Effect of etching agent on dentinal adhesive interface in primary teeth

The purpose of this study was to evaluate in vitro the effect of a phosphoric acid etchant containing benzalkonium chloride on the dentin/adhesive interface in primary teeth. The teeth had caries lesions involving enamel and dentin, and were stored in a 2% glutaraldehyde solution for 2-4 hours. The teeth were divided into five groups of five teeth each: Group 1: Etching for 15 seconds with a semigel 32% phosphoric acid containing benzalkonium chloride; Group 2: Etching with 35% phosphoric acid for 15 seconds; Group 3: Treated with a 2% benzalkonium chloride in a alcoholic solution; Group 4: Conditioned with a 3% benzalkonium chloride in a alcoholic solution (control group); Group 5: The teeth were untreated (control group). The carious tissue was removed with a carbide bur in high-speed and copious air water spray. The overall dimensions and depths of the cavities were determined by the carious tissue removal. After the caries lesion was removed, the cavity was cleaned with an air-water spray and the dentin was treated according to the specific group. The teeth were then restored with Scotchbond Multi-Purpose Plus (3M, St. Paul, MN) and Z-100 resin-based composite (3M, St. Paul, MN) according to the manufacturer's instructions. After the teeth were restored they were stored in water for 24 hours at room temperature and the restorations polished. After storage the teeth were thermally challenged for 500 cycles in temperatures of 50 C and 550 C and then stored in 100% humidity until the sectioning procedures. The teeth were cut into two sections along the longitudinal axis through the center of the teeth and passed the mesial-distal surfaces through the restoration by using a double-face diamond disc with water coolant. The specimens were ground with 320 up to 600 grit silicon carbide paper and polished with 6 mm and 1 mm diamond paste and 0.25 pm alumina solution. The specimens were etched with 10% citric acid for 1 minute and washed with deionized water. After that, they were deproteinized with 10% NaOCl for 5 seconds. The specimens were dried at room temperature sputter-coated with gold and observed with an SEM for assessment of the morphology of the bonded interface. The interface was observed to determine the presence/absence of hybrid layer formation, resin tags, and gaps. In the groups treated only with benzalkonium chloride solutions, spaces were observed in the resin/dentin interface. Similar findings were observed in the control group, which received no treatment on the dentin before primer application. In these groups neither resin tags or hybrid layer formation was observed. The presence of an amorphous layer, which was unremoved smear layer, was noted. The group treated with 35% phosphoric acid showed a hybrid layer formation (8.15 microns). This layer was linked intimately with the peritubular and intertubular dentin. Tags formation was observed towards the pulp under the hybrid layer. In these specimens the gaps were not observed between the dentin layer and bonding materials. The total removal of the smear layer was observed using 37% phosphoric acid with benzalkonium chloride. A hybrid layer (+/- 7.32 microns) and resin-tags attached to this layer were observed similar to the group in which the 35% phosphoric acid was used. The samples showed total removal of the smear layer and no gaps were observed in the dentin/adhesive interface.