Effect of ultraviolet A-induced crosslinking on dentin collagen matrix

Effect of applying carbodiimide combined with a two-step self-etch adhesive durability

BACKGROUND

This study investigated the effect of carbodiimide (EDC) combined with Clearfil SE self-etch adhesive on the shear bond strength (SBS), crosslinking degree, denaturation temperature, and enzyme activity of dentin in vitro.

MATERIALS AND METHODS

Collected human sound third molars were randomly divided into different groups with or without EDC treatment (0.01-1 M). The specimens (n = 16)were stored for 24 h (immediate) or 12 months (aging) before testing the SBS. Fine dentin powder was obtained and treated with the same solutions. Then the crosslinking degree, denaturation temperature (Td), and enzyme activity were tested. Statistical analysis was performed using a one-way analysis of variance (ANOVA) to compare the differences of data between groups (α = 0.05).

RESULTS

There was a significant drop in immediate SBS and more adhesive fracture of 1.0 M EDC group, while there were no significant differences among the other groups. SEM showed a homogeneous interface under all treatments. After 12 months of aging, the SBS significantly decreased. Less decreases of SBS in the 0.3 and 0.5 M groups were found. Due to thermal and enzymatical properties consideration, the 0.3 and 0.5 M treatments also showed higher cross-link degree and Td with lower enzyme activity.

CONCLUSION

0.3 and 0.5 M EDC may be favorable for delaying the aging of self-etch bond strength for 12 months. But it is still needed thoroughly study.

Crosslinking Improve Demineralized Dentin Performance and Synergistically Promote Biomimetic Mineralization by CaP_PILP

OBJECTIVE

to explore the effects of optimal crosslinking (chemical treatment) on demineralized dentin matrix and the possible synergism with calcium phosphate polymer-induced liquid precursor (CaP-PILP) bionic remineralization (physical treatment), and offer benefit to the clinic of resin-dentin bonding and dentin hypersensitivity.

METHODS

demineralized dentin was treated with glutaraldehyde (GA), carbodiimide (EDC), and procyanidin (PA) for crosslinking, followed by CaP-PILP biomimetic remineralization. The morphology, surface mechanical and physio-chemical properties, and enzymatic resistance were evaluated regardless of the modification.

RESULTS

the collagen fibers appeared morphologically complete with higher surface microhardness and characteristic peaks of amide I-III bands were visible after GA, PA, and EDC crosslinking. Collagen collapse and dissolution were seen in untreated demineralized dentin with enzyme attack, while the collagen fiber structure remained intact in GA- and PA-treated specimens. The lamellar mineral phase was visible at 2 days and the dentin tubules were almost completely enclosed at 4-6 days after PA crosslinking and mineralization. However, demineralized collagen fibers and open tubules were still visible between the dentinal tubules on day 8 in the control group.

CONCLUSION

the structure integrity, enzyme resistance, and mechanical properties of the collagen fiber network could be significantly preserved by GA and PA crosslinking than EDC and no treatment. While, strongest synergistic effects were observed in PA on bionic remineralization by CaP-PILP, and further significantly improve the quality and shorten the duration of mineralization. These findings would be beneficial for dental clinical practice of resin-dentin bonding and dentin hypersensitivity.

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.

Riboflavin and Its Effect on Dentin Bond Strength: Considerations for Clinical Applicability-An In Vitro Study

Bioactive collagen crosslinkers propose to render the dentin hybrid layer less perceptive to hydrolytic challenge. This study aims to evaluate whether bond strength of dental resin composite to dentin benefits from riboflavin (RB)-sensitized crosslinking when used in a clinically applicable protocol. A total of 300 human dentin specimens were prepared consistent with the requirements for a macro-shear bond test. RB was applied on dentin, either incorporated in the primer (RBp) of a two-step self-etch adhesive or as an aqueous solution (RBs) before applying the adhesive, and blue light from a commercial polymerization device was used for RB photoactivation. Bonding protocol executed according to the manufacturer’s information served as control. Groups (n = 20) were tested after 1 week, 1 month, 3 months, 6 months or 1 year immersion times (37 °C, distilled water). The different application methods of RB significantly influenced bond strength (p < 0.001) with a medium impact (η²_p = 0.119). After 1 year immersion, post hoc analysis identified a significant advantage for RB groups compared to RBp (p = 0.018), which is attributed to a pH-/solvent-dependent efficiency of RB-sensitized crosslinking, stressing the importance of formulation adjustments. We developed an application protocol for RB-sensitized crosslinking with emphasis on clinical applicability to test its performance against a gold-standard adhesive, and are confident that, with a few adjustments to the application solution, RB-sensitized crosslinking can improve the longevity of adhesive restorations in clinics.

Synthesis and Incorporation of Quaternary Ammonium Silane Antimicrobial into Self-Crosslinked Type I Collagen Scaffold: A Hybrid Formulation for 3D Printing

Novel 3D-biomaterial scaffold is constructed having a combination of a new quaternary ammonium silane (k21) antimicrobial impregnated in 3D collagen printed scaffolds cross linked with Riboflavin in presence of d-alpha-tocopheryl poly(ethyleneglycol)-1000-succinate. Groups of "0.1% and 0.2% k21", and "0.1% and 0.2% Chlorhexidine (CHX)" are prepared. k21/CHX with neutralized collagen is printed with BioX. Riboflavin is photo-activated and examined using epifluorescence for Aggregatibacter actinomycetemcomitans (7-days). Collagen is examined using TEM and measured for porosity, and shape-fitting. Raman and tandem mass/solid-state are performed with molecular-docking and circular-dichroism. X-ray diffractions, rheological tests, contact angle, and ninhydrin assay are conducted. k21 samples demonstrated collagen aggregates while 0.1% CHX and 0.2% CHX showed irregularities. Porosity of control and "0.1% and 0.2% k21" scaffolds show no differences. Low contact angle, improved elastic-modulus, rigidity, and smaller strain in k21 groups are seen. Bacteria are reduced and strong organic intensities are seen in k21 scaffolds. Simulation shows hydrophobicity/electrostatic interaction. Crosslinking is observed in 0.2% CHX/79% and 0.2% k21/80%. Circular dichroism for k21 are suggestive of triple helix. XRD patterns appear at d = 5.97, 3.03, 2.78, 2.1, and 2.90 A°. 3D-printing of collagen impregnated with quaternary ammonium silane produces a promising scaffold with antimicrobial potency and structural stability.

New antimicrobial and collagen crosslinking formulated dentin adhesive with improved bond durability

OBJECTIVE

Here we describe a novel formulation, based on quaternary ammonium (QA) and riboflavin (RF), which combines antimicrobial activities and protease inhibitory properties with collagen crosslinking without interference to bonding capabilities, was investigated.

METHODS

Experimental adhesives modified with different fractions of dioctadecyldimethyl ammonium bromide quaternary ammonium and riboflavin (QARF) were formulated. Dentine specimens were bonded to resincomposites with control or the experimental adhesives to be evaluated for bond strength, interfacial morphology, micro-Raman analysis, nano-CT and nano-leakage expression. In addition, the antibacterial and biocompatibilities of the experimental adhesives were investigated. The endogenous proteases activities and their molecular binding-sites were studied.

RESULTS

Modifying the experimental adhesives with QARF did not adversely affect micro-tensile bond strength or the degree of conversion along with the demonstration of anti-proteases and antibacterial abilities with acceptable biocompatibilities. In general, all experimental adhesives demonstrated favourable bond strength with increased and improved values in 1% QARF adhesive at 24 h (39.2 ± 3.0 MPa) and following thermocycling (34.8 ± 4.3 MPa).

SIGNIFICANCE

It is possible to conclude that the use of QARF with defined concentration can maintain bond strength values when an appropriate protocol is used and have contributed in ensuring a significant decrease in microbial growth of biofilms. Incorporation of 1% QARF in the experimental adhesive lead to simultaneous antimicrobial and anti-proteolytic effects with low cytotoxic effects, acceptable bond strength and interfacial morphology.

UVA-activated riboflavin promotes collagen crosslinking to prevent root caries

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

Synergistic effects of VE-TPGS and riboflavin in crosslinking of dentine

OBJECTIVE

Effect of d-alpha-tocopheryl poly(ethyleneglycol)-1000-succinate (VE-TPGS) with riboflavin-5'-phosphate solution on crosslinking of dentine collagen was investigated to analyze collagen's structural integrity.

METHODS

VE-TPGS was added to RF-solution, at RF/VE-TPGS (w/w) ratios of 0.125/0.250 and 0.125/0.500. Demineralized dentine beams were used (10wt.% phosphoric acid), rinsed using deionized-water and analysed using ELISA (Human MMP2 ELISA; Human CTSK/Cathepsin-K for MMP2 and Cathepsin K analysis). AFM of dentine collagen-fibrils structure was done before and after dentine specimens' placement in mineralization solution and tested after 14days in artificial saliva/collagenase (AS/Co) solution. The specimens were tested after 24h in mineralization solution for surface/bulk elastic modulus. Nano-indentation was carried out for each specimen on intertubular-dentine with lateral spacing of 400nm. Reduced elastic-modulus and nano-hardness were calculated and collagen content was determined using hydroxyproline-assay. Micro-Raman were performed. TEM was carried out to study structural variations of dentine-collagen in artificial-saliva (collagenase). Data were presented as mean±standard deviation and analyzed by SPSS v.15, by analysis of variance.

RESULTS

Synergetic effect of VE-TPGS was observed with RF through higher structural integrity of dentine collagen-fibrils shown by TEM/AFM. Superior surface/bulk mechanical stability was shown by nano-indentation/mechanical testing. Improvement in collagenase degradation resistance for hydroxyproline release was observed and lower endogenous-protease release of MMP-2/Cathepsin-K. Raman-analysis analysed chemical interactions between RF and collagen confirming structural-integrity of collagen fibrils after crosslinking. After 24h mineralization, AFM showed mineral depositions in close association with dentine-collagen fibrils with RF/VE-TPGS formulations.

SIGNIFICANCE

Potential synergetic effect of RF/VE-TPGS was observed by reflection of higher structural integrity and conformational-stability of dentine-collagen fibrils.

Novel Biomedical Applications of Crosslinked Collagen

Collagen is one of the most useful biopolymers because of its low immunogenicity and biocompatibility. The biomedical potential of natural collagen is limited by its poor mechanical strength, thermal stability, and enzyme resistance, but exogenous chemical, physical, or biological crosslinks have been used to modify the molecular structure of collagen to minimize degradation and enhance mechanical stability. Although crosslinked collagen-based materials have been widely used in biomedicine, there is no standard crosslinking protocol that can achieve a perfect balance between stability and functional remodeling of collagen. Understanding the role of crosslinking agents in the modification of collagen performance and their potential biomedical applications are crucial for developing novel collagen-based biopolymers for therapeutic gain.

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.