Host-derived proteinases and degradation of dentine collagen in situ

The action of microbial collagenases in dentinal matrix degradation in root caries and potential strategies for its management: a comprehensive state-of-the-art review

Conventional views associate microbial biofilm with demineralization in root caries (RC) onset, while research on their collagenases role in the breakdown of collagen matrix has been sporadically developed, primarily in vitro. Recent discoveries, however, reveal proteolytic bacteria enrichment, specially Porphyromonas and other periodontitis-associated bacteria in subgingivally extended lesions, suggesting a potential role in RC by the catabolism of dentin organic matrix. Moreover, genes encoding proteases and bacterial collagenases, including the U32 family collagenases, were found to be overexpressed in both coronal and root dentinal caries. Despite these advancements, to prove microbial collagenolytic proteases' definitive role in RC remains a significant challenge. A more thorough investigation is warranted to explore the potential of anti-collagenolytic agents in modulating biofilm metabolic processes or inhibiting/reducing the size of RC lesions. Prospective treatments targeting collagenases and promoting biomodification through collagen fibril cross-linking show promise for RC prevention and management. However, these studies are currently in the in vitro phase, necessitating additional research to translate findings into clinical applications. This is a comprehensive state-of-the-art review aimed to explore contributing factors to the formation of RC lesions, particularly focusing on collagen degradation in root tissues by microbial collagenases.

The activity, distribution, and colocalization of cathepsin K and matrix metalloproteases in intact and eroded dentin

OBJECTIVES

This study aimed to assess the activity, distribution, and colocalization of cathepsin K (catK) and matrix metalloproteases (MMPs) in both intact and eroded dentin in vitro.

MATERIALS AND METHODS

Eroded dentin was obtained by consecutive treatment with 5% citric acid (pH = 2.3) for 7 days, while intact dentin remained untreated. Pulverized dentin powder (1.0 g) was extracted from both intact and eroded dentin using 5 mL of 50 mM Tris-HCl buffer (0.2 g/1 mL, pH = 7.4) for 60 h to measure the activity of catK and MMPs spectrofluorometrically. In addition, three 200-μm-thick dentin slices were prepared from intact and eroded dentin for double-labeling immunofluorescence to evaluate the distribution and colocalization of catK and MMPs (MMP-2 and MMP-9). The distribution and colocalization of enzymes were analyzed using inverted confocal laser scanning microscopy (CLSM), with colocalization rates quantified using Leica Application Suite Advanced Fluorescent (LAS AF) software. One-way analysis of variance (ANOVA) was used to analyze the fluorescence data related to enzyme activity (α = 0.05).

RESULTS

The activity of catK and MMPs was significantly increased in eroded dentin compared with intact dentin. After erosive attacks, catK, MMP-2, and MMP-9 were prominently localized in the eroded regions. The colocalization rates of catK with MMP-2 and MMP-9 were 13- and 26-fold higher in eroded dentin, respectively, than in intact dentin.

CONCLUSIONS

Erosive attacks amplified the activity of catK and MMPs in dentin while also altering their distribution patterns. Colocalization between catK and MMPs increased following erosive attacks.

CLINICAL RELEVANCE

CatK, MMP-2, and MMP-9 likely play synergistic roles in the pathophysiology of dentin erosion.

Enhanced Bonding to Caries-Affected Dentin Using an Isocyanate-Based Primer

Dental caries is the most common oral disease and the most common cause of resin restorations. In minimally invasive dentistry, the principle behind cavity preparation is to remove external caries-infected dentin (CID) and preserve internal caries-affected dentin (CAD) and sound dentin (SD). The cavity floor is mainly composed of CAD, but the poor bonding performance of CAD has become a widespread concern. This study evaluated the performance of a new collagen-reactive monomer (ITCM) used as a primer to improve the bonding performance of CAD. The experimental specimens were grouped as follows: SD, CAD, and ITCM-pretreated CAD (CAD-ITCM). Dentin slices were obtained for attenuated total reflectance-Fourier transform infrared (ATR-FTIR) analysis. The bonded samples were subjected to microtensile bond strength analysis after 24 h of water storage or aging by thermocycling, and the bonding interface quality was evaluated by nanoleakage assessment, interfacial nanoindentation testing, and in situ zymography. Cytotoxicity experiments with ITCM were performed. ATR-FTIR showed that the isocyanate groups in ITCM can covalently bind and form hydrogen bonds with the collagen in CAD to mediate chemical bonding. ITCM pretreatment significantly improved the bond strength of CAD (P < 0.05), reduced interfacial nanoleakage, improved the sealing of the bonding interface, enhanced the homogeneity of the hybrid layer, and inhibited matrix metalloproteinase activity. In addition, ITCM presented acceptable biocompatibility for dental restorative application. Taken together, this study reported the application of ITCM to induce collagen-based chemical bonding in the CAD bonding system, which fills the gap in strategies to improve the bonding performance of CAD immediately and after aging and has important clinical application prospects.

Mass spectrometry-based proteomic approaches for salivary protein biomarkers discovery and dental caries diagnosis: A critical review

Dental caries is a multifactorial chronic disease resulting from the intricate interplay among acid-generating bacteria, fermentable carbohydrates, and several host factors such as saliva. Saliva comprises several proteins which could be utilized as biomarkers for caries prevention, diagnosis, and prognosis. Mass spectrometry-based salivary proteomics approaches, owing to their sensitivity, provide the opportunity to investigate and unveil crucial cariogenic pathogen activity and host indicators and may demonstrate clinically relevant biomarkers to improve caries diagnosis and management. The present review outlines the published literature of human clinical proteomics investigations on caries and extensively elucidates frequently reported salivary proteins as biomarkers. This review also discusses important aspects while designing an experimental proteomics workflow. The protein-protein interactions and the clinical relevance of salivary proteins as biomarkers for caries, together with uninvestigated domains of the discipline are also discussed critically.

Effect of the cranberry ( Vaccinium macrocarpon ) juice on reducing dentin erosion: an in vitro study

Vaccinium macrocarpon (cranberry) is a fruit that has an inhibitory effect on matrix metalloproteinases (MMPs) present in dentin and saliva. The inhibition of MMPs has been shown to prevent dentin erosion. The aim of this study was to analyze the effect of cranberry juice on the reduction of dentin erosion in vitro. Specimens of bovine dentin (4×4×2 mm) were randomized and divided into 4 groups (n = 17/group): distilled water (C-control, pH 7.2); green tea extract solution containing 400 µm epigallo-catechin-gallate (EGCg, positive control, pH 4.5); 10% cranberry extract (CrE, pH 3.9), and cranberry juice (CrJ, Cranberry JuxxTM, pH 2.8). Specimens were submitted to erosive pH cycles for 5 days. Each day, four demineralizations were carried out with 0.1% citric acid (90 s). After the acid challenges, specimens were rinsed and kept in treatment solutions for 1 min; afterwards, they were rinsed and stored in artificial saliva for 1 h at 37°C (or overnight at the end of each day). After the experimental period of 5 days, dentin loss was evaluated by contact profilometry. Data were analyzed by ANOVA and Tukey's test (p < 0.05). Dentin loss (µm ± SD) was significantly lower for all treatments (EGCg = 9.93 ± 2.90; CrE = 12.10 ± 5.44; CrJ = 11.04 ± 5.70) compared to control (21.23 ± 11.96), but it did not significantly differ from each other. These results indicate that the commercial cranberry juice, despite its low pH, is able to reduce dentin erosion, which might be due to the ability of cranberry components to inhibit MMPs.

Chemical Properties of Human Dentin Blocks and Vertical Augmentation by Ultrasonically Demineralized Dentin Matrix Blocks on Scratched Skull without Periosteum of Adult-Aged Rats

Vertical augmentation is one of the most challenging techniques in bone engineering. Several parameters, such mechano-chemical characteristics, are important to optimize vertical bone regeneration using biomaterials. The aims of this study were to chemically characterize human dentin blocks (calcified demineralized dentin matrix: CDM, partially demineralized dentin matrix: PDDM and completely demineralized dentin matrix: CDDM) (2 × 2 × 1 mm³) chemically and evaluate the behavior of PDDM blocks on non-scratched or scratched skulls without periosteum of adult rats (10–12 months old, female) as a vertical augmentation model. The dissolved efficiency of CDM showed 32.3% after ultrasonic demineralization in 1.0 L of 2% HNO₃ for 30 min. The 30 min-demineralized dentin was named PDDM. The SEM images of PDDM showed the opening of dentinal tubes, nano-microcracks and the smooth surface. In the collagenase digestion test, the weight-decreasing rates of CDM, PDDM and CDDM were 9.2%, 25.5% and 78.3% at 12 weeks, respectively. CDM inhibited the collagenase digestion, compared with PDDM and CDDM. In the PDDM onlay graft on an ultrasonically scratched skull, the bone marrow-space opening from original bone was found in the bony bridge formation between the human PDDM block and dense skull of adult senior rats at 4 and 8 weeks. On the other hand, in the cases of the marrow-space closing in both non-scratched skulls and scratched skulls, the bony bridge was not formed. The results indicated that the ultrasonic scratching into the compact parietal bone might contribute greatly to the marrow-space opening from skull and the supply of marrow cells, and then bony bridge formation could occur in the vertical augmentation model without a periosteum.

Extracellular matrix degradation by host matrix metalloproteinases in restorative dentistry and endodontics: An overview

Matrix metalloproteinases (MMPs) are a group of over 25 secreted and membrane-bound enzymes responsible for pericellular substrate degeneration. In response to injury, they play key roles in morphogenesis, wound healing, tissue repair and remodeling. They have been isolated from dentin, odontoblasts, pulp and periapical tissue. They play a major role in the formation of dentin matrix and secondary and tertiary dentin. These are also responsible for releasing dentinal growth factors. MMP family proteins elicit a dual role in the pathogenesis of inflammation, stimulating protective innate and/or adaptive immune functions, as well as tissue destruction. The main organic component of tooth structure is collagen, and MMPs that degrade collagen and the extracellular matrix have been implicated in the progression of dental caries, dental erosion as well as degradation of the hybrid layer. MMPs have also been shown to be active in pulpitis, and studies have shown that they can be used as diagnostic markers of pulpal and periapical inflammation. This review describes the role of MMPs in dental caries, dental erosion, bond stability as well as in pulpal and periapical inflammation.

Levels of Selected Matrix Metalloproteinases-MMP-1, MMP-2 and Fibronectin in the Saliva of Patients Planned for Endodontic Treatment or Surgical Extraction

OBJECTIVES

Composition of saliva reflects the condition of the oral cavity.

THE AIM OF THE STUDY

Investigation of the concentrations of MMP-1 (Matrix metalloproteinase-1), MMP-2 (Matrix metalloproteinase-2) and fibronectin in the saliva of patients planned for endodontic treatment or surgical extraction.

MATERIAL AND METHODS

Seventy-five patients with caries and 14 healthy subjects were included in the study. Subjects were divided into group 1, in which 50 patients were planned for endodontic treatment, and group 2, in which 25 patients were planned for surgical extraction. For the measurements, we used a surface plasmon resonance imaging biosensor.

RESULTS

We found higher levels of MMP-1, MMP-2 and fibronectin in the saliva of patients planned for dental treatment than in healthy donors. We found lower concentrations of MMP-2 in subjects planned for surgical extraction, than in patients planned for endodontic treatment; however, there were no such differences in salivary concentrations of MMP-1 and fibronectin. There were no statistically significant differences in MMP-1 concentrations in the saliva before and after any type of dental treatment, but contrary to that, we found a statistically significant decrease in MMP-2 concentrations after endodontic treatment and after surgical extraction. We found a significant rise in the concentrations of fibronectin after surgical extraction but not after endodontic treatment.

CONCLUSIONS

The concentrations of MMP-1 and MMP-2 in the saliva of our patients with caries were increased in comparison to healthy individuals, but after the treatment-so sanation of the oral cavity-we noted a decrease in matrix metalloproteinases (MMPs) levels. MMPs can be found in gingival crevicular fluid and saliva, carious dentin and plaque. According to our observations, the main source of MMPs in patients with caries is probably carious dentin. Increase in the salivary levels of fibronectin (FN) after surgical extraction may be connected with soft tissue injury caused by surgical extraction. Our results are another example of the fact that higher salivary concentrations of MMP-1, MMP-2 and FN can reflect the health status of the oral cavity in patients with caries.

Is it possible for a simultaneous biomodification during acid etching on naturally caries-affected dentin bonding?

OBJECTIVES

This study investigated the ability of modified phosphoric acids containing chlorhexidine (CHX) or grape seed extract (GSE) for promoting simultaneous biomodification during acid etching on bonding properties in caries-affected dentin (CAD).

MATERIALS AND METHODS

Thirty-two human molars (8 with sound dentin [SD] and 24 naturally CAD) were selected for the study. The SD and CAD were initially exposed, then randomized and etched according to the following groups: (1) SD (SD-CT) and CAD (CAD-CT) both with 37% phosphoric acid, (2) CAD with 2% CHX containing 37% phosphoric acid (CAD-CHX), and (3) CAD with 2% GSE containing 10% phosphoric acid (CAD-GSE). The bonding procedure and composite build-ups were performed after acid etching. Subsequently, they were sectioned in resin-dentin specimens. The specimens were submitted for chemical profiling by micro-Raman, microtensile bond strength (μTBS), failure mode with chemical characterization by FEG/SEM-EDX, and in situ zymography by CLSM. The data from μTBS and CLSM were statistically analyzed (1-way ANOVA and Tukey's test; α = 0.05).

RESULTS

The highest μTBS results were shown for SD-CT in comparison with all CAD groups (p < 0.001), and the lowest for CAD-CT and CAD-CHX (p < 0.001). The etching with CHX did not increase the μTBS for CAD when compared with CT (p = 0.52). However, the etching with GSE improved significantly the μTBS for CAD when compared with CT and CHX (p < 0.001). The chemical profile detected chemical and structural changes in collagen peaks for CAD-CT, which were not detected when the CAD was etched by modified acids. Also, the poorest hybridization ability was detected in CAD for CT, which was significantly improved with modified acids, especially the GSE, as evaluated by chemical profile and failure mode. A significant reduction of MMP activity on CAD was promoted by modified acids in comparison with CT (both p < 0.001).

CONCLUSIONS

The GSE-containing acid was able to promote biomodification during the acid etching, increasing the bonding properties and reducing the activity of the MMPs within the hybrid layer.

CLINICAL RELEVANCE

The use of GSE-containing phosphoric acid can be a promising alternative to improve the bonding performance on caries-affected dentin, since it is capable of biomodifying the dentin during the acid etching, without adding any extra step in bonding procedures.

Antimicrobial antidegradative dental adhesive preserves restoration-tooth bond

OBJECTIVE

Assess the ability of an antimicrobial drug-releasing resin adhesive, containing octenidine dihydrochloride (OCT)-silica co-assembled particles (DSPs), to enhance the biostability and preserve the interfacial fracture toughness (FT) of composite restorations bonded to dentin. Enzyme-catalyzed degradation compromises the dental restoration-tooth interface, increasing cariogenic bacterial infiltration. In addition to bacterial ingress inhibition, antimicrobial-releasing adhesives may exhibit direct interfacial biodegradation inhibition as an additional benefit.

METHODS

Mini short-rod restoration bonding specimens with total-etch adhesive with/without 10% wt. DSPs were made. Interfacial fracture toughness (FT) was measured as-manufactured or post-incubation in simulated human salivary esterase (SHSE) for up to 6-months. Effect of OCT on SHSE and whole saliva/bacterial enzyme activity was assessed. Release of OCT outside the restoration interface was assessed.

RESULTS

No deleterious effect of DSPs on initial bonding capacity was observed. Aging specimens in SHSE reduced FT of control but not DSP-adhesive-bonded specimens. OCT inhibited SHSE degradation of adhesive monomer and may inhibit endogenous proteases. OCT inhibited bacterial esterase and collagenase. No endogenous collagen breakdown was detected in the present study. OCT increased human saliva degradative esterase activity below its minimum inhibitory concentration towards S. mutans (MIC), but inhibited degradation above MIC. OCT release outside restoration margins was below detection.

SIGNIFICANCE

DSP-adhesive preserves the restoration bond through a secondary enzyme-inhibitory effect of released OCT, which is virtually confined to the restoration interface microgap. Enzyme activity modulation may produce a positive-to-negative feedback switch, by increasing OCT concentration via biodegradation-triggered release to an effective dose, then subsequently slowing degradation and degradation-triggered release.

In situ effect of a proanthocyanidin mouthrinse on dentin subjected to erosion

Proanthocyanidin has been shown to be efficient in inhibiting matrix metalloproteinases.

Effect of protease inhibitor specificity on dentin matrix properties

OBJECTIVE

To evaluate protease activity of dentin matrices subjected to treatment with non-specific (chlorhexidine - CHX), cysteine cathepsin specific (E-64), and cysteine cathepsin-K (CT-K) specific (Odanacatib - ODN) inhibitors.

METHODS

Pulverized dentin powder obtained from human dentin disks (0.5 mm thickness) completely demineralized with 10% H₃PO₄ were challenged in 1 mL lactic acid (LA) (0.1M, pH 5.5) or stored in deionized water for 30 min. Aliquots of dentin powder were then immersed in 1 mL of CHX (2%), E-64 (10 μM and 20 μM) or Odanacatib (0.2 nM and 1 μM) for 30min. Degradation of dentin collagen was determined by telopeptide assays measuring the sub-product release of C-terminal cross-linked telopeptides (ICTP) and C-terminal peptide (CTX) in incubation media, which correlates with matrix metalloproteinases (MMP) and CT-K activities respectively (n = 3). The ICTP and CTX data were normalized to concentration of total protein (ICTP_tp and CTX_tp) in the media, measured by bicinchoninic acid assay. Dentin matrix properties were also measured by gravimetric change (n = 8) and ultimate tensile strength (UTS) (n = 10). Data were analyzed by one-way ANOVA followed by Tukey's post-hoc test and independent t-test (α = 5%).

RESULTS

Telopeptide assays showed significantly lower CTX_tp values after treatment with E-64 and Odanacatib. E-64 and Odanacatib at all tested concentrations significantly reduced the release of ICTP_tp. Gravimetric analysis showed no significant difference between the tested inhibitors and control except for CHX after lactic acid challenge. UTS results showed significantly higher values for E-64 (20 μM) and Odanacatib (0.2 nM and 1 μM) groups in deionized water.

SIGNIFICANCE

Dentin therapies targeting enzymes such as CT-K by specific inhibitors may provide superior pharmacokinetics and optimum efficacy due to precise protein binding, consequently limiting collagen degradation directly or indirectly by enzyme related pathways.

A new method for dentine matrix metalloproteinase extraction

In addition to their involvement in tissue remodelling, matrix metalloproteinases (MMPs), in the oral environment, are linked to leakage in the resin-dentine interface through their involvement in the proteolytic degradation of the resin-dentine hybrid layer. Numerous studies have evaluated dentine MMP activity and the vast majority of those studies have used an MMP extraction protocol to semi-purify the MMPs from dentine, first described around 20 years ago. This is a protocol that requires 32 days for completion. The technique is based on the three-step sequential use of NaCl solution for pulverised dentine washing, then guanidine HCl and EDTA to demineralise the pulverised dentine to extract the MMPs. In this study, a new one-step dentine MMP extraction protocol was adapted to extract dentine MMPs in only four days. This was achieved by eliminating the NaCl washing step and combining the guanidine HCl and EDTA into one extraction solution that also contained proteinase inhibitors. Fifty-two dentine MMP extracts were obtained utilising the two different extraction methods. The amount of total and endogenously active MMP-2 in the specimens was assayed utilising a human MMP-2 activity enzyme-linked immunosorbent assay (ELISA). The study results showed that the new extraction method is as effective as the traditional three-step extraction method in semi-purifying dentine MMP-2.

Dentin degradonomics - The potential role of salivary MMP-8 in dentin caries

Background

Dentin caries involves dissolution of minerals which eventually leads to degradation of organic matrix. This degradation which was thought to be by bacterial proteases is now considered to be orchestrated by endogenous collagenases such as Matrix Metalloproteinases (MMPs). This paper aims to estimate the salivary levels of MMP-8 in dental caries and also to asses the various risk factors that contribute to the formation of dental caries.

Material and Methods

A random sample of 75 adults aged 18-35 were included and categorized based on the number of caries lesions (MCL). Standard clinical examinations were performed, and stimulated saliva was collected and analyzed for concentrations of MMP-8 using enzyme-linked immunosorbent assay. Caries risk factors were assessed using a chair-side kit. Correlation of MMP-8 in varying MCL using Spearman’s correlation was done. Multiple linear regression analysis was done to asses the relationship between various caries risk factors with MMP-8 and MCL as dependent variable.

Results

The study results showed a statistically significant higher concentration of MMP-8 in carious group (MCL 1-2) and MCL ≥3 compared to non-carious group. On correlating, the levels of MMP-8 were seen to be higher in MCL ≥3 than in MCL = 0 and MCL 1-2. The mean MMP-8 of controls, MCL 1-2, and MCL ≥3 were 131.34ng/ml, 230.14ng/ml, and 391.91ng/ml respectively. Multiple linear regression analysis with MMP-8 as the dependent variable revealed caries, buffer capacity and S. mutans count as significant variables. Using MCL as the dependent variable the only significant variable was MMP-8 levels.

Conclusions

The study suggests that subjects with caries have elevated MMP-8 levels compared with subjects with no carious lesions. There is also a positive correlation between the number of carious lesions and MMP-8 levels suggesting that MMP-8 plays an important role in the degradation of dentin and causes progression of caries.

Key words:Caries, Dentin, Enzyme-linked Immunosorbent Assay, MMP-8.

Bonding Performance of Universal Adhesive Systems Applied in Etch-and-Rinse and Self-Etch Strategies on Natural Dentin Caries

Objective:

This study investigated the bonding performance of three universal adhesive systems applied using etch-and-rinse (ER) or self-etch (SE) strategies on natural dentin caries.

Materials and Methods:

Sixty human third molars were selected for this study: 30 naturally carious (CAD) and 30 sound (SD) teeth. The dentin surfaces were exposed, and teeth were randomly assigned to each evaluated adhesive system: Scotchbond Universal (SBU), Futurabond U (FBU), and Prime&Bond Elect (PBE) and an adhesive strategy: ER or SE. The adhesive systems were applied following the manufacturer's instructions, and the teeth were restored using a resin composite (Filtek Supreme Ultra, 3M). After 24 hours (distilled water at 37°C), samples were sectioned and evaluated using microtensile bond strength analysis (μTBS), micro-Raman spectroscopy to evaluate the degree of conversion within the hybrid layer (DC), and scanning electronic microscopy (SEM) to describe the morphology of the hybrid layer. The μTBS and DC data were analyzed using three-way analysis of variance and Tukey's test for means comparison (α=0.05). The SEM images were analyzed qualitatively.

Results:

Reduced μTBS values were observed when comparing CAD with SD, regardless of adhesive system or strategy (p&lt;0.0001). SBU showed statistically higher μTBS for both dentin substrates and strategies (p&lt;0.0001). Furthermore, SBU showed greater integrity of the hybrid layer and resin tag formation compared with FBU and PBE. Mean μTBS values for FBU were higher for SD in the SE mode, whereas higher mean μTBS values were observed for CAD in the ER mode, both compared with PBE (p&lt;0.001).

Conclusion:

Bonding performance is reduced on a caries-affected substrate. The ER strategy was not able to improve the bonding performance on natural CAD for universal adhesive systems. Improved bonding performance was obtained when using the Scotchbond Universal system.

Human neutrophils degrade methacrylate resin composites and tooth dentin

Cholesterol esterase-like (CE) activity from saliva and esterase from cariogenic bacteria hydrolyze ester linkages of dental methacrylate resins. Collagenolytic, matrix metalloproteinase-like (MMP) activities from dentin and bacteria degrade collagen in demineralized tooth dentin. Human neutrophils in the oral cavity contain factors that are hypothesized to have CE and MMP activities that could contribute to the degradation of methacrylate resins and dentinal collagen. OBJECTIVES: To measure the CE and MMP activities from human neutrophils and their ability to degrade dental methacrylate resin composite and dentinal collagen. Neutrophils' CE and MMP activities were measured using nitrophenyl-esters or fluorimetric MMP substrates, respectively. Neutrophils' degradation of resin composite and dentinal collagen was quantified by measuring release of a universal 2,2-Bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bisGMA)-derived resin composite degradation byproduct, bishydroxy-propoxy-phenyl-propane (bisHPPP), or a collagen degradation by-product, hydroxyproline, respectively using ultra performance liquid chromatography/mass spectrometry. Neutrophils' CE activity increased the release of bisHPPP from bisGMA monomer compared to control after 24 and 48 h (p < 0.05). Neutrophils degraded polymerized resin composite and produced higher amounts of bisHPPP than buffer after 48 h of incubation (p < 0.05). Neutrophils show generic MMP, gelatinase, MMP-2 and MMP-9, and collagenase, MMP-1 and MMP-8 activities that were stable or increased over the first 24 h (p < 0.05). Neutrophils degraded demineralized dentin more than buffer-only groups, indicated by higher amounts of hydroxyproline (p < 0.05). The ability of neutrophils to degrade both dental resin composite and tooth dentin, suggest neutrophil's potential role in root caries, and in recurrent carries by accelerating the degradation of resin-dentin interfaces, and compromising the longevity of the restoration. STATEMENT OF SIGNIFICANCE: Neutrophils are part of the innate immune system and are constantly entering the oral cavity through the gingival sulcus, in direct contact with the tooth, restoration, restoration-tooth margins and pathogenic bacteria. The current study is the first to characterize and quantify degradative activities from neutrophils toward methacrylate resin and demineralized dentin, the two main components of the restoration-tooth interface, suggesting that this interface could be negatively influenced by neutrophils, potentially contributing to increase in caries formation and progression, and premature restoration failure. This study provides a significant finding to the biomaterials and oral health fields by identifying a potential weakness in current restorative procedures and materials used to manage gingival proximal and cervical gingival or sub-gingival carious lesions.

Resin-Dentin Bonding Interface: Mechanisms of Degradation and Strategies for Stabilization of the Hybrid Layer

Several studies have shown that the dentin-resin interface is unstable due to poor infiltration of resin monomers into the demineralized dentin matrix. This phenomenon is related to the incomplete infiltration of the adhesive system into the network of exposed collagen fibrils, mainly due to the difficulty of displacement and subsequent replacement of trapped water between interfibrillar spaces, avoiding adequate hybridization within the network of collagen fibrils. Thus, unprotected fibrils are exposed to undergo denaturation and are susceptible to cyclic fatigue rupture after being subjected to repetitive loads during function. The aqueous inclusions within the hybrid layer serve as a functional medium for the hydrolysis of the resin matrix, giving rise to the activity of esterases and collagenolytic enzymes, such as matrix metalloproteinases, which play a fundamental role in the degradation process of the hybrid layer. Achieving better interdiffusion of the adhesive system in the network of collagen fibrils and the substrate stability in the hybrid layer through different strategies are key events for the interfacial microstructure to adequately function. Hence, it is important to review the factors related to the mechanisms of degradation and stabilization of the hybrid layer to support the implementation of new materials and techniques in the future. The enzymatic degradation of collagen matrix, together with resin leaching, has led to seeking strategies that inhibit the endogenous proteases, cross-linking the denudated collagen fibrils and improving the adhesive penetration removing water from the interface. Some of dentin treatments have yielded promising results and require more research to be validated. A longer durability of adhesive restorations could resolve a variety of clinical problems, such as microleakage, recurrent caries, postoperative sensitivity, and restoration integrity.

Effect of Er:YAG laser irradiation and chitosan biomodification on the stability of resin/demineralized bovine dentin bond

OBJECTIVE

The purpose of this study was to evaluate the effect of Er:YAG laser for selective removal of carious lesion, followed by biomodification with chitosan on the microtensile bond strength (µTBS), adhesive interface, dry mass loss and hydroxyproline release (HYP).

METHODS

Artificial lesions were created in 104 bovine dentin blocks. Blocks were divided according to caries removal method: bur or Er:YAG laser. Seventy-six blocks were acid etched and subdivided according to dentin biomodification: no chitosan and 2.5% chitosan. Composite resin restorations were performed. Blocks were sectioned into beams and stored in water. After 24 h, 6 and 12 months, beams were submitted to μTBS test (n = 10) and analysis of adhesive interface by SEM (n = 3). The other 28 blocks were sectioned into beams and initial dry mass (DM) was determined (n = 7). Beams were stored and after 7 days, DM was redetermined. HYP release (n = 7) was evaluated by ELISA. Data were analyzed by ANOVA and Bonferroni's tests (α = 0.05).

RESULTS

After 24 h, the highest µTBS was found for bur (p < 0.001). After 6 months, methods were similar (p = 0.432). After 12 months, laser-irradiated dentin showed the highest µTBS values (p = 0.025). Chitosan promoted higher µTBS values after 6 (p = 0.011) and 12 months (p < 0.001) preserving adhesive interface. Dry mass loss and HYP release were not influenced (p > 0.05) by caries removal method or by dentin biomodification.

CONCLUSION

The bond strength to demineralized dentin reduced over 50% in all groups after water storage. From 6 months of water storage, Er:YAG laser irradiation and biomodification with chitosan maintained the stability of the resin-dentin bonds, but did not influence dry mass loss and HYP release.

Doxycycline-loaded nanotube-modified adhesives inhibit MMP in a dose-dependent fashion

OBJECTIVES

This article evaluated the drug loading, release kinetics, and matrix metalloproteinase (MMP) inhibition of doxycycline (DOX) released from DOX-loaded nanotube-modified adhesives. DOX was chosen as the model drug, since it is the only MMP inhibitor approved by the U.S. Food and Drug Administration.

MATERIALS AND METHODS

Drug loading into the nanotubes was accomplished using DOX solution at distinct concentrations. Increased concentrations of DOX significantly improved the amount of loaded DOX. The modified adhesives were fabricated by incorporating DOX-loaded nanotubes into the adhesive resin of a commercial product. The degree of conversion (DC), Knoop microhardness, DOX release kinetics, antimicrobial, cytocompatibility, and anti-MMP activity of the modified adhesives were investigated.

RESULTS

Incorporation of DOX-loaded nanotubes did not compromise DC, Knoop microhardness, or cell compatibility. Higher concentrations of DOX led to an increase in DOX release in a concentration-dependent manner from the modified adhesives. DOX released from the modified adhesives did not inhibit the growth of caries-related bacteria, but more importantly, it did inhibit MMP-1 activity.

CONCLUSIONS

The loading of DOX into the nanotube-modified adhesives did not compromise the physicochemical properties of the adhesives and the released levels of DOX were able to inhibit MMP activity without cytotoxicity.

CLINICAL SIGNIFICANCE

Doxycycline released from the nanotube-modified adhesives inhibited MMP activity in a concentration-dependent fashion. Therefore, the proposed nanotube-modified adhesive may hold clinical potential as a strategy to preserve resin/dentin bond stability.

Dual function of proanthocyanidins as both MMP inhibitor and crosslinker in dentin biomodification: A literature review

Proanthocyanidin, a natural phytochemical bioactive agent, simultaneously can silence the activity of dentinal proteases and crosslink the collagen matrix; both of these phenomena would be the fundamentals for bio-stability of resin-dentin interface which is essential for a promising adhesive dentistry. This review provides an overview of the data developed by different groups of researchers and highlighted topics are proanthocyanidin chemistry, natural resources and the unique interactions between proanthocyanidincollagen and proanthocyanidin-MMPs in dentin. Besides, clinical applications of proanthocyanidin in the form of proanthocyanidin-containing adhesives, preconditioners and etchants have been reviewed. One hundred and twelve studies have been published in peer-reviewed journals from 1981 to 2017, all were comprised in this review, some of them have been actually proven to be promising from clinical point of view and others need further assessment before their adoption as clinically practicable protocols.

The Effect of Chemically Modified Tetracycline-3 on the Progression of Dental Caries in Rats

OBJECTIVE

Matrix metalloproteinases (MMPs) exist in human saliva and dentin and play an important role in the degradation of organic matrix in teeth. Chemically modified tetracycline-3 (CMT-3) is an inhibitor of MMPs. CMT-3 has been used experimentally to treat caries since 1999, but no distinction between dental caries prevalence and dentin caries prevalence has been described.

METHODS

A total of 65 Sprague-Dawley rats were randomly divided into three groups. The positive control group (25 rats) was inoculated with Streptococcus mutans (ATCC700610) and fed the cariogenic feed of improved Keyes Diet 2000. The CMT-3 group (25 rats) was also inoculated with S. mutans and fed the cariogenic feed of improved Keyes Diet 2000; the surfaces of rats' molars were daily treated with 0.02% CMT-3. The negative control group (15 rats) was only fed the standard rodent chow. At the end of the 10th week, the dental caries prevalence and dentin caries prevalence of each group were calculated, and the regions of caries were assessed.

RESULTS

No caries was found in the negative control group. The dental caries prevalence of the CMT-3 and the positive control group was 75.0 and 83.3%, respectively (p > 0.05, Table 2). The dentin caries prevalence of the CMT-3 and the positive control group was 33.3 and 70.8%, respectively (p < 0.05, Table 2). The Keyes scoring of dentin caries in the CMT-3 group was significantly lower than that in the positive control group (p < 0.05, Table 3).

CONCLUSIONS

CMT-3 had no effect on the prevalence of dental caries, but could lower the prevalence and slow down the progression of dentin caries.

Salivary Protein Roles in Oral Health and as Predictors of Caries Risk

This work describes the current state of research on the potential relationship between protein content in human saliva and dental caries, which remains among the most common oral diseases and causes irreversible damage in the oral cavity. An understanding the whole saliva proteome in the oral cavity could serve as a prerequisite to obtaining insight into the etiology of tooth decay at early stages. To date, however, there is no comprehensive evidence showing that salivary proteins could serve as potential indicators for the early diagnosis of the risk factors causing dental caries. Therefore, proteomics indicates the promising direction of future investigations of such factors, including diagnosis and thus prevention in dental therapy.

Influence of Infected Root Dentin on the Bond Strength of a Self-adhesive Resin Cement

AIM

The aim of this study was to determine the bond strength (BS) of a self-adhesive resin cement to the contaminated root dentin.

MATERIALS AND METHODS

The crown and apical third of twenty single-rooted teeth were removed. The root canals were flared and 1-mm-thick root sections were obtained. The sections were rinsed, dried, and sterilized. The control group (n=20) was composed of one section of each third, which remained immersed in sterile trypticase soy broth (TSB) for 2 months. The other sections comprised the experimental group (n = 40) and were immersed in a suspension of Enterococcus faecalis. The culture medium was changed at every 4 days for 2 months. The sections were rinsed with distilled water, dried, and the root canal space was filled with the self-adhesive resin cement RelyX™ U200. After 24 h, the push-out test was performed and the types of interface failure were observed on a stereo microscope.

STATISTICAL ANALYSIS

Data were statistically analyzed by the nonparametric Mann-Whitney test (α=5%).

RESULTS

A significant reduction was observed in the BS of resin cement to the contaminated dentin compared to the healthy dentin, for both thirds analyzed (P < 0.05). The BS was significantly greater at the cervical third compared to the middle third for specimens in the experimental group (P < 0.05). Adhesive and mixed failures were observed more frequently in specimens contaminated with E. faecalis.

CONCLUSION

Bacterial contamination negatively infl uenced the BS of the self-adhesive resin cement to the root dentin, and there was a predominance of adhesive and mixed failures.

Effect of Proanthocyanidin-enriched extracts on the inhibition of wear and degradation of dentin demineralized organic matrix

OBJECTIVES

The aim of this study was to evaluate the effect of Cranberry and Grape seed-enriched extract gels in inhibiting wear and degradation of demineralized organic matrix (DOM).

DESIGN

225 dentin specimens obtained from bovine incisors were randomly allocated into 5 groups (n=45): 10% Grape seed extract gel (GSE), 10% Cranberry extract gel (CE), 0.012% Chlorhexidine gel (CX), 1.23% NaF gel (F), and no active compound gel (P, placebo). Before the treatments, samples were demineralized by immersion in 0.87M citric acid, pH 2.3 (36h). Then, the studied gels were applied once over dentin for 1min. Next, the samples were immersed in artificial saliva containing collagenase obtained from Clostridium histolyticum for 5days. The response variable for dentin wear was depth of dentin loss measured by profilometry and for collagen degradation was hydroxyproline determination. Data were analyzed by ANOVA followed by Tukey's test and Pearson Correlation Test (p<0.05).

RESULTS

Grape seed extract significantly reduced dentin wear compared to the other groups (p<0.05). Cranberry extract and Chlorhexidine did not differ statistically and were able to reduce wear when compared to NaF and placebo treatments. The hydroxyproline analysis showed that there was no significant difference among groups for all treatments (p<0.05). Correlation analysis showed a significant correlation between the amount of degraded DOM evaluated by profilometry and the determination of hydroxyproline.

CONCLUSION

Cranberry extract was able to reduce the dentin wear and collagen degradation, likely due to the proanthocyanidin content and its action. Therefore, Cranberry could be suggested as an interesting natural-based agent to prevent dentin erosion.

Omega-3 and Omega-6 Fatty Acids Act as Inhibitors of the Matrix Metalloproteinase-2 and Matrix Metalloproteinase-9 Activity

Polyunsaturated fatty acids have been reported to play a protective role in a wide range of diseases characterized by an increased metalloproteinases (MMPs) activity. The recent finding that omega-3 and omega-6 fatty acids exert an anti-inflammatory effect in periodontal diseases has stimulated the present study, designed to determine whether such properties derive from a direct inhibitory action of these compounds on the activity of MMPs. To this issue, we investigated the effect exerted by omega-3 and omega-6 fatty acids on the activity of MMP-2 and MMP-9, two enzymes that actively participate to the destruction of the organic matrix of dentin following demineralization operated by bacteria acids. Data obtained (both in vitro and on ex-vivo teeth) reveal that omega-3 and omega-6 fatty acids inhibit the proteolytic activity of MMP-2 and MMP-9, two enzymes present in dentin. This observation is of interest since it assigns to these compounds a key role as MMPs inhibitors, and stimulates further study to better define their therapeutic potentialities in carious decay.

Postradiation Matrix Metalloproteinase-20 Expression and Its Impact on Dental Micromorphology and Radiation-Related Caries

Recent evidence suggests that head-and-neck radiotherapy (HNRT) increases active forms of matrix metalloproteinase-20 (MMP-20) in human tooth crowns, degrading the dentin-enamel junction (DEJ) and leading to enamel delamination, which is a pivotal step in the formation of radiation-related caries (RRC). Additional participation of enzymatic degradation of organic matrix components in caries progression was attributed to MMP-20 in dentin. Therefore, the current study tested the hypothesis that MMP-20 is overexpressed in the DEJ, dentin-pulp complex components, and carious dentin of post-HNRT patients, leading to detectable micromorphological changes to the enamel and dentin. Thirty-six teeth were studied, including 19 post-HNRT specimens and 17 nonirradiated controls. Optical light microscopy was used to investigate the micromorphological components of the DEJ, dentin-pulp complex components, and carious dentin. The samples were divided into 2 subgroups: nondemineralized ground sections (n = 20) and demineralized histological sections (n = 16). In addition, immunohistochemical analysis using the immunoperoxidase technique was conducted to semiquantitatively assess MMP-20 expression in the DEJ, dentin-pulp complex components, and carious dentin. No apparent damage to the DEJ microstructure or other dentin-pulp complex components was observed and no statistically significant differences were detected in MMP-20 expression (p > 0.05) between the irradiated and control groups. This study rejected the hypothesis that MMP-20 is overexpressed in the DEJ, dentin-pulp complex components, and carious dentin of post-HNRT patients, leading to detectable micromorphological changes. Hence, direct effects of radiation may not be regarded as an independent factor to explain aggressive clinical patterns of RRC.

Quercetin as a simple but versatile primer in dentin bonding

A quercetin/ethanol solution may serve as a simple but versatile primer to obtain desirable bonding stability and prevent secondary caries.

Effect of Tannic Acid on Bond Strength of Etch and Rinse and Self-etch Adhesive Systems in Dentin of Primary Teeth

INTRODUCTION

One of the possible mechanisms for the gradual destruction of bond strength in dentin-resin interface, could be due to the demineralized unstable collagen matrix. Use of protease inhibitors, such as tannic acid (TA) could prevent destruction of collagen fibers. The aim of this study was to compare the TA effect on bond strength of etch and rinse and self-etch adhesive systems in the dentin of primary teeth.

MATERIALS AND METHODS

This in vitro study was done on 40 extracted primary molar teeth. The teeth were sectioned in the mesiodistal direction, and enamel of buccal and lingual surfaces was removed. Samples were randomly divided into four groups: Single bond (SB) + TA, SB, Clearfil SE Bond (CSB) + TA, and CSB. Then, Z250 and Clearfil AP-X composites were cured on the surfaces of SB and CSB groups respectively. After that, all samples were divided into aging and non-aging groups. For 3 months, samples were placed under 1,000 thermal cycles in aging group. Subsequently, the shear bond strengths of all groups were measured by the International testing machine, and failure mode was evaluated by an optical stereomicroscope. Data were analyzed with paired t-test and independent t-test.

RESULTS

Tannic acid induced a significant reduction in the immediate bond strength of adhesive SB. Meanwhile, TA had no significant effect on shear bond strength of the CSB system.

CONCLUSION

Based on our findings, use of TA is not recommended with SB and CSB adhesives on primary teeth.

CLINICAL SIGNIFICANCE

Tannic acid may not be considered in resin restorations of primary teeth.

The Role of Matrix Metalloproteinases (MMPs) in Human Caries

The objective of this review is to summarize our understanding of the role of host matrix metalloproteinases (MMPs) in the caries process and to discuss new therapeutic avenues. MMPs hydrolyze components of the extracellular matrix and play a central role in many biological and pathological processes. MMPs have been suggested to play an important role in the destruction of dentin organic matrix following demineralization by bacterial acids and, therefore, in the control or progression of carious decay. Host-derived MMPs can originate both from saliva and from dentin. They may be activated by an acidic pH brought about by lactate release from cariogenic bacteria. Once activated, they are able to digest demineralized dentin matrix after pH neutralization by salivary buffers. Furthermore, the degradation of SIBLINGs (Small Integrin-binding Ligand N-linked Glycoproteins) by the caries process may potentially enhance the release of MMPs and their activation. This review also explores the different available MMP inhibitors, natural or synthetic, and suggests that MMP inhibition by several inhibitors, particularly by natural substances, could provide a potential therapeutic pathway to limit caries progression in dentin.

Collagen Degradation by Host-derived Enzymes during Aging

Incompletely infiltrated collagen fibrils in acid-etched dentin are susceptible to degradation. We hypothesize that degradation can occur in the absence of bacteria. Partially demineralized collagen matrices (DCMs) prepared from human dentin were stored in artificial saliva. Control specimens were stored in artificial saliva containing proteolytic enzyme inhibitors, or pure mineral oil. We retrieved them at 24 hrs, 90 and 250 days to examine the extent of degradation of DCM. In the 24-hour experimental and 90- and 250-day control specimens, we observed 5- to 6-μm-thick layers of DCM containing banded collagen fibrils. DCMs were almost completely destroyed in the 250-day experimental specimens, but not when incubated with enzyme inhibitors or mineral oil. Functional enzyme analysis of dentin powder revealed low levels of collagenolytic activity that was inhibited by protease inhibitors or 0.2% chlorhexidine. We hypothesize that collagen degradation occurred over time, via host-derived matrix metalloproteinases that are released slowly over time.

Effects of Contamination by Hemostatic Agents and Use of Cleaning Agent on Etch-and-Rinse Dentin Bond Strength

Abstract The aim of this study was to evaluate the influence of contamination by hemostatic agents and rinsing with chlorhexidine on bond strength between dentin and resin composite. Ninety-six bovine teeth were sectioned to expose a flat dentin surface area. A standardized cavity with 2.0 mm in thickness, superficial diameter of 4.0 mm and bottom diameter of 3.0 mm was prepared with a diamond bur in each dentin specimen. The teeth were divided into four groups according to the hemostatic employed: G1: control; G2: use of ViscoStat, Ultradent; G3: Hemosthasegel, FGM; and G4: Hemostop, Dentsply. The groups were divided into two subgroups according to the cleaning protocol method (n=12): A: without any further cleaning; and B: cleaning with chlorhexidine at 0.2%. All cavities were filled using a dentin adhesive and a resin composite, following the manufacturer's instructions. After 24 h, the specimens were aged by thermal and mechanical cycling. The bond strength was determined by the push out bond test (MPa), Statistical analysis was performed using two-way ANOVA and Tukey test (p<0.05). Statistically significant differences were detected among all groups treated with hemostatic agents and the control group. The post-hoc test showed that cleaning the cavity with chlorhexidine significantly improves the bond strength between dentin and resin composite. Our results suggested that the use of chlorhexidine can reestablish the bond strength between dentin and resin composite when a hemostatic agent was applied.

Investigation of ethanol infiltration into demineralized dentin collagen fibrils using molecular dynamics simulations

The purpose of this study is to investigate the interaction of neat ethanol with bound and non-bound water in completely demineralized dentin that is fully hydrated, using molecular dynamics (MD) simulation method. The key to creating ideal resin-dentin bonds is the removal of residual free water layers and its replacement by ethanol solvent in which resin monomers are soluble, using the ethanol wet-bonding technique. The test null hypotheses were that ethanol cannot remove any collagen-bound water, and that ethanol cannot infiltrate into the spacing between collagen triple helix due to narrow interlayer spacing. Collagen fibrillar structures of overlap and gap regions were constructed by aligning the collagen triple helix of infinite length in hexagonal packing. Three layers of the water molecules were specified as the layers of 0.15-0.22nm, 0.22-0.43nm and 0.43-0.63nm from collagen atoms by investigating the water distribution surrounding collagen molecules. Our simulation results show that ethanol molecules infiltrated into the intermolecular spacing in the gap region, which increased due to the lateral shrinkage of the collagen structures in contact with ethanol solution, while there was no ethanol infiltration observed in the overlap region. Infiltrated ethanol molecules in the gap region removed residual water molecules via modifying mostly the third water layer (50% decrease), which would be considered as a loosely-bound water layer. The first and second hydration layers, which would be considered as tightly bound water layers, were not removed by the ethanol molecules, thus maintaining the helical structures of the collagen molecules.

Effect of sealing infected dentin with glass ionomer cement on the abundance and localization of MMP-2, MMP-8, and MMP-9 in young permanent molars in vivo

BACKGROUND

The study of MMPs' behavior in carious lesions contributes to the understanding of the mechanisms involved in dentin reorganization after restoration.

AIM

To compare the abundance and localization of MMPs 2, 8, and 9 in infected dentin before and after restoration.

DESIGN

The sample consisted of 23 young permanent molars with active deep carious lesions. Infected carious dentin samples were collected from the same tooth at baseline and 60 days after cavity lining with GIC and composite resin restoration and processed for immunohistochemistry assays. After digital images were obtained, two calibrated operators analyzed the samples according to the immunostaining intensity and the MMPs' localization. Chi-square test was used for statistical analysis.

RESULTS

The intensity of immunostaining for MMP-8 was reduced after 60 days (P = 0.02), and no difference was observed for MMP-2 (P = 0.32) and MMP-9 (P = 0.14). The MMPs' distribution was generalized in the intertubular dentin and absent or located in the intratubular dentin, regardless of the period.

CONCLUSION

The sealing of infected carious dentin in young permanent molars reduced the expression of MMP-8, which is consistent with the initial remodeling process of the dentin matrix.

Inhibition of dentine collagen degradation by hesperidin: an in situ study

Dentine caries is a process of demineralization and subsequent degradation of the collagenous matrix. Host-derived proteolytic enzymes, such as matrix metalloproteinases (MMPs), play a role in this process of dentine collagen degradation. Hampering this degradation retards the caries process. Dietary antioxidants, such as the flavonoid hesperidin, can inhibit the proteolytic activity of MMPs and act as natural stabilizers of collagen. The aim of this study was to investigate the anti-collagenolytic activity of hesperidin in an in situ model. A single-blind, split-mouth, in situ experiment was designed. Seventeen participants received two completely demineralized dentine specimens placed contralaterally in the buccal flanges of their partial prosthesis. During the 4-wk experimental period, the participants immersed the dentine specimens in a test solution [1,000 parts per million (p.p.m.) hesperidin] or a control solution (saline), twice daily for 3 min. After the in situ period, the specimens were retrieved and their collagen content was determined. A saliva sample was taken at the start and at the end of the experimental period, to assess collagenolytic activity. A significant protection of collagen, of 24%, was observed in the hesperidin-treated specimens compared with the control-treated specimens. No correlation was found between salivary collagenolytic activity and loss of collagen in the control-treated specimens. The results of this in situ study show that hesperidin could play a role in the preservation of dentine collagen matrix.

Effect of EDTA Conditioning and Carbodiimide Pretreatment on the Bonding Performance of All-in-One Self-Etch Adhesives

Objective. This study evaluated the effect of ethylenediaminetetraacetic acid (EDTA) conditioning and carbodiimide (EDC) pretreatment on the shear bond strength of two all-in-one self-etch adhesives to dentin. Methods. Flat coronal dentin surfaces were prepared on one hundred and sixty extracted human molars. Teeth were randomly divided into eight groups according to two different self-etch adhesives used [G-Bond and OptiBond-All-In-One] and four different surface pretreatments: (a) adhesive applied following manufacturer's instructions; (b) dentin conditioning with 24% EDTA gel prior to application of adhesive; (c) EDC pretreatment followed by application of adhesive; (d) application of EDC on EDTA conditioned dentin surface followed by application of adhesive. Composite restorations were placed in all the samples. Ten samples from each group were subjected to immediate and delayed (6-month storage in artificial saliva) shear bond strength evaluation. Data collected was subjected to statistical analysis using three-way ANOVA and post hoc Tukey's test at a significance level of p < 0.05.  Results and Conclusion. EDTA preconditioning as well as EDC pretreatment alone had no significant effect on the immediate and delayed bond strengths of either of the adhesives. However, EDC pretreatment on EDTA conditioned dentin surface resulted in preservation of resin-dentin bond strength of both adhesives with no significant fall over six months.

Distinct decalcification process of dentin by different cariogenic organic acids: Kinetics, ultrastructure and mechanical properties

OBJECTIVES

We studied artificial dentin lesions in human teeth generated by lactate and acetate buffers (pH 5.0), the two most abundant acids in caries. The objective of this study was to determine differences in mechanical properties, mineral density profiles and ultrastructural variations of two different artificial lesions with the same approximate depth.

METHODS

0.05M (pH 5.0) acetate or lactate buffer was used to create 1) 180μm-deep lesions in non-carious human dentin blocks (acetate 130h; lactate 14days); (2) demineralized, ∼180μm-thick non-carious dentin discs (3 weeks). We performed nanoindentation to determine mechanical properties across the hydrated lesions, and micro X-ray computed tomography (MicroXCT) to determine mineral profiles. Ultrastructure in lesions was analyzed by TEM/selected area electron diffraction (SAED). Demineralized dentin discs were analyzed by small angle X-ray scattering (SAXS).

RESULTS

Diffusion-dominated demineralization was shown based on the linearity between lesion depths versus the square root of exposure time in either solution, with faster kinetics in acetate buffer. Nanoindentation revealed lactate induced a significantly sharper transition in reduced elastic modulus across the lesions. MicroXCT showed lactate demineralized lesions had swelling and more disorganized matrix structure, whereas acetate lesions had abrupt X-ray absorption near the margin. At the ultrastructural level, TEM showed lactate was more effective in removing minerals from the collagenous matrix, which was confirmed by SAXS analysis.

CONCLUSIONS

These findings indicated the different acids yielded lesions with different characteristics that could influence lesion formation resulting in their distinct predominance in different caries activities, and these differences may impact strategies for dentin caries remineralization.

Role of matrix metalloproteinases in dental caries, pulp and periapical inflammation: An overview

Matrix metalloproteinases (MMPs) are a group of more than 25 secreted and membrane bound enzymes that represent class of enzymes responsible for degradation of pericellular substrates. They have been isolated from dentine, odontoblasts, pulp and periapical tissue. They play an important role in dentine matrix formation, modulating caries progression and secondary dentine formation. Earlier microbial proteolytic enzymes were believed to be responsible for degradation of dentine organic matrix, but lately the accumulated body of evidence suggests that MMPs have an important role in the process. During normal tissue modelling, differentiation during development, in modulating the cell behaviour, maintaining homeostasis and in numerous extracellular pathologic conditions, MMPs tends to be an equally important participant. Odontoblasts secrete some of the essential MMPs for both physiologic and pathologic conditions. MMPs also appear to be a participant in the process of reversible and irreversible pulpitis. Although they tend to have low expression and activity in adult tissues but at the onset of any destructive pathologic process, their production shoots up. They appear to have a significant presence during times of inflammation in the periapical region as well. We take a look at the various factors and evidence pointing towards the role of MMPs in the progression of caries, pulpal and periapical inflammation.

Matrix metalloproteinases and other matrix proteinases in relation to cariology: the era of 'dentin degradomics'

Dentin organic matrix, with type I collagen as the main component, is exposed after demineralization in dentinal caries, erosion or acidic conditioning during adhesive composite restorative treatment. This exposed matrix is prone to slow hydrolytic degradation by host collagenolytic enzymes, matrix metalloproteinases (MMPs) and cysteine cathepsins. Here we review the recent findings demonstrating that inhibition of salivary or dentin endogenous collagenolytic enzymes may provide preventive means against progression of caries or erosion, just as they have been shown to retain the integrity and improve the longevity of resin composite filling bonding to dentin. This paper also presents the case that the organic matrix in caries-affected dentin may not be preserved as intact as previously considered. In partially demineralized dentin, MMPs and cysteine cathepsins with the ability to cleave off the terminal non-helical ends of collagen molecules (telopeptides) may lead to the gradual loss of intramolecular gap areas. This would seriously compromise the matrix ability for intrafibrillar remineralization, which is considered essential in restoring the dentin's mechanical properties. More detailed data of the enzymes responsible and their detailed function in dentin-destructive conditions may not only help to find new and better preventive means, but better preservation of demineralized dentin collagenous matrix may also facilitate true biological remineralization for the better restoration of tooth structural and mechanical integrity and mechanical properties.

Role of dentin MMPs in caries progression and bond stability

Dentin can be described as a biological composite with collagen matrix embedded with nanosized hydroxyapatite mineral crystallites. Matrix metalloproteinases (MMPs) and cysteine cathepsins are families of endopeptidases. Enzymes of both families are present in dentin and collectively capable of degrading virtually all extracellular matrix components. This review describes these enzymes and their presence in dentin, mainly focusing on their role in dentin caries pathogenesis and loss of collagen in the adhesive hybrid layer under composite restorations. MMPs and cysteine cathepsins present in saliva, mineralized dentin, and/or dentinal fluid may affect the dentin caries process at the early phases of demineralization. Changes in collagen and noncollagenous protein structure may participate in observed decreases in mechanical properties of caries-affected dentin and reduce the ability of caries-affected dentin to remineralize. These endogenous enzymes also remain entrapped within the hybrid layer during the resin infiltration process, and the acidic bonding agents themselves (irrespective of whether they are etch-and-rinse or self-etch) can activate these endogenous protease proforms. Since resin impregnation is frequently incomplete, denuded collagen matrices associated with free water (which serves as a collagen cleavage reagent for these endogenous hydrolase enzymes) can be enzymatically disrupted, finally contributing to the degradation of the hybrid layer. There are multiple in vitro and in vivo reports showing that the longevity of the adhesive interface is increased when nonspecific enzyme-inhibiting strategies are used. Different chemicals (i.e., chlorhexidine, galardin, and benzalkonium chloride) or collagen cross-linker agents have been successfully employed as therapeutic primers in the bonding procedure. In addition, the incorporation of enzyme inhibitors (i.e., quaternary ammonium methacrylates) into the resin blends has been recently promoted. This review will describe MMP functions in caries and hybrid layer degradation and explore the potential therapeutic role of MMP inhibitors for the development of improved intervention strategies for MMP-related oral diseases.

Grape seed extracts inhibit dentin matrix degradation by MMP-3

Since Matrix metalloproteinases (MMPs) have been suggested to contribute to dentin caries progression, the hypothesis that MMP inhibition would affect the progression of dentin caries is clinically relevant. Grape seed extracts (GSE) have been previously reported to be natural inhibitors of MMPs.

OBJECTIVE

To evaluate the capacity of a GSE mouthrinse to prevent the degradation of demineralized dentin matrix by MMP-3 (stromelysin-1).

MATERIALS AND METHODS

Standardized blocks of dentin obtained from sound permanent teeth extracted for orthodontic reasons were demineralized with Ethylenediaminetetraacetic acid (EDTA) and pretreated either with (A) GSE (0.2% w/v), (B) amine fluoride (AmF) (20% w/v), (C) a mouthrinse which contains both, (D) placebo, (E) sodium fluoride (0.15 mg.ml(-1)), (F) PBS, (G) Chlorhexidine digluconate (CHX), or (H) zinc chloride (ZnCl2). The dentin blocks were then incubated with activated recombinant MMP-3. The supernatants were analyzed by Western Blot for several dentin matrix proteins known to be MMP-3 substrate. In parallel, scanning electron microscopy (SEM) was performed on resin replica of the dentin blocks.

RESULTS

Western blot analysis of the supernatants revealed that MMP-3 released from the dentin matrix small proteoglycans (decorin and biglycan) and dentin sialoprotein (DSP) in the AmF, sodium fluoride, PBS and placebo pretreated groups, but not in the GSE and mouthrinse pretreated groups. SEM examination of resin replica showed that the mouthrinse and its active components not only had an anti-MMP action but also modified the dentin surface accessibility.

CONCLUSION

This study shows that GSE either alone or combined with AmF as in the evaluated mouthrinse limits dentin matrix degradation. This association may be promising to prevent the progression of caries within dentin. However, the procedure should be adapted to clinically relevant durations.

Doxycycline-encapsulated nanotube-modified dentin adhesives

This article presents details of fabrication, biological activity (i.e., anti-matrix metalloproteinase [anti-MMP] inhibition), cytocompatibility, and bonding characteristics to dentin of a unique doxycycline (DOX)-encapsulated halloysite nanotube (HNT)-modified adhesive. We tested the hypothesis that the release of DOX from the DOX-encapsulated nanotube-modified adhesive can effectively inhibit MMP activity. We incorporated nanotubes, encapsulated or not with DOX, into the adhesive resin of a commercially available bonding system (Scotchbond Multi-Purpose [SBMP]). The following groups were tested: unmodified SBMP (control), SBMP with nanotubes (HNT), and DOX-encapsulated nanotube-modified adhesive (HNT+DOX). Changes in degree of conversion (DC) and microtensile bond strength were evaluated. Cytotoxicity was examined on human dental pulp stem cells (hDPSCs). To prove the successful encapsulation of DOX within the adhesives-but, more important, to support the hypothesis that the HNT+DOX adhesive would release DOX at subantimicrobial levels-we tested the antimicrobial activity of synthesized adhesives and the DOX-containing eluates against Streptococcus mutans through agar diffusion assays. Anti-MMP properties were assessed via β-casein cleavage assays. Increasing curing times (10, 20, 40 sec) led to increased DC values. There were no statistically significant differences (p > .05) in DC within each increasing curing time between the modified adhesives compared to SBMP. No statistically significant differences in microtensile bond strength were noted. None of the adhesives eluates were cytotoxic to the human dental pulp stem cells. A significant growth inhibition of S. mutans by direct contact illustrates successful encapsulation of DOX into the experimental adhesive. More important, DOX-containing eluates promoted inhibition of MMP-1 activity when compared to the control. Collectively, our findings provide a solid background for further testing of encapsulated MMP inhibitors into the synthesis of therapeutic adhesives that may enhance the longevity of hybrid layers and the overall clinical performance of adhesively bonded resin composite restorations.

Effects of chlorhexidine in self-etching adhesive: 24 hours results

It is known that chlorhexidine (CHX) does not inhibit micro-tensile bond strengths (MTBS) when it is used in etch-and-rinse adhesives. In that technique, CHX is applied to dentin as a primer after phosphoric acid-etching before bonding with Single Bond. It would be more convenient if it is possible to incorporate CHX into the adhesive. The purpose of this study was to compare the MTBS and the FT-IR percent conversion of an all-in-one self-etching adhesives contained varying concentration of CHX. Extracted human third molars were bonded with a control all-in-one adhesive or experimental versions containing 0.5, 1, 2 or 5% CHX. The MTBS and the percent conversion of experimental adhesives containing up to 1% CHX were not significantly CHX-free control adhesives. However, addition of 2 or especially 5% CHX experimental adhesives produced significant reductions in both the MTBS and the percent conversion.

Can 1% chlorhexidine diacetate and ethanol stabilize resin-dentin bonds?

OBJECTIVES

To examine the effects of the combined use of chlorhexidine and ethanol on the durability of resin-dentin bonds.

METHODS

Forty-eight flat dentin surfaces were etched (32% phosphoric acid), rinsed (15 s) and kept wet until bonding procedures. Dentin surfaces were blot-dried with absorbent paper and re-wetted with water (water, control), 1% chlorhexidine diacetate in water (CHD/water), 100% ethanol (ethanol), or 1% chlorhexidine diacetate in ethanol (CHD/ethanol) solutions for 30 s. They were then bonded with All Bond 3 (AB3, Bisco) or Excite (EX, Ivoclar-Vivadent) using a smooth, continuous rubbing application (10 s), followed by 15 s gentle air stream to evaporate solvents. The adhesives were light-cured (20 s) and resin composite build-ups constructed for the microtensile method. Bonded beams were obtained and tested after 24-h, 6-months and 15-months of water storage at 37°C. Storage water was changed every month. Effects of treatment and testing periods were analyzed (ANOVA, Holm-Sidak, p<0.05) for each adhesive.

RESULTS

There were no interactions between factors for both etch-and-rinse adhesives. AB3 was significantly affected only by storage (p=0.003). Excite was significantly affected only by treatments (p=0.048). AB3 treated either with ethanol or CHD/ethanol resulted in reduced bond strengths after 15 months. The use of CHD/ethanol resulted in higher bond strengths values for Excite.

CONCLUSIONS

Combined use of ethanol/1% chlorhexidine diacetate did not stabilize bond strengths after 15 months.

Adjunctive application of chlorhexidine and ethanol-wet bonding on durability of bonds to sound and caries-affected dentine

OBJECTIVES

To examine the effect of adjunctive application of chlorhexidine (CHX) and ethanol-wet bonding (EWB) on bond durability and nanoleakage of hydrophobic adhesive to sound (SD) and caries-affected dentine (CAD).

METHODS

Dentine surfaces of molars were etched after caries removal and randomly allocated to four groups (n=12). In Groups 1 and 2, dentine surfaces were saturated with either 2 ml of 100% ethanol or 2 ml of ethanol with 2% CHX for 60s. In Groups 3 and 4, dentine surfaces were saturated with either 15 μL of distilled water or 15 μL of distilled water with 2% CHX for 60s. Two coats of primer, followed by neat resin were applied and light-cured for 40s. Resin composite build-ups were placed and bonded specimens were sectioned for bond strength testing after 24 h and 12 months' storage in artificial saliva. Bond strength data were analyzed using 3-way ANOVA and SNK tests. Interfacial nanoleakage was evaluated after 24 h and 12 months using a field-emission scanning electron microscopy and data were analyzed using Kruskal-Wallis test.

RESULTS

Significant differences were observed for the three factors: "substrate" (p<0.001), "rewetting agents" (p<0.001) and "time" (p<0.001) on bond strength. Incorporation of 2% CHX to EWB preserved bond strength to SD and CAD and reduced interfacial nanoleakage after 12 months. Incorporation of 2% CHX to WWB also preserved bond strength to SD after ageing.

CONCLUSIONS

Incorporation of chlorhexidine to ethanol-wet bonding has an interaction effect on preservation of bond durability to sound and caries-affected dentine.

CLINICAL SIGNIFICANCE

Incorporation of chlorhexidine to ethanol-wet bonding with hydrophobic adhesive enhances the success rate of aesthetic bonded restorations.