title: Torque removal evaluation of prosthetic screws after tightening and loosening cycles: an in vitro study.
abstract: OBJECTIVE
  The aim of this study was to evaluate the variation in removal torque of implant prosthetic abutment screws after successive tightening and loosening cycles, in addition to evaluating the influence of the hexagon at the abutment base on screw removal torque.
  
  
  METHODS
  Twenty hexagonal abutments were tightened to 20 regular external hex implants with a titanium alloy screw, with an insertion torque of 32 N cm, measured with a digital torque gauge. The implant/abutment/screw assemblies were divided into two groups: (1) abutments without hexagon at the base and (2) abutments with a hexagon at the base. Each assembly received a provisional restoration and was submitted to mechanical loading cycles. After this, the screws were removed and the removal torque was measured. This sequence was repeated 10 times, then the screw was replaced by a new one, and another cycle was performed. Linear regression analysis was performed.
  
  
  RESULTS
  Removal torque values tended to decrease as the number of insertion/removal cycles increased, for both groups. Comparisons of the slopes and the intercepts between groups showed no statistical difference. There was no significant difference between the mean values of last five cycles and the 11th cycle. Within the limitations of this in vitro study, it was concluded that (1) repeated insertion/removal cycles promoted gradual reduction in removal torque of screws, (2) replacing the screw with a new one after 10 cycles did not increase resistance to loosening, and (3) removal of the hexagon from the abutment base had no effect on the removal torque of the screws.
authors: Department of Prosthodontics, Dental School, State University of Rio de Janeiro, Rio de Janeiro, Brazil. mayra.cardoso@bol.com.br
authors: Mayra
authors: M
authors: Cardoso
authors: Marcelo Ferreira
authors: MF
authors: Torres
authors: Eduardo José Veras
authors: EJ
authors: Lourenço
authors: Daniel
authors: D
authors: de Moraes Telles
authors: Renata Cristina Silveira
authors: RC
authors: Rodrigues
authors: Ricardo Faria
authors: RF
authors: Ribeiro
mesh_terms: D001863:Bone Screws; D000044:Dental Abutments; D015921:Dental Implants; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention; D003799:Dental Stress Analysis; D020878:Device Removal; D066298:In Vitro Techniques; D016014:Linear Models; D008422:Materials Testing; D018709:Statistics, Nonparametric; D013314:Stress, Mechanical; D019415:Torque
chemical_list: D015921:Dental Implants