Long-term bond strength and endogenous enzymatic activity of a chlorhexidine-containing commercially available adhesive.

OBJECTIVES: The aim of this study was to investigate, by the means of microtensile bond strength (µTBS) test, gelatin and in situ zymography, the influence of 0.2% CHX contained within a commercially available adhesive on long-term bond strength and endogenous enzymatic activity. METHODS: Non-carious teeth were subjected to µTBS test (N = 15 for each group) and stressed until failure. µTBS was evaluated immediately and after 12-month storage in artificial saliva at 37 °C. Dentin powder was obtained from additional teeth (N = 7) for gelatin zymography, while for in situ zymography, 3 teeth for each group were selected. Gelatin and in situ zymography were performed in dentin powder and slices of dentin, respectively, to assess the ability of 0.2% CHX blended within the adhesive to inhibit endogenous enzymatic activity. RESULTS: µTBS bond strength was higher in the CHX-containing groups, immediately as well as after aging. The bond strength significantly decreased after 12-month aging. The activation of endogenous MMPs was found to be related to the presence of CHX within the adhesive system and the bonding strategy employed. CONCLUSIONS: Under this perspective 0.2% CHX blended within Peak Universal adhesive monomer seems to increase immediate bond strength, to preserve bond strength over time and to efficiently inhibit endogenous enzymatic activity in dentin. Hence, blending the CHX in low concentrations within the adhesive could be recommended as a feasible technique in every-day clinical practice. CLINICAL SIGNIFICANCE: Using CHX-containing adhesives could be recommended due to several benefits: it seems to increase the longevity of the hybrid layer; the inhibitor appears to be efficiently delivered to the dentinal substrate and to inhibit endogenous enzymatic activity, without prolonging chair time.

Cross-linking effect on dentin bond strength and MMPs activity.

OBJECTIVE: The objectives of the study were to evaluate the ability of a 1-ethyl-3 (3-dimethylaminopropyl) carbodiimide (EDC)-containing primer to improve immediate bond strength of either self-etch or etch-and-rinse adhesive systems and to stabilize the adhesive interfaces over time. A further objective was to investigate the effect of EDC on the dentinal MMPs activity using zymographic analysis. METHODS: Freshly extracted molars (n=80, 20 for each group) were selected to conduct microtensile bond strength tests. The following groups were tested, immediately or after 1-year aging in artificial saliva: G1: Clearfil SE (CSE) primer applied on unetched dentin, pretreated with 0.3M EDC water-solution for 1min and bonded with CSE Bond; G2: as G1 but without EDC pre-treatment; G3: acid-etched (35% phosphoric-acid for 15s) dentin pretreated with 0.3M EDC, then bonded with XP Bond (XPB); Group 4 (G4): as G3 without EDC pre-treatment. Further, gelatinase activity in dentin powder treated with CSE and XPB with and without EDC pre-treatment, was analyzed using gelatin zymography. RESULTS: The use of 0.3M EDC-containing conditioner did not affect the immediate bond strength of XPB or CSE adhesive systems (p>0.05), while it improved the bond strength after 1year of aging (p<0.05). Pre-treatment with EDC followed by the application of CSE resulted in an incomplete MMPs inactivation, while EDC pretreatment followed by the application of XPB resulted in an almost complete inactivation of dentinal gelatinases. SIGNIFICANCE: The µTBS and zymography results support the efficacy of EDC over time and reveal that changes within the dentin matrix promoted by EDC are not adhesive-system-dependent.

Experimental use of an acrolein-based primer as collagen cross-linker for dentine bonding.

OBJECTIVES: The objective of the present study was to investigate the long-term effect of 0.01% acrolein (ACR) aqueous solution, employed as an additional primer, on the mechanical durability and enzymatic activity of resin-dentine interfaces created with a simplified etch-and-rinse adhesive. METHODS: Dentine surfaces were etched with 35% phosphoric acid for 15s, rinsed and blot-dried. Specimens were then assigned to: Group 1: dentine pre-treated with 0.01% ACR aqueous solution for 1min and bonded with Adper Scotchbond 1 XT (SB1XT), a 2-step etch-and-rinse adhesive; Group 2: SB1XT was applied on untreated acid-etched dentine (control). Resin composite build-ups were made using Filtek Z250. Microtensile bond strength was tested by stressing sectioned specimens to failure immediately or after 1year of storage in artificial saliva at 37°C. Zymography and in-situ zymography assays were performed for examining dentine matrix metalloproteinase (MMP) activities. RESULTS: The use of 0.01% ACR as conditioning primer appeared to have contributed better to preservation of bond strength over time without affecting immediate bond strength. Zymography and in-situ zymography showed reduction in MMP activities after the application of ACR. CONCLUSION: Dentine collagen cross-linking produced by an ACR-based primer increases the longevity of resin-dentine bonds by reinforcement of the adhesive interface and reduction of dentine MMP activities. Further studies are required to evaluate the potential in vivo and in vivo cytotoxicity of ACR. CLINICAL SIGNIFICANCE: The acrolein-based primer is a potentially useful clinical bonding tool because it demonstrates good collagen cross-linking ability within a clinically-acceptable working time. Although a low ACR concentration was employed in the present study, the cytotoxicity of ACR should be tested prior to clinical use.

Role of Chlorhexidine on Long-term Bond Strength of Self-adhesive Composite Cements to Intraradicular Dentin.

PURPOSE: To examine the effect of CHX pre-treatment on long-term bond strength of fiber posts luted with self-adhesive resin cements. MATERIALS AND METHODS: Seventy-two single-rooted teeth were selected for root canal treatment and post space preparation. The tested self-adhesive cement/post combinations were (N = 36): 1. RelyX Fiber-Posts luted with RelyX Unicem; 2. Rebilda Posts luted with Bifix SE Cement. For both self-adhesive cements, half of the specimens (experimental groups) were luted after the application of a solution of 2% CHX, while no CHX application was performed for the remaining specimens (control groups). Luted specimens were cut and used for push-out bond strength evaluation immediately, and after storage in artificial saliva for 6 months or 1 year. Additional specimens were processed for quantitative interfacial nanoleakage analysis. RESULTS: ANOVA showed that the variable times of storage had a significant influence on the results (p < 0.05), while no influence of the luting procedure (cements with or without CHX) on the final outcome (p > 0.05) was found. Tukey's pairwise post-hoc test showed that the radicular bond strength decreased with time of storage. In particular, a significant difference was found between T0 and T1y, but not between T0 and T6m. In contrast, in terms of pretreatment, no significant reduction in push-out bond strength was observed, irrespective of the aging time. CONCLUSION: CHX pretreatment did not prevent bond strength degradation of fiber posts luted with self-adhesive cements.

Effect of a one-step self-etch adhesive on endogenous dentin matrix metalloproteinases.

Degradation of the hybrid layer created in dentin by dentin adhesives is caused by enzyme activities present within the dentin matrix that destroy unprotected collagen fibrils. The aim of the present study was to evaluate the effect of a one-step self-etch adhesive system on dentinal matrix metalloproteinases 2 and 4 (MMP-2 and MMP-9, respectively) using in situ zymography and an enzymatic activity assay. The null hypothesis tested was that there are no differences in the activities of dentinal MMPs before and after treatment with a one-step adhesive system. The MMP-2 and MMP-9 activities in dentin treated with the one-step adhesive, Adper Easy Bond, were quantified using an enzymatic activity assay system. The MMP activities within the hybrid layer created by the one-step adhesive tested were also evaluated using in situ zymography. The enzymatic assay revealed an increase in MMP-2 and MMP-9 activities after treatment with adhesive. In situ zymography indicated that gelatinolytic activity is present within the hybrid layer created with the one-step self-etch adhesive. The host-derived gelatinases were localized within the hybrid layer and remained active after the bonding procedure. It is concluded that the one-step self-etch adhesive investigated activates endogenous MMP-2 and MMP-9 with the dentin matrix, which may cause collagen degradation over time.

Effect of carbodiimide (EDC) on the bond stability of etch-and-rinse adhesive systems.

OBJECTIVE: Recent studies supported the use of protein cross-linking agents during bonding procedures to inactivate endogenous dentin proteases, preventing dentin collagen degradation thus improving bond durability. The aim of this study was to evaluate the effect of a 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-containing conditioner on the stability of the adhesive interface created by two etch-and-rinse adhesives. METHODS: Human dentin was etched with 35% phosphoric acid, treated with 0.3M EDC-containing conditioner followed by a three-step or a two-step etch-and-rinse adhesive. Adhesives were applied to control specimens without EDC pre-treatment. Specimens were subjected to microtensile bond strength test and pulled to failure after 24h or 1 year of storage and interfacial nanoleakage expression was evaluated and quantified by light microscopy. Additionally, to investigate endogenous dentin matrix metalloproteinase activity a zymographic assay was performed on protein extracts obtained from phosphoric-acid-etched dentin powder with or without EDC treatment. RESULTS: The use of the EDC-containing conditioner did not affect immediate bond strength to dentin but contributed to preserve the bond strength after 1 year (p<0.05) for both tested adhesives. No difference was found in the interfacial nanoleakage expression that increased after aging irrespective from the treatment. EDC pre-treatment inhibited dentin endogenous MMPs as assayed with the zymography. SIGNIFICANCE: In conclusion, the results of the study provide proof that EDC can produce long-term inactivation of MMPs in acid-etched dentin matrices contributing to bond strength preservation over time. Future studies are needed to support the use of EDC in vivo.