Does inhibition of proteolytic activity improve adhesive luting?

Polymerizable Matrix Metalloproteinases' Inhibitors with Potential Application for Dental Restorations

Collagen cleavage by matrix metalloproteinase (MMP) is considered a major cause of dental resins long term failure. Most MMP inhibitors display significant toxicity and are unsuitable for dental resins’ applications. Here we report a study of a new class of inhibitors that display the unique property of being co-polymerizable with other vinyl compounds present in commercial dental resins, limiting their release and potential toxicity. Computational affinity towards the active site of different MMP-1; -2; -8; -9 and -13 of several compounds showed interesting properties and were synthesized. These free compounds were tested concerning their toxicity upon contact with two different cell types, with no substantial decrease in cell viability at high concentrations. Even so, compound’s safety can be further improved upon copolymerization with commercial dental resins, limiting their release.

Interfacial fracture toughness of self-adhesive and conventional flowable composites to dentin using different dentin pretreatments

AIM

The aim of the present study was to investigate the effect of different dentin pretreatments on the interfacial fracture toughness of a self-adhesive flowable composite to dentin compared with that of a conventional flowable composite.

METHODS

Caries-free human molars were sectioned to expose the underlying dentin and were randomly divided into seven groups (N = 12) of dentin pretreatments bonded to a self-adhesive flowable composite (Vetise Flow, VF) or a conventional flowable composite (Clearfil Magesty Flow, CM). For VF; Control group (group C-VF), there was no pretreatment, self-etching primer (SP), oxalate dentin desensitizer (OX), and chlorhexidine gluconate (CH) were used. For CM; SP (group SP-CM), OX followed by SP (OX-CM), and CH followed by SP (CH-CM) were used. The interfacial fracture toughness was measured using a universal testing machine. Data were analyzed by Kruskal-Wallis test and analysis of variance.

RESULTS

For VF, the fracture toughness of SP-VF was significantly higher than that of other groups. For CM, a significantly higher fracture toughness for SP-CM than that of OX-CM was found. For all dentin pretreatments, the fracture toughness values were significantly higher for CM compared with the VF.

CONCLUSIONS

The self-adhesive flowable composite had reduced bonding efficacy to dentin compared with that of the conventional flowable composite, regardless of the type of dentin pretreatment.

Effects of caffeic acid phenethyl ester application on dentin MMP-2, stability of bond strength and failure mode of total-etch and self-etch adhesive systems

OBJECTIVE

Investigate the long-term effect of dentin pretreatment with 0.05 or 0.1% caffeic acid phenethyl ester (CAPE) on (1) bond strength of resin composite to dentin by a three-step etch-and-rinse (Adper Scotchbond Multipurpose/ ASB) or a two-step self-etch adhesive system (Clearfil SE Bond/ CSE), (2) their fracture mode, (3) the micromorphological features of the hybrid layer formed; and (4) the level of MMP-2 in dentin (after application, using a correlative immunoexpression/quantification approach).

DESIGN

Composite resin blocks were fabricated on 48 third molars (n = 6), according to the type of adhesive and treatment (control, CAPE 0.05% and CAPE 0.1%). Slices were obtained for scanning electron microscopy (SEM) evaluation, and sticks were fabricated for microtensile tests (24 h and 1 year). Aliquots of dentin powder were distributed (n = 12) according to the treatment and the MMP-2 concentration was determined by ELISA.

RESULTS

Tukey test showed that ASB groups presented higher BS in 24 h than CSE groups. ASB presented a reduction in BS values after 1-year. ASB and CSE presented no significant differences in BS after 1-year. CAPE had no effect on BS for both adhesive systems. The predominant failure mode for the ASB groups were adhesive; when 0.1% CAPE was applied there was a predominance of mixed fractures. Regarding the CSE group, 0.05% CAPE led to more adhesive failures, and the 0.1% concentration resulted in a higher number of cohesive failures in dentin. Higher MMP-2 concentrations were detected for the groups that did not undergo demineralization treatment, and the lowest values for the ASB groups treated with CAPE. SEM analysis showed no influence of pretreatment with CAPE.

CONCLUSIONS

CAPE did not influence the BS of the adhesives tested, or the micromorphology of the hybrid layer, irrespective of concentration or storage time. CAPE affected the fracture pattern at 24 h, depending on the concentration and the adhesive system used. Immunoassay analysis showed that CAPE 0.1% reduced the MMP-2 concentration in the ASB adhesive without affecting bond strength to dentin.

[Progress on matrix metalloproteinase inhibitors]

Continuing advances in dentin bonding technology and adhesives revolutionized bonding of resin-based composite restorations. However, hybrid layers created by contemporary dentin adhesives present imperfect durability, and degradation of collagen matrix by endogenous enzymes is a significant factor causing destruction of hybrid layers. Bond durability can be improved by using enzyme inhibitors to prevent collagen degradation and to preserve integrity of collagen matrix. This review summarizes progress on matrix metalloproteinase inhibitors (including chlorhexidine, ethylenediaminetetraacetic acid, quaternary ammonium salt, tetracycline and its derivatives, hydroxamic acid inhibitors, bisphosphonate derivative, and cross-linking agents) and suggests prospects for these compounds.

Effect of Carbodiimide on Bonding Durability of Adhesive-cemented Fiber Posts in Root Canals

This study was undertaken to investigate whether using a protein cross-linker, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), improves bonding stability of fiber posts to root dentin using three resin cements. Sixty human maxillary central incisor roots were randomly divided into six groups after endodontic treatment, according to the cements used with and without EDC pretreatment. In the etch-and-rinse group, 0.3 M EDC aqueous solution was applied on acid-etched root dentin prior to Excite DSC/Variolink II for post cementation. In the self-etch and self-adhesive groups, EDC was used on EDTA-conditioned root space prior to application of ED Primer II/Panavia F2.0 and Clearfil SA, respectively. After microslicing the root dentin, a push-out bond strength (BS) test was performed immediately or after one-year of water storage for each group. Data were analyzed using three-way analysis of variance and Tukey tests (α=0.05). A significant effect of cement type, time, EDC, and Time × Cement and Time × EDC interactions were observed (p≤0.001). EDC pretreatment did not affect immediate bonding of the three cements (p>0.05). Aging significantly reduced the BS in all the groups (p≤0.001), but EDC groups exhibited a higher BS compared with the respective control groups (p<0.001). Despite the significant effect of aging on decreasing the BS of fiber post to radicular dentin, EDC could diminish this effect for the three tested cements.

Cytotoxicity of a novel nano-silver particle endodontic irrigant

Purpose

The aim of this study was to evaluate the cytotoxic effect of a novel nano-silver particle (25.2±6.5 nm) endodontic irrigant (0.2 mM) and compare it with 3% sodium hypochlorite.

Materials and methods

Two cell types, mouse fibroblast National Institutes of Health 3T3 (NIH 3T3) and primary human periodontal ligament stem cell (hPDLSCs) were used in a test for the effect of direct and indirect (by separating the agent and cell with a layer of agar) exposure to the two solutions. In the direct exposure experiment, ten groups of cell cultures were exposed to one dilution (3:1, 2:1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6 or 1:7) of a nano-silver irrigant for 48 hours; the concentration-response function was estimated by determining the number of viable cells in each group by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The 50% lethal dose of the testing irrigant for NIH3T3 and hPDLSCs were estimated. In the second part of the experiment, a modified agar overlaying technique was applied. Twelve culture wells (6-well plate) were divided into three groups (n=4). The cell lysis zone (cytotoxic range) created by the stock nano-silver solution, 3% sodium hypochlorite, and an isotonic phosphate buffering saline (control) was measured by two double blinded observers (Kappa score =100%). The cytotoxic score of specific irrigant was derived by modified Sjögren’s method.

Results

The 50% lethal doses of the testing nano silver irrigant for NIH 3T3 and hPDLSCs after 48 hours of direct exposure were 0.58 and 0.608 dilution of stock solution, respectively. The cytotoxic scores of nano-silver irrigant and control (phosphate buffered saline) on NIH 3T3 were 0.25 (95% confidence interval [CI] =0 to 1.04) and 0 (95% CI =0 to 0); and on hPDLSCs were 0.13 (95% CI =0 to 0.52) and 0.25 (95% CI =0 to 1.04), respectively. Toxicity of the test and control group on both mouse fibroblasts (P>0.05) and hPDLSCs (P=1.00) was not statistically different.

Conclusion

Our results showed that the nano-silver irrigant was non-cytotoxic to both NIH 3T3 and hPDLSCs.

Effects of Internal Bleaching on the Adhesion of Glass-Fiber Posts

Objective:

We evaluated the effects of internal bleaching on the adhesion of glass-fiber posts (GFPs) luted with different resin cements.

Methods:

Forty extracted human single-root teeth were endodontically treated and divided into four groups (n=10): G1- conventional resin cement (CRC); G2- self-adhesive resin cement (SARC); G3- bleaching + CRC; and G4- bleaching + SARC. Specimens were sectioned transversally into three slices to perform the push-out test at the coronal, middle and apical regions of the root canals. Data were analyzed using analysis of variance and Tukey's test (p<0.05).

Results:

The push-out bond strength of GFPs luted with SARC after bleaching (G4) was significantly lower than that of the other groups (p<0.001). We found no statistically significant differences in push-out bond strength among the other groups.

Significance:

Internal bleaching reduced the adhesion of GFPs luted with SARC. The adhesion of GFPs luted with CRC was not decreased after bleaching.

Addition of benzalkonium chloride to self-adhesive resin-cements: some clinically relevant properties

OBJECTIVE

The clinical survival rates of the adhesive restorations are limited due to the deterioration of resin-dentin bonds over time, partly due to the endogenous enzymatic activity of dentin. Recently, benzalkonium chloride (BAC) has been shown to effectively inhibit endogenous protease activity of dentin. This study evaluated the effect of different concentrations of benzalkonium chloride (BAC) on the degree of conversion (DC), vickers hardness (VH), setting time (ST) and biaxial flexural strength (FS) of two self-adhesive resin luting cements (RC).

METHODS

Two RC SpeedCEM (Ivoclar-Vivadent) and BisCem (Bisco) were modified by addition of 0.1, 0.5, 1, 1.5, 2 wt% BAC. The luting cements without the addition of BAC served as control. The DC (FT-IR/ATR from the bottom of the resin disc), vickers hardness (from top and bottom of the light-cured specimen), setting time (ISO 4049) and biaxial flexural strength (0.6 × 6 mm discs) of the specimens were tested. Data were analyzed using ANOVA and Tukeys HSD.

RESULTS

DC results were in the range of 70-80%, with some significant changes in BisCem (p < 0.05). VH values of both materials increased significantly compared to control, with no significant change as the BAC percentage increases. BAC addition influenced the ST differently for both materials. For BisCem, a gradual decrease (p < 0.05) was observed whereas, for SpeedCEM, a gradual increase was observed until 1% BAC (p < 0.05). For FS values, a gradual decrease was observed for both materials with increased amounts of BAC (p < 0.05), compared to the control group.

CONCLUSIONS

BAC addition of up to 1% seems to be acceptable considering the properties tested. Clinical significance. Incorporation of benzalkonium chloride to self-adhesive resin luting cements during the mixing procedure does not significantly affect the degree of conversion or flexural strength of the luting agent and may be a good option to improve the durability of adhesive interface.

Influence of metalloproteinases on dentin hybridization of one-bottle or self-etch dental bonding systems

AIM

To assess the influence of dentin substrate and chlorhexidine on the marginal seal of composite resin restorations.

MATERIALS AND METHODS

The sample comprised 20 third molars. Four cavities were drilled in the dentin sur face, followed by sealing and restoration of sound dentin (n = 10) or carious dentin (n = 10). In the control group, cavities were immediately restored as follows: G1: one-bottle bonding agent (OB) + composite resin (CR); G2: chlorhexidine 2.0% (CLX) + OB + CR; G3: self-etch bonding agent (SE) + CR; G4: CLX + SE + CR. In the experimental group (carious dentin), carious lesions were induced with S. mutans and cavities were restored as in the control group. Five specimens from each group (sound and carious) were stored in brain-heart infusion (BHI) medium for 6 months. All specimens were submerged in methylene blue 0.5% to test for microleakage. The Kruskal-Wallis and Student-Newman-Keuls tests were used to assess results.

RESULTS

On immediate assessment, there were no significant between-group differences in the sound dentin group, whereas in carious dentin, there was less leakage when OB and CLX were used. At 6 months, there was less leakage in the sound dentin group when OB and CLX were used; there were no between-group differences in carious dentin. Comparison of immediate and 6-month assessments showed a significant increase in leakage at 6 months when sound dentin was treated with SE and CLX and when carious dentin was treated with OB and CLX.

CONCLUSION

To ensure better dentin hybridization and preservation of the organic constituents of the dentin matrix, the properties of chlorhexidine digluconate and the components of the resin matrix must be taken into account.

CLINICAL SIGNIFICANCE

Metalloproteinases influence degradation of the hybrid layer in composite resin restorations, regardless of whether the bonding system used is one-bottle or self-etching.

MMP Inhibitors on Dentin Stability: A Systematic Review and Meta-analysis

The aim of this study was to systematically review the literature for in vitro and ex vivo studies that evaluated the effect of matrix metalloproteinase (MMP) inhibitors during the adhesive procedure on the immediate and long-term resin-dentin bond strength. The search was conducted in 6 databases with no publication year or language limits, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. From 1,336 potentially eligible studies, 48 were selected for full-text analysis, and 30 were included for review, with 17 considered in the meta-analysis. Two reviewers independently selected the studies, extracted the data, and assessed the risk of bias. Pooled effect estimates were expressed as the weighted mean difference between groups. The most used MMP inhibitor was chlorhexidine (CHX). Immediate bond strength results showed no difference between 2% CHX and control; however, a difference was found between 0.2% CHX and control at baseline. After aging, CHX presented higher bond strength values compared to control groups (p < .05). However, this was not observed for longer periods of aging. High heterogeneity was found in some comparisons, especially for the water storage aging subgroup. Subgroup analyses showed that self-etching and etch-and-rinse adhesives are benefited by the CHX use. From the studies included, only 1 presented low risk of bias, while the others showed medium or high risk of bias. The use of MMP inhibitors did not affect the immediate bond strength overall, while it influenced the aged bond strength. Aging procedures influenced bond strength values of the dentin adhesion stability.