Potential role of surface wettability on the long-term stability of dentin bonds after surface biomodification

Prodelphinidins enhance dentin matrix properties and promote adhesion to methacrylate resin

OBJECTIVE

Investigate the bioactivity and stability of Rhodiola rosea (RR) fractions as a natural source of prodelphinidin gallate (PDg) on dentin collagen via analysis of the viscoelastic and resin-dentin adhesive properties of the dentin matrix.

METHODS

The biomimicry and stability of RR subfractions (F1, F2, F3 and F4) with collagen were determined by dynamic mechanical analysis (DMA). DMA used a strain sweep method to assess the dentin matrix viscoelastic properties [storage (E'), loss (E"), and complex (E*) moduli and tan δ] after treatment, 7-, 30- and 90-days of storage in simulated body fluids (SBF). Resin-dentin interface properties were assessed after 1 and 90-days in SBF by microtensile bond strength test and confocal laser scanning microscopy. Data were analyzed using two and one-way ANOVA and post-hoc tests (α = 0.05).

RESULTS

RR fractions increased dentin matrix complex (96 - 69 MPa) and storage (95 - 68 MPa) moduli, compared to the control (∼9 MPa) in the ranking order: F2 ≥ F3 = F1 = F4 > control (p < 0.001). Treatment did not affect tan δ values. After 30- and 90-days, RR-treated dentin E*, E' and tan δ decreased (p < 0.001). F2 fraction yielded the highest microtensile bond strength (43.9 MPa), compared to F1, F4 (35.9 - 31.7 MPa), and control (29 MPa). RR-treated interfaces mediated stable surface modifications and enhanced collagen-methacrylate resin interactions at the bioadhesive interface.

SIGNIFICANCE

Prodelphinidin gallates from RR are potent and reasonably stable biomimetic agents to dentin. Higher potency of F2 fraction with the dentin matrix and the adhesive interface is associated with a degree of polymerization of 2-3 and gallo(yl) motifs.

Chemical Transformation of B- to A-type Proanthocyanidins and 3D Structural Implications

In nature, proanthocyanidins (PACs) with A-type linkages are relatively rare, likely due to biosynthetic constraints in the formation of additional ether bonds to be introduced into the more common B-type precursors. However, A-type linkages confer greater structural rigidity on PACs than do B-type linkages. Prior investigations into the structure-activity relationships (SAR) describing how plant-derived PACs with B- and complex AB-type linkages affect their capacity for dentin biomodification indicate that a higher ratio of double linkages leads to a greater interaction with dentin type I collagen. Thus, A-type PACs emerge as particularly intriguing candidates for interventional functional biomaterials. This study employed a free-radical-mediated oxidation using DPPH to transform trimeric and tetrameric B-type PACs, 2 and 4, respectively, into their exclusively A-type linked analogues, 3 and 5, respectively. The structures and absolute configurations of the semisynthetic products, including the new all-A-type tetramer 5, were determined by comprehensive spectroscopic analysis. Additionally, molecular modeling investigated the conformational characteristics of all trimers and tetramers, 1-5. Our findings suggest that the specific interflavan linkages significantly impact the flexibility and low-energy conformations of the connected monomeric units, which conversely can affect the bioactive conformations relevant for dentin biomodification.

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.

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.

Topographical Analysis of Human Enamel after Phosphoric Acid Etching and Er,Cr:YSGG Laser Irradiation

Introduction: Dental hard and soft tissues have been successfully removed by using the Er,Cr:YSGG laser, but there is a controversy about using lasers over conventional tooth surface preparation for bonding aesthetic restoration. Surface roughness and wettability in response to Er,Cr:YSGG laser irradiation are essential properties for restoration longevity. Methods: Fifty-one intact human premolars removed in orthodontic treatment were included in this study and divided into three groups (n=17). The first group (G1) was the control without surface treatment, (G2) was treated with 37% phosphoric acid for 15 seconds, and (G3) was treated with the Er,Cr:YSGG laser using the following parameters: 2 W or 3 W at 20 Hz, 10% air and water ratio using the MZ6 laser tip. The standardization of laser irradiation was accomplished by a computerized numerical control unit. The surface of the samples was evaluated by using a light microscope, profilometer, atomic force microscopy (AFM), SEM, and wettability tests. Results: The SEM examination revealed that the lased enamel surface was clean, irregular, and devoid of a smear layer, while the acid etch surface was relatively smooth and covered with a smear layer. The surface roughness of the lased enamel surface was significantly higher than that of other groups, according to the results of the profilometer as well as the AFM tests. The wettability test showed that the lased enamel surface recorded a significant reduction in the contact angle in comparison to the other groups. Conclusion: It can be concluded that the Er,Cr:YSGG laser can be used as an alternative and safe method to the acid-etching technique for surface treatment.

Enhancing adhesive-dentin interface stability of primary teeth: From ethanol wet-bonding to plant-derived polyphenol application

OBJECTIVES

To investigate whether the adhesive-dentin interface stability of primary teeth would be enhanced by epigallocatechin-3-gallate (EGCG) with ethanol wet-bonding.

METHODS

Non-caries primary molars were sliced to achieve a flat dentin surface and etched then randomly distributed into five groups in accordance with different treatments: group 1, no treatment; group 2, applying absolute ethanol wet-bonding for 60 s; groups 3-5, applying 0.1%, 0.5%, and 1% (w/v) EGCG-incorporating ethanol wet-bonding (0.1%, 0.5%, and 1% EGCG) for 60 s. Singlebond universal adhesive was then applied followed by resin composite construction. Microtensile bond strength, fracture mode, and nanoleakage at adhesive-dentin interface were evaluated after 24 h of water storage or 10,000 times of thermocycling. Zymography of hybrid layer, biofilm formation of Streptococcus mutans by CLSM, FESEM, and MTT test, and cytotoxicity by CCK-8 assay were respectively assessed.

RESULTS

Irrespective of thermocycling, the dentin bond strength was preserved with reduced nanoleakage in the 0.5% and 1% EGCG groups. Furthermore, the activity of endogenous proteases and the growth of Streptococcus mutans biofilm were inhibited after treatment with 0.5% and 1% EGCG/ethanol solutions (groups 4 and 5). CCK-8 results of the 0.1% and 0.5% EGCG groups showed acceptable biocompatibility.

CONCLUSIONS

Treatment by EGCG/ethanol solutions effectively enhanced the bond stability of primary teeth at the adhesive-dentin interface.

CLINICAL SIGNIFICANCE

Synergistic application of EGCG and ethanol wet-bonding suggesting a promising strategy to improve dentin bonding durability with bacterial biofilm inhibition, thus increasing resin-based restorations' service life in primary dentition.

Development and Assessment of Bioactive Coatings for the Prevention of Recurrent Caries Around Resin Composite Restorations

OBJECTIVE

To develop hydrophilic resin-based surface coatings containing bioactive agents (proanthocyanidins from Vitis vinifera and calcium silicate) and assess their protective role at the dentin and enamel margins of cervical restorations against demineralization under simulated conditions of high and low caries activity.

METHODS

Suboptimal resin composite restorations were placed on cervical cavity preparations on buccal and lingual surfaces of thirty-two molars after a contamination protocol. Groups were divided according to the resin-based coatings (n=8): resin without bioactive (C), resin containing 2% enriched Vitis Vinifera (VVE), and resin coat containing 10% calcium silicate (CaSi). The control group did not receive a resin (NC). To simulate a hydrolyticenzymatic degradation, specimens were subjected to 2-month storage followed by incubation in esterase at 37°C for 8 days. Afterwards, recurrent caries was induced using a pH-proteolytic model on half of the specimens to simulate high caries activity, and the other half remained in simulated body fluid (SBF). Measurements of cross-section microhardness (KHN) and infiltration with rhodamine-B assessed the micropermeability (MP), the extent of demineralization (ED), and the demineralization area (DA). Data were analyzed using analysis of variance (ANOVA) and post-hoc tests (α=0.05).

RESULTS

VVE and CaSi presented higher cross-sectional KHN values for enamel and dentin (p<0.001). The bioactive coatings resulted in lower MP, ED, and DA compared to NC (p<0.005) in enamel and dentin. CaSi coating preserved the enamel from demineralization (p=0.160).

CONCLUSION

The application of bioactive coatings represents a potential strategy to protect the enamel-dentin margins of resin restorations.

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

Objective

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

Materials and Methods

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

Results

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

Conclusions

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

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

OBJECTIVES

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

METHODS

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

RESULTS

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

SIGNIFICANCE

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

New perspective to improve dentin-adhesive interface stability by using dimethyl sulfoxide wet-bonding and epigallocatechin-3-gallate

OBJECTIVES

To determine whether dentin-adhesive interface stability would be improved by dimethyl sulfoxide (DMSO) wet-bonding and epigallocatechin-3-gallate (EGCG).

METHODS

Etched dentin surfaces from sound third molars were randomly assigned to five groups according to different pretreatments: group 1, water wet-bonding (WWB); group 2, 50% (v/v) DMSO wet-bonding (DWB); groups 3-5, 0.01, 0.1, and 1 wt% EGCG-incorporated 50% (v/v) DMSO wet-bonding (0.01%, 0.1%, and 1%EGCG/DWB). Singlebond universal adhesive was applied to the pretreated dentin surfaces, and composite buildups were constructed. Microtensile bond strength (μTBS) and interfacial nanoleakage were respectively examined after 24 h water storage or 1-month collagenase ageing. In situ zymography andStreptococcus mutans (S. mutans) biofilm formation were also investigated.

RESULTS

After collagenase ageing, μTBS of groups 4 (0.1%EGCG/DWB) and 5 (1%EGCG/DWB) did not decrease (p > 0.05) and was higher than that of the other three groups (p < 0.05). Nanoleakage expression of groups 4 and 5 was less than that of the other three groups (p < 0.05), regardless of collagenase ageing. Metalloproteinase activities within the hybrid layer in groups 4 and 5 were suppressed. Furthermore, pretreatment with 1%EGCG/DWB (group 5) efficiently inhibited S. mutans biofilm formation along the dentin-adhesive interface.

SIGNIFICANCE

This study suggested that the synergistic action of DMSO wet-bonding and EGCG can effectively improve dentin-adhesive interface stability. This strategy provides clinicians with promising benefits to achieve desirable dentin bonding performance and to prevent secondary caries, thereby extending the longevity of adhesive restorations.

Removal of water binding proteins from dentin increases the adhesion strength of low-hydrophilicity dental resins

OBJECTIVES

To investigate the role of proteoglycans (PGs) on the physical properties of the dentin matrix and the bond strength of methacrylate resins with varying hydrophilicities.

METHODS

Dentin were obtained from crowns of human molars. Enzymatic removal of PGs followed a standard protocol using 1 mg/mL trypsin (Try) for 24 h. Controls were incubated in ammonium bicarbonate buffer. Removal of PGs was assessed by visualization of glycosaminoglycan chains (GAGs) in dentin under transmission electron microscopy (TEM). The dentin matrix swelling ratio was estimated using fully demineralized dentin. Dentin wettability was assessed on wet, dry and re-wetted dentin surfaces through water contact angle measurements. Microtensile bond strength test (TBS) was performed with experimental adhesives containing 6% HEMA (H₆) and 18% HEMA (H₁₈) and a commercial dental adhesive. Data were statistically analyzed using ANOVA and post-hoc tests (α = 0.05).

RESULTS

The enzymatic removal of PGs was confirmed by the absence and fragmentation of GAGs. There was statistically significant difference between the swelling ratio of Try-treated and control dentin (p < 0.001). Significantly lower contact angle was found for Try-treated on wet and dry dentin (p < 0.002). The contact angle on re-wet dentin was not recovered in Try-treated group (p = 0.9). Removal of PGs significantly improved the TBS of H₆ (109% higher, p < 0.001) and H₁₈ (29% higher, p = 0.002) when compared to control. The TBS of commercial adhesive was not affected by trypsin treatment (p = 0.9).

SIGNIFICANCE

Changing the surface energy of dentin by PGs removal improved resin adhesion, likely due to more efficient water displacement, aiding to improved resin infiltration and polymerization.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

CLINICAL SIGNIFICANCE

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

Effects of resveratrol/ethanol pretreatment on dentin bonding durability

To determine the effects of resveratrol/ethanol solution on the durability of resin-dentin bonding interfaces. Sixty-four non-caries third molars were randomly divided into four groups (n = 16) after sectioning, and then pretreated with one of the following concentrations of resveratrol/ethanol solutions: 0 (control group), 1, 10 and 20 mg/mL, followed by a universal adhesive and resin composites. All microtensile samples were divided into three subgroups: immediate group, collagenase ageing group and thermocycled group. The microtensile bond strength (MTBS), failure modes, interfacial nanoleakage and in situ zymography were measured, whereas the inhibitory effects of pretreated dentin slices on S. mutans biofilms were determined by confocal laser scanning microscopy and MTT assay. The results indicated that bonding strength was not only influenced by pretreatment factors (P < 0.05) but also ageing factors (P < 0.05). Regardless of collagenase ageing or thermocycling, the 10 mg/mL resveratrol/ethanol pretreatment group presented significantly higher (P < 0.05) MTBS and lower (P < 0.05) expression of nanoleakage than the control group, showed better inhibitory effect of matrix metalloproteinases and S. mutans activity with acceptable cytotoxicity. Meanwhile, cohesive failure in dentin decreased gradually with increasing resveratrol concentration. Therefore, the resveratrol/ethanol solution had the potential to serve as a versatile dentin primer, which can effectively improve dentin bonding durability and prevent secondary caries.

Dimeric Proanthocyanidins on the Stability of Dentin and Adhesive Biointerfaces

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

Caries removal with Er:YAG laser followed by dentin biomodification with carbodiimide and chitosan: Wettability and surface morphology analysis

This study aimed to investigate dentin wettability and surface morphology after selective removal of carious lesion by erbium-doped yttrium aluminum garnet (Er:YAG) laser, followed by dentin biomodification with carbodiimide (EDC) and chitosan (CHI). Seventy-eight bovine dentin specimens were submitted to caries induction. Specimens were distributed according to methods of carious removal (n = 39): bur at low-speed (40,000 rpm) or Er:YAG laser (noncontact mode, 250 mJ/pulse and 4Hz). All specimens were etched with 35% phosphoric acid, and subdivided according to dentin biomodification (n = 13): Control (no biomodification), EDC or CHI. The contact angle (n = 10) between adhesive system (3M ESPE) and dentin surface was measured by a goniometer. Eighteen specimens (n = 3) were analyzed by scanning electron microscopy. Data were analyzed by two-way ANOVA and Tukey's test (α = .05). The method used to remove carious lesion did not influence the wettability of dentinal surface (p = .748). The angles produced on the remaining dentin after biomodification were influenced (p = .007). CHI promoted higher contact angles (p = .007) and EDC did not differ from the control group (p = .586). In the bur-treated group, most tubules were open, regardless of which biomodifier was used. Laser modified the organic matrix layer. CHI promoted partially closed tubules in some areas while EDC exposed dentinal tubules. Regardless of which method was used for selective removal of carious lesion, biomodification with EDC did not affect the dentin wettability, whereas CHI changed the wettability of remaining dentin. Both biomodifiers promoted a slight change on dentin morphology.

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.

Combination of baicalein and ethanol-wet-bonding improves dentin bonding durability

OBJECTIVES

This study aimed to investigate the potential of baicalein combined with ethanol-wet bonding (EWB) in improving dentin bonding durability.

METHODS

Sixty caries-free human third molars were randomly allocated into four groups and pretreated with solutions after sectioning and polishing. The pretreatments were prepared via dissolving baicalein in ethanol at concentrations of 0, 0.01%, 0.05% and 0.1% (w/v). Microtensile bond strength (MTBS) test, failure mode analysis and interfacial nanoleakage evaluation were conducted immediately or after thermocycling or 1 month of collagenase aging. In situ zymography, contact angle, antibacterial activity and bioactivity were comprehensively assessed.

RESULTS

Results demonstrated that the three experimental groups exhibited higher MTBS and lower nanoleakage expression regardless of aging. MMP activity within hybrid layer and Streptococcus. mutans biofilm formation were inhibited in the experimental groups in a dose-dependent manner. Baicalein also reduced reactive oxygen species (ROS) expression in human dental pulp cells and resisted adhesive-induced cytotoxicity. Baicalein exhibited remarkable capabilities at concentrations higher than 0.05% (w/v).

CONCLUSION

Baicalein is a prospective candidate as bioactive dentin bonding agent. Combined with EWB, baicalein may form a functional bonding interface, thereby enhancing dentin bond strength and durability.

SIGNIFICANCE

Joint efforts by baicalein and EWB provides a novel therapeutic strategy for obtaining ideal adhesive-dentin interface and prolonging the longevity of restorations.

Analysis of the bond interface between self-adhesive resin cement to eroded dentin in vitro

The purpose of this study was to evaluate the bonding interface between a self-adhesive resin cement to in vitro eroded dentin. Seventy-two third molars were used and divided into two groups: sound dentin and in vitro eroded dentin. The in vitro erosion was performed following a demineralization protocol, in which the specimens were immersed in a demineralizing solution for 2 minutes per cycle and remineralizing solution for 10 minutes per cycle for 9 days. Both groups were submitted to four dentin surface treatments: control group (without any treatment), 2% chlorhexidine, 20% polyacrylic acid, and 0.1 M EDTA (n = 9). Blocks of resin-based composite were bonded with RelyX U200 self-adhesive resin cement applied on the pretreated dentin surfaces. The teeth were sectioned into beams (1mm²) and submitted to microtensile bond strength testing to evaluate the bond strength of self-adhesive resin cement to dentin after 24 hours and 8 months of immersion in artificial saliva. Three specimens of each group were longitudinally cut and evaluated using confocal laser scanning microscopy to analyze the dentin/cement interface. Eroded dentin showed higher bond strength values when compared to sound dentin for the 2% chlorhexidine group (p = 0.03), 24 hours after adhesion. When considering eroded dentin, the 0.1M EDTA group showed higher bond strength values with a statistically significant difference only for the control group (p = 0.002). After 8 months of storage, the present results showed that there was no statistically significant difference between the two substrates for all experimental groups (p>0.05). Analysis of the microscopy confocal showed different types of treatments performed on dentin generally increased tags formation when compared to the control group. The eroded dentin showed a significant increase in density and depth of resinous tags when compared to sound dentin. The storage of samples for 8 months seems to have not caused significant degradation of the adhesive interface.

An Overview of Dental Adhesive Systems and the Dynamic Tooth-Adhesive Interface

From the conception of resin-enamel adhesion to today's contemporary dental adhesive systems, clinicians are no longer afraid of exploring the many advantages brought by adhesive restorative concepts. To maximize the performance of adhesive-based restorative procedures, practitioners must be familiar with the mechanism of adhesion, clinical indications, proper handling, the inherent limitations of the materials and the biological challenges. This review provides an overview of the current status of restorative dental adhesives, their mechanism of adhesion, mechanisms of degradation of dental adhesive interfaces, how to maximize performance, and future trends in adhesive dentistry.

Switchable presentation of cytokines on electroactive polypyrrole surfaces for hematopoietic stem and progenitor cells

Hematopoietic stem cells are used in transplantations for patients with hematologic malignancies. Scarce sources require efficient strategies of expansion, including polymeric biomaterials mimicking architectures of bone marrow tissue. Tissue microenvironment and mode of cytokine presentation strongly influence cell fate. Although several cytokines with different functions as soluble or membrane-bound mediators have already been identified, their precise roles have not yet been clarified. A need exists for in vitro systems that mimic the in vivo situation to enable such studies. One way is to establish surfaces mimicking physiological presentation using protein-immobilization onto polymer films. However these films merely provide a static presentation of the immobilized proteins. It would be advantageous to also dynamically change protein presentation and functionality to better reflect the in vivo conditions. The electroactive polymer polypyrrole shows excellent biocompatibility and electrochemically alters its surface properties, becoming an interesting choice for such setups. Here, we present an in vitro system for switchable presentation of membrane-bound cytokines. We use interleukin IL-3, known to affect hematopoiesis, and show that when immobilized on polypyrrole films, IL-3 is bioavailable for the bone marrow-derived FDC-P1 progenitor cell line. Moreover, IL-3 presentation can be successfully altered by changing the redox state of the film, in turn influencing FDC-P1 cell viability. This novel in vitro system provides a valuable tool for stimuli-responsive switchable protein presentation allowing the dissection of relevant mediators in stem and progenitor cell behavior.

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.

Fatigue resistance of dentin bonds prepared with two- vs. three-step adhesives: Effect of carbodiimide

The application of a cross-linker to demineralized dentin is reportedly effective at extending the durability of dentin bonds.

OBJECTIVE

To compare the effect of a cross-linker pretreatment on the fatigue crack growth resistance of resin-dentin bonds prepared with a two- vs. three-step adhesive system.

METHODS

Bonded interface Compact Tension (CT) specimens were prepared using commercial two- and three-step etch-and-rinse adhesives and compatible hybrid resin-composite. For the treated groups, adhesive bonding was preceded by a 1min application of an experimental carbodiimide (EDC) conditioner to the acid-etched dentin. The control groups received no such treatment. The fatigue crack growth resistance was examined after storage in artificial saliva at 37°C for 0, 3 and 6 months.

RESULTS

There was no significant difference in the immediate fatigue crack growth resistance the control and EDC-treated groups at 0 months for either adhesive system. After 3 and 6 months of storage, the EDC-treated groups exhibited significantly greater (p≤0.05) fatigue crack growth resistance than the controls. Although the EDC treatment was equally effective in deterring degradation for both adhesives, bonds prepared with the three-step system exhibited the lowest resistance to fatigue crack growth overall.

SIGNIFICANCE

An EDC treatment applied during dentin bonding could help maintain the durability of bonds prepared with two or three-step adhesive bonding systems.

Absolute Configuration of Native Oligomeric Proanthocyanidins with Dentin Biomodification Potency

The structurally complex oligomeric proanthocyanidins (OPACs) are promising biomimetic agents, capable of strengthening the macromolecular backbone of teeth via intermolecular and intermicrofibrillar cross-linking. This study establishes analytical methods capable of determining the absolute configuration of the catechin-type monomeric units of underivatized OPACs. This preserves the capacity of their biological evaluation, aimed at understanding the inevitably stereospecific interactions between the OPACs and dentin collagen. Guided by dental bioassays (modulus of elasticity, long-term stability), two new trimeric and tetrameric A-type OPACs were discovered as dentin biomodifiers from pine (Pinus massoniana) bark: epicatechin-(2β→O→7,4β→8)-epicatechin-(2β→O→7,4β→8)-catechin (5) and epicatechin-(2β→O→7,4β→8)-epicatechin-(2β→O→7,4β→6)-epicatechin-(2β→O→7,4β→8)-catechin (6), respectively. Combining 1D/2D NMR, HRESIMS, ECD, 1H iterative full spin analysis (HiFSA), and gauge-invariant atomic orbital (GIAO) δ calculations, we demonstrate how 13C NMR chemical shifts (diastereomeric building blocks (A-type dimers)) empower the determination of the absolute configuration of monomeric units in the higher oligomers 5 and 6. Collectively, NMR with ECD reference data elevates the level of structural information achievable for these structurally demanding molecules when degradation analysis is to be avoided. Considering their numerous and deceptively subtle, but 3D impactful, structural variations, this advances the probing of OPAC chemical spaces for species that bind selectively to collagenous and potentially other biologically important biomacromolecules.

Quercetin as a simple but versatile primer in dentin bonding

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

Biostability of the Proanthocyanidins-Dentin Complex and Adhesion Studies

Oligomeric proanthocyanidins (OPACs) are potent and renewable natural bioactives possible to be refined into chemically standardized mixtures for biological applications. Herein, we found that multiscale interactions of OPACs with the dentin matrix create tight biointerfaces with hydrophobic methacrylate adhesives on wet surfaces. An enriched mixture of OPACs, with a known phytochemical profile, was produced from grape seed crude extract ( Vitis vinifera; enriched grape seed extract [e-GSE]) and applied to dentin matrices to determine changes to the mechanical properties and biodegradability of the dentin matrix and favorable resin adhesion mechanisms. Methods included a 3-point flexural test, quantification of hydroxyproline (collagen solubilization), static and dynamic nanomechanical analyses, resin-dentin microtensile bond strength, and micropermeability at the adhesive interface. The e-GSE-modified dentin matrix exhibited remarkably low collagen solubilization and sustained the bulk elastic properties over 12 mo. Tan δ findings reveal a more elastic-like behavior of the e-GSE-modified dentin matrix, which was not affected by H-bond destabilization by urea. Dentin-methacrylate biointerfaces with robust and stable adhesion were created on e-GSE-primed dentin surfaces, leading to a dramatic decrease of the interfacial permeability. Standardized OPAC mixtures provide a new mechanism of adhesion to type I collagen-rich tissues that does not rely on hydrophilic monomers. The bioadhesion mechanism involves physicochemical modifications to the dentin matrix, reduced tissue biodegradation, and bridging to methacrylate resins.

Dental adhesives and strategies for displacement of water/solvents from collagen fibrils

OBJECTIVES

To evaluate the influence of temperature of evaporation in adhesive systems with different solvents on the apparent modulus of elasticity and mass change of macro-hybrid layers modified by proanthocyanidins (PACs).

METHODS

Adhesive resin beams (A) from Single Bond Plus (SB), Excite (EX) and One Step Plus (OS) were prepared after solvent evaporation at 23°C or 40°C (n=12). Macro-hybrid layers (M) (n=12) were prepared using demineralized dentin beams sectioned from extracted human third molars. The demineralized dentin specimens were infiltrated with each one of the three adhesive systems at 23°C or 40°C; with or without prior dentin treatment with PACs for 10min. The apparent modulus of elasticity (E) and mass change (Wmc, %) of adhesives beams and resin-infiltrated specimens were assessed in dry and wet conditions after immersion in water (24h, 1, 3 and 6 months). The E was statistically analyzed by Tukey-Kramer test and the Wmc, % by Kruskal Wallis, and Dunn (α=0.05).

RESULTS

Solvent evaporation at 40°C resulted in higher E values for adhesive resin beams at all storage conditions, regardless of the adhesive system (p<0.05). Increased mass loss (3 months: -0.01%; 6 months: -0.05%) was observed in One Step resin beams (p≤0.05). In the macro-hybrid layer models the pretreatment with PACs along with solvent evaporation at 40°C increased E and decreased the Wmc, % (3 months: -2.5; 6 months: 2.75%) for adhesives evaluated over time (p<0.05). No significant differences in ratio (resin/dentin) were found for the macro-hybrid layers (p>0.05).

SIGNIFICANCE

Improved solvent evaporation at higher temperature, and increased collagen cross-linking induced by PACs, enhanced the mechanical properties resulting in highly stable macro-hybrid layers over 6 months storage.

Effect of carbodiimide on the structural stability of resin/dentin interface

Clinical longevity of composite resin restorations is a significant problem in adhesive dentistry. Most of the current simplified adhesives present good immediate bonding, but the bond strength gradually falls over a period due to biodegradation at the resin-dentin interface. Various strategies have been proposed to improve the durability of resin-dentin bond including the use of matrix metalloproteinases inhibitors and collagen cross-linkers, biomimetic remineralization, ethanol wet bonding, to improve the physical and mechanical properties of the bonding substrate, i.e., dentin. However, all are under preliminary research and without any conclusive evidence. Therefore, this paper addresses the current challenge in dental adhesion, i.e., poor durability of resin-dentin bond and introduces the concept of dentin biomodification as an alternative way for improving the long-term bonding effectiveness of current adhesives to dentin and also provides an overview of a synthetic collagen cross-linking agent carbodiimide (EDC) including its mechanism of action, literature review of studies evaluating EDC, variables associated with its use and its cytotoxicity. Search was performed across the electronic databases (PubMed, Ebsco host, and Google search engine) to identify manuscripts for inclusion, using the keywords: carbodiimide, dentin bonding, durability, resin-dentin interface, and collagen cross-linking. Thirty-five articles were finally included, and the last search was made in February 2016.