title: The effect of repeated torque in small diameter implants with machined and premachined abutments.
abstract: BACKGROUND
  Detorquing value is an important factor in the amount of preload stresses during abutment screw fastening. This study evaluated the percentage of detorque values in two-piece machined titanium and premachined cast abutments in small diameter implants.
  
  
  METHODS
  Three groups of five samples were evaluated. Group 1 (G1), machined titanium abutments, group 2 (G2), premachined cast straight abutments that cast with gold-palladium, and group 3 (G3), premachined angled cast abutments that cast with the same alloy, were angled before casting. Each abutment was torque to 24 Ncm according to the manufacturer's instructions and detorqued five times. The means of detorquing and torquing values in all groups were recorded. The mean of detorque in each group as a percentage of the toque value was calculated. The data for all groups were compared and calculated using analysis of variance (ANOVA) and t-test.
  
  
  RESULTS
  Mean detorque values in G1, G2, and G3 were 88.1 ± 1.69, 93.1 ± 2.68, and 80.9 ± 4.95%, respectively. The ANOVA showed significant differences in mean of applied detorque (p < .001) and torque (p = .06) tightening among different groups. G2 had significantly greater detorque values (p < .05). No significant differences were found between G1 and G2. Surprisingly, abutment screw fracture occurred in three samples of G3.
  
  
  CONCLUSIONS
  G3 showed significant percentage torque reduction (p < .05) and exhibited abutment screw fracture during evaluation. G2 presented the lowest torque reduction. Screw fracture occurred only in G3.
authors.affiliation: Department of Prosthodontics, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Abolfazl
authors.initials: A
authors.lastname: Saboury
authors.forename: Hamid
authors.initials: H
authors.lastname: Neshandar Asli
authors.forename: Shahram
authors.initials: S
authors.lastname: Vaziri
mesh_terms: D000044:Dental Abutments; D003734:Dental Casting Investment / Q000737:chemistry; D059605:Dental Implant-Abutment Design; D015921:Dental Implants; D003764:Dental Materials / Q000737:chemistry; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D010165:Palladium / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D019415:Torque
chemical_list: D003734:Dental Casting Investment; D015921:Dental Implants; D003764:Dental Materials; D006047:Gold Alloys; D010165:Palladium; D014025:Titanium