Effects of increased exposure times of simplified etch-and-rinse adhesives on the degradation of resin-dentin bonds and quality of the polymer network.

One of the reasons for resin-dentin degradation is poor polymerization of the adhesive layer. This study evaluated the effect of prolonged polymerization times on the immediate and 6-month resin-dentin bond strengths, silver nitrate uptake, and polymer quality of etch-and-rinse adhesives. Thirty extracted teeth were obtained, and a flat dentin surface was exposed on each tooth. Adhesives (Adper Single Bond 2 and One Step Plus) were applied to the dentin surface of these teeth and light-cured for 10, 20, or 40 s at 600 mW cm(-2) . Bonded sticks (0.6 mm(2) ) were tested in tension (0.5 mm min(-1) ) and analyzed, after immersion in 50% silver nitrate, using scanning electron microscopy. The polymer quality of adhesive films was evaluated using thermogravimetric analysis. Statistically higher bond strengths were observed for both adhesives when light-cured for 40 s. Degradation of dentin bonds occurred under all experimental conditions but it was less pronounced for adhesives light-cured for 40 s. Longer exposure times reduced silver nitrate uptake for Adper Single Bond 2. Solvent retention and the amount of residual monomer were statistically lower when both adhesives were light-cured for 40 s. Although longer exposure times than those recommended cannot prevent degradation of the dentin bonds, they can increase bond strength, probably because of the removal of an increased amount of solvent and the presence of a lower amount of residual monomer.

Durability of surface treatments and intermediate agents used for repair of a polished composite.

OBJECTIVE: To evaluate the effects of surface treatment and intermediate agent hydrophilicity on durability of the composite repair by means of the microtensile bond strength test (microTBS) and silver nitrate uptake (SNU) and the effects of surface treatment on composite roughness (Ra) and micromorphological features (SEM). METHODS: Thirty resin composite blocks (4x6x6 mm) (Opallis, FGM) were polished after seven days and divided into three groups: no treatment (NT); roughening with a fine-grit diamond bur (DB); 50 microm aluminum oxide sandblasting (AO). A hydrophobic (Adhesive bottle, Scotchbond MultiPurpose [SBMP]) or hydrophilic adhesive (Adper Single Bond 2 [SB]) was then applied. The same composite was used for repair. Composite-composite bonded sticks (0.6 mm2) were tested immediately ([IM) or after six months (6 M) of water storage in tension (1.0 mm/minute). Two bonded sticks from each resin composite block were immersed in a 50% (w/v) solution of silver nitrate, photo-developed and analyzed by SEM. The composite specimens after surface treatments were analyzed with a contact profilometer (Ra) and SEM. Three-way repeated measures and one-way ANOVA were used to analyze data from the microTBS and Ra, respectively (alpha = 0.05). RESULTS: AO showed the highest composite repair strength (MPa) and Ra (microm) (52.7 +/- 6.4; 4.1 +/- 0.5), while the no treatment group (36.1 +/- 6.1; 0.57 +/- 0.5) showed the low est. DB (44.1 +/- 5.6; 1.5 +/- 0.2) had an intermediate performance. The Ra results were confirmed by SEM images. SNU was observed only in SB specimens after 6M for all groups. CONCLUSIONS: Aluminum oxide treatment provides the highest composite repair strength, regardless of the hydrophilicity of the intermediate agent and storage period. Early signs of degradation were detected for SB after six months as silver nitrate deposits within the adhesive layer.