An ultra-morphological characterization of collagen-depleted etched dentin

Purpose: To evaluate the ultramorphology of superficial and deep dentin aft er etching with 35% phosphoric acid (H3PO4) and after etching with 35% H3PO 4 followed by deproteinization with 5% sodium hypochlorite (NaOCl). Materia ls and Methods: Two dentin disks (superficial and deep dentin) were obtaine d from each of 10 extracted human third molars by slow-speed sectioning. De ntin was polished with wet 600-grit SiC abrasive paper for 1 min to provide smooth surfaces. The occlusal surface of each disk was etched with 35% H3P O4 for 15 s and thoroughly rinsed. The specimens were kept moist and analyz ed using Atomic Force Microscopy (AFM). Half of the specimens were deprotei nized by rubbing with 5% NaOCl for 2 min, followed by a 30 s rinse with dei onized water. After AFM analysis of the deproteinized specimens, all disks were fixed in a solution of glutaraldehyde and paraformaldehyde, dehydrated in ethanol and dried in hexamethyldisilazane. The dentin disks were then m ounted on aluminum stubs for field-emission scanning electron microscope (F ESEM) observation. Results: The surface of etched dentin displayed a granul ar layer of silica, which did not reach the peritubular collagen area. The silica was more uniformly distributed in superficial dentin than in deep de ntin. In spite of the silica deposition, the intertubular porosity remained unobstructed when observed at high magnification. Under a lateral view, in tertubular dentin was demineralized to a depth of 2.0 to 2.5 mu m for super ficial dentin, and 2.5 to 3.0 mu m for deep dentin. Deproteinization with 5 % NaOCl removed the exposed collagen both for superficial and deep dentin. The number of open tubules was greater for deep dentin. Deproteinization of superficial dentin revealed an extensive labyrinth of lateral secondary tu bules and anastomoses, which opened on the intertubular region and on the p eritubular area close to the surface. This phenomenon decreased the area of exposed intertubular dentin as compared to etched specimens. In deproteini zed deep dentin, the lateral anastomotic tubules were not consistently obse rved on the intertubular area, but were easily depicted on the peritubular area.