Characterization of biomodified dentin matrices for potential preventive and reparative therapies

Effects on dentin nanomechanical properties, cell viability and dentin wettability of a novel plant-derived biomodification monomer

OBJECTIVES

To evaluate the effects of dentin biomodification agents (Proanthocyanidin (PAC), Cardol (CD) and Cardol-methacrylate (CDMA) on dentin hydrophilicity by contact angle measurement, viability of dental pulp stem cells (DPSCs) and nanomechanical properties of the hybrid layer (HL).

METHODS

CDMA monomer was synthesized from cardol through methacrylic acid esterification. Human extracted third molars were used for all experiments. For nanomechanical tests, specimens were divided in four groups according to the primer solutions (CD, CDMA, PAC and control) were applied before adhesive and composite coating. Nanomechanical properties of the HL were analyzed by nanoindentation test using a Berkovich probe in a nanoindenter. Wettability test was performed on dentin surfaces after 1 min biomodification and measured by contact angle analysis. Cytotoxicity was assessed by a MTT assay with DPSCs after 48 and 72 h. Data were analyzed with Student's t test or Two-way ANOVA and Tukey HSD test (p < 0.05).

RESULTS

CD and CDMA solutions achieved greater hydrophobicity and increased the water-surface contact angles when compared to PAC and control groups (p < 0.05). PAC group showed a greater reduction of elastic modulus in nanoindentation experiments when compared to CD and CDMA groups (p < 0.05) after 4 months of aging. CD inhibited cell proliferation compared to all further materials (p < 0.05), whilst CDMA and PAC indicated no cell cytotoxicity to human DPSCs.

SIGNIFICANCE

Cardol-methacrylate provided significantly higher hydrophobicity to dentin and demonstrated remarkable potential as collagen crosslinking, attaining the lowest decrease of HL's mechanical properties. Furthermore, such monomer did not affect pulp cytotoxicity, thereby highlighting promising feasibility for clinical applications.

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.

Herbal medicines to prevent dental caries

This is a protocol for a Cochrane Review (intervention). The objectives are as follows:

To assess the effects of herbs/herbal extracts to prevent or minimise tooth decay in children and adults.

Polyphenols for Preventing Dental Erosion in Pre-clinical Studies with in situ Designs and Simulated Acid Attack

Dental erosion is a chemical process characterized by acid dissolution of dental hard tissue, and its etiology is multifactorial. Dietary polyphenols can be a strategy for dental erosion management, collaborating to preserve dental tissues through resistance to biodegradation. This study describes a comprehensive review to interpret the effects of polyphenols on dental erosion of pre-clinical models with in situ designs and simulated acid attacks on enamel and dentin samples. We aim to evaluate evidence about Polyphenols' effects in the type of dental substrate, parameters of erosive cycling chosen in the in situ models, and the possible mechanisms involved. An evidence-based literature review was conducted using appropriate search strategies developed for main electronic databases (PubMed, Scopus, Web of Science, LILACS, EMBASE, LIVIVO, CINAHL, and DOSS) and gray literature (Google Scholar). The Joanna Briggs Institute checklist was used to evaluate the quality of the evidence. From a total of 1900 articles, 8 were selected for evidence synthesis, including 224 specimens treated with polyphenols and 224 control samples. Considering the studies included in this review, we could observe that polyphenols tend to promote a reduction in erosive and abrasive wear compared to control groups. However, as the few studies included have a high risk of bias with different methodologies and the estimated effect size is low, this conclusion should not be extrapolated to clinical reality.

Effects of the Combined Application of Trimethylated Chitosan and Carbodiimide on the Biostability and Antibacterial Activity of Dentin Collagen Matrix

The structural integrity of a dentin matrix that has been demineralized by the clinical use of etchants or calcium-depleting endodontic irrigants, such as endodontic ethylenediaminetetraacetic acid (EDTA), is often deteriorated due to the collagenolytic activities of reactivated endogenous enzymes as well as the infiltration of extrinsic bacteria. Therefore, the biomodification of dentin collagen with improved stability and antibacterial activity holds great promise in conservative dentistry. The purpose of this study was to evaluate the effects of the combined application of trimethylated chitosan (TMC) and 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) on the biostability and antibacterial activity of the demineralized dentin collagen matrix. The morphological changes in the collagen matrix were observed by scanning electron microscopy (SEM), the amount of TMC adsorbed on the collagen surface was detected by X-ray photoelectron spectroscopy, and the elastic modulus was measured by a three-point bending device. Dry weight loss and amino acid release were detected to evaluate its anti-collagenase degradation performance. The antibacterial performance was detected by confocal microscopy. The TMC-treated group had less collagen space and a more compact collagen arrangement, while the untreated group had a looser collagen arrangement. The combined application of TMC and EDC can increase the elastic modulus, reduce the loss of elastic modulus, and result in good antibacterial performance. The current study proved that a dentin collagen matrix biomodified by TMC and EDC showed improved biodegradation resistance and antibacterial activities.

Collagen Cross-Linking Lignin Improves the Bonding Performance of Etch-and-Rinse Adhesives to Dentin

To evaluate the biomodification ability of lignin used as pre-treatment in human dentin before the application of an etch-and-rinse adhesive. Experimental hydroethanolic solutions with different cross-linking agents were used: 6.5% proanthocyanidins (PAC, from grape-seed extract); 2% cardanol (CARD, from cashew-nut shell liquid); lignin (LIG, from eucalyptus) at 1, 2 or 4% concentrations. The negative control (NC) was ethanol 50 v%. Extracted molars were prepared, and dentin microtensile bond strength (μTBS) was evaluated after 24 h water storage or 10,000 thermocycling aging. Further specimens were processed for SEM nanoleakage, micropermeability confocal microscopy evaluation and in situ degree of conversion (DC) through micro-Raman spectroscopy. Demineralized dentin sticks were submitted to a three-point bending test to evaluate the elastic modulus (E) before and after 1 min biomodification using the tested solutions. Moreover, it was also evaluated the mass changes and hydroxyproline (HYP) release after 4-weeks of water storage. Vibrational collagen crosslinking identification was evaluated through micro-Raman spectroscopy. The results were analyzed by analysis of variance (ANOVA) and Tukey’s test (α = 0.05). A significant reduction in μTBS was observed in groups NC (p < 0.001) and CARD (p = 0.026). LIG-4% showed no significant reduction in μTBS after aging (p = 0.022). Nanoleakage micrographs showed hybrid layer protection with all agents, but reduced micropermeability was attained only with lignin. Polymerization was negatively affected in the presence of all tested cross-linking agents, except LIG-1%. Lignin and cardanol increased the dentin E values, but only lignin reduced the mass loss in dentin specimens. Effective collagen crosslinking (1117 cm−1 and 1235 cm−1) was detected for all agents. HYP release was significantly lower with LIG-1% than NC (p < 0.001). Lignin was able to perform collagen cross-linking and prevent the degradation of unprotected dentin collagen, thereby improving the bonding performance of the composite restorations performed in this study.

Dentin collagen denaturation status assessed by collagen hybridizing peptide and its effect on bio-stabilization of proanthocyanidins

OBJECTIVE

To assess dentin collagen denaturation from phosphoric acid and enzyme treatments using collagen hybridizing peptide (CHP) and to investigate the effect of collagen denaturation on bio-stabilization promoted by proanthocyanidins (PA).

METHODS

Human molars were sectioned into 7-µm-thick dentin films, demineralized, and assigned to six groups: control with/without PA modification, H₃PO₄-treated collagen with/without PA modification, enzyme-treated collagen with/without PA modification. PA modification involved immersing collagen films in 0.65% PA for 30 s. H₃PO₄ and enzyme treatments were used to experimentally induce collagen denaturation, which was quantitated by fluorescence intensity (FI) from the fluorescently-conjugated-CHP (F-CHP) staining (n = 4). FTIR was used to characterize collagen structures. All groups were subject to collagenase digestion to test the bio-stabilization effect of PA on denatured collagen using weight loss analysis and hydroxyproline assay (n = 6). Data were analyzed using two-factor ANOVA and Games-Howell post hoc tests (α = 0.05).

RESULTS

FTIR showed collagen secondary structural changes after denaturation treatments and confirmed the incorporation and cross-linking of PA in control and treated collagen. F-CHP staining indicated high-degree, medium-degree, and low-degree collagen denaturation from H₃PO₄-treatment (FI = 83.22), enzyme-treatment (FI = 36.54), and control (FI = 6.01) respectively. PA modification significantly reduced the weight loss and hydroxyproline release of all groups after digestion (p < 0.0001), with the results correlated with FI values at r = 0.96-0.98.

SIGNIFICANCE

A molecular method CHP is introduced as a sensitive technique to quantitate dentin collagen denaturation for the first time. PA modification is shown to effectively stabilize denatured collagen against collagenase digestion, with the stabilization effect negatively associated with the collagen denaturation degree.

A Novel Chemical Binding Primer to Improve Dentin Bonding Durability

The dentin collagen matrix that is not completely enveloped by resin adhesive is vulnerable to degradation by intrinsic collagenases during the etch-and-rinse process, which contributes to the deterioration of the bonding interface. Current commercial adhesives have no functional components that can form covalent bonds to the dentin collagen matrix. In this study, a photocurable aldehyde, 4-formylphenyl acrylate (FA), was synthesized and for the first time applied as a primer in adhesive dentistry to covalently bind to collagen. Experimental groups with different concentrations of FA (1%, 3%, 5%, 7%, 9%) were prepared as primers. The cytotoxicity was evaluated by live/dead-cell staining and thiazolyl blue tetrazolium bromide assay. The interaction of FA with collagen was examined by attenuated total reflection Fourier transform infrared spectroscopy, hydroxyproline release under the degradation of type I collagenase, and thermogravimetric analysis. An optimal group was selected based on the degree of conversion of 2 universal adhesives and further divided depending on the treatment time (20 s, 30 s, 1 min, 2 min). The bonding performances were evaluated by microtensile strength before and after aging. Finally, the bonding interface was observed under confocal laser scanning microscopy and scanning electron microscope. The results indicated that FA demonstrated good biocompatibility, dentin modification capability, and infiltration. It not only effectively cross-linked dentin collagen to improve its stability against enzymatic hydrolysis and modify the adhesive interface but also potentially acted as a diluting monomer to induce deep penetration of adhesive resin monomers into the dentin. The bonding strength after aging was improved without jeopardizing the degree of conversion of 2 commercial adhesives. Such prominent advantages of using FA to improve the bonding performance promotes its further application in adhesive dentistry.

Changes to dentin extracellular matrix following treatment with plant-based polyphenols

This study investigated whether treatment with plant-based polyphenols (PB-P) affected the biochemical and/or biomechanical properties of dentin extracellular matrix (ECM). Three PB-Ps were evaluated: luteolin (LT), galangin (GL), and proanthocyanidin (PAC). Because dentin ECM requires demineralization before treatment, this study also assessed the effect of these PB-Ps on dentin demineralized by two different chemicals. Dentin samples from extracted third molars were obtained, sectioned, and randomly assigned for demineralization with either phosphoric acid (PA) or ethylenediaminetetraacetic acid (EDTA). Following demineralization, baseline infrared (IR) spectra and apparent elastic modulus (AE) of each specimen were independently acquired. Based upon these initial tests, samples were randomly assigned to one of the PB-P treatments to ensure that distribution of baseline AE was similar across treatment groups. IR and AE specimens were individually immersed in either 0.2% LT, 0.4% GL or 1% PAC for 2 min. IR spectra of treated samples were compared to baseline IR spectra, looking for any interaction of PB-Ps with the demineralized dentin. The IR spectrum and AE of each PB-P-treated specimen were compared with their own correspondent baseline measurement. The ability of PB-Ps to inhibit proteolytic activity of dentin ECM was assessed by the hydroxyproline assay. Finally, the effect of PB-Ps on immediate bond strength of a dental adhesive to PA- or EDTA-etched dentin was also evaluated. PB-Ps exhibited distinctively binding affinity to dentin ECM and promoted significant increase in AE. PB-P treatment reduced the degradation rate of dentin ECM without causing detrimental effect on immediate bond strength to dentin. Our work represents the first-time that LT and GL have been assessed as dentin ECM biomodifiers.

Evaluation of Novel Plant-derived Monomers-based Pretreatment on Bonding to Sound and Caries-affected Dentin

This study evaluated the influence of new monomers derived from cashew nut shell liquid (CNSL) applied for dentin biomodification on resin-dentin bond strength, nanoleakage, and micropermeability to sound and artificially-created caries-affected dentin. Human dentin specimens were assigned to five groups, according to the following dentin pretreatment solutions: Absolute ethanol (control), 2 wt% grape seed extract (Vitis vinifera), 2 wt% cardol [from cashew nut shell liquid (CNSL)], 2 wt% cardol-methacrylate or 2 wt% cardanol-methacrylate applied on sound and artificial caries-affected dentin. Specimens were analyzed after 24 hour or 1 year of water storage. Microtensile bond strength (μTBS) (n=6), interface micropermeability (n=3), and silver nanoleakage (n=6) were assessed using a universal testing machine, confocal laser scanning microscope, and scanning electron microscope, respectively. In sound dentin, no difference in bond strength was observed between the groups in either storage period. In artificial caries-affected dentin, pretreatment with cardol-methacrylate resulted in statistically higher bond strength than all the other treatments in both storage periods. Cardol-methacrylate treatment resulted in less nanoleakage, along with improved interfacial integrity, compared to further treatments in artificial caries-affected dentin. Regarding micropermeability analysis, all treatments depicted deficient sealing ability when applied on artificial caries-affected dentin, with the presence of gaps in the control group. In conclusion, cardol-methacrylate is a promising plant-derived monomer to reinforce the hybrid layer, since it preserved resin-dentin bond strength and improved dentin bonding, especially to caries-affected dentin, a well-known harsh substrate for adhesion longevity.

Theaflavins as a novel cross-linker quickly stabilize demineralized dentin collagen against degradation

To investigate the ability of theaflavins (TF) from black tea to protect dentin collagen against enzymatic degradation via cross-linking effect under clinically relevant conditions. 10-µm-thick dentin films were microtomed from dentin slabs of human molars. Following demineralization, films or slabs were treated with TF at two concentrations (0.4% and 2%) for 30 s. A well-known collagen cross-linker grape seed proanthocyanidins (PA) was used as control. Collagen cross-linking interactions and stabilization against enzymatic degradation were investigated by Fourier transform infrared spectroscopy, weight loss, hydroxyproline release, and scanning/transmission electron microscopy. Data were analyzed by ANOVA, Tukey’s and Student’s T test (α = 0.05%). The results showed collagen cross-linking and stabilization efficacy was dependent on TF/PA concentrations. At 2.0%, TF and PA offered nearly full protection to collagen; at 0.4%, TF exhibited a significantly better collagen stabilization effect than PA (P < 0.05), while untreated collagen was completely digested. It’s concluded that TF cross-links dentin collagen within a clinically relevant time (30 s) and offers excellent collagen protection against enzymatic degradation, with efficacy comparable to or better than PA. The study supports the potential use of TF as a novel, promising collagen cross-linker for degradation resistant, long-lasting dentin bonding in composite restorations.

Stability and remineralization of proteoglycan-infused dentin substrate

OBJECTIVE

This study tested the effects of small leucine-rich proteoglycan (SLRP) proteins on phosphoric acid (PA)-treated dentin bonding overtime and the role of such SLRPs in the remineralization potential of demineralized dentin collagen.

METHODS

Coronal dentin sections of human molars were used. SLRPs were either decorin (DCN) or biglycan (BGN) in core or proteoglycan form (with glycosaminoglycans, GAGs). Groups were: No treatment (control), DCN core, DCN + GAGs, BGN core, BGN + GAGs. Samples were etched with PA for 15 s and prior to application of Adper Single Bond Plus and composite buildup an aliquot of the specific SLRPs was applied over dentin. Twenty-four hours or 6 months after the bonding procedure, samples were tested for microtensile bond strength (MTBS). Debonded beams were analyzed by scanning electron microscopy (SEM). For remineralization studies, dentin blocks were fully demineralized, infused with the SLRPs, placed in artificial saliva for 2 weeks, and evaluated by transmission electron microscopy (TEM).

RESULTS

MTBS test presented a mean of 51.4 ± 9.1 MPa in control with no statistically significant difference to DCN core (47.6 ± 8.3) and BGN core (48.3 ± 6.5). The full proteoglycan groups DCN + GAGs (27.4 ± 4.5) and BGN + GAGs (36.4 ± 13.6) showed decreased MTBS compared to control (p < 0.001). At 6 months, control or core-treated samples did not have a statistically significant difference in MTBS. However, SLRPs with GAGs showed statistically significant improvement of bonding (62.5 ± 6.0 for DCN and 52.8 ± 8.1 for BGN, p < 0.001) compared to their baseline values. SEM showed that GAGs seem to favor water retention but overtime help remineralization. TEM of demineralized dentin indicated a larger collagen fibril diameter pattern of samples treated with core proteins compared to control and a smaller diameter with DCN + GAGs in water with evidence of mineralization with DCN + GAGS, BGN core and BGN + GAGs.

SIGNIFICANCE

In conclusion, core proteins seem not to affect dentin adhesion significantly but the presence of GAGs can be detrimental to immediate bonding. However, after ageing of samples, full proteoglycans, particularly DCN, can significantly improve bonding overtime while promoting remineralization which can prove to be clinically beneficial.

Proanthocyanidin-functionalized hydroxyapatite nanoparticles as dentin biomodifier

OBJECTIVE

This study evaluated the potential combined effects of nanohydroxyapatite and proanthocyanidin on the remineralization and collagen stabilization of demineralized dentin.

METHODS

Seventy-five coronal dentin beams (6 × 1 × 1 mm³) were randomly allocated into five experimental groups (n = 15): Sound (no treatment), Control (pH-cycling), nHAp (nanohydroxyapatite), nHAp_PA (Proanthocyanidin-functionalized nanohydroxyapatite), and PA (proanthocyanidin) treatments. The sound group (negative control) were immersed in distilled water over the experimental period. The remaining groups were submitted to a pH-cycling process for 14 days. Following the de-re mineralization process, specimens corresponding to the control group (positive control) were immersed in distilled water whereas the test groups were immersed in 1 mL of respective solution treatment (nHAp, nHAp_PA, or PA) for 1 min. The dentin samples were analyzed to determine their chemical composition (ATR-FTIR and Thermogravimetric) and mineralogical (XRD) characteristics as well as their mechanical response, obtained by three-point bending test.

RESULTS

Higher phosphate content (v₄ PO₄: ATR-FTIR) and amount of mineral (XRD) was observed in the nHAp_PA group. Furthermore, a larger induction of collagen cross-links (ATR-FTIR) and %Organic Matter (TGA) would indicate the PA incorporation and the achievement of dentin matrix stability. These effects on dentin properties were related to increasing flexural strength (MPa), demonstrating that 15% w/v nHAp_PA treatment improved the mechanical properties of the samples.

SIGNIFICANCE

nHAp_PA shows significant potential for promoting remineralization while improving collagen stability into demineralized dentin in a clinically feasible period of 1 min.

Influence of Dentin Priming with Tannin-Rich Plant Extracts on the Longevity of Bonded Composite Restorations

Objective

This in vitro study evaluated the influence of bioactive plant extracts as dentin biomodifying agents to improve the longevity of bonded restorations. For that, plant extracts were applied to the dentin surface prior to the adhesive system.

Materials and Methods

Bovine incisors were ground flat to obtain 2 mm thick slices in which conical preparations were made (N = 10). Tannin-containing plant extracts were applied to dentin before the application of the restorative system, as follows: control group (untreated, CTL), chlorhexidine 0.12% (CHX), mastruz (Dysphania ambrosioides, MTZ), cat's claw (Uncaria tomentosa, CTC), guarana (Paullinia cupana, GUA), galla chinensis (Rhus chinensis, GCH), and tannic acid (extracted from Acacia decurrens, TNA). The push-out bond strength test was conducted (0.5 mm/min). Dentin biomodification was assessed by the modulus of elasticity and mass change in bovine tooth sections (0.5 × 1.7 × 7.0 mm). The dentin staining after extract treatments of dentin slices was compared. The dentin surface wettability was also evaluated by means of the contact angles of the adhesive system with the dentin surface and compared with the untreated control group. Data were subjected to ANOVA/Tukey's test (α = 0.05).

Results

The bond strength of the restoratives to dentin was not significantly improved by the plant extracts, irrespective of the evaluation time (p > 0.05). Except for TNA, the elastic modulus of demineralized dentin significantly reduced after treatment with the plant extracts (p < 0.05). The dentin staining correlated with the tannin content of the extracts. The contact angle was significantly reduced when treated with CTC, GCH, and TNA.

Conclusions

The tannin-containing extracts had a questionable effect on the longevity of bonded restorations. The dentin modulus was negatively affected by the extract treatments. Although some of the extracts changed the contact angle, which seems to improve the adhesive monomer permeation, the tannin-rich plant extract application prior to adhesive application was proven to be clinically unfeasible due to dentin staining.

Quercetin as an Auxiliary Endodontic Irrigant for Root Canal Treatment: Anti-Biofilm and Dentin Collagen-Stabilizing Effects In Vitro

Bacterial reinfection and root fracture are the main culprits related to root canal treatment failure. This study aimed to assess the utility of quercetin solution as an adjunctive endodontic irrigant that does not weaken root canal dentin with commitment anti-biofilm activity and bio-safety. Based on a noninvasive dentin infection model, dentin tubules infected with Enterococcus faecalis (E. faecalis) were irrigated with sterile water (control group), and 0, 1, 2, 4 wt% quercetin-containing ethanol solutions. Live and dead bacteria percentages in E. faecalis biofilms were analyzed by confocal laser scanning microscopy (CLSM). Elastic modulus, hydroxyproline release and X-ray photoelectron spectroscopy (XPS) characterization were tested to evaluate the irrigants’ collagen-stabilizing effect. The cytotoxicity was tested by CCK-8 assay. Quercetin increased the proportion of dead bacteria volumes within E. faecalis and improved the flexural strength of dentin compared to control group (p < 0.05). Quercetin-treated dentin matrix had less elasticity loss and hydroxyproline release after collagenase degradation (p < 0.05). Moreover, quercetin solutions revealed an increase in the C-O peak area under both C1s and O1s narrow-scan spectra of XPS characterization, and no cytotoxicity (p > 0.05). Quercetin exhibited anti-biofilm activity, a collagen-stabilizing effect with cytocompatibility, supporting quercetin as a potential candidate for endodontic irrigant.

Remineralising effects of fluoride varnishes containing calcium phosphate on artificial root caries lesions with adjunctive application of proanthocyanidin

OBJECTIVES

To evaluate the remineralising effects of fluoride (F) varnishes containing bioavailable calcium-phosphate compound (Ca-P) based remineralisation systems and 5000 ppm F toothpaste (FTP) on root caries lesions (RCLs) and the potential effects of proanthocyanidin (PA) for the treatments of RCLs when used as an adjunct to F regimens.

METHODS

Demineralised root dentine and a pH-cycling model were used to mimic RCLs and the oral environment. Remineralising effects of MI Varnish^TM (MIV) containing casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and Clinpro™ White Varnish (CPWV) containing tri-calcium phosphate (TCP) along with FTP and PA were evaluated regarding the birefringence, elemental composition, mechanical properties and mineral density of remineralised dentine with Duraphat^TM as a comparison.

RESULTS

MIV, CPWV and Duraphat^TM promoted the incorporation of F into RCLs and increased mineral density but did not change microhardness of root dentine significantly. Surface microhardness increased significantly when MIV or CPWV was used with 5000 ppm FTP. Application of PA with F regimens significantly increased subsurface mineral density. When PA was applied with MIV or CPWV along with FTP, the highest ion uptake and relative mineral gain (%ΔZ) was achieved, and significant increase of microhardness was up to 30 μm depth. Generally, MIV was associated with a higher mineral content gain than CPWV.

SIGNIFICANCE

Treatment of carious root surfaces remains challenging due to the complex pathological processes and difficulty in restoring the highly organised structure of root dentine. Treatment strategies targeting both remineralisation and preservation of the dentinal organic matrix have the potential to improve the fluoride-mediated remineralisation approaches.

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.

A dynamic mechanical method to assess bulk viscoelastic behavior of the dentin extracellular matrix

OBJECTIVES

To develop a protocol for assessment of the bulk viscoelastic behavior of dentin extracellular matrix (ECM), and to assess relationships between induced collagen cross-linking and viscoelasticity of the dentin ECM.

METHODS

Dentin ECM was treated with agents to induce exogenous collagen cross-linking: proanthocyanidins (PACs) from Vitis vinifera - VVe, PACs from Pinus massoniana - PMe, glutaraldehyde - (GA), or kept untreated (control). A dynamic mechanical strain sweep method was carried out in a 3-point bending submersion clamp at treatment; after protein destabilization with 4 M urea and after 7-day, 6-month, and 12-month incubation in simulated body fluid. Tan δ, storage (E'), loss (E"), and complex moduli (E*) were calculated and data were statistically analyzed using two-way ANOVA and post-hoc tests (α = 0.05). Chemical analysis of dentin ECM before and after protein destabilization was assessed with ATR-FTIR spectroscopy.

RESULTS

Significant interactions between study factors (treatment vs. time points, p < 0.001) were found for all viscoelastic parameters. Despite a significant decrease in all moduli after destabilization, PAC-treated dentin remained statistically higher than control (p < 0.001), indicating permanent mechanical enhancement after biomodification. Covalently crosslinked, GA-treated dentin was unaffected by destabilization (p = 0.873) and showed the lowest damping capacity (tan δ) at all time points (p < 0.001). After 12 months, the damping capacity of PMe and VVe groups decreased significantly. Changes in all amide IR resonances revealed a partial chemical reversal of PAC-mediated biomodification.

SIGNIFICANCE

Viscoelastic measurements and IR spectroscopy aid in elucidating the role of inter-molecular collagen cross-linking in the mechanical behavior of dentin ECM.

Evaluation of the effect of collagen stabilizing agents like chitosan and proanthocyanidin on the shear bond strength to dentin and microleakage of resin composite at enamel and cemental walls: An in vitro study

Objectives:

The objective is to evaluate the effect of collagen stabilizing agents-chitosan and proanthocyanidin (PA) on the shear bond strength to dentin and microleakage of resin composite at enamel and cemental walls.

Materials and Methods:

Thirty premolars were decoronated 2 mm above cemento-enamel junction and restored with composite resin. Teeth were then randomly divided into three groups: Group I - Control, Group II - Pre-treatment with chitosan, and Group III - Pre-treatment with PA. Samples were then subjected to thermocycling for 500 cycles at 5°C and 55°C with the dwell time of 30 s and transfer time of 5–10 s. Then, the samples were subjected to shear bond strength evaluation on Universal testing machine. Shear load was applied until failure occurred. The load to failure was recorded individually and statistical analysis was done. Microleakage was determined by methylene blue dye penetration method and subjected to stereomicroscopic evaluation. Statistical analysis was carried out using Mann–Whitney test and Chi-square test.

Results:

Group II specimens produced the highest median shear bond strength and group I showed the least. In addition, Group I, Group II, and Group III showed no statistically significant difference in microleakage.

Conclusions:

Application of Chitosan and PA improved the shear bond strength to dentin as compared to the control. However, no significant difference in shear bond strength and microleakage was found between them.

Could applying gels containing chlorhexidine, epigallocatechin-3-gallate, or proanthocyanidin to control tooth wear progression improve bond strength to eroded dentin?

STATEMENT OF PROBLEM

A consensus on whether or how to treat eroded dentin to bond to composite resins is lacking. The role of gels containing chlorhexidine (CHX), epigallocatechin-3-gallate (EGCG), and proanthocyanidin (PAC) in controlling erosive wear progression needs to be evaluated for bonding.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of gels containing antiproteolytic agents (CHX or EGCG) or an antiproteolytic and also collagen crosslinking agent (PAC) to control tooth wear progression on the microtensile bond strength (μTBS) of an adhesive system plus a composite resin to simulated eroded dentin.

MATERIAL AND METHODS

Superficial occlusal dentin surfaces obtained from sectioned third molars were ground with SiC paper (600-grit; 1 minute; N-normal dentin) or subsequently submitted to an initial erosive challenge (Coca-Cola; 5 minutes). They then received one of the following treatments: application of a placebo (P), a 0.12% CHX digluconate, an EGCG at 400 μM, or a 10% PAC gel (vehicle: hydroxyethylcellulose, propylene glycol, methylparaben, imidazolidinyl urea, and deionized water; active principle: as per the experimental groups when applicable) or no treatment (C: control). Initially demineralized dentin was also submitted to pH cycling (Coca-Cola; 5 minutes, 3×/day, 5 days) to simulate eroded dentin (E). After acid etching all the specimens, adhesive Adper Single Bond 2 was applied, and composite resin (Filtek Z350 XT) was placed. After 24 hours storage in distilled water at 37 °C, the specimens were sectioned into beams, and the μTBS was tested at 0.5 mm/minute. The μTBS values obtained were evaluated considering each tooth as an experimental unit, and 2-way ANOVA and the Tukey post hoc test for multiple comparisons were applied (α=.05).

RESULTS

Immediate μTBS values for the eroded dentin were always lower than those for the normal dentin, irrespective of whether any of the gels were applied for wear control.

CONCLUSIONS

CHX, EGCG, PAC, and placebo gels, applied after the initial demineralization and before the pH cycling to simulate the eroded dentin, had a similar effect on the μTBS of the adhesive system plus the composite resin to simulated eroded dentin when compared with nonapplication (control).

Quercetin reduces erosive dentin wear: Evidence from laboratory and clinical studies

OBJECTIVE

The aim of the present study was to evaluate the effect of quercetin on the acid resistance of human dentin through both laboratory and clinical studies.

METHODS

Two hundred and twelve dentin blocks (2 mm × 2 mm × 2 mm) were prepared and used. For the laboratory study, dentin specimens were randomly divided into 8 groups (n = 12): deionized water, ethanol, 1.23 × 10⁴ μg/ml sodium fluoride (NaF), 120 μg/ml chlorhexidine, 183.2 μg/ml epigallocatechin gallate (EGCG), and 75 μg/ml, 150 μg/ml, and 300 μg/ml quercetin (Q75, Q150, and Q300). The specimens were treated with the respective solutions for 2 min and then subjected to in vitro erosion (4 cycles/d for 7 d). The surface microhardness loss (%SMH_l), erosive dentin wear, and surface morphology were evaluated and compared. For the impact on MMP inhibition, the release of crosslinked carboxyterminal telopeptide of type I collagen (ICTP) and the thickness of the demineralized organic matrix (DOM) were measured using additional dentin specimens. For the clinical study, the specimens were treated with NaF or Q300 for 2 min and then subjected to in vivo erosion (4 cycles/d for 7 d). The %SMH_l and erosive dentin wear of the specimens were measured to determine whether quercetin similarly inhibits erosion in situ.

RESULTS

The quercetin-treated group had a significantly lower %SMH_l and erosive dentin wear than any other group, and the effect was concentration-dependent in vitro (P < 0.05). Dentin treated with quercetin produced significantly less ICTP and had a thicker DOM than the control dentin (P < 0.05). After in vivo erosion, the %SMH_l and erosive dentin wear of the Q300 group were significantly lower than those of the control group (P < 0.05).

SIGNIFICANCE

The application of quercetin was shown, for the first time, to increase the acid resistance of human dentin, possibly through MMP inhibition and DOM preservation.

Polyphenol-enriched extract of Arrabidaea chica used as a dentin pretreatment or incorporated into a total-etching adhesive system: Effects on bonding stability and physical characterization

The aim of this paper was to evaluate the physical properties and the long-term bond strength of a 2.5% polyphenol-enriched extract of Arrabidaea chica (AC) incorporated into both the phosphoric acid and the primer of a three-step total-etch adhesive, or into an aqueous solution as a dentin pretreatment. Fifty dentin surfaces received the treatments (n = 10): CON (control) - application of the three-step adhesive system (Adper Scotchbond Multipurpose, 3M ESPE); WAT - distilled water used as a pretreatment after dentin etching and before application of the adhesive system; ACPA - AC incorporated into the phosphoric acid; ACW - dentin pre-treatment with AC incorporated into an aqueous solution after etching; ACP - AC incorporated into the primer. Microtensile bond strength tests were performed after 24 h, 6 and 12 months of storage. Slices from the resin-dentin interface were obtained for scanning electron microscopy analysis of the hybrid layer. Degree of conversion of AC incorporated into the primer was evaluated. The particle size, polydispersity index and zeta potential of all the solutions prepared by incorporating AC (phosphoric acid, primer and distilled water) were measured by dynamic light scattering, which brought about changes after incorporation. Degree of conversion of the primer was not affected after incorporating AC. ACP showed lower microtensile bond strength values than the other groups. Bond strength decreased after 6 months of storage, stabilizing at the 12-month evaluation. Therefore, use of AC incorporated into the primer led to lower bond strength values, since AC modified the physical properties (particle size, polydispersity index and zeta potential) of the primer, but did not change the degree of conversion. Application of AC as a dentin pretreatment did not affect bond strength or the micromorphological characteristics of the hybrid layer.

Effect of dentin biomodification delivered by experimental acidic and neutral primers on resin adhesion

OBJECTIVES

Proanthocyanidins (PACs) are biocompounds mimicking native collagen cross-links. The effective and practical delivery of any biocompound is pivotal for clinical usage. The aim was to investigate the dentin biomodification and effective formation of dentin-resin biointerfaces of two highly bioactive PAC-rich extracts, Vitis vinifera (Vv) and Camellia sinensis (Cs), delivered using neutral (NP) or acidic (AP) rinse-out primer approaches.

METHODS

The depth of dentin demineralization (optical profilometry), dentin biomodification (apparent modulus of elasticity, collagen auto-fluorescence) and properties of dentin-resin interfaces (microtensile bond strength - μTBS, and micro-permeability) were investigated. NP consisted of either 15% Vv or Cs applied for 60 s after surface etching; while AP contained 15% Vv or Cs in either 35% glycolic acid or tartaric acid applied for 30 s or 60 s. Data were analyzed using ANOVA and post-hoc tests (α = 0.05).

RESULTS

The depth of demineralization was statistically higher when applied for 60 s, regardless of rinse-out primer approach (p < 0.001). Compared to the AP strategy, NP exhibited statistically higher apparent modulus of elasticity, regardless of PAC extract (p < 0.001). Highest μTBS were obtained for NP_Vv, which were statistically similar to AP_GAVv, when applied for 60 s (p < 0.001); both resulted in a dramatic decrease of the interfacial permeability. NP_Cs group showed the lowest μTBS (p < 0.001).

CONCLUSIONS

A combination of high bond strength and low micro-permeability can be accomplished using glycolic acid with the mid- and high-PAC oligomer enriched extract (Vv). Cs extract containing mostly catechins and dimeric PACs, was found unsuitable for resin-dentin adhesion despite exhibiting high initial dentin biomodification.

CLINICAL SIGNIFICANCE

This study provides a new conceptual delivery of PAC-mediated dentin biomodification and conservative dentin surface etching using rinse-out primers. The strategy requires a specific combination of PAC source, α-hydroxy acid, and application time.

Dimeric Proanthocyanidins on the Stability of Dentin and Adhesive Biointerfaces

A dentin biomodification strategy with selective proanthocyanidin (PAC)-enriched extracts reinforces dentin and dentin-resin interfaces. Enrichment of the extracts according to the degree of polymerization allows exploration of bioactive principles of PACs and structure-activity relationships. This study investigated the sustained dentin matrix biomodification and dentin-resin bioadhesion of 2 fractions consisting exclusively of B-type PAC dimers with or without a single galloyl motif (specifically, DIMER_G and DIMER_NG) and their precursor material, enriched grape seed extract (e-GSE; Vitis vinifera). The biomodification potential was determined by long-term evaluation of the apparent modulus of elasticity and collagen solubility (hydroxyproline release). Chemical characterization of the dentin matrix was performed by attenuated total reflectance-Fourier-transform infrared spectroscopy. The bioadhesive properties were assessed by a microtensile bond strength test at different time points, and macro-hybrid layers were produced to verify the degree of conversion of the adhesive resin. Fractions consisting of DIMER_G, DIMER_NG, and their precursor, e-GSE, increased the modulus of elasticity at all time points and reduced collagen degradation. Specimens treated with DIMER_NG remained stable throughout 12 mo of storage, whereas a significant drop in the modulus of elasticity was observed for the DIMER_G and e-GSE groups at 6 mo. The fractions and precursor did not affect the degree of resin conversion at the hybrid layer. Changes in infrared resonances corresponding to collagen cross-links in the dentin matrix occurred for all treatments. Higher bond strength was observed for dentin treated with e-GSE as compared with DIMER_G and DIMER_NG; all biointerfaces remained stable after 12 mo. Nongalloylated PACs mediate stable dentin biomodification, which includes protective activity against collagen degradation and reinforcement of the anchoring dentin matrix. Collectively, PACs with a higher degree of oligomerization offer a robust bioadhesion between the hydrophilic dentin matrix and the hydrophobic adhesive.

Effect of grape seed extract-containing phosphoric acid formulations on bonding to enamel and dentin

The aim was to evaluate the effect of 2% grape seed extract (GSE) containing phosphoric acid (PhA) on the bond strength to enamel and dentin. The control group was 37% PhA. The following three PhA formulations with 2% GSE and 20% ethanol were obtained: GSE5 = 5% PhA; GSE10 = 10% PhA; and GSE20 = 20% PhA. The enamel and dentin surfaces of molars were etched with the acid solutions, followed by Scotchbond Multi-Purpose adhesive and composite resin application. The tensile bond strength (TBS) test evaluated the bond to enamel after 24 h, and the microtensile bond strength (μTBS) test evaluated the bond to dentin after 24 h and 12-month water storage. Etched enamel and dentin were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The TBS data were submitted to one-way ANOVA, while µTBS data were submitted to two-way ANOVA and Tukey's test (α = 0.05). The TBS (MPa) to enamel did not significantly differ among the control (48.1 ± 15.7), GSE5 (46.1 ± 9.6), GSE10 (49.8 ± 13.6) and GSE20 (44.1 ± 11.9) groups (p = 0.537). The µTBS (MPa) to dentin of the control (28.4 ± 14.4) and GSE20 (24.1 ± 8.1) groups were significantly higher than those of the GSE5 (16.8 ± 7.4) and GSE10 (17.5 ± 6.6) groups at 24 h (p < 0.006). After 12-month storage, only GSE5 (21.0 ± 7.8) and GSE10 (17.6 ± 8.0) did not show significantly decreased μTBS (p > 0.145). SEM micrographs showed a shallower enamel etching pattern for GSE5. AFM images showed the formation of collagenous globular structures for GSE5 and GSE10. The different acid solutions did not influence the TBS to enamel, and the µTBS to dentin was stable over time when dentin was etched with GSE5 and GSE10.

The effect of different cross-linking conditions of EDC/NHS on type II collagen scaffolds: an in vitro evaluation

The purpose of this paper is to analyze the properties of porcine cartilage type II collagen scaffolds crosslinked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxy-succinamide (EDC/NHS) under different conditions. The porous EDC/NHS-crosslinked scaffolds were obtained through a two-step freeze-drying process. To determine the optimal crosslinking condition, we used different solvents and various crosslinking temperatures to prepare the scaffolds. Three crosslinking solutions were prepared with different solvents, photographs were taken with a flash in the darkroom, and light transmission was observed. Type II collagen was crosslinked on a horizontal shaker at a speed of 60 r/min according to the above grouping conditions, and then the structural change of the scaffold in each group was observed. To investigate the swelling ratio and the in vitro degradation of the collagen scaffold, tests were also carried out by immersion of the scaffolds in a PBS solution and digestion in type II collagenase, respectively. The influence of the scaffolds on the proliferation of chondrocytes was assessed by the methyl thiazolyl tetrazolium colorimetric assay. The morphology of the crosslinked scaffolds cocultured with chondrocytes was characterized by a scanning electron microscope. The results proved that 75% alcohol and a crosslinking temperature of 37 °C are recommended. Collagen fibrils are more densely packed after crosslinking with EDC/NHS and have a more uniform structure than that of noncrosslinked ones. The EDC-crosslinked scaffolds possessed excellent mechanical property and biocompatibility.

Effect of gallic acid addition on some mechanical properties of self-adhesive resin cements

Self-adhesive resin cements (RCs) activate matrix metalloproteinase (MMP) and cathepsin-related collagen degradation, and gallic acid (GA) inhibits the activity of both MMPs and cysteine cathepsins. The purpose of this study was to evaluate the setting time, biaxial flexural strength, and Vickers hardness of self-adhesive RCs after the addition of two different concentrations of GA. RelyX U200 (3M ESPE) and Panavia SA (Kuraray) were modified with 0.5 and 1 wt% GA. The setting time of five samples in each RC group was assessed using a thermocouple apparatus as described in the ISO 4049 test. Biaxial flexure strength was measured using a universal testing machine until failure. Vickers hardness was measured with three randomized indentations on the surface of each resin disc. RCs without GA were used as control. Data were analyzed using a one-way analysis of variance and Tukey's HSD test (α = 0.05). The setting times ranged from 2.4 to 4.6 min for RelyX and from 4.9 to 6.0 min for Panavia. The biaxial flexure strength ranged from 76.5 to 109.7 MPa for RelyX and from 73.3 to 108.2 MPa for Panavia. Vickers hardness values ranged from 41.6 to 58.6 for RelyX and 27.2 to 33.6 for Panavia. The addition of 0.5 and 1 wt% GA to improve durability of resin-dentin bonds had no adverse effects on setting time, whereas the biaxial flexure strength and Vickers hardness values for the tested materials were significantly reduced.

Effects of silver diamine fluoride/potassium iodide on artificial root caries lesions with adjunctive application of proanthocyanidin

Treatment of carious root surfaces remains challenging due to the complex pathological processes and difficulty in restoring the original structure of root dentine. Current treatments targeting the de-/re-mineralisation processes are not entirely satisfactory in terms of the protection of the dentinal organic matrix and the highly organised structure of dentine. In this in vitro study, a cross-linking agent - proanthocyanidin (PA) was used in conjunction with a fluoride-based treatment - silver diamine fluoride/potassium iodide (SDF/KI) to putatively stabilise the organic dentinal framework as well as strengthen the collagen-mineral phase interaction. The effectiveness of this strategy was evaluated 24 h after application in terms of the distribution of ion uptake and microstructure of dentine after treatment as well as analysis of the nano-mechanical properties using a dynamic behaviour model. Results showed that individual use of SDF/KI significantly improved the surface microhardness and integrated mineral density (Z) up to 60 µm depth and the recovery of creep behaviour of demineralised dentine in the surface area compared to that treated with deionised distilled water (DDW). The combined treatment of PA and SDF/KI achieved a more homogenous mineral distribution throughout the lesions than SDF/KI alone; a more significant incremental increase in surface microhardness and Z was observed. Specifically, a superior effect on the subsurface area occurred with PA + SDF/KI, with significant improvements in microhardness, elastic modulus and recovery of creep behaviour of the demineralised dentine. Application of SDF/KI induced small discrete crystal formation distributed over the dentine surface and PA contributed to the formation of slit-shaped orifices of the dentinal tubules that were partially occluded. STATEMENT OF SIGNIFICANCE: Demographic transitions and improved oral health behaviour have resulted in increased tooth retention in elderly people. As a consequence, the risk of root dentine caries is increasing due to the age-associated gingival recession and the related frequent exposure of cervical root dentine. Root caries is difficult to repair because of the complex aetiology and dentine structure. The recovery of dentine quality depends not only on reincorporation of minerals but also an intact dentinal organic matrix and the organic-inorganic interfacial structure, which contribute to the biomechanics of dentine. With the capability of dentine modification, cross-linking agents were applied with a fluoride regimen, which improved its treatment efficacy of root caries regarding the distribution of ion uptake and recovery of dentine biomechanics.

Structural and biomechanical changes to dentin extracellular matrix following chemical removal of proteoglycans

Proteoglycans are biomacromolecules with significant biomineralization and structural roles in the dentin extracellular matrix. This study comprehensively assessed the mechanical properties and morphology of the dentin extracellular matrix following chemical removal of proteoglycans to elucidate the structural roles of proteoglycans in dentin. Dentin extracellular matrix was prepared from extracted teeth after complete tissue demineralization. Chemical removal of proteoglycans was carried-out using guanidine hydrochloride for up to 10 days. The removal of proteoglycans was determined by dimethylmethylene blue colorimetric assay and histological staining analyses using transmission electron microscopy and optical microscopy. The modulus of elasticity of dentin matrix was determined by a 3-point bending test method. Partial removal of proteoglycans induced significant modifications to the dentin matrix, particularly to type I collagen. Removal of proteoglycans significantly decreased the modulus of elasticity of dentin extracellular matrix (p < 0.0001). In conclusion, the subtle disruption of proteoglycans induces pronounced changes to the collagen network packing and the bulk modulus of elasticity of dentin matrix.

Collagen/Polyethylene Oxide Nanofibrous Membranes with Improved Hemostasis and Cytocompatibility for Wound Dressing

As a promising agent for biomedical application, collagen has been used as a nanofiber to architecturally mimic its fibrillar structure in Extracellular Matrix (ECM); however, it has to be modified by techniques, such as crosslinking, to overcome its limitations in structural stability along with potential toxicity. Here, we prepared collagen/polyethylene oxide (PEO) nanofibrous membranes with varying crosslinking degrees and their properties, such as water stability, mechanical properties, blood clotting capacity and cytocompatibility, were studied systematically. By investigating the relationship between crosslinking degree and their properties, nanofibrous membranes with improved morphology retention, blood clotting capacity and cytocompatibility have been achieved. The result of circular dichroism measurement demonstrated that a triple helical fraction around 60.5% was retained. Moreover, the electrospun collagen/PEO at crosslinking degrees above 60.6% could maintain more than 72% of its original weight and its nanofibrous morphology under physiological conditions could be well preserved for up to 7 days. Furthermore, the crosslinked collagen/PEO membrane could provide a more friendly and suitable environment to promote cell proliferation, and about 70% of the clot can be formed in 5 min. With its superior performance in water stability, hemostasis and cytocompatibility, we anticipate that this nanofibrous membrane has great potential for wound dressing.

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.

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.

Effects of Collagen Crosslinkers on Dentine: A Literature Review

This aim of this review is to explore the current research related to crosslinking agents used on dentine. A systematic search of publications in PubMed and Web of Science databases was performed. Further retrieval was conducted using the search terms of specific names of crosslinkers. Reviews, conference abstracts, dissertation and theses, non-English articles, studies of intrinsic crosslinking of dentine, studies of adhesives without specific crosslinker components, studies of crosslinker applications in other collagenous tissues or tooth-like structures and irrelevant studies were excluded. Manual screening was conducted on the bibliographies of remaining papers to identify other relevant articles. One hundred and one articles were included in this systematic review and full texts were retrieved. Both synthetic and naturally derived crosslinkers have been found to exhibit significant effects in biomodification of dentine via their multiple interactions with the dentine matrix. A stable matrix network or a durable hybrid layer in dentine bonding could be achieved, where the dentine collagen fibrils show improved biochemical and biomechanical properties and enzymatic biodegradation is reduced. Although no crosslinkers have been tested in clinical trials, extensive research has been conducted in laboratory studies to investigate their potential applicability for inhibition of demineralisation and/or promotion of remineralisation, caries prevention as well as improvement of bonding performance of adhesive systems. Further studies are needed to develop the feasibility for clinical use, reduce side effects as well as explore mechanisms of action and long-term effectiveness.

Remineralization Potential of Mints Containing Bioactive Agents in Artificially Induced Root Caries

This study investigated the remineralization effect of experimental mint formulations containing bioactive agents (xylitol; green tea extract, GT; and amorphous calcium phosphate, ACP) in the progression of artificially induced root caries. Root caries lesions were induced by demineralization solution (pH 4.6; 96 h; 37°C). The lesions were treated with mint A, mint B, mint C, xylitol, GT, ACP, or remineralization solution (RS; negative control). Specimens were pH-cycled through treatments (5×/day; 3 min) and 6 cycles of acidic (pH 5.0; 30 min) and neutral (pH 7.0; 10 min) buffers for 8 days. Bacterial collagenase (Clostridium histolyticum) was used overnight to simulate proteolytic challenge. Caries depth and porosity as well as mineral density were estimated using fluorescence microscopy (n = 15) and microcomputed tomography (n = 6). Analysis of variance (ANOVA, α = 0.05) showed no statistically significant difference in caries depth among all groups (p = 0.172). The highest fluorescence intensity decrease was observed for GT followed by mint C, with no significant difference between them (p = 0.868). There were significant differences among GT and mints A, B, and C when compared to RS (p < 0.001). No statistically significant differences in fluorescence intensity were observed among ACP, xylitol, and RS (p > 0.05). The mineral density of the lesions in GT, mints A, B, and C, and ACP was statistically similar (p > 0.05) and significantly higher than that in RS (p < 0.05). No significant difference was observed between xylitol and RS (p = 0.728). The experimental mints showed remineralization action on artificial root caries, and GT was found to be the main active ingredient in the investigated formulations.

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.

High-performance therapeutic quercetin-doped adhesive for adhesive-dentin interfaces

Almost half of dental restorations have failed in less than 10 years, and approximately 60% of practice time has been consumed to replace these dental restorations. As such, contemporary dentin adhesives should be modified to treat secondary caries and prevent the degradation of adhesive–dentin interfaces. To achieve this goal, we developed a versatile therapeutic adhesive in the present study by incorporating quercetin, which is a naturally derived plant extract, into a commercial adhesive at three concentrations (100, 500 and 1000 µg/mL). An unmodified adhesive served as a control. The antibacterial ability on Streptococcus mutans biofilm, conversion degree, microtensile bond strength, failure modes, in situ zymography, nanoleakage expression and cytotoxicity of quercetin-doped adhesive were comprehensively evaluated. Results showed that the quercetin-doped adhesive (500 µg/mL) preserved its bonding properties against collagenase ageing and inhibited the growth of S. mutans biofilm. Efficient bonding interface sealing ability, matrix metalloproteinase inhibition and acceptable biocompatibility were also achieved. Thus, a simple, safe and workable strategy was successfully developed to produce therapeutic adhesives for the extension of the service life of adhesive restorations.

Role of proteoglycans on the biochemical and biomechanical properties of dentin organic matrix

OBJECTIVE

Proteoglycans (PGs) are multifunctional biomacromolecules of the extracellular matrix of collagen-based tissues. In teeth, besides a pivotal regulatory role on dentin biomineralization, PGs provide mechanical support to the mineralized tissue and compressive strength to the biosystem. This study assessed enzymatic protocols for selective PGs removal from demineralized dentin to determine the roles of these biomacromolecules in the bulk mechanical properties and biostability of type I collagen.

METHODS

Selective removal of glycosaminoglycans chains (GAGs) and PGs from demineralized dentin was carried out by enzymatic digestion protocols using chondroitinase ABC (c-ABC) and trypsin (Try). A comprehensive study design included assessment of dentin matrix mass loss, biodegradability of the PGs/GAGs-depleted dentin matrix, ultimate tensile strength (UTS) and energy to fracture tests. Quantitative data was statistically analyzed by two-way and one-way ANOVA followed by the appropriate post hoc tests (α=0.05).

RESULTS

Transmission electron microscopy images show effective GAGs removal by c-ABC and Try and both enzymatic methods released statistically similar amounts of GAGs from the demineralized dentin. Try digestion resulted in about 25% dentin matrix mass loss and increased susceptibility to collagenolytic digestion when compared to c-ABC (p=0.0224) and control (p=0.0901). Moreover, PGs digestion by Try decreased the tensile strengths of dentin. Statistically lower energy to fracture was observed in c-ABC-treated dentin matrix.

CONCLUSIONS

GAGs plays a pivotal role on tissue mechanics and anisotropy, while the core protein of PGs have a protective role on matrix biostability.

UVA-activated riboflavin improves the strength of human dentin

The aim of this study was to evaluate the effects of UVA-activated riboflavin (UVA-RF) on the mechanical properties of non-demineralized human dentin. Dentin specimens obtained from 20 teeth were randomly divided into the following four groups: group 1 (control): no treatment, group 2 (low UVA-RF): specimens were exposed to UVA-RF for 10 min, group 3 (medium UVA-RF): specimens were exposed to UVA-RF for 30 min, and group 4 (high UVA-RF): specimens were exposed to UVA-RF for 60 min. Three-point flexural test and Raman spectroscopic analyses were performed. The mean flexural strengths (MPa) were 129.96, 128.96, 144.21, and 147.54, and the mean elastic modulus (GPa) were 8.59, 8.38, 10.21, and 9.87 for groups 1 to 4, respectively. Raman spectra showed chemical modifications of dental collagen under medium and high UVA-RF treatment. We conclude that medium and high UVA-RF increases the strength of non-demineralized human dentin by collagen crosslinking.