title: An ultrastructural study of the influence of acidity of self-etching primers and smear layer thickness on bonding to intact dentin.
abstract: OBJECTIVE
  The objectives of this study were (1) to determine the depth of demineralization into intact dentin using several self-etching primer systems with different pH values, and (2) to evaluate whether hybridization of intact dentin in Clearfil SE Bond may be affected by variation in the thickness of the smear layers.
  
  
  METHODS
  Dentin disks were created from mid-coronal dentin in extracted, human third molars. Three self-etching primer systems (Clearfil Liner Bond II, Liner Bond 2V, and SE Bond) were applied separately to these disks to evaluate how deep self-etching systems penetrate through smear layers into intact dentin. Dentin treated with All-Bond 2 using the "no-etch" technique was used as a control group. In the second part of the study, dentin disks with different smear-layer thicknesses were produced. The cryofractured control group was devoid of a smear layer. The experimental teeth were ground with 60-, 180-, or 600-grit SiC paper and bonded using SE Bond. Dentin disks were bonded together and examined with TEM.
  
  
  RESULTS
  All-Bond 2 did not etch beyond the smear layer. The three self-etching primers etched beyond the smear layer to form true hybrid layers within intact dentin. This layer was thickest with Liner Bond 2 (ca 1.2 to 1.4 microns), but very thin (0.5 micron) using both Liner Bond 2V and SE Bond. Application of SE Bond to dentin of different surface roughness produced hybridized smear layers of variable thickness. However, the thickness of the underlying true hybrid remained consistent for the four groups (ca 0.4 to 0.5 micron).
  
  
  CONCLUSIONS
  Self-etching primers create thin hybrid layers that incorporate the smear layer. The suspicion that thick smear layers may interfere with the diffusion of self-etching primers into the underlying intact dentin was not confirmed.
authors.affiliation: Department of Conservative Dentistry, Faculty of Dentistry, University of Hong Kong, Hong Kong, China.
authors.forename: F R
authors.initials: FR
authors.lastname: Tay
authors.forename: H
authors.initials: H
authors.lastname: Sano
authors.forename: R
authors.initials: R
authors.lastname: Carvalho
authors.forename: E L
authors.initials: EL
authors.lastname: Pashley
authors.forename: D H
authors.initials: DH
authors.lastname: Pashley
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods*; D000143:Acids; D001840:Dental Bonding; D003804:Dentin / Q000187:drug effects / Q000648:ultrastructure*; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D004058:Diffusion; D005614:Freeze Fracturing; D006801:Humans; D008689:Methacrylates / Q000737:chemistry; D008854:Microscopy, Electron; D019279:Resin Cements / Q000737:chemistry; D016369:Smear Layer; D013499:Surface Properties
chemical_list: D000143:Acids; C029849:Clearfil Bonding Agent; C112274:Clearfil Liner Bond 2; C084544:Clearfil Linerbond System; D017220:Dentin-Bonding Agents; D008689:Methacrylates; D019279:Resin Cements; C100742:All-Bond 2