title: Apatite crystal protection against acid-attack beneath resin-dentin interface with four adhesives: TEM and crystallography evidence.
abstract: OBJECTIVE
  Interaction between specific functional groups and apatite crystals may contribute to adhesion. The present study investigated effects of four adhesives with different compositions on protection of crystals beneath the hybrid layer against acid-attack using transmission electron microscopy (TEM) and selected area electron diffraction (SAED).
  
  
  METHODS
  Human dentin was bonded with four adhesives; two with a carboxylic-based functional co-polymer (PAA): three-step etch-and-rinse Scotchbond Multi-Purpose (SMP, 3M ESPE) and one-step self-etch Adper Easy Bond (AEB, 3M ESPE), and two with a phosphate-based functional monomer (MDP): two-step etch-and-rinse Clearfil Photo Bond (CPB, Kuraray Medical) and two-step self-etch Clearfil SE Bond (CSE, Kuraray Medical). The specimens were the either left untreated (control) or subjected to acid-base challenge with demineralizing solution (pH 4.5) and 5% NaClO. All specimens were processed and observed by TEM. SAED was used to identify the presence or absence of apatite crystallites at the base or beneath hybrid layer before and after acid-base challenge.
  
  
  RESULTS
  An apatite-rich zone was observed beneath the partially demineralized hybrid layer of CSE. The zone was thinner in AEB, but a demineralization-susceptible area was found beneath it. The etch-and-rinse adhesives (SMP and CPB) demonstrated completely or predominantly demineralized hybrid layers, which were devoid of the acid-resistant apatite-rich zone.
  
  
  CONCLUSIONS
  TEM/SAED evidence disclosed that the preserved dentin apatite crystals beneath the thin hybrid layer of the mild self-etch adhesives were protected against acid. Diffusion of reactive components beyond the hybrid layer, and their chemical bonding potential with the remaining crystals created the acid-base resistant zone.
authors.affiliation: Cariology and Operative Dentistry, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Yushima, Bunkyo-ku, Tokyo, Japan.
authors.forename: Hamid
authors.initials: H
authors.lastname: Nurrohman
authors.forename: Toru
authors.initials: T
authors.lastname: Nikaido
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Takagaki
authors.forename: Alireza
authors.initials: A
authors.lastname: Sadr
authors.forename: Shizuko
authors.initials: S
authors.lastname: Ichinose
authors.forename: Junji
authors.initials: J
authors.lastname: Tagami
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods*; D000143:Acids / Q000494:pharmacology; D000704:Analysis of Variance; D001031:Apatites / Q000737:chemistry*; D018360:Crystallography, X-Ray; D001840:Dental Bonding / Q000379:methods*; D003804:Dentin / Q000737:chemistry* / Q000000981:diagnostic imaging; D006801:Humans; D046529:Microscopy, Electron, Transmission; D011859:Radiography; D019279:Resin Cements / Q000737:chemistry*
chemical_list: D000143:Acids; D001031:Apatites; D019279:Resin Cements