Adhesive Evaporation Implication in Dentin Bond Strength and MMP Activation

(1) Background: This study aimed to assess how two different adhesive solvent evaporation techniques affect the microtensile bond strength (µTBS) of a universal adhesive to dentin, as well as the enzymatic activity of dentinal matrix metalloproteinases (MMPs) at baseline and after 6-month aging under simulated pulpal pressure. (2) Methods: Middle-depth dentin surfaces of 32 sound extracted human molars were bonded under simulated pulpal pressure using a universal adhesive (Clearfil Universal Bond Quick) in either etch-and-rinse (ER) or self-etch (SE) mode. Two solvent evaporation approaches were compared: evaporation with a disposable air/water syringe (air) and with a disposable suction device (suction), yielding four experimental groups (n = 8): ER/air, ER/suction, SE/air, and SE/suction. After light-curing for 10 s, a 4 mm composite build-up was created. Specimens were stored in distilled water under simulated pulpal pressure at 37 °C for either 24 h (T0) or 6 months (T6) and then sectioned into sticks and subjected to µTBS testing. Fracture surfaces were examined by scanning electron microscopy (SEM). An additional subset of teeth from each group (n = 3) underwent in situ zymographic analysis, in which bonded sticks were ground and exposed to fluorescein-conjugated gelatin, with enzymatic activity quantified by confocal microscopy. Statistical analysis was performed at a significance threshold of p < 0.05. (3) Results: Air-drying yielded significantly higher µTBS values than suction drying, irrespective of adhesive application mode (p < 0.05). At T6, SE groups retained bond strength values comparable to baseline (p > 0.05), whereas ER groups showed a significant reduction in bond strength with aging (p < 0.05). The ER mode and suction were associated with significantly increased MMP activity at T0 (p < 0.05), while there were no differences between SE/ER at T6 (p > 0.05), and air increased MMP activity (p < 0.05). (4) Conclusions: When using an ethanol-based universal adhesive under pulpal pressure, evaporation with a disposable air syringe combined with the self-etch application mode appears to offer greater bonding reliability and stability.