title: Torque loss of different abutment sizes before and after cyclic loading.
abstract: OBJECTIVE
  The aim of this study was to compare 3.8- and 4.8-mm abutments submitted to simulations of masticatory cycles to examine whether abutment diameter and cemented vs screw-retained crowns affect torque loss of the abutments and crowns.
  
  
  METHODS
  Forty implant/abutment sets were divided into the following groups (n = 10 in each group): (1) G4.8S included 4.8-mm abutment with screw-retained crown; (2) G4.8C included 4.8-mm abutment with cemented crown; (3) G3.8S included 3.8-mm abutment with screw-retained crown; and (4) G3.8C included 3.8-mm abutment with cemented crown. All abutments were tightened with torque values of 20 Ncm, and 10 Ncm for screw-retained crowns. Torque loss was measured before and after cycling loading (300,000 cycles).
  
  
  RESULTS
  Torque loss of screw-retained crowns significantly increased after cycling in abutments of groups G3.8S (P ≤ .05) and G4.8S (P = .001). No difference was noted between the abutments before cycling (P = .735), but G3.8S abutments presented greater torque loss than the other groups after cycling (P = .008). Significant differences were noted in the abutment torque loss before and after cycling loading only for the G3.8C group (P ≤ .05).
  
  
  CONCLUSIONS
  The abutment diameter affects torque loss of screw-retained crowns and leads to failure during the test; mechanical cycling increases torque loss of abutment screw and screw-retained crowns.
authors.forename: Izabela Cristina
authors.initials: IC
authors.lastname: Moris
authors.forename: Adriana Cláudia
authors.initials: AC
authors.lastname: Faria
authors.forename: Ricardo Faria
authors.initials: RF
authors.lastname: Ribeiro
authors.forename: Renata Cristina
authors.initials: RC
authors.lastname: Rodrigues
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws; D003442:Crowns / Q000592:standards*; D000044:Dental Abutments / Q000592:standards*; D059605:Dental Implant-Abutment Design; D015921:Dental Implants / Q000592:standards; D003799:Dental Stress Analysis / Q000379:methods; D006801:Humans; D019415:Torque
chemical_list: D015921:Dental Implants