Collagen cross-linkers on dentin bonding: Stability of the adhesive interfaces, degree of conversion of the adhesive, cytotoxicity and in situ MMP inhibition

Performance of self-etching adhesives on caries-affected primary dentin treated with glutaraldehyde or silver diamine fluoride

OBJECTIVES

to evaluate the quality and stability of adhesive interfaces established by self-etching adhesives on caries-affected primary dentin (CAD) treated with glutaraldehyde (GA) or silver diamine fluoride (SDF).

METHODS

42 primary molars were exposed to a microbiological caries-inducing protocol and divided into 6 groups according to the adhesive system (Clearfil SE - CL or FL Bond II - FL) and pretreatment (water, GA or SDF) applied on CAD. One tooth from each group was analyzed for surface modification using infrared spectroscopy. Crowns were restored with resin composite (n = 36) and cut into beams and slices. The beams were subjected to microtensile testing, Raman spectroscopy and SEM after 24 h and 6 months of storage. The slices were analyzed using Micro-Raman spectroscopy to determine the diffusion zone thickness (DZ) in each period. Data were analyzed by ANOVA and Tukey or Kruskal-Wallis and Dunn tests (α = 0.05%).

RESULTS

SDF reduced the immediate bond strength for both adhesives. The control groups showed a decrease in BS after 6 months in artificial saliva. GA increased immediate DZ for FL, while SDF had the opposite effect on CL. GA decreased the DZ for FL at 6 months. There was a predominance of adhesive failures with areas of cohesive dentin fractures within control groups.

SIGNIFICANCE

Modifications caused by dentin surface treatments may directly affect the performance of adhesive systems and the quality and stability of adhesive restorations.

Enhancing dentin bonding through new adhesives formulations with natural polyphenols, tricalcium phosphate and chitosan

OBJECTIVES

The aim of the study was to develop new adhesive formulations that include natural polyphenols extracted from green tea (GTE), tricalcium phosphate (TCP) and chitosan to improve dentin bonding characteristics and cytotoxicity.

METHODS

Four experimental adhesives were formulated under laboratory conditions. The groups differed in the integration of either GTE and/or TCP + chitosan. The four experimental and one clinically proven reference adhesive underwent shear bond testing after 24 h and 6 months of aging (n = 200) with subsequent fractographic analysis. Bond morphology was analyzed under a scanning electron microscope. The presence of phenolic compounds was validated by high performance liquid chromatography. Cytotoxicity was assessed by the WST-1 colorimetric assay on eluates up to 6 months. Statistical analysis was performed by one- and three-way ANOVA, Games-Howell and Tukey's post-hoc test as well as multiple students t-tests (α = 0.05). Weibull analysis was further conducted.

RESULTS

The addition of GTE into the bonding agent did show immediate (p = 0.023, p = 0.013) and long-term (p < 0.001) effects on bond strength. After 24 h, GTE doped groups performed equal to the reference (p = 0.501, p = 0.270) and TCP and chitosan displayed improvements in reliability (m=4.0, m=4.3). Bond strength is retained after aging by adding GTE (p = 0.983). The additional presence of TCP and chitosan reduces it (p = 0.026). Excluding cohesive and mixed failures, the reference adhesive performed statistically equal to three of the four experimental groups. No long-term cytotoxic effects were shown.

SIGNIFICANCE

The integration of GTE can enhance bond strength and a calcium source helps to improve immediate bond reliability.

Tissue Stabilization, Bacterial Adhesion, and Stem Cell Viability in Trans-cinnamaldehyde-conditioned Dentin

INTRODUCTION

This laboratory study aimed to evaluate the effect of trans-cinnamaldehyde (TC) conditioning on dentin tissue stabilization, bacterial adhesion, and stem cell toxicity.

METHODS

Dentin beams (n = 204) from extracted human molars were demineralized in phosphoric acid and treated with TC (2.5, 5, and 7.5%), 50% ethanol-water mixture (vehicle control) or 2.5% glutaraldehyde (GA) (positive control) for 30 minutes. Demineralized but untreated specimens served as the negative control. After treatment, collagen crosslinking was characterized by measuring the elastic modulus (Er) and hardness (n = 5). Biodegradation resistance was examined by determining the loss of dry mass (n = 8), hydroxyproline release (n = 4) and scanning electron microscopy (n = 2), after exposure to bacterial collagenase. Inhibition of bacterial adhesion was investigated by colony counting assay (n = 12) and scanning electron microscopy (n = 2). Viability of stem cells of the apical papilla on TC-conditioned dentin was determined using the Cell Counting Kit-8 assay (n = 8). Data were statistically analyzed using one-way analysis of variance (ANOVA) test followed by Dunnett's multiple comparisons at a significance level of 5%.

RESULTS

TC-conditioned dentin showed a concentration-dependent increase in Er and hardness. The Er and hardness of 5% and 7.5% TC-conditioned dentin were significantly greater than that of the negative control and vehicle control groups (P < .05). There was no significant difference in the biodegradation resistance between GA and 5% TC-conditioned dentin (P > .05). TC-conditioned dentin showed a well-preserved collagen fibril network with clear cross-banding, comparable to GA-conditioned dentin. All concentrations of TC inhibited bacterial adhesion on dentin, significantly greater than the negative control (P < .05). There was no reduction in viability of stem cells of the apical papilla viability on TC-conditioned dentin compared to the negative control (P > .05).

CONCLUSIONS

TC conditioning stabilized the dentin and protected it from enzymatic degradation. TC prevented bacterial adhesion on the dentin but maintained stem cell viability.

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.

Effect of etchant containing an Urushiol monomer from lacquer sap on dentin biostability and bonding performance

Objectives: This study aimed to evaluate the effectiveness of urushiol as an additive to surface acid etchant on dentin structure, by assessing the biostability of dentin, and determine the bonding strengths of dentin and enamel to the composite in the complicated oral microecology. Methods: Etchants with different concentrations of urushiol (0.5, 1, or 3 wt%) were formulated and tested for their bonding performance. Demineralized dentin beams that were etched with experimental etchants were incubated in simulated body fluid solutions by evaluating the weight decrement after 1 month. The effects of urushiol on dentin and matrix metalloproteinases were confirmed by scanning electron microscopy (SEM). Moreover, the antibiotic actions of urushiol on the common cariogenic bacteria Streptococcus mutans, Streptococcus sanguinis, and Streptococcus gordonii as well as the biofilm were evaluated, and its effect on bacterial morphology was observed by scanning electron microscopy. Finally, enamel and dentin specimens were prepared from human molars to determine the depth of demineralization by the etchants and the relationship with the resin bond strengths to enamel and dentin (μTBS) and the morphology of the bonding interface. Results: Urushiol could interact with dentine and inhibit collagenase activity, resulting in biostable dentine. The application of the etchants containing 0.5, 1, or 3 wt% urushiol significantly improved the durability of the dentin bonding interface with its instinctive antibacterial property (p < 0.05). Conclusion: Urushiol not only improves dentin stability by interacting with collagen and inactivating MMP activity but also plays a role in the antibacterial effects in the complicated oral microecology. The effectiveness of urushiol etchant prolongs the longevity of bonded dental restorations without compromising clinical operation time.

Impact of Dentine Pretreatment with Matrix Metalloproteinase Inhibitors on Bond Strength of Coronal Composite Restorations: A Systematic Review and Meta-analysis of In Vitro Studies

Matrix metalloproteinase (MMP) enzymes participate in collagen matrix degradation, including in dentine, potentially compromising bond strength. Therefore, MMP inhibitors have been hypothesized to improve restoration bond strength and stability. This systematic review aimed to evaluate the influence of different MMP inhibitors applied as dentine surface pretreatments on the immediate (24 hours) and longer term (months) bond strength of direct coronal composite restorations. This systematic literature review followed the Preferred Reporting Items for Systematic Review and Meta-analyses (PRISMA) statement. A systematic literature search of three databases (Ovid MEDLINE, Ovid Embase, and Google Scholar) was conducted independently by two reviewers from inception to April 2022. An adapted quality assessment tool was independently applied by two reviewers for risk of bias assessment. RevMan v5.4 software was used for meta-analyses. A randomeffectsmodel was used to generatemean differences with 95% confidence intervals for treatment and control comparisons. The Q-test and I2-test were used to test for heterogeneity. The proportion of total variance across studies attributable to heterogeneity rather than chance was calculated. Overall effects were tested using the Z-test, while subgroup differences were tested using Chi-squared tests. Of 934 studies, 64 studies were included in the systematic review and 42 in the meta-analysis. Thirty-one MMP inhibitors were reported, three of which were included in the meta-analysis: 2% chlorhexidine (CHX), 0.3M carbodiimide (EDC), and 0.1% riboflavin (RIBO). Pretreatment with 2% CHX for 30 and 60 seconds did not significantly improve bond strength compared with controls either immediately or after long-termageing. However, pretreatment with 0.3MEDC and 0.1% RIBO (but not CHX) significantly improved bond strength compared with control groups both immediately and over time. Most studies showed a medium risk of bias. These in vitro findings pave the way for rationale clinical trialing of dentine surface pretreatment with MMP inhibitors to improve clinical outcomes.

Application of modified aldehyde compounds in self-etching bonding of dentin

OBJECTIVE

The aim of this study was to evaluate the ability of 4-formylphenyl acrylate (FA) to enhance the bond strength and stabilize the resin-dentin bonding interface of universal adhesives in self-etching mode over time.

METHODS

Different concentrations of FA (1%, 3%, 5%, 7%, 9%) were prepared as primer. The optimal group was selected according to degree of conversion of 2 universal adhesives (Single Bond Universal (SBU)/All-Bond Universal (ABU)), and grouped according to the pre-treatment time (30s, 1min, 2min). The micro-tensile strength before and after 10,000 times thermocycling aging was used to evaluate the bonding performance.

RESULTS

The 1min application of FA (5%) increased the conversion rate of the adhesive. The expressions of microtensile bond strength and nanoleakage in the FA treatment group did not decrease significantly compared with their immediate values even after 10,000 thermocycling of aging. In situ zymography results showed that the hydrolytic activity of endogenous proteins decreased significantly in FA-1min group.

CONCLUSIONS

Treatment by FA primer can effectively enhance the bond stability at the bonding interface.

CLINICAL RELEVANCE

FA can be used as a functional monomer in self-etching bonding system to dentin, which not only had high biocompatibility, but also can show good collagen cross-linking ability within clinically acceptable application time.

Glutaraldehyde-based desensitizers' influence on bonding performances and dentin enzymatic activity of universal adhesives

OBJECTIVES

To evaluate the influence of two glutaraldehyde-based desensitizers (L: GLUMA Desensitizer, Heraeus Kulzer and G: GLUMA Desensitizer PowerGel) prior to the adhesive procedures on microtensile bond strength (µTBS) to dentin and endogenous enzymatic activity.

METHODS

Noncarious human third molars (N = 48) were cut to expose middle coronal dentin. Six experimental groups were formed according to the dentin pre-treatment (L or G) and the universal adhesives (IBU - iBond universal, Kulzer or AU - Adhese Universal, Ivoclar Vivadent) used in the self-etch mode (n = 8): 1) L/IBU; 2) G/IBU; 3) IBU; 4) L/AU; 5) G/AU; 6) AU. Specimens were cut into sticks and stressed until failure after 24 h (T0) or 1 yr of aging (T12). Additional 4 teeth were used for in situ zymography evaluation and data were statistically analyzed (α = 0.05).

RESULTS

Dentin pre-treatment, adhesive and aging statistically influenced bond strength and enzymatic activity (P<0.001). AU demonstrated higher bond strength values than IBU (P<0.001). The L resulted in higher bond strength compared to the G and control groups (P<0.001). aging statistically influenced bonding performance, especially when no dentin pre-treatment was performed (P<0.001). In situ zymography revealed that at baseline the control groups exhibited lower interfacial fluorescence compared to the experimental groups, irrespective of the adhesive used (P<0,001). However, after 1 yr of artificial storage, no differences were found among the groups (P>0.05).

CONCLUSIONS

Glutharldeadeyde-based products increased bond strength and determined a stabilization of the adhesive interface over time apparently not related to the MMPs inhibition.

CLINICAL SIGNIFICANCE

The results of this in vitro study suggest that the application of glutaraldehyde-based desensitizers prior to the adhesive procedures when associated with universal adhesives could result in increased bond strength and stabilization of the adhesive interface over time.

EDTA-functionalized silica nanoparticles as a conditioning agent for dentin bonding using etch-and-rinse technique

OBJECTIVE

This study investigated the possibility of using ethylenediaminetetraacetic acid functionalized silica nanoparticles (EDTA-SiO₂) as a dentin-conditioning agent using etch-and-rinse technique to promote the durability of dentin bonding.

METHODS

The SiO₂-EDTA were synthesized by N- [(3- trimethoxysilyl) propyl] ethylenediamine triacetic acid (EDTA-TMS) and SiO₂ (50 nm), then characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The capacity of SiO₂-EDTA to chelate calcium ions from dentin was examined by inductively coupled plasma-optic emission spectrometry (ICP-OES). The dentin surfaces conditioned with SiO₂-EDTA were detected by field emission scanning electron microscopy (SEM), TEM and microhardness testing. For dentin bonding, dentin surfaces were adopted wet- or dry-bonding technique and bonded with adhesive (Adper^TM Single Bond2) and applied composite resin (Filtek Z350) on them. The durability of dentin bonding was evaluated by mircotensile bond strength test, in-situ zymography and nanoleakage testing.

RESULTS

FTIR, TGA and XPS results showed that SiO₂-EDTA contained N element and carboxyl groups. SEM, TEM and microhardness results indicated that SiO₂-EDTA group created extrafibrillar demineralization and retained more intrafibrillar minerals within dentin surface. In the dentin bonding experiment, SiO₂-EDTA group achieved acceptable bond strength, and reduced the activity of matrix metalloproteinase and nanoleakage along bonding interface.

CONCLUSION

It was possible to generate a feasible dentin conditioning agent (SiO₂-EDTA), which could create dentin extrafibrillar demineralization and improve dentin bond durability.

CLINICAL SIGNIFICANCE

This study introduces a new dentin conditioning scheme based on SiO₂-EDTA to create extrafibrillar demineralization for dentin bonding. This strategy has the potential to be used in clinic to promote the life of restoration bonding.

Degradation and Failure Phenomena at the Dentin Bonding Interface

Damage in the bonding interface is a significant factor that leads to premature failure of dental bonded restorations. The imperfectly bonded dentin-adhesive interface is susceptible to hydrolytic degradation and bacterial and enzyme attack, severely jeopardizing restorations' longevity. Developing caries around previously made restorations, also called "recurrent or secondary caries," is a significant health problem. The replacement of restorations is the most prevailing treatment in dental clinics, leading to the so-called "tooth death spiral". In other words, every time a restoration is replaced, more tooth tissue is removed, increasing the size of the restorations until the tooth is eventually lost. This process leads to high financial costs and detriment to patients' quality of life. Since the complexity of the oral cavity makes prevention a challenging task, novel strategies in Dental Materials and Operative fields are required. This article briefly overviews the physiological dentin substrate, features of dentin bonding, challenges and clinical relevance. We discussed the anatomy of the dental bonding interface, aspects of the degradation at the resin-dentin interface, extrinsic and intrinsic factors affecting dental bonding longevity, perspectives on resin and collagen degradation and how these subjects are connected. In this narrative review, we also outlined the recent progress in overcoming dental bonding challenges through bioinspiration, nanotechnology and advanced techniques to reduce degradation and improve dental bonding longevity.

Are universal adhesives in etch-and-rinse mode better than old 2-step etch-and-rinse adhesives? One-year evaluation of bonding properties to dentin

OBJECTIVES

This study compared the bonding properties of dentin of three 2-step etch-and-rinse adhesives (2-ERAs) to those of three universal adhesives (UAs) applied with an etch-and-rinse strategy (ER), immediately and after 1 year of water storage.

METHODS

Sixty caries-free molars were divided into 6 groups according to the adhesive systems used (n = 10). The 2-ERA systems included were: 1) Adper Single Bond 2 (SB), 2) Tetric N-Bond (TB), and 3) Ambar (AM); and the UAs systems were: 4) Single Bond Universal (SBU) 5) Tetric N-Bond Universal (TBU), and 6) Ambar Universal (AMU). The occlusal third of each tooth was removed and the adhesives were applied. After the composite build-up, specimens were sectioned and tested for microtensile bond strength (µTBS) and nanoleakage (NL) immediately and after 1 year of water storage. In situ degree of conversion (DC) was only evaluated in the immediate time. For water sorption (WS), solubility (SO), and mass change (MC) tests, 48 disk-shaped specimens were prepared (n = 8) and assessed according to ISO 4049:2009.

RESULTS

UAs showed higher µTBS and lower NL values than 2-ERAs did after 1 year of water storage (p = 0.001). Regarding DC, 2-ERAs showed higher DC values than UAs (p = 0.001). Regarding WS, 2-ERAs showed higher WS values than those of UAs (p = 0.00001), except for AM and AMU. Lower WS was observed for AM than for other 2-ERAs (p = 0.00001).

CONCLUSION

The use of UAs applied with the ER strategy seems to be a more effective technique for maintaining adhesion to dentin substrate than 2-ERAS.

CLINICAL SIGNIFICANCE

This study may support clinicians in selecting the most adequate adhesive system to be used in ER strategy in dentin, demonstrating that UAs were more effective, considering the longevity of the resin restorations.

Effect of polyhydroxy-terminated PAMAM dendrimer on dentin matrix metalloproteinases within the hybrid layers

BACKGROUND

Intrafibrillar remineralization within the hybrid layers (HLs) has recently attracted extensive attention in achieving durable resin-dentin bonds. The polyhydroxy-terminated poly(amidoamine) dendrimer (PAMAM-OH) at fourth generation becomes a desirable candidate to induce intrafibrillar remineralization to protect exposed collagen fibrils within HLs based on the size exclusion effect of fibrillar collagen. However, the remineralization process in vivo is time-consuming, during which the exposed collagen fibrils are vulnerable to enzymatic degradation, resulting in unsatisfactory remineralization. Thereby, if PAMAM-OH itself possesses concomitant anti-proteolytic activity during the induction of remineralization, it would be very beneficial to obtain satisfactory remineralization.

METHODS

Binding capacity tests using adsorption isotherm and confocal laser scanning microscopy (CLSM) were performed to assess if the PAMAM-OH had adsorption capacity on dentin. Anti-proteolytic testings were detected by MMPs assay kit, in-situ zymography and ICTP assay. Adhesive infiltration of resin-dentin interface and tensile bond strength before and after thermomechanical cycling were implemented to assess if the PAMAM-OH adversely affected resin-dentin bonds.

RESULTS

Anti-proteolytic testings performed using MMPs assay kit, in-situ zymography and ICTP assay indicated that PAMAM-OH inhibited exogenous soluble MMP-9 as well as had inhibitory effect on the endogenous proteases. Adhesive infiltration of resin-dentin interface and tensile bond strength before and after thermomechanical cycling were implemented to indicate that the PAMAM-OH pretreatment had no adverse effects on immediate dentin bonding and prolonged the durability of resin-dentin bonds.

CONCLUSIONS

PAMAM-OH possesses anti-proteolytic activity and prevents exposed collagen fibrils within HLs from degradation, which lays the foundation for the satisfactory intrafibrillar remineralization induced by PAMAM-OH within HLs to achieve durable resin-dentin bonds in the next work.

Effects of Riboflavin Collagen Crosslinker on Dentin Adhesive Bonding Efficiency: A Systematic Review and Meta-Analysis

The aim of this study was to evaluate published data regarding riboflavin (RF) as a cross-linker for improved adhesive bond strength to dentin and to analyze previous studies for optimal concentration of riboflavin range suitable for dentin bond. Saliva and distilled water were used as storage media and aging time was 24 h and 6 months. Results of meta-analysis were synthesized using a statistical method of inverse variance in random effects with a 95% Confidence Interval (CI). Cochrane review manager 5.4.1 was used to determine results of the meta-analysis. In total, 3172 articles were found from search databases "PubMed", "Scopus", and "Google Scholar". Six of the fifteen studies were eligible for meta-analysis. Micro tensile strength shows significant improvement with the addition of riboflavin (p < 0.05) compared to without the addition of riboflavin from with 95% CI. A significant difference has been found in micro tensile bond strength between use of the riboflavin cross-linker and without use of the riboflavin crosslinker in the dentin adhesive system. With a 95% confidence interval (CI), the I² for micro tensile strength was 89% with strong heterogeneity, Chi² = 44.76, df = 5 (p < 0.00001), and overall effect size is Z = 2.22 (p = 0.03) after immediate aging. Chiang et al. 2013 shows maximum mean differences which is 38.50 [17.93-59.07]. After 6 months of aging in distilled water or artificial saliva micro tensile bond strength has been increased with the addition of riboflavin (p < 0.05). It can be clearly seen that pooled effect and 95% CI did not cross the line of no effect. With a 95% confidence interval (CI), the I² for micro tensile strength was 96% with strong heterogeneity, Chi² = 117.56, df = 5 (p < 0.00001), and overall effect size is Z = 2.30 (p = 0.02). Subgroup analysis proved a similar effect of distilled water and artificial saliva as storage media on micro tensile bond strength after incorporating riboflavin as a collagen crosslinker. An artificial saliva aged forest plot also showed considerable heterogeneity with I² = 96%; Tau² = 257.32; Chi² = 94.37; df = 2 (p < 0.00001); test for overall effect, Z = 1.06 (p = 0.29). Riboflavin prior to or with bonding is recommended to improve the bonding of different adhesive systems.

Effect of natural antioxidants on bond strength recovery of resin-modified glass ionomers to the NaOCl-affected pulp chamber dentin

OBJECTIVE

This study evaluated the effect of two natural antioxidants on the compromised bond strength of a resin-modified glass ionomer (RMGI) to the sodium hypochlorite (NaOCl)-affected pulp chamber dentin.

METHODS

Forty-two sound third molars were split into halves. The exposed pulp chamber dentin was ground to provide the flat dentin surfaces and divided into seven groups (n = 12), according to the solutions used for immersion: (1) Control, distilled water; (2) NaOCl, 5.25% NaOCl for 20 min; (3) NaOCl/Ethylenediaminetetraacetic acid (EDTA); 5.25% NaOCl for 20 min + 17% EDTA for 1 min; (4) NaOCl/TA, 5.25% NaOCl + 10% tanic acid (TA) for 5 min; (5) NaOCl/EDTA/TA, 5.25% NaOCl + 17% EDTA + 10% TA for 5 min; (6) NaOCl/PA, 5.25% NaOCl+ 10% proanthocyanidin for 5 min; and (7) NaOCl/EDTA/PA, 5.25% NaOCl+ 17% EDTA + 10% PA for 5 min. The RMGI was bonded on the treated dentin using a Tygon tube. After 24 h of storage, microshear bond strength (µSBS) was tested. Data in MPa were submitted to one-way analysis of variance and Tamhane test.

RESULTS

NaOCl significantly decreased the µSBS; NaOCl/EDTA and NaOCl/TA significantly increased the µSBS, higher than the control group (p < .05); and in the NaOCl/EDTA/TA group, the increased bond strength was at the level of the control group (p > .05). NaOCl/PA and NaOCl/EDTA/PA and NaOCl groups had comparable µSBS.

CONCLUSION

TA could be suggested to provide effective bonding of RMGI and immediate sealing of the pulp chamber dentin after NaOCl irrigation.

Effect of dentin biomodification using natural collagen cross-linkers on the durability of the resin-dentin bond and demineralized dentin stiffness

OBJECTIVE

The purpose of this study was to evaluate the effect of using natural cross-linkers as sumac and curcumin on the durability of the resin-dentin bond and stiffness of demineralized dentin matrix.

METHODS

Thirty sound molars were divided into 5 groups: Control (CO), Grape Seed extract (GSE), Cacao seed extract (CSE), Sumac extract (SE) and Curcumin extract (CE). The teeth had their coronal dentin exposed, etched, and pre-treated for 1 min with the extracts. Teeth were then bonded using Single-Bond II adhesive and 4 mm composite was built up on dentin surface. Teeth were sectioned into 1 × 1 × 8mm beams and their micro-tensile bond strength (μTBS) was tested after 24 h and 6 months of water storage. For stiffness testing, 15 teeth were sectioned to obtain dentin beams (1 × 1 × 6.5 mm), the beams were demineralized in 10% phosphoric acid then rinsed and divided into 5 groups. Beams were then immersed in their respective extract solution for 1 min after which they were subjected to a 3- point loading test using a universal testing machine to calculate their modulus of elasticity.

RESULTS

After 24 h, no significant difference in μTBS was shown between all groups. After 6 Months, GSE, CE, and SE showed significantly higher μTBS compared to CO (p ≥ 0.05). For the modulus of elasticity; only GSE showed a significantly higher modulus compared to other groups.

CLINICAL RELEVANCE

The application of grape seed extract, curcumin and sumac extract as dentin pre-treatments appear to be a promising approach to enhance the durability of the resin-dentin bond in a clinically relevant application time.

Effect of collagen cross-linkers on dentin bond strength: A systematic review and network meta-analysis

Objective: This study aimed to evaluate the role of collagen cross-linkers in the bonding performance of the resin-dentin interface through a systematic review and a network meta-analysis. Sources: The literature search was conducted in several databases like PubMed, EMBASE, Cochrane, Scopus and Web of Science from their inception till 30 April 2022. Study selection: The inclusion criteria consisted of in vitro studies evaluating the micro-tensile and micro-shear bond strengths of different cross-linkers acting on dentin. Bayesian network meta-analysis was conducted using RStudio. Data: Out of the 294 studies evaluated in the full-text analysis, 40 were included in the systematic review and meta-analysis. Most studies have used cross-linkers as primer (65.1%), followed by incorporating them into in adhesives and acid etching agents. The application methods of the adhesive system were classified as "etch-and-rinse (ER) adhesives" (77%) and "self-etching (SE) adhesives". Moreover, there were six types of cross-linkers in this presented review, of which the most numerous were polyphenols. Conclusion: Different application methods of cross-linkers, the long-term results showed that were only effective when used for longer durations, the immediate results were not statistically different. According to immediate and long-term results, etch-and-rinse (ER) adhesives showed a greater bonding performance than the control groups (p ≤ 0.05), whereas self-etching (SE) adhesives showed similar bond strength values (p ≥ 0.05). The result of network meta-analysis (NMA) showed that Dope like compound showed higher long-term bonding performance than other cross-linkers. Clinical significance: Long-term clinical studies may be needed to determine the effect of the cross-linkers on the bonding properties.

Torilis japonica Extract Suppresses the Induction of Atopic Inflammation

As one of the major intractable allergic disorders, atopic inflammation is commonly accompanied by itching, dry skin, and inflammation. Atopic inflammation deteriorates the quality of life and has no fundamental cure, so it is crucial to urgently explore and develop natural resources for long-term treatment without any side effects. This study aimed to verify Torilis japonica extract (TJE)'s relieving effect and mechanism against atopic inflammation using skin cells and skin equivalent models, as well as to investigate torilin's effect (obtained from TJE) and other unknown components as marker compounds. Torilin concentration was verified in TJE using high-performance liquid chromatography and analyzed the unknown components using nuclear magnetic resonance spectroscopy. Furthermore, TJE's cytotoxicity, regenerative effect, and cell cycle regulation effects were confirmed using skin cells with atopic inflammation (human dermal fibroblasts and HaCaT keratinocytes) by using TNF-α and IFN-γ treatments. Consequently, TJE was demonstrated to regulate TARC and CTACK expressions as chemokines and those of interleukin-4, -5, and -13 as cytokines related to atopic inflammation. TJE was further confirmed to affect the matrix metalloproteinase-1, -2, and -9 expressions, which are essential in skin damage. Lastly, this study confirmed TJE's relieving effect against atopic inflammation through a 3D skin model and RhCE model using human dermal fibroblasts and HaCaT keratinocytes. These findings on atopic inflammation verified torilin's relieving effects and TJE's other components.

Effect of chitosan-oleuropein nanoparticles on dentin collagen cross-linking

BACKGROUND

The integrity and stability of collagen are crucial for the dentin structure and bonding strength at dentin-resin interface. Natural plant-derived polypehenols have been used as collagen crosslinkers.

OBJECTIVE

The aims of the study were to develop novel chitosan oleuropein nanoparticles (CS-OL-NPs), and to investigate the CS-OL-NPs treated dentin's the resistance to enzymatic degradation and mechanic property.

METHODS

CS-OL-NPs were developed using the ionotropic gelation method. Release and biocompatibility of the CS-OL-NPs were tested. Twenty demineralized dentin collage specimens were randomized into four interventions groups: A, Deionized Water (DW); B, 5% glutaraldehyde solution (GA); C, 1 mg/ml chitosan (CS); and D, 100 mg/L CS-OL-NPs. After 1-min interventions, dentin matrix were evaluated by the micro-Raman spectroscopy for the modulus of elasticity test. Collagen degradation was assessed using hydroxyproline (HYP) assay.

RESULTS

CS-OL-NPs were spherical core-shape with a size of 161.29 ± 8.19 nm and Zeta potential of 19.53 ± 0.26 mV. After a burst release of oleuropein in the initial 6 h, there was a long-lasting steady slow release. CS-OL-NPs showed a good biocompatibility for the hPDLSCs. The modulus of elasticity in the crosslinked groups were significantly higher than that in the control group (P< 0.05 for all). The specimens treated with CS-OL-NP showed a greater modulus of elasticity than those treated with GA and CS (P< 0.05 for both). The release of HYP in the crosslinked group was significantly lower than that in the non-crosslinked groups (P< 0.05 for all).

CONCLUSION

CS-OL-NPs enhanced the dentin mechanical property and resistance to biodegradation, with biocompatibility and potential for clinical application.

Salivary esterases dramatically reduce biostability of dentin collagen treated with galloylated polyphenols

OBJECTIVE

To investigate the effects of salivary esterases on biostability of collagen treated by galloylated polyphenols.

METHODS

Human dentin was microtomed into 6-μm-thick films, which were demineralized and treated for 60 s using solutions containing 0.6% and 2% of one of the crosslinkers: tannic acid (TAC), epigallocatechin gallate (EGCG), epigallocatechin (EGC), and N-[3-dimethylaminopropyl]-N'-ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS), and for 1 h using EDC/NHS. Half of the treated and untreated (control) films were subjected to human saliva incubation. Collagen biostability was assessed via exogenous protease biodegradation by weight loss and hydroxyproline release, and endogenous MMPs by in situ zymography. The degradation products of galloylated polyphenols (TAC and EGCG) by saliva were monitored using proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). The esterase activity of saliva induced by the crosslinkers was also assessed.

RESULTS

Collagen films treated with TAC and EGCG exhibited significantly improved biostability (p < 0.05); however, the enhanced biostability was severely reduced after saliva incubation (p < 0.001). For EDC/NHS treated collagen, saliva incubation showed negligible effect on the biostability. 1H NMR studies confirmed the esterase-catalyzed hydrolysis of the galloyl. GPC measurements showed decreased molecular weight of TAC in saliva indicating its chemical degradation. Both TAC and EGCG showed much higher esterase activity than other treatment groups.

SIGNIFICANCE

The galloyl group plays important role in collagen crosslinking, inducing higher biostability. However, galloylated polyphenols crosslinked on collagen are highly susceptible to metabolism of human saliva by salivary esterase, dramatically compromising the enhanced biostability.

Evaluation of Bond Durability, Surface Morphology, and Remineralization at the Adhesive Interface with Dentin Bonding Agents Modified with Silica-doped Nanohydroxyapatite

Objectives

To compare and evaluate the bond durability, surface morphology, and remineralization of the adhesive layer with newer adhesive systems modified with novel bioactive nanoparticles.

Methodology

Bonding agents evaluated in this study include (a) Conventional dentin bonding agent (CN-DBA) (b) Nanohydroxyapatite (nanoHAP) incorporated dentin bonding agent (NH DBA); (c) Silica doped nanohydroxyapatite (Si nanoHAP) incorporated dentin bonding agent (Si NH DBA). A total of 104 human dentin discs (5 mm × 5 mm × 2 mm) were sectioned. Elemental analysis (Ca/P ratio) and surface morphology of the adhesive layer with different dentin adhesives were evaluated under scanning electron microscopy with energy-dispersive X-ray analysis after speculated storage time of 1 day and 6 months. Microshear bond strength of adhesive restorations with different dentin adhesives was evaluated under universal testing machine and fractographic analysis under scanning electron microscope after speculated storage time of 1 day and 6 months. The results were analyzed using analysis of variance and post hoc analysis.

Results

Si-NH-DBA showed highest mean microshear bond strength for both 1 day and 6 months, which was significantly higher compared to conventional nanofilled dentin bonding agent (CN-DBA) and NH-DBA. Si-NH-DBA group showed only 10% reduction in bond strength after 6 months, which was less compared to that of other groups. Similarly, Si-NH-DBA showed higher remineralization with stellate-shaped crystals at the adhesive layer after 6 months with hydrolytic resistant hybrid layer, compared to CN-DBA and NH-DBA.

Conclusion

Silica-doped nanohydroxyapatite proved its efficiency on bond stability, remineralization, and hydrolytic resistance when incorporated into dentin bonding agents because of its bioactivity and carbonate-containing apatite-forming ability.

Dental Adhesives-Surface Modifications of Dentin Structure for Stable Bonding

The latest advancements in dentin bonding have focused on strategies to impair degradation mechanisms in order to extend the longevity of bonded interfaces. Protease inhibitors can reduce collagen degradation within the hybrid layer (HL). Collagen cross-linkers allow better adhesive infiltration and also inhibit proteases activity. Particles added to adhesive can promote mineral precipitation within the HL, reducing nanoleakage and micropermeability, besides possible antimicrobial and enzymatic inhibition effects. Most of these approaches are still experimental, and aspects of the adhesive under the clinician's control are still determinant for the long-term stability of adhesive restorations.

Role of Natural Cross Linkers in Resin-Dentin Bond Durability: A Systematic Review and Meta-Analysis

BACKGROUND

The role of endogenous Matrix Metallo Proteinases in resin dentin bond deterioration over time has been well documented. The present study aimed to systematically review the literature; in vitro and ex vivo studies that assessed the outcomes of natural cross-linkers for immediate and long-term tensile bond strength were included.

METHODS

The manuscript search was carried out in six electronic databases-PubMed/MEDLINE, LILACS, SciELO, Cochrane, Web of Science and DOAJ, without publication year limits. Only manuscripts in English (including the translated articles) were selected, and the last search was performed in December 2020. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was followed.

RESULTS

From the 128 potentially eligible studies, 48 full-text articles were assessed for eligibility. After eligibility assessment and exclusions, 14 studies were considered for systematic review and seven studies for meta-analysis. Amongst the selected studies for meta-analysis, three had a medium and four had a low risk of bias.

CONCLUSIONS

It was evidenced by the available data that Proanthocyanidin is the most efficient natural cross-linker to date, in preserving the bond strength even after ageing.

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.

Phosphoric acid containing proanthocyanidin enhances bond stability of resin/dentin interface

Proanthocyanidin (PA) is a promising dentin biomodifier due to its ability to stabilize collagen fibrils against degradation by matrix metalloproteinases (MMPs); however, the most effective protocol to incorporate PA into bonding procedures is still unclear. This study evaluated the effect of dentin biomodification with a PA acid etchant on MMP activity, adhesive interface morphology and resin-dentin microtensile bond strength. Sound extracted human molars were flattened to expose dentin and acid-etched for 15 s according to the groups: EXP - experimental phosphoric acid; EXP+PA - experimental phosphoric acid 10% PA; TE - total-etching system; SE - self-etching system. Samples were restored with composite resin and stored in distilled water (37ºC). MMP activity and interface morphology were analyzed after 24 h by in situ zymography (n=6) and scanning electron microscopy (n=3), respectively. The resin-dentin microtensile bond strength (μTBS) was evaluated after 24 h and 6 months storage (n=6). Significantly higher MMP activity was detected in etched dentin compared with untreated dentin (p<0.05), but no difference among acid groups was found. Resin tags and microtags, indicative of proper adhesive system penetration in dentinal tubules and microtubules, were observed along the hybrid layer in all groups. There was no difference in μTBS between 24 h and 6 months for EXP+PA; moreover, it showed higher long-term μTBS compared with TE and EXP (p<0.05). The results suggest that 15 s of biomodification was not sufficient to significantly reduce MMP activity; nonetheless, EXP+PA was still able to improve resin-dentin bond stability compared with total- and self-etching commercial systems.

Mussel-inspired monomer - A new selective protease inhibitor against dentine collagen degradation

OBJECTIVES

To evaluate the inhibitory effect of a novel mussel-inspired monomer (N-(3,4-dihydroxyphenethyl)methacrylamide (DMA) on the soluble and matrix-bound proteases.

METHODS

The inhibitory effect of DMA (0, 1, 5, and 10 mM) and 1 mM chlorhexidine (CHX) dissolved in 50% ethanol/water on soluble recombinant human matrix metalloproteinases (rhMMP-2, -8, and -9), as well as cysteine cathepsins (B and K) were evaluated using both fluorometric assay kits and molecular docking. The effect of CHX and DMA on matrix-bound proteases was examined by in situ zymography, and the fluorescence intensity and relative area were calculated by Image J software. All data obtained were analyzed by one-way ANOVA followed by Tukey test (α = 0.05).

RESULTS

The anti-proteolytic ability of DMA increased in a dose-dependent manner except that of rhMMP-9. Inhibitory effect of 1 mM DMA against rhMMP-2, - 8, - 9, as well as cathepsin B and K was all significantly lower than 1 mM CHX (p < 0.05). The molecular docking analysis was in good agreement with the experimental results, that the binding energy of DMA was lower than CHX for all proteases. In situ zymography revealed that all DMA- and CHX-treated groups significantly inactivated the matrix-bound proteases, with a dramatic reduction of the fluorescence intensity and relative area compared with the control group (p < 0.05).

SIGNIFICANCE

Under the prerequisite condition that the overall inhibitory performance on matrix-bound proteases was comparable by DMA and CHX, the more selective property of DMA could avoid inducing potential negative effects by suppressing MMP-9 when applied in dental treatment compared with CHX.

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.

Effects of Plant Extracts on Dentin Bonding Strength: A Systematic Review and Meta-Analysis

Objective: To systematically review in vitro studies that evaluated the effects of plant extracts on dentin bonding strength.

Materials and Methods: Six electronic databases (PubMed, Embase, VIP, CNKI, Wanfang and The Cochrane Library) were searched from inception to September 2021 in accordance with the Preferred Reporting Items for Systematic Reviews (PRISMA). In vitro studies that compared the performance of dental adhesives with and without the plant extracts participation were included. The reference lists of the included studies were manually searched. Two researchers carried out study screening, data extraction and risk of bias assessment, independently and in duplicate. Meta-analysis was conducted using Review Manager 5.3.

Results: A total of 62 studies were selected for full-text analysis. 25 articles used the plant extracts as primers, while five added the plant extracts into adhesives. The meta-analysis included 14 articles of in vitro studies investigating the effects of different plant extract primers on dentin bonding strength of etch-and-rinse and self-etch adhesives, respectively. The global analysis showed statistically significant difference between dental adhesives with and without plant extract primers. It showed that the immediate bond strength of dental adhesives was improved with the application of plant extract primers.

Conclusion: The application of proanthocyanidin (PA) primers have positive effect on the in vitro immediate bonding strength of dental adhesives irrespective of etch-and-rinse or self-etch modes.

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.

Tannic acid induces dentin biomineralization by crosslinking and surface modification

It is currently known that crosslinking agents can effectively improve the mechanical properties of dentin by crosslinking type I collagen. However, few scholars have focused on the influence of crosslinking agents on the collagen-mineral interface after crosslinking. Analysis of the Fourier transform infrared spectroscopy (FTIR) results showed that hydrogen bonding occurs between the tannic acid (TA) molecule and the collagen. The crosslinking degree of TA to collagen reached a maximum 41.28 ± 1.52. This study used TA crosslinked collagen fibers to successfully induce dentin biomineralization, and the complete remineralization was achieved within 4 days. The crosslinking effect of TA can improve the mechanical properties and anti-enzyme properties of dentin. The elastic modulus (mean and standard deviation) and hardness values of the remineralized dentin pretreated with TA reached 19.1 ± 1.12 GPa and 0.68 ± 0.06 GPa, respectively, which were close to those of healthy dentin measurements, but significantly higher than those of dentin without crosslinking (8.91 ± 1.82 GPa and 0.16 ± 0.01 GPa). The interface energy between the surface of collagen fibers and minerals decreased from 10.59 mJ m^-2 to 4.19 mJ m^-2 with the influence of TA. The current work reveals the importance of tannic acid crosslinking for dentin remineralization while providing profound insights into the interfacial control of biomolecules in collagen mineralization.

Captopril inhibits matrix metalloproteinase activity and improves dentin bonding durability

OBJECTIVES

We investigated the inhibitory effects of captopril on matrix metalloproteinases (MMPs) and its effect as a primer on dentin bonding durability.

MATERIALS AND METHODS

One hundred fifty human third molars were selected. Flat surfaces of the middle dentin were exposed, etched 15 s, and followed by pretreatment with a primer for 60 s, including distilled water (control, the negative control primer), 2% chlorhexidine digluconate (CHD, the positive control primer), and captopril solution. Inhibitory effects of primers on MMPs were evaluated by hydroxyproline and gelatinase activity tests. All primers were applied on dentin followed by bonding. Some of the samples were sliced into slabs, placed in a fluorescent solution containing gelatin, and incubated for in situ zymography. Some were cut into sticks, and after aging for 1 day, 12 months, or 24 months, microtensile bonding strength was tested. Some were cut into slabs, aged for 1 day, 12 months, or 24 months, and taken out for nanoleakage tests to reveal interface defects.

RESULTS

Hydroxyproline and gelatinase activity analyses showed that captopril exerted better inhibitory effects on MMPs, relative to 2% CHD (p < 0.05). A 0.2% captopril aqueous solution (0.2% CapW) was chosen to apply to the dentin. In situ zymography showed that inhibitory effects of captopril on gelatinase were significantly higher compared to 2% CHD (p < 0.01). Microtensile strength revealed that the bonding effects of the 0.2% CapW group lasted longer, compared to the control and 2% CHD groups (p < 0.05). Interface defects, detected by nanoleakage, were significantly reduced in the 0.2% CapW group, compared to the control and 2% CHD groups (p < 0.05).

CONCLUSIONS

Captopril inhibits dentin MMP activities and effectively improves dentin bonding durability.

CLINICAL RELEVANCE

Captopril is a promising dentin bonding primer for improving bonding durability.

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.

Effect of an extrafibrillar dentin demineralization strategy on the durability of the resin-dentin bond

OBJECTIVES

This study aimed to evaluate the potential of the extrafibrillar dentin demineralization strategy on the long-term dentin bond strength of an etch-and-rinse adhesive.

METHODS

A water-soluble glycol chitosan-EDTA (GCE), a chelating conditioner, was synthesized and subjected to size-exclusion dialysis to obtain molecules >40 kDa. The conjugation of EDTA to glycol chitosan was analyzed by Fourier transform infrared (FTIR) spectroscopy. Mid-coronal dentin surfaces of 80 teeth were either acid-etched with 35% phosphoric acid or conditioned with 25 mg/mL GCE (n = 40) and thoroughly water-sprayed before applying the etch-and-rinse adhesive Adper Single Bond Plus and placing Z250 composite resin (3 M Oral Care; St Paul, MN, USA). Resin-bonded specimens were prepared into beams with a cross-sectional area of about 0.9 mm² vertically through the resin-dentin interfaces before the microtensile bond strengths (MTBS) were determined immediately or after 3, 6, or 12 months of water storage. The resin-dentin interfaces were analyzed using transmission electron microscopy (TEM). The MTBS data were analyzed using two-way ANOVA followed by the LSD post-hoc multiple comparisons (P < 0.05).

RESULTS

FTIR spectra showed that EDTA was successfully conjugated to glycol chitosan. The phosphoric acid-etching group and GCE-conditioning group showed similar bond strength values after 24 h of water storage. The bond strength of the phosphoric acid-etching group after 12-month water aging was significantly reduced from 51.61 ± 3.30 MPa to 38.57 ± 4.81 MPa, while the bond strength of the GCE-conditioning group was not significantly reduced from 50.28 ± 3.62 MPa to 46.40 ± 4.71 MPa.The degradation of the hybrid layer could be detected in the phosphoric acid-etching group after 12 months of water aging, but not in the GCE-conditioning group.

CONCLUSION

The extrafibrillar dentin demineralization strategy using GCE conditioner could defy the hybrid layer degradation of the dentin bond after 12 months of water aging and enhance the dentin bond durability of the etch-and-rinse adhesive Adper Single Bond Plus.

A mussel glue-inspired monomer-etchant cocktail for improving dentine bonding

OBJECTIVES

The humid oral environment adversely affects the interaction between a functionalised primer and dentine collagen after acid-etching. Robust adhesion of marine mussels to their wet substrates instigates the quest for a strategy that improves the longevity of resin-dentine bonds. In the present study, an etching strategy based on the incorporation of biomimetic dopamine methacrylamide (DMA) as a functionalised primer into phosphoric acid etchant was developed. The mechanism and effect of this DMA-containing acid-etching strategy on bond durability were examined.

METHODS

Etchants with different concentrations of DMA (1, 3 or 5 mM) were formulated and tested for their demineralisation efficacy. The interaction between DMA and dentine collagen, the effect of DMA on collagen stability and the collagenase inhibition capacity of the DMA-containing etchants were evaluated. The effectiveness of this new etching strategy on resin-dentine bond durability was investigated.

RESULTS

All etchants were capable of demineralising dentine and exposing the collagen matrix. The latter strongly integrated with DMA via covalent bond, hydrogen bond and Van der Waals' forces. These interactions significantly improve collagen stability and inhibited collagenase activity. Application of the etchant containing 5 mM DMA achieved the most durable bonding interface.

CONCLUSION

Dopamine methacrylamide interacts with dentine collagen in a humid environment and improves collagen stability. The monomer effectively inactivates collagenase activity. Acid-etching with 5 mM DMA-containing phosphoric acid has the potential to prolong the longevity of bonded dental restorations without compromising clinical operation time.

CLINICAL SIGNIFICANCE

The use of 5 mM dopamine methacrylamide-containing phosphoric acid for etching dentine does not require an additional clinical step and has potential to improve the adhesive performance of bonded dental 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.

Shelf Life and Storage Conditions of Universal Adhesives: A Literature Review

This paper presents state of the art universal adhesive systems and the effect of shelf-life and storage conditions on their bond performance. Three topics are explored in this review: an introduction to the topic, the mechanisms responsible for the degradation of the hybrid layer, and the factors that play a role in the stability of universal adhesives. In addition, issues such as potential durability and clinical importance are discussed. Universal adhesive systems are promising but must be handled and stored according to the manufacturer's instructions, with careful attention given to the details of shelf-life and storage conditions for maximal success. It appears that the components of universal adhesives play an important role in their stability. Furthermore, HEMA-free formulations using methacrylamides lead to longer shelf-life. Further research is needed to prove these hypotheses.

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.

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.

Effect of chlorhexidine-loaded poly(amido amine) dendrimer on matrix metalloproteinase activities and remineralization in etched human dentin in vitro

To investigate the effect of chlorhexidine (CHX)-loaded carboxyl-terminated poly (amido amine) dendrimer (CHX-PAMAM-COOH) on matrix metalloproteinase (MMP) activities and remineralization in human dentin, CHX-PAMAM-COOH was prepared and characterized by Fourier-transform infrared spectroscopy. The inhibitory effects of CHX, PAMAM-COOH, and CHX-PAMAM-COOH on soluble recombinant human matrix metalloproteinase (rhMMP-2) and dentin-bound endogenous MMP activity were measured using an MMP Activity Assay Kit. In situ zymography was performed to evaluate the gelatinase activity in dentin pretreated with CHX, PAMAM-COOH, and CHX-PAMAM-COOH. The remineralization of etched dentin pretreated with CHX, PAMAM-COOH, and CHX-PAMAM-COOH was evaluated by field emission-scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS) after incubation in artificial saliva for 14 days. The results of the rhMMP-2 activity assay showed that the MMP-2 activity in the CHX-PAMAM-COOH group and the CHX group decreased significantly to 5.58 ± 0.85% (P < 0.05) and 4.86 ± 1.12% (P < 0.05), respectively, but that in the PAMAM-COOH group increased significantly to 213.38 ± 0.11% (P < 0.05). The results of total MMP activity and in situ zymography showed a significant reduction in endogenous gelatinase activity in dentin in the CHX-PAMAM-COOH group and the CHX group. The SEM and EDS results showed that rod-like crystals were formed on the etched dentin surface in the PAMAM-COOH group and the CHX-PAMAM-COOH group, and their Ca/P ratios were 1.73 and 1.71, respectively. In conclusion, CHX-PAMAM-COOH can inhibit dentin-bound endogenous MMPs and induce remineralization in etched dentin simultaneously. However, it is important to note that the catalytic role of PAMAM dendrimers may have an undesired excitatory effect on MMP activity, which cannot be ignored if PAMAM dendrimers were used alone in the oral environment.

MMP Inhibitors and Dentin Bonding: Systematic Review and Meta-Analysis

Objectives

Resin-dentin bond strength decreases over time. This reduction is related to the loss of hybrid layer integrity. Collagenolytic enzymes, especially matrix metalloproteinases (MMPs), are responsible for the degradation of the collagen matrix of the hybrid layer. Various MMP inhibitors with the ability to prevent enzymatic degradation have been identified. This study aimed to systematically review the literature for studies which evaluated the effect of MMP inhibitors on the immediate and aged dentin bond strengths. Study SelectionScreening and analysis were carried out by two reviewers. Two databases were searched, and from a total of 740 articles, 43 were accepted for full review. 21 articles with 0.2%–2% chlorhexidine (CHX) treatments were included for meta-analysis. A risk of bias assessment was performed on all studies chosen for meta-analysis. A variety of MMP inhibitors have been studied, CHX being the most widely used.

Conclusions

A clear trend for a lower loss of dentin bond strength was observed with different MMP inhibitors. In meta-analysis, no significant difference was seen between the CHX and control in the immediate bond strengths. Bond strengths in the CHX group were significantly higher than the control group after aging (P < 0.001). The percentage of fractures occurring at the adhesive interface increased after aging. Five out of 21 studies included in the meta-analysis had high and the rest medium risk of bias. More long-term studies with lower risks of bias should be carried out to increase the reliability of results. Clinical RelevanceThe use of MMP inhibition with chlorhexidine can be recommended to increase the longevity of resin-dentin bond strength.

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.

Antibacterial and Bonding Properties of Universal Adhesive Dental Polymers Doped with Pyrogallol

This study investigated the antibacterial activity, bond strength to dentin (SBS), and ultra-morphology of the polymer-dentin interface of experimental adhesive systems doped with pyrogallol (PY), which is a ubiquitous phenolic moiety that is present in flavonoids and polyphenols. A universal adhesive containing 4-META and 10-MDP was used in this study. PY behaves as an antioxidant and anti-cancerogenic agent and it was incorporated into the adhesive at different concentrations (0.5 and 1 wt.%). The antibacterial activity and SBS were analyzed and the results were statistically analyzed. The ultra-morphology of the polymer-dentin interface was assessed using scanning electron microscopy (SEM). At 24 h, a lower antibacterial activity was observed for the control adhesive compared to those with 0.5% and 1% PY. No difference was seen in SBS between the three groups at 24 h. After 6 months, the SBS of the 0.5% PY adhesive was significantly lower than the other tested adhesives. The specimens created with 1% PY adhesive presented a higher bond strength at six months compared with that found at 24 h. No morphological differences were found at the polymer-dentin interfaces of the tested adhesives. Pyrogallol may be incorporated into modern universal adhesive systems to preserve the polymer-dentin bonding interface and confer a certain degree of antibacterial activity.

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 side-group methylation on the performance of methacrylamides and methacrylates for dentin hybridization

The stability of the bond between polymeric adhesives to mineralized substrates is crucial in many biomedical applications. The objective of this study was to determine the effect of methyl substitution at the α- and β-carbons on the kinetics of polymerization, monomer hydrolytic stability, and long-term bond strength to dentin for methacrylamide- and methacrylate-based crosslinked networks for dental adhesive applications.

METHODS

Secondary methacrylamides (α-CH3 substituted=1-methyl HEMAM, β-CH3 substituted=2-methyl HEMAM, and unsubstituted=HEMAM) and OH-terminated methacrylates (α- and β-CH3 mixture=1-methyl HEMA and 2-methyl HEMA, and unsubstituted=HEMA) were copolymerized with urethane dimethacrylate. The kinetics of photopolymerization were followed in real-time using near-IR spectroscopy. Monomer hydrolysis kinetics were followed by NMR spectroscopy in water at pH 1 over 30 days. Solvated adhesives (40 vol% ethanol) were used to bond composite to dentin and microtensile bond strength (μTBS) measured after 24h and 6 months storage in water at 37°C.

RESULTS

The rate of polymerization increased in the following order: OH-terminated methacrylates≥methacrylamides>NH2-terminated methacrylates, with minimal effect of the substitution. Final conversion ranged between 79% for 1-methyl AEMA and 94% for HEMA. 1-methyl-HEMAM showed the highest and most stable μTBS, while HEMA showed a 37% reduction after six months All groups showed measurable degradation after up to 4 days in pH 1, with the methacrylamides showing less degradation than the methacrylates. Additionally, transesterification products were observed in the methacrylamide groups.

SIGNIFICANCE

Amide monomers were significantly more stable to hydrolysis than the analogous methacrylates. The addition of a α- or β-CH3 groups increased the rate of hydrolysis, with the magnitude of the effect tracking with the expected base-catalyzed hydrolysis of esters or amides, but opposite in influence. The α-CH3 substituted secondary methacrylamide, 1-methyl HEMAM, showed the most stable adhesive interface. A side reaction was observed with transesterification of the monomers studied under ambient conditions, which was not expected under the relatively mild conditions used here, which warrants further investigation.

Bond Strength of Universal Adhesives to Dentin: A Systematic Review and Meta-Analysis

Currently, the availability of a wide variety of universal adhesives makes it difficult for clinicians to choose the correct system for specific bonding situations to dentin substrate. This study aimed to determine whether there are any alternative techniques or additional strategies available to enhance the bond strength of universal adhesives to dentin through a systematic review and meta-analysis. Two reviewers executed a literature search up to September 2020 in four electronic databases: PubMed, ISI Web of Science, Scopus, and EMBASE. Only in vitro studies that reported the dentin bond strength of universal adhesives using additional strategies were included. An analysis was carried out using Review Manager Software version 5.3.5 (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, Denmark). The methodological quality of each in vitro study was assessed according to the parameters of a previous systematic. A total of 5671 potentially relevant studies were identified. After title and abstract examination, 74 studies remained in systematic review. From these, a total of 61 studies were included in the meta-analysis. The bond strength of universal adhesives to dentin was improved by the use of one of the following techniques: Previous application of matrix metalloproteinases (MMP) inhibitors (p < 0.001), prolonged application time (p = 0.007), scrubbing technique (p < 0.001), selective dentin etching (p < 0.001), non-atmospheric plasma (p = 0.01), ethanol-wet bonding (p < 0.01), prolonged blowing time (p = 0.02), multiple layer application (p = 0.005), prolonged curing time (p = 0.006), and hydrophobic layer coating (p < 0.001). On the other hand, the use of a shortened application time (p = 0.006), and dentin desensitizers (p = 0.01) impaired the bond strength of universal adhesives to dentin. Most of the analyses performed showed a high heterogenicity. The in vitro evidence suggests that the application of universal adhesives using some alternative techniques or additional strategies may be beneficial for improving their bonding performance to dentin. This research received no external funding. Considering that this systematic review was carried out only with in vitro studies, registration was not performed.

Reinforced Universal Adhesive by Ribose Crosslinker: A Novel Strategy in Adhesive Dentistry

Enzymatic biodegradation of demineralized collagen fibrils could lead to the reduction of resin-dentin bond strength. Therefore, methods that provide protection to collagen fibrils appear to be a pragmatic solution to improve bond strength. Thus, the study's aim was to investigate the effect of ribose (RB) on demineralized resin-dentin specimens in a modified universal adhesive. Dentin specimens were obtained, standardized and then bonded in vitro with a commercial multi-mode adhesive modified with 0, 0.5%, 1%, and 2% RB, restored with resin composite, and tested for micro-tensile bond strength (µTBS) after storage for 24 h in artificial saliva. Scanning electron microscopy (SEM) was performed to analyze resin-dentin interface. Contact angles were analyzed using a contact angle analyzer. Depth of penetration of adhesives and nanoleakage were assessed using micro-Raman spectroscopy and silver tracing. Molecular docking studies were carried out using Schrodinger small-molecule drug discovery suite 2019-4. Matrix metalloproteinases-2 (MMP-2) and cathepsin-K activities in RB-treated specimens were quantified using enzyme-linked immunosorbent assay (ELISA). The significance level was set at α = 0.05 for all statistical analyses. Incorporation of RB at 1% or 2% is of significant potential (p < 0.05) as it can be associated with improved wettability on dentin surfaces (0.5% had the lowest contact angle) as well as appreciable hybrid layer quality, and higher resin penetration. Improvement of the adhesive bond strength was shown when adding RB at 1% concentration to universal adhesive (p < 0.05). Modified adhesive increased the resistance of collagen degradation by inhibiting MMP-2 and cathepsin-K. A higher RB concentration was associated with improved results (p < 0.01). D-ribose showed favorable negative binding to collagen. In conclusion, universal adhesive using 1% or 2% RB helped in maintaining dentin collagen scaffold and proved to be successful in improving wettability, protease inhibition, and stability of demineralized dentin substrates. A more favorable substrate is created which, in turn, leads to a more stable dentin-adhesive bond. This could lead to more advantageous outcomes in a clinical scenario where a stable bond may result in longevity of the dental restoration.