title: Changes in shear bond strength of ceramic and stainless steel brackets with different visible light curing times and directions.
abstract: BACKGROUND
  Selection of the appropriate curing time and light direction may enable the appropriate shear bond strength to be obtained and avoid enamel fracture during debonding.
  
  
  OBJECTIVE
  To determine the effects of different curing times and light directions on the shear bond strengths of ceramic and stainless steel brackets.
  
  
  METHODS
  Ninety-two recently extracted, upper premolars were randomly assigned to six groups. Either stainless steel or ceramic brackets were bonded to the buccal surfaces of the teeth. Group I, stainless steel brackets cured for 40 seconds from buccal surface; Group II, stainless steel brackets cured for 40 seconds from palatal surface; Group III, stainless steel brackets cured for 80 seconds from palatal surface; Group IV, ceramic brackets cured for 40 seconds from the buccal surface; Group V, ceramic brackets cured for 40 seconds from the palatal surface; Group VI, ceramic brackets cured for 80 seconds from the palatal surface. The shear bond strength was measured with a universal testing machine and the resin remaining after debonding scored with the Adhesive Remnant Index (ARI). The data were analysed with the oneway ANOVA, Tukey's HSD test and the Kruskal-Wallis test. Associations between the ARI and shear bond strength were determined with Pearson's correlation coefficient.
  
  
  RESULTS
  Group IV (ceramic brackets cured for 40 seconds from buccal surface) had the highest shear bond strength (21.26 MPa) and Group II (metal brackets cured for 40 seconds from palatal surface) had the lowest shear bond strength (6.95 MPa).There was no significant difference in ARI scores among the groups. The association between the ARI scores and bond strength values was not statistically significant.
  
  
  CONCLUSIONS
  Curing from the buccal surface for 40 seconds gave unacceptably high shear bond strength values for both stainless steel and ceramic brackets. Lower shear bond strengths occurred when the light was directed from the palatal surface, but a shorter curing time is more likely to be preferred by clinicians. Future studies should investigate the possibility of reducing the curing time for both brackets.
authors.affiliation: Department of Orthodontics and the Dental Research Center, School of Dentistry, Mashad, Iran. heravif@mums.ac.ir
authors.forename: Farzin
authors.initials: F
authors.lastname: Heravi
authors.forename: Shahin
authors.initials: S
authors.lastname: Bayani
mesh_terms: D002516:Ceramics; D003722:Dental Alloys; D017005:Dental Debonding / Q000009:adverse effects; D003743:Dental Enamel / Q000293:injuries; D003799:Dental Stress Analysis; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000009:adverse effects / Q000379:methods*; D016910:Orthodontic Brackets; D019279:Resin Cements / Q000528:radiation effects*; D033081:Shear Strength; D013193:Stainless Steel; D013997:Time Factors
chemical_list: D003722:Dental Alloys; D019279:Resin Cements; D013193:Stainless Steel