Objectives: Endogenous MMP-2 or MMP-9 enzymes released by adhesive treatment procedures can hydrolyze collagen fibrils in the hybrid layer and so compromise bonding effectiveness. The purpose of this study was to evaluate this degradation pattern for ‘mild' self-etch adhesives that were modified with MMP-inhibitors.
Methods: 1) Identification of enzyme release: Fresh human dentin powder was mixed with 35% solution of H3PO4 or a self-etch primer (Clearfil SE and Protect Bond, Kuraray; G-Bond, GC). Gelatinases were extracted by Sodium Dodecyl Sulphate and identified by gelatin zymography. 2) Micro-tensile bond strength (µTBS) testing: Self-etch primers were modified by adding two MMP-inhibitors: chlorhexidine (CHX, 0.05%) or SB-3CT (10 µM), a very specific mechanism-based inhibitor with a minimal inhibitory concentration in the nano-molar range. µTBS was evaluated after 1 week, 3 months and 6 months water storage.
Results: MMP-9 was not released and MMP-2 was released by H3PO4, but not by the self-etch primers.
Mean ± SD (n) in MPa | months | Clearfil SE
| Protect Bond | G-Bond |
Control (no MMP-inhibitor) | 0 | 69.8 ± 23.7 (12)a,b | 55.3 ± 21.3 (12)A | 14.2 ± 8.5 (16)I,II |
3 | 69 ± 14 (9) a,b | 55.4 ± 14.2 (10) A | 12.8 ± 9.6 (10) I,II | |
6 | 50.8 ± 17.2 (14)b | 43.7 ± 14.3 (12) A | 6.8 ± 6.4 (19)II | |
CHX | 0 | 55.4 ± 20.6 (12) a,b | 60.5 ± 16.6 (12) A | 13.9 ± 12.8 (16) I,II |
3 | 63.5 ± 14.5 (10) a,b | 49.3 ± 10.2 (9) A | 23.9 ± 26.3 (8)I I,II | |
6 | 50.0 ± 16.1 (11)b | 40.5 ± 17.5 (13) A | 9 ± 10.4 (12) I,II | |
SB-3CT | 0 | 70.3 ± 15.7 (10 a,b) | 57.2 ± 19 (13) A | 20.4 ± 7.5 (12)I |
3 | 64.3 ± 16.9 (10 a,b) | 50.4 ± 22.8 (10) A | 19.2 ± 12.2 (10) I,II | |
6 | 74.4 ± 11.2 (10)a | 39.8 ± 19.6 (13) A | 7.7 ± 5.6 (12) I,II |
Means with the same superscript are not significantly different (Tukey multiple comparisons test, p < 0.05)
Regarding µTBS, no degradation in µTBS was measured (2-way ANOVA, p=0.1690) for Clearfil SE, in contrast to Protect Bond (p=0.0006) and G-Bond (p=0.0002).
Conclusions: As the release of proteinases was minimal and specific MMP-inhibitors had no effect, the effect of endogenous MMP-2 (and MMP-9) on the stability of hybrid layers produced by ‘mild' self-etch adhesives must be considered as minimal.