Gelatinolytic activity in dentin upon adhesive treatment

Abstract

<p><strong>Objectives: </strong>Controversy remains over the impact of dental adhesives on gelatinolytic activity in dentin. In this study, we aimed to confirm or reject the existence of a definitive cause/effect relationship between dental adhesive application and the activation of host-derived gelatinases.<br><br><strong>Methods: </strong>The considered gold-standard three-step etch-and-rinse adhesive Optibond FL (Kerr) and the two-step self-etch adhesive Clearfil SE Bond 2 (Kuraray Noritake) were tested, so the data gathered concerned well-performing adhesives. The presence of gelatinases in dentin powder upon contact with two adhesives was assessed by gelatin zymography. Gelatinolytic activity along adhesive-dentin interfaces was imaged using <em>in-situ</em> zymography. Changes in MMP-2/9 activity upon interaction with adhesives, 37°C incubation, and temperature increase during light-curing of adhesives were evaluated by a high-throughput fluorogenic DQ-gelatin assay. Furthermore, the actual degree of involvement of enzymatic activity in bond degradation was investigated by intentionally challenging adhesive-dentin interfaces with 0.01-µM activated MMP-9 (a much higher concentration than present in saliva) for 1-month, upon which the micro-tensile bond-strength (µTBS) was measured.<br><br><strong>Results: </strong>Gelatin zymography disclosed the presence of gelatinases in phosphoric acid-etched dentin powder, while the two adhesives generated no measurable MMP activation. <em>In-situ</em> zymography revealed inconsistent interfacial gelatinolytic activity within the same specimen; this challenges the reliability of this technique when used to qualitatively examine gelatinolytic activity along adhesive-dentin interfaces. In solution, MMP-2/9 activity significantly decreased upon interaction with both adhesives (two-way linear mixed effects model [LMEM]: <em>p</em><0.05); gelatinases were almost completely deactivated upon 1-week incubation at 37°C (general linear model:<em> p</em><0.05); light-curing increased temperature up to 70°C, which appeared sufficient to dramatically decrease MMP-2/9 activity (two-way ANOVA:<em> p</em><0.05). Finally, challenging adhesive-dentin interfaces did not significantly affect mTBS (two-way LMEM:<em> p</em>>0.05).<br><br><strong>Conclusions: </strong>The two gold-standard adhesives did not activate but rather inhibited the release and activation of residual gelatinases in dentin.<br></p>