Scanning electron microscopic study of the extent of resin penetration into human coronal dentin following a total etch technique in vivo

It is generally accepted that resin penetration into vital, deep, exposed dentin is hampered by the presence of dentinal fluid and intratubular contents following removal of the smear layer. Deep buccal cavities were prepared in ten vital, caries-free premolars to be extracted for orthodontic reasons and restored with All-Bond 2 (Bisco) and Z100 (3M Corp.) using a total etch wet bonding technique. In addition, ten unrestored, caries-free third molars were used as the control. The roots of the specimens were severed using a diamond disc and the crowns fixed immediately upon removal, cryofractured in liquid nitrogen, post-fixed in 1% osmium tetroxide, dehydrated in an ascending ethanol series, dried by critical point drying and examined in the scanning electron microscope. Resin tag formation in the dentinal tubules was characterized by the initial presence of a solid resin core replacing the original smear plugs, followed by the presence of resin globules further down, attaching to the walls of the dentinal tubules. This did not, however, represent the full extent of resin penetration, as isolated resin globules were also observed further down the predentin and around the odontoblasts. Similar spherical resin globules with a mean size of 0.78 ± 0.33 μm could be reproduced in vitro, when All-Bond 2 primers were applied to water through a polycarbonate disc with a pore size of 1 μm. The fact that similar resin globules were not previously observed within the pulpodentinal complex of a group of specimens that were extracted after a post-restorative period of 21-28 days suggested that they might have been removed by phagocytic cells in the pulp during the period of tissue response.