title: Influence of three types of abutments on preload values before and after cyclic loading with structural analysis by scanning electron microscopy.
abstract: OBJECTIVE
  To evaluate the effectiveness of three types of abutments in the maintenance of screw joint preload before and after cyclic loading as well as to observe possible microdamage in the structure of the components using a scanning electron microscope (SEM).
  
  
  METHODS
  Forty-five external-hex implants were embedded in epoxy resin, received their respective abutments, and were randomly divided into three experimental groups (n = 15): (1) machined titanium (Ti) abutments; (2) pre-machined gold (Au) abutments; and (3) machined zirconia (ZrO(2)) abutments. The abutment screws were tightened according to the manufacturer's recommended torque. Initially, a static bending test was performed using five specimens of each group to determine the load applied in the cyclic loading test. Thus, 10 specimens of each group were used to measure the reverse torque value (preload) of the abutment screw before and after loading. A cyclic loading (0.5 × 10(6) cycles; 15 Hz) between 11 and 211 N was applied at an angle of 30 degrees to the long axis of the implants. The group means were compared using analysis of variance and the Tukey test (α = .05).
  
  
  RESULTS
  The reverse torque analysis before cyclic loading showed no significant difference among the groups (P > .05). After cyclic loading, all preload means decreased significantly. The lowest decrease in preload was observed in the Ti group, whereas the highest decrease was observed in the ZrO(2) group, with a significant difference noted between them (P = .010). The Au group presented an intermediate decrease, with no significant difference compared to the other groups (P > .05). SEM images showed structural changes in the mating surfaces of the abutments after cyclic loading.
  
  
  CONCLUSIONS
  The load application reduced the preload means significantly in all groups, and more significantly in the ZrO(2) group.
authors.affiliation: Department of Dental Materials and Prosthodontics, Araraquara Dental School, UNESP - Univ Estadual Paulista, São Paulo, Brazil. luibut@yahoo.com.br
authors.forename: Luis Eduardo
authors.initials: LE
authors.lastname: Butignon
authors.forename: Mariana de Almeida
authors.initials: Mde A
authors.lastname: Basilio
authors.forename: Rodrigo de Paula
authors.initials: Rde P
authors.lastname: Pereira
authors.forename: Joao Neudenir
authors.initials: JN
authors.lastname: Arioli Filho
mesh_terms: D000704:Analysis of Variance; D001863:Bone Screws; D000044:Dental Abutments; D019250:Dental Implants, Single-Tooth; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000379:methods*; D004853:Epoxy Resins; D006046:Gold; D008855:Microscopy, Electron, Scanning; D011897:Random Allocation; D013314:Stress, Mechanical; D013718:Tensile Strength; D014025:Titanium / Q000737:chemistry; D019415:Torque; D015040:Zirconium
chemical_list: D004853:Epoxy Resins; D006046:Gold; D015040:Zirconium; D014025:Titanium; C028541:zirconium oxide