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.