title: Shear bond strength with increasing light-guide distance from dentin.
abstract: BACKGROUND
  In Class II composite restorations, the adhesive covering the gingival floor of the deep cavity preparation is 2 to 8 mm from the light guide and may not be adequately cured with a typical 10-second curing time.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the dentin bond strengths of resin composite when the curing light guide (quartz-tungsten-halogen light) was placed at various distances and to investigate the relationships between radiant exposure, degree of conversion, and shear bond strength.
  
  
  METHODS
  Single Bond (3M ESPE, St. Paul, MN, USA) was placed onto the dentin following the manufacturer's directions. Four groups of 10 teeth were cured for 20 seconds through a 0, 2.3, 4.6, or 6.9 mm spacer. Two other groups of 10 teeth were cured through a 4.6 mm spacer for 40 seconds and 60 seconds, respectively. Z100 resin composite (3M ESPE) was placed over the cured adhesive and polymerized at the same distance as the adhesive. After 24 hours of storage in water, the shear bond strengths were tested. The irradiance through each spacer was measured using a digital radiometer. The degree of conversion of the adhesive was determined by near infrared spectroscopy. The data were analyzed using analysis of variance and Tukey-B post hoc tests.
  
  
  RESULTS
  Dentin shear bond strengths decreased significantly with increasing distance, but they increased significantly when the curing time increased from 20 to 40 or 60 seconds. There is a linear correlation between shear bond strength, degree of conversion, and logarithm (radiant exposure).
  
  
  CONCLUSIONS
  Increasing curing time can compensate for the decreased bond strength owing to a decreased irradiance associated with increased curing distance.
  
  
  CONCLUSIONS
  Under the conditions of this study, when curing the adhesives in deep proximal boxes with a quartz-tungsten-halogen light, the curing time should be increased to 40 to 60 seconds to ensure optimal polymerization.
authors.affiliation: Department of Operative Dentistry and Biomaterials, Louisiana State University Health Sciences Center School of Dentistry, New Orleans 70119, USA. xxu@lsuhsc.edu
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Xu
authors.forename: Dant A
authors.initials: DA
authors.lastname: Sandras
authors.forename: John O
authors.initials: JO
authors.lastname: Burgess
mesh_terms: D000704:Analysis of Variance; D017438:Bisphenol A-Glycidyl Methacrylate / Q000528:radiation effects*; D003188:Composite Resins; D001840:Dental Bonding / Q000379:methods*; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis; D017220:Dentin-Bonding Agents / Q000528:radiation effects*; D006219:Halogens; D006244:Hardness; D006801:Humans; D008027:Light; D016014:Linear Models; D008963:Molar; D044367:Phase Transition; D033081:Shear Strength; D012822:Silicon Dioxide; D013055:Spectrophotometry, Infrared; D013997:Time Factors; D015040:Zirconium
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; D006219:Halogens; C083568:Z100 composite resin; C115612:single bond; D017438:Bisphenol A-Glycidyl Methacrylate; D012822:Silicon Dioxide; D015040:Zirconium