Adhesive Evaporation Technique Influences Bond Strength and Dentinal Enzymatic Activity

Objectives: To evaluate the influence of two adhesive evaporation techniques on the microtensile bond strength (µTBS) of a universal adhesive to dentin, and the activity of dentinal matrix metalloproteinases (MMPs).
Methods: The middle/deep dentin of 32 sound extracted human molars were bonded under simulated pulpal pressure with a universal adhesive (Clearfil Universal Bond Quick, Tokuyama Inc.) applied in total-etch (TE) or self-etch (SE) mode. Two adhesive evaporation techniques were tested: a) adhesive was air-dried with the disposable air/water syringe (Air); b) adhesive was air-dried with the disposable suction device (Suction). Hence, 4 different groups were investigated (n=8): 1)TE/Air 2)TE/Suction 3)SE/Air 4)SE/Suction. Then, the adhesive was light-cured for 10s, and a 4-mm-thick composite build-up was made. The specimens were stored in artificial saliva at 37°C for 24h (T0) or 6 months (T6), after which they were cut into sticks and submitted to µTBS test. Fractographic analysis was performed using SEM. Additional teeth of the same groups (n=3) were prepared for in situ zymographic analysis. Bonded sticks were ground down and exposed to fluorescein-conjugated gelatin. Enzymatic activity was evaluated on the images obtained using a confocal microscope. Data were statistically analyzed (p<0.05).
Results: Results: Air-drying resulted in significantly higher µTBS values than suction, regardless of the aging and the adhesive application mode (p<0.05). At T6, the SE groups maintained the same bond strength level as at baseline (p>0.05), while in the ER groups aging significantly decreased bond strength (p<0.05) SEM images showed the presence of sparse water-tree formations at the adhesive interface in the Suction groups, irrespective of the application mode. Suction-evaporation, aging and ER mode increased MMPs activity (p<0.05).
Conclusions: The use of air with a disposable syringe to evaporate the adhesive, and the self-etch mode seem to be more reliable choices when an ethanol-based universal adhesive is used for bonding procedures.