title: Bond strengths and debonding characteristics of two types of polycrystalline ceramic brackets.
abstract: OBJECTIVE
  To compare the shear bond strengths and modes of failure of three orthodontic brackets: a polycrystalline ceramic bracket, a collapsible polycrystalline ceramic bracket and a metal bracket.
  
  
  METHODS
  Ninety extracted human premolar teeth were selected and examined at x3 magnification for any enamel defects. Three types of brackets and one orthodontic adhesive were used. One half of the sample was tested in a universal testing machine to determine the shear bond strength. The other half was debonded with the appropriate pliers and the tooth surface examined at x5 magnification. The site of failure was scored with the modified Adhesive Remnant Index (ARI). Teeth with an ARI grade of zero were examined in a SEM to determine any enamel fracture.
  
  
  RESULTS
  No statistically significant differences in bond strength among the samples were found (p > 0.159). The modes of failure after debonding with pliers were predominantly at the bracket-adhesive interface. The mean shear bond strength of the Clarity bracket was 10.78 +/- 2.74 MPa, the InVu bracket was 12.43 +/- 2.40 MPa and the metal bracket was 11.89 +/- 1.83 MPa. There were significant differences in the mean rank of the ARI grade between the three groups (p = 0.006). The Clarity and InVu (p = 0.011) and the Clarity and metal brackets (p = 0.005) were significantly different, but there was no difference between the InVu and metal brackets (p = 0.187).
  
  
  CONCLUSIONS
  All three samples had similar bond strengths. The risk of ceramic fracture on debonding was greatest for the InVu ceramic bracket.
authors.affiliation: Department of Comprehensive Dentistry and Biomaterials, Louisiana State University Health Sciences Center, New Orleans, LA 70119, USA.
authors.forename: Katia
authors.initials: K
authors.lastname: Lemke
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Xu
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Hagan
authors.forename: Paul C
authors.initials: PC
authors.lastname: Armbruster
authors.forename: Richard W
authors.initials: RW
authors.lastname: Ballard
mesh_terms: D000134:Acid Etching, Dental; D000268:Adhesiveness; D002516:Ceramics / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry; D003461:Crystallography; D003722:Dental Alloys / Q000737:chemistry; D001840:Dental Bonding; D017005:Dental Debonding / Q000295:instrumentation; D003743:Dental Enamel / Q000033:anatomy & histology / Q000648:ultrastructure; D003764:Dental Materials / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D016382:Orthodontic Appliance Design; D016910:Orthodontic Brackets / Q000145:classification; D019279:Resin Cements / Q000737:chemistry; D033081:Shear Strength; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D003188:Composite Resins; D003722:Dental Alloys; D003764:Dental Materials; D019279:Resin Cements; C516047:Transbond XT Light Cure Adhesive Primer