Ecomet 4

Ultrastructural observations of representative resindentin interfaces were examined by a field emission SEM. Bonded specimens of each group (n=3) were stored in distilled water at 37°C for 24 h, embedded in self-curing epoxy resin (Epon 812, Nisshin EM, Tokyo, Japan), and stored at 37°C for a further 24 h. These specimens were sectioned along the resin composite post diameter and the surfaces of the cut halves were successively polished with P1200, P2000, and P4000 SiC paper using a grinder-polisher (Ecomet 4, Buehler). The surface was finally polished with a soft cloth using 1.0-µm-girt diamond paste. All SEM specimens were dehydrated by immersion in ascending concentrations of aqueous tertbutanol (50% for 20 min, 75% for 20 min, 95% for 20 min, and 100% for 2 h), and were then transferred to a critical-point dryer (Model ID-3, Elionix, Tokyo, Japan) for 30 min. These polished surfaces were etched for 30 s using an argon ion-beam (Type EIS-200ER, Elionix) directed perpendicularly to the surface at an accelerating voltage of 1.0 kV and an ion current density of 0.4 mA/ cm 2 . This treatment enhances the visibility of the layers in the interface 24) . Surfaces were coated with a thin film of gold in a vacuum evaporator (Quick Coater Type SC-701, Sanyu Electron, Tokyo, Japan) and were observed using a field emission SEM (ERA 8800FE, Elionix).

Ultrastructural observations were conducted on the polished surfaces of the bulk-fill restorative materials using scanning electron microscopy (SEM). A Teflon mold, 10.0 mm in diameter and 2.0 mm in height, was used to form the specimens of the bulk-fill restorative materials. The restorative materials were placed into the mold, pressed with a glass slide and photo polymerized for 30 s. The surfaces of the bulk-fill restorative materials after photo polymerization were polished with #180, #320, #600, #1200, and #4000-grit silicon carbide papers (Struers, Cleveland, OH, USA) using a grinderpolisher (Ecomet 4, Buehler, Lake Bluff, IL, USA). SEM specimens of the polished surfaces were coated with a thin film of gold-palladium in a vacuum evaporator (Emitech SC7620 Mini Sputter Coater, Quorum Technologies, Ashford, UK). SEM observations were carried out using an operating voltage of 15 kV with a TM3000 Tabletop Microscope (Hitachi-High Technologies, Tokyo, Japan).

Custom stainless steel fixtures containing a cylindrical cavity (diameter, 6.5 mm; depth, 4.0 mm) were machined for localized wear testing. Twenty specimens (designated as the dual-cure group) of each resin luting cement were photo-cured in two increments each of approximately 2 mm depth with a quartz-tungsten-halogen unit (Spectrum 800 Curing Unit, DENTSPLY Caulk) set at 600 mW/ cm 2 for 40 s at a standardized distance of 2 mm. Twenty specimens (designated as the chemical-cure group) were not photo-cured. After water storage for 24 h at 37°C, the cement surfaces of dual-and chemical-cure groups were polished flat to 4,000 grit using a sequence of silicon carbide papers (Struers, Cleveland, OH, USA) and a grinder-polisher (Ecomet 4, Buehler, Lake Bluff, IL, USA).

Two halves of each teeth were embedded in epoxy resin (Buehler Ltd., Lake Bluff, IL, USA), so that the area to be analyzed remained exposed. Polishing was performed using a polishing cloth (Ecomet 4, Buehler, Lake Bluff, IL, USA) with 320, 480, 600, 1200, 2500 and 4000-grit silicon carbide abrasive papers, and final polishing was made with diamond paste of 1 µm and 0.25 µm (Buehler Ltd., Lake Bluff, IL, USA). After the last stage of polishing, the specimens were ultrasonically cleaned to remove eventual residues.
Fifteen indentations were made in the center of the caries lesions (C groups) or cavities (pH groups) and 100 µm on each side, at depths of 15, 40, 100, 150 and 250 µm using a Knoop indenter, with a static load of 25 gm for 30 seconds coupled with HMV II microhardness tester (HMV II, Shimadzu, Kyoto, Japan).