Purpose: To evaluate the ultramorphology of superficial and deep dentin after etching with 35% phosphoric acid (H3PO4) and after etching with 35% H3PO4 followed by deproteinization with 5% sodium hypochlorite (NaOCl).
Materials and methods: Two dentin disks (superficial and deep dentin) were obtained from each of 10 extracted human third molars by slow-speed sectioning. Dentin 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% H3PO4 for 15 s and thoroughly rinsed. The specimens were kept moist and analyzed using Atomic Force Microscopy (AFM). Half of the specimens were deproteinized by rubbing with 5% NaOCl for 2 min, followed by a 30 s rinse with deionized 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 mounted on aluminum stubs for field-emission scanning electron microscope (FESEM) observation.
Results: The surface of etched dentin displayed a granular layer of silica, which did not reach the peritubular collagen area. The silica was more uniformly distributed in superficial dentin than in deep dentin. In spite of the silica deposition, the intertubular porosity remained unobstructed when observed at high magnification. Under a lateral view, intertubular dentin was demineralized to a depth of 2.0 to 2.5 microns for superficial dentin, and 2.5 to 3.0 microns 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 tubules and anastomoses, which opened on the intertubular region and on the peritubular area close to the surface. This phenomenon decreased the area of exposed intertubular dentin as compared to etched specimens. In deproteinized deep dentin, the lateral anastomotic tubules were not consistently observed on the intertubular area, but were easily depicted on the peritubular area.