title: Probability of failure of orthodontic brackets bonded with different cementing agents.
abstract: OBJECTIVE
  The aim of this study was to compare the maximum loads at failure and the probability of failure of three glass ionomer cements and a composite cement bonding orthodontic brackets to human premolar teeth.
  
  
  METHODS
  The cements studied included a conventional glass ionomer cement, two resin-modified glass ionomer cements and a composite cement. The roots of 200 human premolar teeth were embedded in acrylic resin and the buccal enamel surface of the crown prepared as required. Each cement used to bond the bracket to the enamel was weighted, and light-cured where required. The specimens were stored for 10 min or 24 h at 37 degrees C and 100% humidity. A tensile shear force was applied via a wire loop placed under the wings of the bracket. The maximum load at failure was noted and subjected to Weibull analysis to compare probabilities of survival for each cement. The data obtained was also analyzed using a Kruskal-Wallis test followed by comparison of the groups using Mann-Whitney tests.
  
  
  RESULTS
  Comparison of the loads at failure revealed that the composite cement was significantly stronger than the glass ionomer cements at 10 min and 24 h (p<0.05). Weibull analysis of the results gave values for the Weibull moduli and probabilities of survival for an orthodontic bracket under a given load for each cement at 10 min and 24 h.
  
  
  CONCLUSIONS
  . Glass ionomer cements give a number of clinically significant advantages over composite cement in the retention of brackets. The resin-modified glass ionomer cements tested had a higher probability of survival than the conventional cement tested at 24 h. However, further improvements in their early bond strength would be clinically beneficial.
authors.affiliation: Department of Restorative Dentistry, School of Clinical Dentistry, The Queen's University of Belfast, Northern Ireland, UK.
authors.forename: C A
authors.initials: CA
authors.lastname: Mitchell
authors.forename: E
authors.initials: E
authors.lastname: O'Hagan
authors.forename: J M
authors.initials: JM
authors.lastname: Walker
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate; D003188:Composite Resins; D001840:Dental Bonding; D003738:Dental Cements; D004868:Equipment Failure; D005899:Glass Ionomer Cements; D006801:Humans; D008422:Materials Testing; D008962:Models, Theoretical; D016910:Orthodontic Brackets; D018709:Statistics, Nonparametric; D016019:Survival Analysis; D013718:Tensile Strength; D013997:Time Factors
chemical_list: D003188:Composite Resins; D003738:Dental Cements; D005899:Glass Ionomer Cements; C084550:Vitremer; C054101:ChemFil II; D017438:Bisphenol A-Glycidyl Methacrylate