Bond strength and SEM observation of CO2 laser irradiated dentin, bonded with simplified-step adhesives

This study investigated, mechanically and morphologically, whether the dentin surface irradiated by CO2 laser could be a possible adherent when bonded with simplified-step adhesives. Buccal enamel and cementum of extracted human premolars were removed to expose a flat dentin surface. The dentin surfaces were irradiated continuously with CO2 laser at 1.0 W. Before bonding with either a single-bottle adhesive (Single Bond) or a self-etching priming system (Mega Bond), the irradiated dentin surface was treated as follows: no treatment, NaHCO3 powder abrasion and wet-grinding with 600-grit SiC paper. The treated dentin surfaces were bonded to resin composite with either of the two adhesives. Non-irradiated dentin surfaces were also used as control. Resin bonded specimens were stored in water at 37 degrees C for 24 hours and subjected to microtensile bond test. Additionally, to observe the resin/irradiated dentin interface, resin-bonded specimens were similarly prepared, sectioned into slabs, embedded in epoxy resin, polished with diamond pastes, sputter coated Au-Pd and examined with scanning electron microscopy (SEM). After SEM observation, the specimens were further polished with diamond paste to remove the Au-Pd sputter-coat, immersed in HCL and NaOCl and finally observed by SEM again. In the presence of carbonized dentin, microtensile bond strength drastically decreased but recovered to the control value by removing the carbonized dentin layer visually with SiC paper for both adhesive systems. However, the laser-affected dentin that remained on the bonded interface was easily dissolved with NaOCl and HCl.