title: Evaluation of shear bond strength of orthodontic brackets using trans-illumination technique with different curing profiles of LED light-curing unit in posterior teeth.
abstract: BACKGROUND
  Although using light-cured composites for bonding orthodontic brackets has become increasingly popular, curing light cannot penetrate the metallic bulk of brackets and polymerization of composites is limited to the edges. Limited access and poor direct sight may be a problem in the posterior teeth. Meanwhile, effectiveness of the trans-illumination technique is questionable due to increased bucco-lingual thickness of the posterior teeth. Light-emitting diode (LED) light-curing units cause less temperature rise and lower risk to the pulpal tissue. The purpose of this study was to evaluate the clinical effectiveness of trans-illumination technique in bonding metallic brackets to premolars, using different light intensities and curing times of an LED light-curing unit.
  
  
  METHODS
  Sixty premolars were randomly divided into six groups. Bonding of brackets was done with 40- and 80-s light curing from the buccal or lingual aspect with different intensities. Shear bond strengths of brackets were measured using a universal testing machine. Data were analyzed by one-way analysis of variance test and Duncan's post hoc test.
  
  
  RESULTS
  The highest shear bond belonged to group 2 (high intensity, 40 s, buccal) and the lowest belonged to group 3 (low intensity, 40 s, lingual). Bond strength means in control groups were significantly higher than those in experimental groups.
  
  
  CONCLUSIONS
  In all experimental groups except group 6 (80 s, high intensity, lingual), shear bond strength was below the clinically accepted values. In clinical limitations where light curing from the same side of the bracket is not possible, doubling the curing time and increasing the light intensity during trans-illumination are recommended for achieving acceptable bond strengths.
authors: Mashhad University of Medical Sciences, Mashhad 91735-984, Iran. negin.ghaffari@gmail.com.
authors: Farzin
authors: F
authors: Heravi
authors: Saied Mostafa
authors: SM
authors: Moazzami
authors: Negin
authors: N
authors: Ghaffari
authors: Javad
authors: J
authors: Jalayer
authors: Yasaman
authors: Y
authors: Bozorgnia
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods; D001641:Bicuspid; D003188:Composite Resins / Q000737:chemistry; D055117:Curing Lights, Dental / Q000145:classification; D003722:Dental Alloys / Q000737:chemistry; D001840:Dental Bonding / Q000379:methods*; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000295:instrumentation / Q000379:methods*; D008422:Materials Testing; D016910:Orthodontic Brackets; D010756:Phosphoric Acids / Q000737:chemistry; D058105:Polymerization; D011829:Radiation Dosage; D033081:Shear Strength; D013193:Stainless Steel / Q000737:chemistry; D013314:Stress, Mechanical; D013696:Temperature; D013997:Time Factors; D014172:Transillumination / Q000295:instrumentation / Q000379:methods*
chemical_list: D003188:Composite Resins; D003722:Dental Alloys; D010756:Phosphoric Acids; C516047:Transbond XT Light Cure Adhesive Primer; D013193:Stainless Steel; C030242:phosphoric acid