Grape seed proanthocyanidins increase collagen biodegradation resistance in the dentin/adhesive interface when included in an adhesive

Preliminary Evaluation of Bioactive Collagen-Polyphenol Surface Nanolayers on Titanium Implants: An X-ray Photoelectron Spectroscopy and Bone Implant Study

To endow an implant surface with enhanced properties to ensure an appropriate seal with the host tissue for inflammation/infection resistance, next-generation bone implant collagen-polyphenol nanolayers were built on conventional titanium surfaces through a multilayer approach. X-ray Photoelectron Spectroscopy (XPS) analysis was performed to investigate the chemical arrangement of molecules within the surface layer and to provide an estimate of their thickness. A short-term (2 and 4 weeks) in vivo test of bone implants in a healthy rabbit model was performed to check possible side effects of the soft surface layer on early phases of osteointegration, leading to secondary stability. Results show the building up of the different nanolayers on top of titanium, resulting in a final composite collagen-polyphenol surface and a layer thickness of about 10 nm. In vivo tests performed on machined and state-of-the-art microrough titanium implants do not show significant differences between coated and uncoated samples, as the surface microroughness remains the main driver of bone-to-implant contact. These results confirm that the surface nanolayer does not interfere with the onset and progression of implant osteointegration and prompt the green light for specific investigations of the potential merits of this bioactive coating as an enhancer of the device/tissue seal.

Theaflavin -3,3'-digallate/ethanol: a novel cross-linker for stabilizing dentin collagen

Objectives

To study the ability of theaflavin-3,3'-digallate (TF3)/ethanol solution to crosslink demineralized dentin collagen, resist collagenase digestion, and explore the potential mechanism.

Methods

Fully demineralized dentin blocks were prepared using human third molars that were caries-free. Then, these blocks were randomly allocated into 14 separate groups (n = 6), namely, control, ethanol, 5% glutaraldehyde (GA), 12.5, 25, 50, and 100 mg/ml TF3/ethanol solution groups. Each group was further divided into two subgroups based on crosslinking time: 30 and 60 s. The efficacy and mechanism of TF3's interaction with dentin type I collagen were predicted through molecular docking. The cross-linking, anti-enzymatic degradation, and biomechanical properties were studied by weight loss, hydroxyproline release, scanning/transmission electron microscopy (SEM/TEM), in situ zymography, surface hardness, thermogravimetric analysis, and swelling ratio. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy were utilized to explore its mechanisms. Statistical analysis was performed using one and two-way analysis of variance and Tukey's test.

Results

TF3/ethanol solution could effectively crosslink demineralized dentin collagen and improve its resistance to collagenase digestion and biomechanical properties (p < 0.05), showing concentration and time dependence. The effect of 25 and 50 mg/ml TF3/ethanol solution was similar to that of 5% GA, whereas the 100 mg/mL TF3/ethanol solution exhibited better performance (p < 0.05). TF3 and dentin type I collagen are mainly cross-linked by hydrogen bonds, and there may be covalent and hydrophobic interactions.

Conclusion

TF3 has the capability to efficiently cross-link demineralized dentin collagen, enhancing its resistance to collagenase enzymatic hydrolysis and biomechanical properties within clinically acceptable timeframes (30 s/60 s). Additionally, it exhibits promise in enhancing the longevity of dentin adhesion.

Evaluation of the Dentinal Shear Bond Strength and Resin Interface in Primary Molars after Pre-Treatment with Various Dentin Bio-Modifiers: An In Vitro Study

Dentine adhesives have demonstrated great success with permanent teeth. Though the results in primary teeth are not well documented, some studies have demonstrated lower values of bond strength in primary teeth than those found in permanent teeth. The aim of this study was to compare and evaluate the effect of grape seed extract (6.5%) (Herbal Bio Solutions, Delhi, India), glutaraldehyde (5%) (Loba Chemie PVT. LTD., Mumbai), hesperidin (0.5%) (Herbal Bio Solutions, Delhi, India), and casein phosphopeptide-amorphous calcium phosphate (tooth mousse) (GC Corporation, Alsip, IL, USA) on the shear bond strength of dentine of primary teeth and to evaluate the resin tags at the resin tooth interface. Seventy-five caries-free human primary molars were collected, and their occlusal surfaces were ground flat. Dentin surfaces were etched using phosphoric acid. Then teeth were randomly assigned in sequential order to five groups according to the dentinal treatment method: Group I (Control group) (no treatment), Group II (5% glutaraldehyde), Group III (6.5% grape seed extract), Group IV (0.5% hesperidin), and Group V (CPP-ACP). Ten teeth from each group were assigned for Shear Bond Strength and five for SEM analysis. ANOVA and a post hoc least significant difference test (p < 0.05) were used for statistical analysis of the collected data. The grape seed extract group showed significantly increased shear bond strength than the control group (p < 0.05), and the mean length of resin tags in different dentine bio modifiers groups was also statistically significant (p < 0.05). The use of dentin bio modifiers such as 5% glutaraldehyde, 6.5% grape seed extract, 0.5% hesperidin, and CPP-ACP in the bonding process for primary teeth did not improve the dentinal bond strength.

The cross-linking and protective effect of artemisinin and its derivatives on collagen fibers of demineralized dentin surface

OBJECTIVE

To investigate the cross-linking and protective effect of artemisinin (ART), dihydroartemisinin (DHA), and artesunate (AST) on collagen fibers of demineralized dentin surface.

METHODS

Molecular docking was used to predict potential interactions of ART, DHA, and AST with dentin type I collagen. Human third molars without caries were completely demineralized and treated with different solutions for 1 min. The molecular interactions and cross-linking degree of ART and its derivatives with dentin collagen were evaluated by FTIR spectroscopy, total extractable protein content, and a ninhydrin assay. Scanning electron microscopy, hydroxyproline release, and ultimate microtensile strength tests (μUTS) were employed to confirm the mechanical properties and anti-collagenase degradation properties of dentin collagen fibers.

RESULTS

ART, DHA, and AST combined with dentin type I collagen mainly through hydrogen bonding and hydrophobic interactions, and the cross-linking reaction sites were mainly C=O and CN functional groups. Compared to the control group, ART and its derivatives significantly increased the degree of cross-linking. Additionally, significant increases were observed in resistance to enzymatic digestion and mechanical properties of the artemisinin and its derivatives group.

CONCLUSION

ART, DHA, and AST could cross-link with demineralized dentin collagen, through improving the mechanical properties and anti-collagenase degradation properties.

CLINICAL SIGNIFICANCE

The study endorses the potential use of ART and its derivatives as a prospective collagen cross-linking agent for degradation-resistant and long-period dentin bonding in composite resin restorations.

Dual-functional etchants that simultaneously demineralize and stabilize dentin render collagen resistant to degradation for resin bonding

OBJECTIVES

To develop dual-functional etchants that could demineralize and stabilize dentin collagen simultaneously, and to assess the effects of these etchants on collagen crosslinking, biostability and resin bonding properties under clinically relevant conditions.

METHODS

Dual-functional etchants were prepared by mixing 56% glycolic acid and 17% phosphoric acid and adding 1% of theaflavins (TF) or proanthocyanidins from grape seed extract (GSE). The etchant without crosslinker was used as control. The prepared human dentin specimens were treated with the 3 etchants for 30 s and analyzed for chemical interaction using Fourier transform infrared spectroscopy and resistance of the demineralized layer to collagenase degradation using electron microscopy (EM). Resin-dentin interfacial bonding properties were evaluated after 24 h and after 10,000 thermocycling through microtensile bond strength (μTBS), nanoleakage and matrix metalloproteinases (MMPs) activity via in situ zymography. Statistical analysis was done using ANOVA and post- hoc Tuckey's test.

RESULTS

Compared to control, TF and GSE dual-functional etchants were able to demineralize dentin, induce collagen crosslinking and protect the demineralized layer from collagenase degradation within 30 s. High resolution EM images showed better protection with TF etchant compared to GSE. There was a significant reduction in μTBS and an increase in nanoleakage and MMPs activity in control after thermocycling (p < 0.05) while these changes weren't seen in dual-functional etchants.

SIGNIFICANCE

Dual-functional etchants, especially TF containing, provide collagen protection against degradation and result in stable μTBS and less nanoleakage and MMPs activity under clinically relevant conditions.

Synergistic effect of collagen cross-linking and remineralization for improving resin-dentin bond durability

In this study, the synergistic effect of glutaraldehyde-cross-linking and remineralization on the strength and durability of resin-dentin bonds was investigated. Dentin surfaces were etched with 35% phosphoric acid. The control specimens were bonded with Adper Single Bond 2 using wet bonding without pretreatment. The experimental specimens were pretreated with 5% (v/v) glutaraldehyde solution for 3 min and placed in a remineralizing solution for 0, 12, and 24 h, followed by dry bonding. After performing composite build-ups on the specimens, they were longitudinally sectioned, immediately, and after aging for 3 h with sodium hypochlorite (NaOCl), to evaluate microtensile bond strength (µTBS). The cross-linked specimens exhibited µTBS values comparable with those of the control group, but the µTBS decreased significantly after NaOCl aging. The cross-linked dentin remineralized for 24 h exhibited an increase in µTBS. After aging in NaOCl, the µTBS of the specimens remineralized for 24 h did not decrease and was significantly higher than for the other experimental groups. Cross-linking with dry bonding maintained µTBS in specimens before aging in NaOCl, but the bonding durability was compromised. Remineralization of cross-linked dentin for 24 h followed by dry bonding increased the immediate µTBS and improved bond durability. Therefore, combining cross-linking with remineralization of collagen fibrils progressively increased resistance to degradation, improving bond durability.

Barrier Membranes for Guided Bone Regeneration (GBR): A Focus on Recent Advances in Collagen Membranes

Guided bone regeneration (GBR) has become a clinically standard modality for the treatment of localized jawbone defects. Barrier membranes play an important role in this process by preventing soft tissue invasion outgoing from the mucosa and creating an underlying space to support bone growth. Different membrane types provide different biological mechanisms due to their different origins, preparation methods and structures. Among them, collagen membranes have attracted great interest due to their excellent biological properties and desired bone regeneration results to non-absorbable membranes even without a second surgery for removal. This work provides a comparative summary of common barrier membranes used in GBR, focusing on recent advances in collagen membranes and their biological mechanisms. In conclusion, the review article highlights the biological and regenerative properties of currently available barrier membranes with a particular focus on bioresorbable collagen-based materials. In addition, the advantages and disadvantages of these biomaterials are highlighted, and possible improvements for future material developments are summarized.

Effect of Collagen Crosslinkers on Dentin Bond Strength of Adhesive Systems: A Systematic Review and Meta-Analysis

This study aimed to identify the role of crosslinking agents in the resin–dentin bond strength (BS) when used as modifiers in adhesives or pretreatments to the dentin surface through a systematic review and meta-analysis. This paper was conducted according to the directions of the PRISMA 2020 statement. The research question of this review was: “Would the use of crosslinkers agents improve the BS of resin-based materials to dentin?” The literature search was conducted in the following databases: Embase, PubMed, Scielo, Scopus, and Web of Science. Manuscripts that reported the effect on the BS after the use of crosslinking agents were included. The meta-analyses were performed using Review Manager v5.4.1. The comparisons were performed by comparing the standardized mean difference between the BS values obtained using the crosslinker agent or the control group. The subgroup comparisons were performed based on the adhesive strategy used (total-etch or self-etch). The immediate and long-term data were analyzed separately. A total of 50 articles were included in the qualitative analysis, while 45 articles were considered for the quantitative analysis. The meta-analysis suggested that pretreatment with epigallocatechin-3-gallate (EGCG), carbodiimide, ethylenediaminetetraacetic acid (EDTA), glutaraldehyde, and riboflavin crosslinking agents improved the long-term BS of resin composites to dentin (p ≤ 0.02). On the other hand, the use of proanthocyanidins as a pretreatment improved both the immediate and long-term BS values (p ≤ 0.02). When incorporated within the adhesive formulation, only glutaraldehyde, riboflavin, and EGCG improved the long-term BS to dentin. It could be concluded that the application of different crosslinking agents such as carbodiimide, EDTA, glutaraldehyde, riboflavin, and EGCG improved the long-term BS of adhesive systems to dentin. This effect was observed when these crosslinkers were used as a separate step and when incorporated within the formulation of the adhesive system.

Degradation and Stabilization of Resin-Dentine Interfaces in Polymeric Dental Adhesives: An Updated Review

Instability of the dentine-resin interface is owed to the partial/incomplete penetration of the resin adhesives in the collagen fibrils. However, interfacial hydrolysis of the resin-matrix hybrid layer complex activates the collagenolytic and esterase enzymes that cause the degradation of the hybrid layer. Adequate hybridization is often prevented due to the water trapped between the interfibrillar spaces of the collagen network. Cyclic fatigue rupture and denaturation of the exposed collagen fibrils have been observed on repeated application of masticatory forces. To prevent interfacial microstructure, various approaches have been explored. Techniques that stabilize the resin–dentine bond have utilized endogenous proteases inhibitors, cross linking agents’ incorporation in the exposed collagen fibrils, an adhesive system free of water, and methods to increase the monomer penetration into the adhesives interface. Therefore, it is important to discover and analyze the causes of interfacial degradation and discover methods to stabilize the hybrid layer to execute new technique and materials. To achieve a predictable and durable adhesive resin, restoration is a solution to the many clinical problems arising due to microleakage, loss of integrity of the restoration, secondary caries, and postoperative sensitivity. To enhance the longevity of the resin-dentine bond strength, several experimental strategies have been carried out to improve the resistance to enzymatic degradation by inhibiting intrinsic collagenolytic activity. In addition, biomimetic remineralization research has advanced considerably to contemporary approaches of both intrafibrillar and extrafibrillar remineralization of dental hard tissues. Thus, in the presence of biomimetic analog complete remineralization of collagen, fibers are identified.

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.

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.

Natural Extracts as Biological Smear Layer Removing Agents: A Literature Review

OBJECTIVES

The aim of this article is to identify whether natural irrigants are better than synthetic conventional irrigants for smear layer removal and to analyze their influence on mechanical and chemical radicular dentin properties.

MATERIALS AND METHODS

The last electronic search was performed on June 2020 through five databases, limited to articles either published or accepted for publication in the English language using the following keywords: "Natural extracts" or "Fruit and plant extracts" and "Smear layer removal."

RESULTS

According to the inclusion criteria, 36 articles were included. Most studies revealed that apple or apple cider vinegars, grape seed extract, citrus aurantifolia, 5-10% glycolic acid, and 0.5-1% phytic acid effectively removed the smear layer better or similar to synthetic conventional agents.

CONCLUSION

Natural irrigants are effective smear layer removing agents with the least deteriorated effect on mechanical and chemical radicular dentin properties compared with synthetic agents.

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.

Comparative evaluation of Emblica officinalis as an etchant and an MMP inhibitor with orthophosphoric acid and chlorhexidine on the microshear bond strength of composite resin: an ex vivo study

Objectives

This study aimed to evaluate Emblica officinalis (Indian gooseberry or amla) as an acid etchant and matrix metalloproteinase (MMP) inhibitor, and to compare its effect on the microshear bond strength of composite resin with orthophosphoric acid (OPA) and 2% chlorhexidine (CHX) as an acid etchant and MMP inhibitor, respectively.

Materials and Methods

The etching effect and MMP-inhibiting action of amla on dentin samples were confirmed by scanning electron microscopy (SEM) and gelatin zymography, respectively. Dentinal slabs (3 mm thick) from 80 extracted human molars were divided into 10 and 20 samples to form 2 control groups and 3 experimental groups. Groups 1, 2, and 4 were etched with OPA and groups 3 and 5 with amla juice. An MMP inhibitor was then applied: CHX for group 2 and amla extract for groups 4 and 5. Groups 1 and 3 received no MMP inhibitor. All specimens received a standardized bonding protocol and composite resin build-up, and were subjected to microshear bond strength testing. The force at which the fracture occurred was recorded and statistically analyzed.

Results

Amla juice had a similar etching effect as a self-etch adhesive in SEM and 100% amla extract was found to inhibit MMP-9 by gelatin zymography. The microshear bond strength values of amla were lower than those obtained for OPA and CHX, but the difference was not statistically significant.

Conclusions

Amla has a promising role as an acid etchant and MMP inhibitor, but further studies are necessary to substantiate its efficacy.

Cranberry Juice Extract Rapidly Protects Demineralized Dentin against Digestion and Inhibits Its Gelatinolytic Activity

Improving the longevity of composite restorations has proven to be difficult when they are bonded to dentin. Dentin demineralization leaves collagen fibrils susceptible to enzymatic digestion, which causes breakdown of the resin-dentin interface. Therefore, measures for counteracting the enzymatic environment by enhancing dentin collagen's resistance to degradation have the potential to improve the durability of dental composite restorations. This study aimed to evaluate the effects of polyphenol-rich extracts and a chemical cross-linker on the cross-linking interaction, resistance to digestion, and endogenous matrix metalloproteinase (MMP) activities of dentin collagen under clinically relevant conditions. Ten-µm-thick films were cut from dentin slabs of non-carious extracted human third molars. Following demineralization, polyphenol-rich extracts-including grape seed (GSE), green tea (GTE), and cranberry juice (CJE)-or chemical cross-linker carbodiimide with n-hydroxysuccinimide (EDC/NHS) were applied to the demineralized dentin surfaces for 30 s. The collagen cross-linking, bio-stabilization, and gelatinolytic activities of MMPs 2 and 9 were studied by using Fourier-transform infrared spectroscopy, weight loss, hydroxyproline release, scanning/transmission electron microscopy, and in situ zymography. All treatments significantly increased resistance to collagenase degradation and reduced the gelatinolytic MMP activity of dentin collagen compared to the untreated control. The CJE- and GSE-treated groups were more resistant to digestion than the GTE- or EDC/NHS-treated ones (p < 0.05), which was consistent with the cross-linking interaction found with FTIR and the in situ performance on the acid-etched dentin surface found with SEM/TEM. The collagen films treated with CJE showed the lowest MMP activity, followed by GSE, GTE, and, finally, EDC/NHS. The CJE-treated dentin collagen rapidly increased its resistance to digestion and MMP inhibition. An application of CJE as short as 30 s may be a clinically feasible approach to improving the longevity of dentin bonding in composite restorations.

Methacrylate-functionalized proanthocyanidins as novel polymerizable collagen cross-linkers - Part 1: Efficacy in dentin collagen bio-stabilization and cross-linking

OBJECTIVE

The aim of the study was to investigate the effects of methacrylate-functionalized proanthocyanidins (MAPAs) on dentin collagen's bio-stabilization against enzymatic degradation and crosslinking capability.

METHODS

Three MAPAs were synthesized via varying methacrylate (MA) to proanthocyanidins (PA) feeding ratios of 1:2, 1:1, and 2:1 to obtain MAPA-1, MAPA-2, and MAPA-3, respectively. The three MAPAs were structurally characterized by proton nuclear magnetic resonance (¹H NMR) and Fourier transform infrared (FTIR) spectroscopic methods. 5-μm-thick dentin films were microtomed from dentin slabs of third molars. Following demineralization, films or slabs were treated with 1% MAPAs or PA in ethanol for 30 s. Collagen bio-stabilization against enzymatic degradation was analyzed by weight loss (WL) and hydroxyproline release (HYP) of films, as well as scanning electron microscopy (SEM) on dentin slabs. Crosslinking capacity and interactions of MAPAs with collagen were investigated by FTIR. Data were analyzed by ANOVA and Tukey's test (α = 0.05%).

RESULTS

MA:PA feeding ratios affected MAPAs' chemical structures which in turn led to different collagen stabilization efficacy against degradation and varied collagen crosslinking capabilities. Higher collagen stabilization efficacy was detected using MAPA-1 (WL 10.52%; HYP 13.53 μg/mg) and MAPA-2 (WL 5.99%; HYP 11.02 μg/mg), which was comparable to that using PA (WL 8.79%; HYP 13.17 μg/mg) (p > 0.05), while a lower collagen stability occurred in MAPA-3 (WL 38.48%; HYP 29.49 μg/mg), indicating excessive MA-functionalization would compromise its stabilization efficacy. In comparison, complete digestion was detected for untreated collagen (WL 100%; HYP 102.76 μg/mg). The above results were consistent with collagen crosslinking efficacy of the three MAPAs revealed by SEM and FTIR.

SIGNIFICANCE

A new class of novel polymerizable collagen cross-linkers MAPAs was synthesized and shown that, when appropriate MA:PA ratios were applied, the resulting MAPAs could render high collagen stability and the ability to copolymerize with resin monomers, overcoming the drawbacks of PA. These new polymerizable crosslinkers, when included in adhesives, could lead to long-lasting dentin bonding.

Methacrylate-functionalized proanthocyanidins as novel polymerizable collagen cross-linkers - Part 2: Effects on polymerization, microhardness and leaching of adhesives

OBJECTIVE

The aim of the study was to investigate the effects of a novel polymerizable collagen cross-linker methacrylate-functionalized proanthocyanidins (MAPA) on the polymerization, microhardness and leaching of a HEMA-based experimental dental adhesive system.

METHODS

Three MAPAs were synthesized using different methacrylate (MA) to proanthocyanidins (PA) feeding ratios of 1:2, 1:1, and 2:1 to obtain MAPA-1, MAPA-2, and MAPA-3, respectively. The resulting three MAPAs and PA were added to an experimental adhesive formulated with HEMA and a tri-component photoinitiator system (0.5 wt% CQ/EDMAB/DPIHP) at 1%, 5% and 10% MAPA or PA concentrations (wt%). The adhesive polymerization kinetics was measured continuously in real-time for 10 min using a Fourier-transform infrared spectroscopy (FTIR) with an attenuated total reflectance (ATR) accessory. Degree of conversion (DC) and Vickers microhardness (MH) of cured adhesives were measured at 72 h post-cure. The leaching of cured adhesives in DI water was monitored using UV-vis spectrophotometer. Statistical analysis was performed using one-way and two-way ANOVA, Tukey's (p < 0.05).

RESULTS

The adhesive formulations with 1%, 5% and 10% MAPAs-1, -2, -3 all generated higher rate of polymerization and 10-min DC than the formulations with PA at the same concentrations. At 72 h post-cure, the adhesive formulation with 5% MAPA-2 exhibited significantly higher DC (99.40%) and more than doubled MH (18.93) values than the formulation with 5% PA (DC = 89.47%, MH = 8.41) and the control (DC = 95.46%, MH = 9.33). Moreover, the cured adhesive with 5% MAPA-2 demonstrated significantly reduced PA leaching in comparison with cured adhesive with 5% PA.

SIGNIFICANCE

Synthesized MAPA is a novel class of polymerizable collagen cross-linker that not only stabilizes dentin collagen via its PA component, but also improves polymerization, mechanical properties and stability of HEMA-based adhesives via its MA component. By inheriting the benefit while overcoming the drawback of PA, MAPA offers a revolutionary solution for improved bond-strength and longevity of dental restorations.

Effect of myricetin on odontoblast-like cells and its potential to preserve resin-dentin Bonds

Stabilization of the resin-dentin interface to increase the durability of adhesive dental restorations is a challenging task. The use of naturally occurring collagen crosslinking agents has been proposed to prevent degradation of the hybrid layer. Myricetin (MYR) is a flavonoid with a wide variety of beneficial effects and it has been used for the treatment of different systemic pathologies. The chemical structure of MYR makes it a powerful antioxidant, an inhibitor of matrix metalloproteinase (MMP) activity, and a collagen cross-linker. This study presents MYR as a novel treatment in operative dentistry to stabilize the resin-dentin interface by inhibiting MMPs and crosslinking the collagen. Viability tests carried out using a resazurin assay showed that MYR had no cytotoxic effects on human odontoblast-like cells and the phenotype was preserved. Fluorometric MMP activity assay and fluorescence microscopy revealed that the MMPs in the demineralized dentin were effectively inhibited by the application of MYR (600 μM for 120 s). A microtensile bond strength test was performed immediately and after six months of storage. The bond strength to dentin was not affected by MYR and was preserved over time. Demineralized dentin beams were evaluated to determine the dentin biomodification using microtensile strength and elastic modulus assays. MYR improved the biomechanical behavior of the demineralized dentin similarly to glutaraldehyde, a recognized crosslinking agent. These findings indicated that MYR acts as an MMP inhibitor, collagen cross-linker, and preserver of the bond strength. Furthermore, MYR is an ethanol-soluble molecule with a lower molecular weight than the other polyphenols; hence, it can be applied for a short time and diffuses deeply through the dentin without any associated cytotoxicity. This molecule has beneficial effects on the biological and mechanical behavior of the resin-dentin interface and may be used to effectively stabilize the hybrid layer in a clinical setting.

Development of collagen/nanohydroxyapatite scaffolds containing plant extract intended for bone regeneration

In this study scaffolds of nanohydroxyapatite (nHA) and anionic collagen (C) combined with plant extracts intended for bone tissue repair were developed. Grape seed (P), pomegranate peel (R) and jabuticaba peel (J) extracts were used as collagen crosslinker agents in order to improve the materials properties. All crude extracts were effective against Staphylococcus aureus, but only for CR scaffold inhibition zone was noticed. The extracts acted as crosslinking agents, increasing enzymatic resistance and thermal stability of collagen. The extracts showed cytotoxicity at the concentrations tested, while nHA increased cell viability. The scaffolds presented porosity and pore size appropriate for bone growth. CR, CnHAP, CnHAR and CnHAJ increased the cell viability after 24 h. The combination of collagen, nHA and plant extracts offers a promising strategy to design novel biomaterials for bone tissue regeneration.

Research Advances in the Use of Bioactive Compounds from Vitis vinifera By-Products in Oral Care

Oral health is considered an important factor of general health and it contributes to the quality of life. Despite the raising awareness of preventive measures, the prevalence of oral health conditions continues to increase. In this context, a growing interest in investigating natural resources like Vitis vinifera (V. vinifera) phenolic compounds (PhCs) as oral health promoters has emerged. This paper aims to review the evidence about the bioactivities of V. vinifera by-products in oral health. Up to date, a high number of studies have thoroughly reported the antimicrobial and antiplaque activity of V. vinifera extracts against S. mutans or in multi-species biofilms. Moreover, the bioactive compounds from V. vinifera by-products have been shown to modulate the periodontal inflammatory response and the underlying oxidative stress imbalance induced by the pathogenic bacteria. Considering these beneficial effects, the utility of V. vinifera by-products in the maintaining of oral health and the necessary steps towards the development of oral care products were emphasized. In conclusion, the high potential of V. vinifera by-products could be valorized in the development of oral hygiene products with multi-target actions in the prevention and progression of several oral conditions.

Anti-caries effect of resin infiltrant modified by quaternary ammonium monomers

OBJECTIVES

Resin infiltrant is used in early enamel caries. However, commercial resin infiltrant lacks persistent antibacterial activity. Dimethylaminododecyl methacrylate (DMADDM) was added to resin infiltrant to give it sustainable antibacterial properties and inhibit demineralization.

METHODS

After the application of resin infiltrant to bovine enamel, cytotoxicity, surface roughness, and aesthetics were assessed. A multi-species biofilm was incubated on the enamel disk before and one month after microbial-aging. After a 48-h anaerobic incubation, biomass accumulation, metabolic activity, and lactic acid were analyzed using a crystal violet assay, an MTT (3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, and a lactic acid assay. Biofilm structure and composition were determined by live/dead staining, exopolysaccharide (EPS) staining, scanning electron microscopy (SEM), and quantitative polymerase chain reaction (qPCR). The depth and content of demineralization were tested by transverse microradiography (TMR).

RESULTS

Incorporating DMADDM did not increase the cytotoxicity or change the physical properties when the mass fraction of the DMADDM was 2.5-10 %. The modification decreased the amount of bacterial biofilm, metabolic activity, lactic acid production, EPS, and the proportion of Streptococcus mutans in the biofilms. It also provided anti-demineralization effects. The surface roughness and antibacterial ability were not changed after one month of microbial-aging.

CONCLUSION

The incorporation of DMADDM improved the antibacterial and anti-demineralization effects of the material. It demonstrated a sustained antibacterial effect.

CLINICAL SIGNIFICANCE

The antibacterial modification might be a potential choice for future clinical applications to inhibit early enamel caries.

Effect of tea root-derived proanthocyanidin fractions on protection of dentin collagen

Objectives

Proanthocyanidins (PAs) have been widely used as effective agents for dentin collagen cross-linking to enhance the biomechanics and biostability of dentin in vitro. However, the effects and protective mechanisms of various tea root-derived PA components on dentin remain undefined. This study evaluated the effects of these tea root-derived PA components on dentin biomechanics and biostability.

Methods

In this study, ethyl acetate and n-butyl alcohol were used to extract PAs with different degrees of polymerization from tea roots; the effects of these PA extracts on dentin were evaluated.

Results

Dentin was treated with glutaraldehyde, ethyl acetate, n-butyl alcohol, or water. PAs with a high degree of polymerization, extracted using n-butyl alcohol, were able to more effectively improve dentin collagen cross-linking, increase resistance to bacterial collagenase digestion, and enhance dentin elasticity, relative to treatment with glutaraldehyde or PAs with a low degree of polymerization (extracted using ethyl acetate). Additionally, treatment with aqueous extract of tea roots was detrimental to dentin stability and function.

Conclusions

PAs with a high degree of polymerization were effective for dentin protection and restoration in vitro, suggesting clinical treatment potential for tea root-derived PAs.

Sealing effects of different Chinese herbal medicines on dentinal tubules: a scanning electron microscopic observation

BACKGROUND AND OBJECTIVES

To evaluate the sealing effects of different Chinese herbal medicines on dentinal tubules, and to provide a reference for the clinical treatment of dentin hypersensitivity.

METHODS

Forty dentin slices prepared by freshly extracted bovine mandibular central incisors were randomly assigned to procyanidins, tannic acid, gallic acid, naringin, epigallocatechin gallate (EGCG), glycyrrhizic acid, paeonol, and blank groups. Dentin slices in each Chinese herbal medicine group were treated three times a day, each for 5 min, and then immersed in a remineralization solution for the rest of the time. Dentin slices in the blank group were directly immersed in the remineralization solution for 7 days. The dentinal tubule sealing effect was observed under the scanning electron microscope (SEM).

RESULTS

SEM results showed that the dentinal tubules were almost completely open in the blank group, which was mostly open in the gallic acid, EGCG, glycyrrhizic acid, and paeonol groups, and were sealed in procyanidins, tannic acid, and naringin groups. Significant differences were detected in mean area, mean diameter of dentinal tubules, and mean plugging rate of dentinal tubules between the remaining Chinese herbal medicine groups and blank group (P < .05). Among them, the dentinal tubule sealing effect of procyanidins, tannic acid, and naringin was obvious.

CONCLUSION

The findings suggested that procyanidins, tannic acid, and naringin can effectively seal dentinal tubules, which provided a basis for clinical treatment of dentin hypersensitivity.

The antibiofilm and collagen-stabilizing effects of proanthocyanidin as an auxiliary endodontic irrigant

AIM

To evaluate the antibiofilm effect of proanthocyanidin (PA) solution as an irrigant against Enterococcus faecalis (E. faecalis) and its influence on the mechanical properties and biodegradation resistance of demineralized root dentine.

METHODOLOGY

Enterococcus faecalis were introduced into human root dentine tubules by a serial centrifugation method and grown for 1 week. Dentine blocks infected with 1-week-old E. faecalis biofilms were treated with the following irrigants: sterile water (control), 2% chlorhexidine (CHX), 2% PA, 5% PA and 10% PA. After treatment, the live and dead bacteria proportions within E. faecalis biofilms were analysed using confocal laser scanning microscopy. To evaluate the biostability of fully demineralized dentine treated by the aforementioned irrigants, the elastic modulus and hydroxyproline release of human dentine incubated in collagenase solution were tested at baseline, after irrigant treatment and after biodegradation, respectively. Furthermore, the surface chemical bond of demineralized dentine collagen treated by various irrigants was characterized by X-ray photoelectron spectroscopy (XPS). Statistical analysis was performed using one-way anova and Tukey's post hoc multiple comparisons with the significance level at 5%.

RESULTS

The proportion of dead E. faecalis volume was significantly higher in the PA and CHX groups than that in the control group (P < 0.05). PA irrigation significantly increased the mechanical properties of demineralized dentine (P < 0.05), and the effect was enhanced with increasing PA concentration. CHX and PA groups had significantly less elasticity loss and hydroxyproline release (P < 0.05). The biomodification of dentine collagen by PA was verified by increased C-O/C-N peak percentage under C1s and C-O peak percentage under O1s narrow-scan XPS spectra.

CONCLUSIONS

Proanthocyanidin killed E. faecalis within biofilms and enhanced the biostability of the collagen matrix of demineralized root dentine. It might be used as an auxiliary endodontic irrigant with antibiofilm and collagen-stabilizing effects.

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 functions of hydrophobic elastic polyurethane combined with an antibacterial triclosan derivative in the dentin restoration interface

Dentin restoration produces weak interfaces because of the effects of bacterial microflora, biofilms, and mechanical, thermal, and shrinkage stresses. This results in secondary caries. Therefore, hydrophobic elastic polyurethane (PU) containing different concentrations of triclosan derivatives was synthesized and applied to solve this problem. The antibacterial PU was characterized according to its tensile strength (TS) and elasticity (ε) via a universal testing machine, and water sorption (Wsp) and solubility testing (Wsl) was performed according to ISO 4049: 2009. Additionally, this study evaluated the antibacterial properties of PU against Streptococcus mutans (ATCC35668) and Escherichia coli (ATCC25922). A marginal leakage test was performed to evaluate the leakage prevention property. As a result, the antibacterial PU showed high TS (>17 MPa), high elasticity (ε > 65%), and low Wsp (>81.06 μg/mm³) and Wsl (>11.22 μg/mm³). The PU exhibited antibacterial effects against both Streptococcus mutans and Escherichia coli. The antibacterial rates were over 90% and >99% for the 3% and 5% groups, respectively. Moreover, the marginal level of leakage was 0. Based on the mechanical properties, Wsp and Wsl values and the antibacterial properties, the 3% group exhibited satisfactory performance and has been deemed a possible solution to reduce the occurrence of secondary caries.

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.

Modifying Adhesive Materials to Improve the Longevity of Resinous Restorations

Dental caries is a common disease on a global scale. Resin composites are the most popular materials to restore caries by bonding to tooth tissues via adhesives. However, multiple factors, such as microleakage and recurrent caries, impair the durability of resinous restorations. Various innovative methods have been applied to develop adhesives with particular functions to tackle these problems, such as incorporating matrix metalloproteinase inhibitors, antibacterial or remineralizing agents into bonding systems, as well as improving the mechanical/chemical properties of adhesives, even combining these methods. This review will sum up the latest achievements in this field.

UVA-activated riboflavin promotes collagen crosslinking to prevent root caries

Root caries is an increasingly problem in aging societies with severe implications for the general health and wellbeing of large numbers of people. Strengthening type-I collagen, a major organic component of human dentin, has proved effective in preventing root caries. This study sought to determine whether exposure to riboflavin followed by UVA irradiation (RF/UVA) could promote additional collagen crosslinking, and thus improve the acid and enzymatic resistance of human dentin under simulated oral environments. If so, it could offer potential for treatment of the intractable problem of root caries. The greatest flexural strengths were found in dentin exposed to a 0.1% riboflavin solution for 1 minute followed by 1,600 mW/cm² UVA irradiation for 10 minutes. Mineral loss and lesion depth were significantly lower in the RF/UVA group than in the control group. The microstructures of dentinal tubules and collagen networks after RF/UVA treatment retained their original forms after acidic and enzymatic degradation. In conclusion, RF/UVA treatment may be a new method for preventing root caries with promising prospects for clinical application.

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.

Two-year clinical evaluation of proanthocyanidins added to a two-step etch-and-rinse adhesive

OBJECTIVE

To compare the clinical behavior of Proanthocyanidins (PA)-free and PA-containing two-step etch-and-rinse adhesive used underneath resin composite restorations in non-carious cervical lesions (NCCLs) over a 6- (6 M) and 24-month (24 M) period.

METHODS

135 restorations were randomly placed in 45 subjects. The NCCLs were conditioned (37% phosphoric acid for 15 s) and distributed into 3 groups: Control (EX0) - ExciTE F (Ivoclar Vivadent) adhesive applied following the manufacturer's recommendations; EX2 and EX5 - 2 wt% and 5 wt% of PA were added to ExciTE F, respectively, and applied as in EX0. Resin composite was placed incrementally and light-cured. The restorations were evaluated at baseline, 6 M and 24 M, using FDI and USPHS criteria. Statistical analyses were performed using Friedman and Wilcoxon tests (α = 0.05).

RESULTS

The retention rates were 98% (95% confidence interval 88-99%) for EX0, 92% (80-97%) for EX2; and 85% (72-93%) for EX5 at 6 M. A significant difference was found only for EX5 at 6 M when compared with the respective baseline findings (p = 0.03) and when compared with EX0 and EX2 (p = 0.001) at 6 M. After 24 M, the retention rates were 98% (88-99%) for EX0, 73% (59-84%) for EX2, and 71% (56-82%) for EX5. Only EX0 did not result in significant difference in retention rate at 24 M when compared with baseline but showed a significant higher retention rate when compared with those of EX2 and EX5 (p = 0.001).

CONCLUSION

Adding proanthocyanidins to the adhesive solution jeopardized the retention of composite resins restorations in non-carious cervical lesions after 24 months.

CLINICAL RELEVANCE

In spite of being user-friendlier than when used separately, the incorporation of proanthocyanidins into the adhesive solution impairs the longevity of composite restorations.

Efficacy of Proanthocyanidins from Pelargonium sidoides Root Extract in Reducing P. gingivalis Viability While Preserving Oral Commensal S. salivarius

Bacterial resistance to antibiotics and the disruption of beneficial microbiota are key problems in contemporary medicine and make the search for new, more efficient infection treatment strategies among the most important tasks in medicine. Multicomponent plant-derived preparations with mild antibacterial activity created by many simultaneous mechanisms together with anti-inflammatory, innate immune and regenerative capacity-stimulating properties are good candidates for this therapy, and proanthocyanidins are among the most promising compounds of this sort. In this study, we have isolated proanthocyanidins from Pelargonium sidoides DC root extract and characterized and compared the composition, antioxidant properties and antibacterial activity of the proanthocyanidin fraction with those of the whole extract. The results revealed that proanthocyanidins had significantly stronger antioxidant capacity compared to the root extract and exhibited a unique antibacterial action profile that selectively targets Gram-negative keystone periodontal and peri-implant pathogenic strains, such as Porphyromonas gingivalis, while preserving the viability of beneficial oral commensal Streptococcus salivarius. The finding suggests that proanthocyanidins from Pelargonium sidoides root extract are good candidates for the prolonged and harmless treatment of infectious diseases.

Polyphenol uses in biomaterials engineering

Polyphenols are micronutrients obtained from diet that have been suggested to play an important role in health. The health benefits of polyphenols and their protective effects in food systems as antioxidant compounds are well known and have been extensively investigated. However, their functional roles as a "processing cofactor" in tissue engineering applications are less widely known. This review focuses on the functionality of polyphenols and their application in biomaterials. Polyphenols have been used to stabilize collagen and to improve its resistance to degradation in biological systems. Therefore, they have been proposed to improve the performance of biomedical devices used in cardiovascular systems by improving the mechanical properties of grafted heart valves, enhancing microcirculation through the relaxation of the arterial walls and improving the capillary blood flow and pressure resistance. Polyphenols have been found to stimulate bone formation, mineralization, as well as the proliferation, differentiation, and the survival of osteoblasts. These effects are brought about by the stimulatory effect of polyphenols on osteoblast cells and their protective effect against oxidative stress and inflammatory cytokines. In addition, polyphenols inhibit the differentiation of the osteoclast cells. Collectively, these actions lead to promote bone formation and to reduce bone resorption, respectively. Moreover, polyphenols can increase the cross-linking of dentine and hence its mechanical stability. Overall, polyphenols provide interesting properties that will stimulate further research in the bioengineering field.

An ex vivo evaluation of effect of dentin pretreatment with various agents for varying time intervals on the shear bond strength of resin

Background:

This article highlights the contribution of collagen structure/stability to the bond strength. We hypothesize that induction of cross-linking in dentin collagen fibrils improves dentin collagen stability and thus bond strength with composite also improves.

Aims:

The aim of the study was to evaluate the effect of collagen cross-linking agents on the shear bond strength of composite resins.

Subjects and Methods:

One hundred human permanent teeth were randomly divided into three groups: Group I (n = 20) – no dentin pretreatment done, Group II – dentin pretreatment with 10% sodium ascorbate for 5 min (IIa) and 10 min (IIb), and Group III – dentin pretreatment with 6.5% proanthocyanidin (PA) for 5 min (IIIa) and 10 min (IIIb). A composite resin was bonded on prepared surfaces and cured. Thermocycling was done, and shear bond strength of the prepared samples was tested using a universal testing machine.

Results:

Values of Group I (control) were lowest whereas that of Group II (sodium ascorbate) were highest. The following order of shear bond strength was observed: IIb > IIa > IIIb ~ IIIa > I. Results for sodium ascorbate were found to be time dependent, whereas for PA, differences were nonsignificant.

Conclusions:

Treatment of dentinal surfaces with collagen cross-linking agent increases the shear bond strengths.

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.

Integrated Oxidized-Hyaluronic Acid/Collagen Hydrogel with β-TCP Using Proanthocyanidins as a Crosslinker for Drug Delivery

The susceptibility of guided bone regeneration (GBR) material to infection by pathogens at wound sites during bone healing has often been overlooked. The objective of this study was the synthesis and characterization of a potential material for antibacterial GBR application. In the current study, the mechanical strength and biocompatibility of a composite restoration material-made of oxidized hyaluronic acid (HA)/type I collagen hydrogel integrated with tricalcium phosphate (β-TCP) using a natural crosslinking agent, oligomeric proanthocyanidins (OPCs)-were evaluated. The suitability of the material as a carrier matrix for antibacterial applications was evaluated by following the drug-release profile of tetracycline loaded within the composite. Results indicated that this composite material had a high swelling ratio of 420% and mechanical strength of 25 kPa while remaining at more than 60% of the weight after 30 days of an in vitro degradation test with good biocompatibility in promoting the proliferation of MG-63 cells. Drug release studies further showed that 93% of the tetracycline was released after 5 days, which supports this GBR material's capability to release antibacterial drugs while keeping other required GBR material design functions.

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.

Effect of crosslinkers on bond strength stability of fiber posts to root canal dentin and in situ proteolytic activity

STATEMENT OF PROBLEM

Improved stability of the adhesive interface can be obtained using crosslinkers. However, research on the use of crosslinkers in root dentin is lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of crosslinkers on the proteolytic activity of root dentin and on the bond strength of resin-cemented fiber posts.

MATERIAL AND METHODS

Single root canals were obtained from premolars (n=48) and endodontically treated before being divided into 4 groups: deionized water (control), 0.5 mol/L carbodiimide, 5% proanthocyanidin, or 5% glutaraldehyde. After removing the canal sealer, the dentin was etched with phosphoric acid, followed by water rinsing and the application of the crosslinkers for 60 seconds. Fiber posts were cemented using an adhesive (Single Bond 2) and resin cement (RelyX ARC). The roots were then transversally sectioned to obtain 1 mm thick specimens from the cervical, middle, and apical thirds and then aged for 24 hours or 9 months. Nine roots per group were used for the push-out test and 3 for determining the proteolytic activity of the root dentin by in situ zymography. Bond strength data were submitted to a mixed-model ANOVA and Bonferroni tests (α=.05).

RESULTS

Only proanthocyanidin negatively affected the 24-hour bond strength. After 9 months, a significant decrease in bond strength was seen for all groups, except for the crosslinked treated specimens from the cervical third of the root canal. Intense gelatinolytic activity was detected in the control group after 24 hours but was inhibited in the crosslinker-treated groups. Proteolytic activity was also not detected after 9 months for the groups treated with the crosslinkers, irrespective of the root canal third. Conversely, proteolytic activity increased for the specimens from the control group.

CONCLUSIONS

Although no proteolytic activity was detected in the hybrid layers along the entire root canal, dentin biomodification with crosslinkers was effective in preventing bond strength loss only in the cervical third.

Mechanical properties, water sorption characteristics, and compound release of grape seed extract-incorporated resins

Objective

This study evaluated the effect of grape seed extract (GSE) incorporation on the mechanical properties, water sorption, solubility, and GSE release from the experimental adhesive resins.

Material and Methods

An experimental comonomer mixture, consisting of 40% Bis-GMA, 30% Bis MP, 28% HEMA, 0.26% camphorquinone and 1% EDMAB, was used to prepare four GSE-incorporated adhesive resins at concentrations of 0.5, 1, 1.5, and 2 wt%. The neat resin without GSE was used as the control. Six resin beams (25 mm x 2 mm x 2 mm) per group were prepared for flexural strength and modulus of elasticity evaluations using a universal testing machine at a crosshead speed of 1 mm/min. Five disks (6 mm in diameter and 2 mm in thickness) per group were used for microhardness measurements using a Leitz micro-hardness tester with Leica Qgo software. Five disks (7 mm in diameter and 2 mm in thickness) per group were prepared and stored in deionized water for 28 days. Water sorption, solubility, and GSE release in deionized water were calculated for each GSE-incorporated adhesive at the end of 28th day. Data was evaluated using one-way ANOVA and Tukey multiple comparisons.

Results

Flexural strength, modulus of elasticity and microhardness of GSE-incorporated adhesive decreased significantly with incorporation of 1.5% of GSE (p<0.05). Addition of GSE had no effect on the water sorption of the adhesive resins (p=0.33). The solubility of the resin also increased significantly with incorporation of 1.5% of GSE (p<0.05). Quantities of GSE release increased with increased concentration of GSE in the adhesive resin.

Conclusion

Up to 1% of GSE can be incorporated into a dental adhesive resin without interfering with the mechanical properties or solubility of the resins.

Proanthocyanidins-Loaded Nanoparticles Enhance Dentin Degradation Resistance

Previous studies reported that grapeseed extract (GSE), which is rich in proanthocyanidins (PAs), improves the biodegradation resistance of demineralized dentin. This study aimed to investigate the effect of a new GSE delivery strategy to demineralized dentin through loading into biodegradable polymer poly-[lactic-co-glycolic acid] (PLGA) nanoparticles on the biodegradation resistance in terms of structural stability and surface/bulk mechanical and biochemical properties with storage time in collagenase-containing solutions. GSE-loaded nanoparticles were synthetized by nanoprecipitation at PLGA/GSE (w/w) ratios of 100:75, 100:50, and 100:25 and characterized for their morphological/structural features, physicochemical characteristics, and drug loading, entrapment, and release. Nanoparticle suspensions in distilled water (12.5% w/v) were applied (1 min) to demineralized dentin specimens by simulating pulpal pressure. The nanoparticle delivery was investigated by scanning electron microscopy (SEM)/transmission electron microscopy (TEM), and the GSE release from the delivered nanoparticles was further characterized. The variations in surface and bulk mechanical properties were characterized in terms of reduced elastic-modulus, hardness, nanoindentation testing, and apparent elastic-modulus with a storage time up to 3 mo. Hydroxyproline release with exposure to collagenase up to 7 d was estimated. An etch-and-rinse dentin adhesive was applied to investigate the morphology of the resin-dentin interface after nanoparticle delivery. Treatment with the GSE-loaded nanoparticles enhanced the collagen fibril structural resistance, reflected from the TEM investigation, and improved the biomechanical and biochemical stability of demineralized dentin. Nanoparticles having PLGA/GSE of 100:75 (w/w) showed the highest cumulative GSE release and were associated with the best improvement in biodegradation resistance. TEM/SEM showed the ability of the nanoparticles to infiltrate dentinal tubules' main and lateral branches. SEM revealed the formation of a uniform hybrid layer and well-formed resin tags with the presence of numerous nanoparticles located within the dentinal tubules and/or attached to the resin tag. This study demonstrated the potential significance of delivering collagen crosslinkers loaded into biodegradable polymer nanoparticles through the dentinal tubules of demineralized dentin on the biodegradation resistance.

Influence of EDC on Dentin-Resin Shear Bond Strength and Demineralized Dentin Thermal Properties

This study aimed to evaluate the bonding strength and thermal properties of demineralized dentin with and without EDC treatment. Sound human molars were randomly divided into seven treatment groups (n = 20): control, 80% ethanol, and five EDC ethanol solutions (0.01–1.0 M). In each group, 16 samples were used for bond strength assessment and 4 samples were used for scanning electron microscopy (SEM) analysis. A further 70 intact molars were used to obtain a fine demineralized dentin powder, treated with the same solutions and were evaluated the crosslink degree by ninhydrin test and denaturation temperature (T_d) by differential scanning calorimetry. EDC-treated specimens (<1.0 M) had a higher bond strength, especially 0.3 and 0.5 M group, than the control counterpart. There was a significant drop in bond strength of 1.0 M EDC group. SEM revealed a homogeneous and regular interface under all treatments. EDC treatment significantly increased the demineralized dentin cross-link degree and T_d compared with the control and ethanol treatments. The 0.3 and 0.5 M treatments showed the highest cross-link degree and T_d. In terms of mechnical and theramal properties consideration, 0.3 and 0.5 M EDC solutions may be favorable for when applied with etch-and-rinse adhesives, but it is still needed further long-term study.