Ultra-morphological characteristics of dentin surfaces after different preparations and treatments

Using transmission electron microscopy (TEM), this study investigated the characteristics of smear layers after preparation of dentin surfaces using different methods. In addition, this study analyzed, using scanning electron microscopy (SEM), the interactions of smear layers with the various acidic agents used subsequently to treat the dentin surface. Mid-coronal dentin surfaces were prepared according to one of five instrumentation methods: fracture; grinding with carbide bur; grinding with regular-grit diamond bur; grinding with superfine-grit diamond bur; or grinding with 600-grit silicon carbide (SiC) abrasive paper. Then, each prepared dentin surface was further divided into control (no further treatment) or treatment with one of the following agents: phosphoric acid solution (PAS); phosphoric acid gel (PAG); Clearfil SE Bond 2 Primer (SE2); or Scotchbond Universal Adhesive (SBU). Longitudinal ultra-thin sections were made for TEM observations. Dentin discs, representing each surface preparation and treatment method described above, were created, and the morphology was examined by SEM. The TEM results revealed differences in thickness and denseness of the smear layer, according to the different methods of instrumentation used to prepare the dentin surface. The two forms of phosphoric acid completely removed the smear layer in all groups. Agglomerated silica particles were observed on the top of the collagen layer after etching with PAG. For all dentin surfaces, except for that prepared with SiC, SE2 demonstrated better etching efficacy on different smear layers, whereas SBU provided only superficial interaction.