
  
  
  CONCLUSIONS
  The Gt and Tt abutment screws with enhanced surfaces that help reduce the coefficient of friction produced greater rotational angles and preload values than the conventional gold alloy and titanium alloy screws.
authors.affiliation: College of Dentistry, University of Florida, Gainesville, FL 32608, USA. wmartin@dental.ufl.edu
authors.forename: W C
authors.initials: WC
authors.lastname: Martin
authors.forename: R D
authors.initials: RD
authors.lastname: Woody
authors.forename: B H
authors.initials: BH
authors.lastname: Miller
authors.forename: A W
authors.initials: AW
authors.lastname: Miller
mesh_terms: D000465:Algorithms; D000497:Alloys; D000704:Analysis of Variance; D000044:Dental Abutments; D003722:Dental Alloys / Q000737:chemistry; D015921:Dental Implants; D003764:Dental Materials / Q000737:chemistry*; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D017276:Friction; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D010165:Palladium / Q000737:chemistry; D012399:Rotation; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D019415:Torque
chemical_list: D000497:Alloys; D003722:Dental Alloys; D015921:Dental Implants; D003764:Dental Materials; D006047:Gold Alloys; C031462:titanium alloy (TiAl6V4); D010165:Palladium; D014025:Titanium