The Size Exclusion Characteristics of Type I Collagen

Extrafibrillar demineralization: Yes or no?

OBJECTIVE

Extrafibrillar demineralization is considered to be an ideal solution for addressing the durability of resin-dentin bonding interfaces. However, its theoretical basis is contradictory to ionization equilibrium of hydroxyapatite dissolution. In this study, various calcium chelators were selected as dentin conditioners to explore the essence of dentin demineralization with chelators and its effect on resin-dentin adhesion.

METHODS

Polyethyleneimine grafted with EDTA and polyacrylic acid sodium (PAAN450k) larger than 40 kDa, as well as PAAN (PAAN3k) and EDTA smaller than 6 kDa, were prepared as dentin conditioners. The dentin powder was designed to characterize whether it would demineralize without contact with PAAN450k. Dentin demineralization effect with four conditioners was evaluated with field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy and quantification of hydroxyproline concentration after enzymatic degradation. Micro-tensile bond strength (µTBS) test and failure mode analysis were employed to assess the bonding effect of the four chelators in both wet and dry bonding, with H3PO4 wet bonding serving as the control group.

RESULTS

Demineralization occurs when PAAN450k was not in direct contact with the dentin powder. The extrafibrillar demineralization cannot be induced by any chelator regardless of its molecular weight. Complete demineralization including extrafibrillar and intrafibrillar demineralization would occur with sufficient interaction time. Moreover, chelators could not provide a reliable dentin bonding effect under a short interaction time.

SIGNIFICANCE

From the perspective of theory and application, extrafibrillar demineralization is not a reliable strategy, which provides a reminder for exploring new strategies in the future.

Advancing dentin remineralization: Exploring amorphous calcium phosphate and its stabilizers in biomimetic approaches

OBJECTIVE

This review elucidates the mechanisms underpinning intrafibrillar mineralization, examines various amorphous calcium phosphate (ACP) stabilizers employed in dentin's intrafibrillar mineralization, and addresses the challenges encountered in clinical applications of ACP-based bioactive materials.

METHODS

The literature search for this review was conducted using three electronic databases: PubMed, Web of Science, and Google Scholar, with specific keywords. Articles were selected based on inclusion and exclusion criteria, allowing for a detailed examination and summary of current research on dentin remineralization facilitated by ACP under the influence of various types of stabilizers.

RESULTS

This review underscores the latest advancements in the role of ACP in promoting dentin remineralization, particularly intrafibrillar mineralization, under the regulation of various stabilizers. These stabilizers predominantly comprise non-collagenous proteins, their analogs, and polymers. Despite the diversity of stabilizers, the mechanisms they employ to enhance intrafibrillar remineralization are found to be interrelated, indicating multiple driving forces behind this process. However, challenges remain in effectively designing clinically viable products using stabilized ACP and maximizing intrafibrillar mineralization with limited materials in practical applications.

SIGNIFICANCE

The role of ACP in remineralization has gained significant attention in dental research, with substantial progress made in the study of dentin biomimetic mineralization. Given ACP's instability without additives, the presence of ACP stabilizers is crucial for achieving in vitro intrafibrillar mineralization. However, there is a lack of comprehensive and exhaustive reviews on ACP bioactive materials under the regulation of stabilizers. A detailed summary of these stabilizers is also instrumental in better understanding the complex process of intrafibrillar mineralization. Compared to traditional remineralization methods, bioactive materials capable of regulating ACP stability and controlling release demonstrate immense potential in enhancing clinical treatment standards.

Effects of endodontic root canal irrigants on tooth dentin revealed by infrared spectroscopy: a systematic literature review

BACKGROUND

Root canal irrigation endodontic solutions have effects on the chemistry of dentin. Infrared spectroscopy is a non-destructive chemical characterization method where the strength of absorption often correlates with mineral or organic composition.

OBJECTIVES

To survey effects of commonly used irrigation solutions on the composition of root dentin as detected by widely-available Fourier transform infrared spectroscopy (FTIR) methods.

METHODS

Electronic databases were searched for articles published between 1983 to 2023. After risk of bias assessments (OHAT), studies were grouped according to effects per irrigation solution. Inclusion criteria comprised in vitro studies that used extracted human or bovine teeth, treated by irrigation solutions characterized using FTIR spectroscopy and presenting spectral data. Publications that did not present spectra were excluded.

RESULTS

A wide range of concentrations, durations, and treatment protocols have been tested but only 30 out of 3452 studies met our inclusion criteria. Different FTIR methods were used with Attenuated Total Reflection (ATR) variant being the most common (21 studies). Investigated solutions included sodium hypochlorite (NaOCl), ethylenediaminetetraacetic-acid (EDTA), 1-hydroxyethylidene-1-1-diphosphonic-acid (HEDP), peracetic-acid (PAA), glycolic-acid (GA), and citric-acid (CA) though most focused on NaOCl and EDTA. All solutions had detectable effects in the FTIR signature of dentin. NaOCl mainly affects the organics, revealing reduced amide/phosphate ratios with increasing concentrations. EDTA mainly effects the inorganic component, with the effects increasing with time and concentration, yet glycolic acid has stronger effects than EDTA on dentin. Beyond the type of irrigant and dentin exposure durations, concentration and protocol of application had strong effects. There is a lack of studies comparing similar irrigants under conditions that mimic clinical scenarios analyzing bulk sample because FTIR of powder dentin differs from FTIR of bulk dentin.

SIGNIFICANCE

The ideal root-canal irrigant should combine local disinfection properties with minimal compositional effects on healthy dentin. FTIR methods appear reliable to identify important changes in root dentin chemical composition. Such information can help understand when endodontic irrigation might lead to root degradation or possibly contribute to long term failures such as vertical fractures. Awareness of chemical damage from irrigation procedures may help clinicians select procedures that reduce deleterious effects on the root canal structures.

Decorin in the spatial control of collagen mineralization

Understanding the molecular mechanism by which the periodontal ligament (PDL) is maintained uncalcified between two mineralized tissues (cementum and bone) may facilitate the functional repair and regeneration of the periodontium complex, disrupted in the context of periodontal diseases. However, research that explores the control of type I collagen (COL I) mineralization fails to clarify the detailed mechanism of regulating spatial collagen mineralization, especially in the periodontium complex. In the present study, decorin (DCN), which is characterized as abundant in the PDL region and rare in mineralized tissues, was hypothesized to be a key regulator in the spatial control of collagen mineralization. The circular dichroism results confirmed that DCN regulated the secondary structure of COL I, and the surface plasmon resonance results indicated that COL I possessed a higher affinity for DCN than for other mineralization promoters, such as DMP-1, OPN, BSP and DSPP. These features of DCN may contribute to blocking intrafibrillar mineralization in COL I fibrils during the polymer-induced liquid-precursor mineralization process when the fibrils are cross-linked with DCN. This effect was more remarkable when the fibrils were phosphorylated by sodium trimetaphosphate, as shown by the observation of a tube-like morphology via TEM and mineral sheath via SEM. This study enhances the understanding of the role of DCN in mineralization regulation among periodontal tissues. This provides insights for the development of biomaterials for the regeneration of interfaces between soft and hard tissues.

Assembled collagen films modified using polyacrylic acid with improved mechanical properties via mineralization

The imperative task of enforcing collagen materials holds paramount significance in the field of hard tissue repair. We hereby present mineralized collagen fiber films via mineralization with improved mechanical properties. Self-extracted collagen was assembled into an array with an aligned fibrous pattern and then modified with polyacrylic acid (PAA) followed by mineralization in cationic polyacrylamide (CPAM)-SBF. Biomineralization occurred at the inner and outer surface of the assembled collagen fiber films. A tensile strength of up to 40.38 ± 3.08 MPa of mineralized collagen was obtained, for the first time, which may be attributed to the synergistic effect of polyanion and polycation on the mineralization process of assembled intrafibrillar collagen fibers. It was argued that PAA may facilitate the intra-fiber interaction of collagen, which extends the elongation at break of collagen fibers. This study introduces a pioneering approach for the preparation of mineralized collagen materials with superior mechanical properties, which would be beneficial for hard tissue repair.

Carbon, nitrogen, and sulfur elemental and isotopic variations in mouse hair and bone collagen during short-term graded calorie restriction

This study characterized the effect of calorie restriction (CR) on elemental content and stable isotope ratio measurements of bone "collagen" and hair keratin. Adult mice on graded CR (10-40%; 84 days) showed decreased hair δ 15N, δ 13C, and δ 34S values (significantly for δ 15N) with increasing CR, alongside a significant increase in bone "collagen" δ 15N values and a decrease in "collagen" δ 13C values. We propose this was likely due to the intensified mobilization of endogenous proteins, as well as lipids in newly synthesized "collagen". Elemental analysis of bone "collagen" revealed decreased carbon, nitrogen, and sulfur % content with increasing CR which is attributed to a change in the in vivo bone "collagen" structure with extent of CR. This complexity challenges the use of elemental indicators in the assessment of collagen quality in archaeological studies where nutritional stress may be a factor.

Citrate Improves Biomimetic Mineralization Induced by Polyelectrolyte-Cation Complexes Using PAsp-Ca&Mg Complexes

Magnesium ions are highly enriched in early stage of biological mineralization of hard tissues. Paradoxically, hydroxyapatite (HAp) crystallization is inhibited significantly by high concentration of magnesium ions. The mechanism to regulate magnesium-doped biomimetic mineralization of collagen fibrils has never been fully elucidated. Herein, it is revealed that citrate can bioinspire the magnesium-stabilized mineral precursors to generate magnesium-doped biomimetic mineralization as follows: Citrate can enhance the electronegativity of collagen fibrils by its absorption to fibrils via hydrogen bonds. Afterward, electronegative collagen fibrils can attract highly concentrated electropositive polyaspartic acid-Ca&Mg (PAsp-Ca&Mg) complexes followed by phosphate solution via strong electrostatic attraction. Meanwhile, citrate adsorbed in/on fibrils can eliminate mineralization inhibitory effects of magnesium ions by breaking hydration layer surrounding magnesium ions and thus reduce dehydration energy barrier for rapid fulfillment of biomimetic mineralization. The remineralized demineralized dentin with magnesium-doped HAp possesses antibacterial ability, and the mineralization mediums possess excellent biocompatibility via cytotoxicity and oral mucosa irritation tests. This strategy shall shed light on cationic ions-doped biomimetic mineralization with antibacterial ability via modifying collagen fibrils and eliminating mineralization inhibitory effects of some cationic ions, as well as can excite attention to the neglected multiple regulations of small biomolecules, such as citrate, during biomineralization process.

STMP and PVPA as Templating Analogs of Noncollagenous Proteins Induce Intrafibrillar Mineralization of Type I Collagen via PCCP Process

The phosphorylated noncollagenous proteins (NCPs) play a vital role in manipulating biomineralization, while the mechanism of phosphorylation of NCPs in intrafibrillar mineralization of collagen fibril has not been completely deciphered. Poly(vinylphosphonic acid) (PVPA) and sodium trimetaphosphate (STMP) as templating analogs of NCPs induce hierarchical mineralization in cooperation with indispensable sequestration analogs such as polyacrylic acid (PAA) via polymer-induced liquid-like precursor (PILP) process. Herein, STMP-Ca and PVPA-Ca complexes are proposed to achieve rapid intrafibrillar mineralization through polyelectrolyte-Ca complexes pre-precursor (PCCP) process. This strategy is further verified effectively for remineralization of demineralized dentin matrix both in vitro and in vivo. Although STMP micromolecule fails to stabilize amorphous calcium phosphate (ACP) precursor, STMP-Ca complexes facilely permeate into intrafibrillar interstices and trigger phase transition of ACP to hydroxyapatite within collagen. In contrast, PVPA-stabilized ACP precursors lack liquid-like characteristic and crystallize outside collagen due to rigid conformation of PVPA macromolecule, while PVPA-Ca complexes infiltrate into partial intrafibrillar intervals under electrostatic attraction and osmotic pressure as evidenced by intuitionistic 3D stochastic optical reconstruction microscopy (3D-STORM). The study not only extends the variety and size range of polyelectrolyte for PCCP process but also sheds light on the role of phosphorylation for NCPs in biomineralization.

Reinforced dentin remineralization via a novel dual-affinity peptide

OBJECTIVES

In light of the constantly flowing saliva, anti-caries remineralization agents are inclined to be taken away. Owing to their limited residence time, the remineralization effect is not as desirable as expected. Hence, our study aimed to synthesize a novel peptide (DGP) with high affinity to both collagen fibrils and hydroxyapatite, and investigated its dentin remineralization efficacy in vitro and anti-caries capability in vivo.

METHODS

DGP was synthesized through Fmoc solid-phase reaction. The binding ability and interaction mechanism of DGP to demineralized dentin were investigated. Dentin specimens were demineralized, then treated with DGP and deionized water respectively. The specimens were incubated in artificial saliva and in-vitro remineralization effectiveness was analyzed after 14 days. The rat caries model was established to further scrutinize the in-vivo efficacy of caries prevention.

RESULTS

DGP possesses an enhanced adhesion force of 12.29 ± 1.12 nN to demineralized dentin. The favorable adsorption capacity is ascribed to the stable hydrogen bonds between S2P-101 and ASP-100 of DGP and GLY33 and PRO-16 of collagen fibers. Abundant mineral deposits and remarkable tubule occlusion were observed in the DGP group. DGP-treated dentin obtained notable microhardness recovery and higher mineral content after a 14-day remineralization regimen. DGP also demonstrated potent caries prevention in vivo, with substantially fewer carious lesions and significantly lower Keyes scoring.

SIGNIFICANCE

DGP proves to possess a high affinity to demineralized dentin regardless of saliva flowing, thus enhancing remineralization potency significantly in vitro and in vivo, potential for dental caries prevention and combatting initial dentin caries clinically.

A glycol chitosan derivative with extrafibrillar demineralization potential for self-etch dentin bonding

OBJECTIVES

Extrafibrillar demineralization is an etching technique that removes only minerals from around the collagen fibrils for resin infiltration. The intrafibrillar minerals are left intact to avoid their replacement by water that is hard for adhesive resin monomers to displace. The present work reported the synthesis of a water-soluble methacryloyloxy glycol chitosan-EDTA conjugate (GCE-MA) and evaluated its potential as an extrafibrillar demineralization agent for self-etch dentin bonding.

METHODS

Glycol chitosan-EDTA was functionalized with a methacryloyloxy functionality. Conjugation was confirmed using Fourier transform-infrared spectroscopy. The GCE-MA was used to prepare experimental self-etch primers. Extrafibrillar demineralization of the primers was evaluated with scaning electron microscopy and transmission electron microscopy. The feasibility of this new self-etch bonding approach was evaluated using microtensile bond strength testing and inhibition of dentin gelatinolytic activity. The antibacterial activity and cytotoxicity of GCE-MA were also analyzed.

RESULTS

Conjugation of EDTA and the methacryloyloxy functionality to glycol chitosan was successful. The functionalized conjugate was capable of extrafibrillar demineralization of mineralized collagen fibrils. Tensile bond strength of the experimental self-etch primer to dentin was comparable to that of phosphoric acid-etched dentin and the commercial self-etch primer Clearfil SE Bond 2. The GCE-MA also inhibited soluble rhMMP-9. In-situ zymography detected minimal fluorescence in hybrid layers conditioned with the experimental primer. The GCE-MA was noncytotoxic and possessed antibacterial activities against planktonic bacteria.

SIGNIFICANCE

Synthesis of GCE-MA brought into fruition a self-etch conditioner that selectively demineralizes the extrafibrillar mineral component of dentin. A self-etch primer prepared with GCE-MA achieved bond strengths comparable to commercial reference adhesive systems.

Remineralization of Dentin with Cerium Oxide and Its Potential Use for Root Canal Disinfection

Objective

This study was to investigate a novel antibacterial biomimetic mineralization strategy for exploring its potential application for root canal disinfection when stabilized cerium oxide was used.

Material and Methods

A biomimetic mineralization solution (BMS) consisting of cerium nitrate and dextran was prepared. Single-layer collagen fibrils, collagen membranes, demineralized dentin, and root canal system were treated with the BMS for mineralization. The mineralized samples underwent comprehensive characterization using various techniques, including transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transform infrared spectroscopy (FTIR), scanning transmission electron microscopy (STEM), selected-area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and micro-CT. Additionally, the antimicrobial properties of the BMS and the remineralized dentin were also analyzed with broth microdilution method, live/dead staining, and SEM.

Results

Cerium ions in the BMS underwent a transformation into cerium oxide nanoparticles, which were deposited in the inter- and intra-fibrillar collagen spaces through a meticulous bottom-up process. XPS analysis disclosed the presence of both Ce (III) and Ce (IV) of the generated cerium oxides. A comprehensive examination utilizing SEM and micro-CT identified the presence of cerium oxide nanoparticles deposited within the dentinal tubules and lateral canals of the root canal system. The BMS and remineralized dentin exhibited substantial antibacterial efficacy against E. faecalis, as substantiated by assessments involving the broth dilution method and live/dead staining technique. The SEM findings revealed the cell morphological changes of deceased E. faecalis.

Conclusion

This study successfully demonstrated antibacterial biomimetic mineralization as well as sealing dentinal tubules and lateral branches of root canals using cerium nitrate and dextran. This novel biomimetic mineralization could be used as an alternative strategy for root canal disinfection.

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.

Er:YAG Laser Physical Etching and Ultra-High-Molecular-Weight Cross-Linked Sodium Polyacrylate Chemical Etching for a Reliable Dentin Dry Bonding

Dentin bond interface stability is the key issue of dental adhesion in present clinical dentistry. The concept of selective extrafibrillar demineralization has opened a new way to maintain intrafibrillar minerals to prevent interface degradation. Here, using ultra-high-molecular-weight sodium polyacrylate [Carbopol (Carbo) > 40 kDa] as a calcium chelator, we challenge this concept and propose a protocol for reliable dentin dry bonding. The results of high-resolution transmission electron microscopy revealed periodic bands of 67 nm dentin collagen fibrils after Carbo etching, and the hydroxyproline concentration increasing with prolonged chelating time denied the concept of extrafibrillar demineralization. The results that wet and dry bonding with Carbo-based demineralization produced a weaker bond strength than the traditional phosphoric acid wet adhesion suggested that the Carbo-based demineralization is an unreliable adhesion strategy. A novel protocol of Er:YAG laser physical etching followed by Carbo chemical etching for dentin adhesion revealed that a micro-/nano-level rough, rigid, and non-collagen exposed dentin surface was produced, the micro-tensile bond strength was maintained after aging under dry and wet bonding modes, and in situ zymography and nanoleakage within the hybrid layers presented lower signals after aging. Cell culture in vitro and a rabbit deep dentin adhesion model in vivo proved that this protocol is safe and biocompatible. Taken together, the concept of extrafibrillar demineralization is limited and insufficient to use in the clinic. The strategy of Er:YAG laser physical etching followed by Carbo chemical etching for dentin adhesion produces a bonding effect with reliability, durability, and safety.

Elasticity and material anisotropy of lamellar cortical bone in adult bovine tibia characterized via AFM nanoindentation

The research focuses on the evaluation of the mechanical properties of osteonal cortical bone at the lamellar level. Elastic properties of the mid-diaphysis region of the bovine tibia are investigated via cantilever-based nanoindentation at the submicron length scale utilizing Atomic Force Microscopy, where the force-displacement curves are used for the elastic assessment using the Derjaguin-Muller-Toropov model to calculate indentation modulus. Variations of the modulus and the directional mechanical response of the osteonal bone at different distances from the Haversian canal are investigated. Additionally, the effects of demineralization on the indentation modulus are discussed. It was found that in the axial direction, the first and last untreated thick lamella layers show a significant indentation modulus difference compared to all other layers (4.26 ± 0.4 and 4.6 ± 0.3 GPa vs ∼3.5 GPa). On the other hand, the indentation modulus of transverse thick lamella layers shows a periodic variation between ∼3 ± 0.7 GPa and ∼4 ± 0.3 GPa from near the Haversian canal to near the interstitial bone. A periodic variation in the anisotropy ratio was found. Mineral content was quantified via energy-dispersive X-ray microanalysis at different levels of mineralization and shows a positive correlation with the indentation modulus.

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.

Remineralization of Dentinal Lesions Using Biomimetic Agents: A Systematic Review and Meta-Analysis

The objective of this article was to systematically provide an up-to-date review on the different methods of remineralizing human dentine using different biomimetic agents. The authors performed a systematic search within PubMed, Scopus, and Web of Science in addition to the grey literature in Google Scholar^® using MeSH terms. The PICO question was P: human teeth dentinal sections; I: application of biomimetic remineralizing agents; C: other non-biomimetic approaches; O: extent of remineralization and physical properties of remineralized dentine. The initially identified studies were screened for titles and abstracts. Non-English articles, reviews, animal studies, studies involving the resin-dentine interface, and other irrelevant articles were then excluded. The other remaining full-text articles were retrieved. Bibliographies of the remaining articles were searched for relevant studies that could be included. A total of 4741 articles were found, and finally, 39 full-text articles were incorporated in the current systematic review. From these, twenty-six research studies used non-collagenous protein (NCP) analogs to biomineralize dentine, six studies used bioactive materials derived from natural sources, six studies used zinc hydroxyapatite, and one study used amelogenin peptide to induce hydroxyapatite formation on the surface of demineralized dentine. Additive effects of triclosan and epigenin were assessed when combined with commonly available NCPs. Overall, a moderate risk of bias was observed and, hence, the findings of the included studies could be acceptable. A meta-analysis of some similar studies was performed to assess the depth of remineralization and elastic modulus. Despite having high heterogeneity (I² > 90), all the studies showed a significant improvement in biomimetic remineralization efficacy as compared to the control. All the included studies carried out a functional remineralization assessment and found a 90-98% efficacy in the extent of remineralization while the elastic modulus reached 88.78 ± 8.35 GPa, which is close to natural dentine. It is pertinent to note the limitations of these studies that have been carried out in vitro under controlled settings, which lack the effects of a natural oral environment. To conclude, the authors suggest that the biomimetic remineralization of dentine using NCP analogs, bioactive materials, and natural products carries significant potential in treating dentinal lesions; however, more long-term studies are needed to assess their clinical applications in vivo.

Mineralization promotion and protection effect of carboxymethyl chitosan biomodification in biomimetic mineralization

Biomimetic mineralization emphasizes reversing the process of dental caries through bio-inspired strategies, in which mineralization promotion and collagen protection are equally important. In this study, carboxymethyl chitosan (CMC) was deemed as an analog of glycosaminoglycan for biomimetic modification of collagen, both of the mineralization facilitation and collagen protection effect were evaluated. Experiments were carried out simultaneously on two-dimensional monolayer reconstituted collagen model, three-dimensional reconstituted collagen model and demineralized dentin model. In three models, CMC was successfully cross-linked onto collagen utilizing biocompatible 1-Ethyl-3(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxy sulfosuccinimide sodium salt to achieve biomodification. Results showed that CMC biomodification increased collagen's hydrophilicity, calcium absorption capacity and thermal degradation resistance. In demineralized dentin model, the activity of endogenous matrix metalloproteinases was significantly inhibited by CMC biomodification. Furthermore, CMC biomodification significantly improved cross-linking and intrafibrillar mineralization of collagen, especially in the two-dimensional monolayer reconstituted collagen model. This study provided a biomimetic mineralization strategy with comprehensive consideration of collagen protection, and enriched the application of chitosan-based materials in dentistry.

Differential analysis of the dentin soluble proteomic

OBJECTIVES

To perform a differential analysis of the dentin soluble proteomic and assess the effects of tissue health state and protocol for protein extraction. We hypothesized the dentin soluble proteomic varies according to the tissue physiopathological state (intact vs. caries-affected) and protocol used to extract its proteins.

METHODS

Dentin from freshly extracted non-carious and carious teeth were randomly assigned for protein extraction using either guanidine-HCl/ethylenediaminetetraacetic acid (EDTA) or acetic acid. Protein extracts from intact and caries-affected dentin were processed and digested with trypsin for shotgun label-free proteomic analysis (nLC-ESI-MS/MS). Peptides identification was performed on a nanoACQUITY UPLC-Xevo Q-Tof MS system. Peptides identified with scores of confidence greater than 95% were included in the quantitative statistical analysis embedded in the PLGS software. Differences between experimental conditions were calculated using Student test-t with significance pre-set at α=0.05.

RESULTS

A total of 158 human proteins were identified. Approximately one-sixth of proteins (24/158) were present in at least two different extracts. Conversely, the greatest number of proteins (134/158) was identified uniquely in only one of the extracts. Overall, a larger number of soluble proteins was retrieved from caries-affected than intact dentin (86/158). Likewise, a greater number of proteins was extracted by the guanidine-HCl/EDTA (106/158) in comparison to acetic acid protocol. Several proteins detected in dentin extracts, mainly those from caries-affected teeth, are biological and/or metabolically involved with tissue turnover/remodeling.

CONCLUSION

The identity/abundance of soluble proteins retrieved from and remained in dentin noticeably depend on this tissue physiopathological state and protocol used to remove its minerals.

CLINICAL SIGNIFICANCE

The present findings brought new insight into the proteomic phenotype of human dentin and may provide targets for the development of novel caries disease-prevention therapies.

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.

The Dosidicus gigas Collagen for Scaffold Preparation and Cell Cultivation: Mechanical and Physicochemical Properties, Morphology, Composition and Cell Viability

Directed formation of the structure of the culture of living cells is the most important task of tissue engineering. New materials for 3D scaffolds of living tissue are critical for the mass adoption of regenerative medicine protocols. In this manuscript, we demonstrate the results of the molecular structure study of collagen from Dosidicus gigas and reveal the possibility of obtaining a thin membrane material. The collagen membrane is characterized by high flexibility and plasticity as well as mechanical strength. The technology of obtaining collagen scaffolds, as well as the results of studies of its mechanical properties, surface morphology, protein composition, and the process of cell proliferation on its surface, are shown in the given manuscript. The investigation of living tissue culture grown on the surface of a collagen scaffold by X-ray tomography on a synchrotron source made it possible to remodel the structure of the extracellular matrix. It was found that the scaffolds obtained from squid collagen are characterized by a high degree of fibril ordering and high surface roughness and provide efficient directed growth of the cell culture. The resulting material provides the formation of the extracellular matrix and is characterized by a short time to living tissue sorption.

Poly(acrylic acid)-Assisted Intrafibrillar Mineralization of Type I Collagen: A Review

The mineralization of type I collagen is a biological process occurring in vertebrates by which some hard tissues such as bone and dentin are constructed. Due to the extensive clinical needs for bone defect repair and remineralization of mineral-depleted dentin, biomimetic mineralization of collagen is attracting more and more interests. Synthetic analogs of noncollagenous proteins are necessary for directing the in vitro mineralization. In this paper, the function and mechanism of poly(acrylic acid) (PAA) in regulating the mineralization, especially intrafibrillar mineralization (IM) of collagen are reviewed. As two mineralization patterns (extrafibrillar and intrafibrillar) co-exist in natural hard tissues, differences between them in terms of microstructure, biodegradation, cytocompatibility, osteoinduction in vitro, and performance in vivo are systematically compared. Then the roles of PAA in biomimetic collagen IM within one-analog and two-analog systems are discussed, respectively. Moreover, mineralization of some self-mineralizable collagen matrices is described. Due to the interactions between collagen and PAA play a crucial role in the processes of collagen mineralization, some reference researches are also provided involving the collagen/PAA interactions in some other fields. Finally, this review is ended with an outlook for future potential improvements based on the collection of existing bottlenecks in this field.

Extrafibrillarly Demineralized Dentin Matrix for Bone Regeneration

Dentin is a natural extracellular matrix, but its availability in bone grafting and tissue engineering applications is underestimated due to a lack of proper treatment. In this study, the concept of extrafibrillar demineralization is introduced into the construction of dentin-derived biomaterials for bone regeneration for the first time. Calcium chelating agents with large molecular weights are used to selectively remove the extrafibrillar apatite minerals without disturbing the intrafibrillar minerals within dentin collagen, resulting in the formation of an extrafibrillarly demineralized dentin matrix (EDM). EDM with distinctive nanotopography and bone-like mechanical properties is found to significantly promote cell adhesion, migration, and osteogenic differentiation in vitro while enhancing in vivo bone healing of rat calvarial defects. The outstanding osteogenic performance of EDM is further confirmed to be related to the activation of the focal adhesion-cytoskeleton-nucleus mechanotransduction axis. Overall, this study shows that extrafibrillar demineralization of dentin has great potential to produce hierarchical collagen-based scaffolds for bone regeneration, and this facile top-down fabrication method brings about new ideas for the biomedical application of naturally derived bioactive materials.

Role of Collagen in Vascular Calcification

ABSTRACT

Vascular calcification is a pathological process characterized by ectopic calcification of the vascular wall. Medial calcifications are most often associated with kidney disease, diabetes, hypertension, and advanced age. Intimal calcifications are associated with atherosclerosis. Collagen can regulate mineralization by binding to apatite minerals and promoting their deposition, binding to collagen receptors to initiate signal transduction, and inducing cell transdifferentiation. In the process of vascular calcification, type I collagen is not only the scaffold for mineral deposition but also a signal entity, guiding the distribution, aggregation, and nucleation of vesicles and promoting the transformation of vascular smooth muscle cells into osteochondral-like cells. In recent years, collagen has been shown to affect vascular calcification through collagen disc-domain receptors, matrix vesicles, and transdifferentiation of vascular smooth muscle cells.

Promoting effect of a calcium-responsive self-assembly β-sheet peptide on collagen intrafibrillar mineralization

Recently, a de novo synthetic calcium-responsive self-assembly β-sheet peptide ID8 (Ile-Asp-Ile-Asp-Ile-Asp-Ile-Asp) has been developed to serve as the template inducing hydroxyapatite nucleation. The aim of this study was to evaluate the effect of ID8 on intrafibrillar mineralization of collagen making full use of its self-assembly ability. The mineralization experiments were carried out in vitro on both bare Type I collagen and fully demineralized dentin samples. The calcium-responsive self-assembly of ID8 was revealed by circular dichroism spectrum, 8-anilino-1-naphthalenesulfonic acid ammonium salt hydrate assay, attenuated total reflection Fourier transform infrared spectrum (ATR-FTIR) and transmission electron microscope (TEM). Polyacrylic acid (450 kDa) with a concentration of 100 μg ml⁻¹ was selected as the nucleation inhibitor based on the determination of turbidimetry and TEM with selected area electron diffraction (TEM-SAED). The results showed that collagen intrafibrillar mineralization was significantly promoted with the pretreatment of self-assembly ID8 detected by TEM-SAED, SEM, X-ray diffraction and ATR-FTIR. The pretreatment of collagen utilizing self-assembly ID8 not only enhanced intermolecular hydrogen bonding but also contributed to calcium retention inside collagen and significantly increased the hydrophilicity of collagen. These results indicated that peptides with self-assembly properties like ID8 are expected to be potential tools for biomimetic mineralization of collagen.

Retention of Intrafibrillar Minerals Improves Resin-Dentin Bond Durability

The concept of extrafibrillar demineralization involves selective removal of apatite crystallites from the extrafibrillar spaces of mineralized dentin without disturbing the intrafibrillar minerals within collagen. This helps avoiding activation of endogenous proteases and enables air-drying of partially demineralized dentin without causing collapse of completely demineralized collagen matrix that adversely affects resin infiltration. The objective of the present study was to evaluate the potential of quaternized carboxymethyl chitosan (QCMC)-based extrafibrillar demineralization in improving resin-dentin bond durability. Isothermal titration calorimetry indicated that QCMC synthesized by quaternization of O-carboxymethyl chitosan had moderate affinity for Ca²⁺ (binding constant: 8.9 × 10⁴ M^-1). Wet and dry bonding with the QCMC-based demineralization produced tensile bond strengths equivalent to the phosphoric acid (H₃PO₄)-based etch-and-rinse technique. Those bond strengths were maintained after thermocycling. Amide I and PO₄^3- mappings of QCMC-conditioned dentin were performed with atomic force microscope-infrared spectroscopy (AFM-IR). Whereas H₃PO₄-etched dentin exhibited an extensive reduction in PO₄^3- signals corresponding to apatite depletion, QCMC-conditioned dentin showed scattered dark areas and bright PO₄^3- streak signals. The latter were consistent with areas identified as collagen fibrils in the amide I mapping and were suggestive of the presence of intrafibrillar minerals in QCMC-conditioned dentin. Young's modulus mapping of QCMC-demineralized dentin obtained by AFM-based amplitude modulation-frequency modulation recorded moduli that were the same order of magnitude as those in mineralized dentin and at least 1 order higher than H₃PO₄-etched dentin. In situ zymography of the gelatinolytic activity within hybrid layers created with QCMC conditioning revealed extremely low signals before and after thermocycling, compared with H₃PO₄-etched dentin for both wet and dry bonding. Confocal laser scanning microscopy identified the antibacterial potential of QCMC against Streptococcus mutans and Enterococcus faecalis biofilms. Taken together, the QCMC-based demineralization retains intrafibrillar minerals, preserves the elastic modulus of collagen fibrils, reduces endogenous proteolytic activity, and inhibits bacteria biofilms to extend dentin bond durability.

Chlorhexidine-loaded poly (amido amine) dendrimer and a dental adhesive containing amorphous calcium phosphate nanofillers for enhancing bonding durability

OBJECTIVE

A novel method of combining chlorhexidine (CHX) loaded poly (amido amine) (PAMAM) dendrimers with a dental adhesive containing amorphous calcium phosphate (ACP) nanofillers are proposed for etch-and-rinse bonding system to enhance resin-dentin bonding durability.

METHODS

The CHX-loaded PAMAM and ACP nanofillers were synthesized and characterized. Their effects on the cytotoxicity were tested by MTT assay. Micro-tensile bond strength (μTBS) before and after thermomechanical challenges were used to evaluate the bonding durability. Anti-matrix metalloproteinase (MMPs) property was examined using in-situ zymography. A double-fluorescence technique was used to examine interfacial permeability after bonding. Dentin remineralization in Ca/P lacking solution was observed under scanning electron microscopy.

RESULTS

Compared with a 0.2 wt% CHX solution, the PAMAM loaded CHX had less cytotoxicity, while the in situ zymography showed it could still inhibit MMPs activity within the hybrid layer after released from PAMAM. The application of the novel method maintained the μTBS better than the control group after thermomechanical challenges, and it did not negatively affect water permeability of the bonding interfaces. CHX-loaded PAMAM regulated the calcium (Ca) and phosphate (P) ions provided by the ACP-containing adhesives to remineralize the demineralized dentin surfaces without initial Ca/P in the environment.

SIGNIFICANCE

The novel method can reduce the cytotoxicity of CHX, inhibit MMPs activities, maintain μTBS, and induce dentin remineralization, which are crucial factors for enhancing bonding durability.

Remineralization of human dentin type I collagen fibrils induced by carboxylated polyamidoamine dendrimer/amorphous calcium phosphate nanocomposite: an in vitro study

Intrafibrillar mineralization of type I collagen fibrils is of great significance in dental remineralization, which is the key of caries prevention and treatment. Herein, two substances that have the remineralization ability, carboxylated polyamidoamine dendrimer (PAMAM-COOH) and nano-sized amorphous calcium phosphate (n-ACP) were combined to synthesize a novel nanomaterial, carboxylated polyamidoamine dendrimer/amorphous calcium phosphate nanocomposite (PAMAM-COOH/ACP). This article aims to evaluate the remineralization effect of PAMAM-COOH/ACP of dentin type I collagen fibrils in vitro. Fluorescence labeling technique was innovatively used to observe and evaluate the remineralization effect. PAMAM-COOH/ACP showed superior remineralization ability of human dentin type I collagen fibrils, especially the intrafibrillar remineralization. Therefore, the novel nanomaterial PAMAM-COOH/ACP is promising to prevent and treat various diseases caused by dentin demineralization and to improve various dental materials.

Comparison of Synthetic vs. Biogenic Polymeric Process-Directing Agents for Intrafibrillar Mineralization of Collagen

With the aging population, there is a growing need for mineralized tissue restoration and synthetic bone substitutes. Previous studies have shown that a polymer-induced liquid-precursor (PILP) process can successfully mineralize collagen substrates to achieve compositions found in native bone and dentin. This process also leads to intrafibrillar apatitic crystals with their [001] axes aligned roughly parallel to the long axis of the collagen fibril, emulating the nanostructural organization found in native bone and dentin. When demineralized bovine bone was remineralized via the PILP process using osteopontin (OPN), the samples were able to activate mouse marrow-derived osteoclasts to similar levels to those of native bone, suggesting a means for fabricating bioactive bone substitutes that could trigger remodeling through the native bone multicellular unit (BMU). In order to determine if OPN derived from bovine milk could be a cost-effective process-directing agent, the mineralization of type I collagen scaffolds using this protein was compared to the benchmark polypeptide of polyaspartic acid (sodium salt; pAsp). In this set of experiments, we found that OPN led to much faster and more uniform mineralization when compared with pAsp, making it a cheaper and commercially attractive alternative for mineralized tissue restorations.

Assessment of the size selectivity of peritoneal permeability by the restriction coefficient to protein transport

Transport of serum proteins from the circulation to peritoneal dialysate in peritoneal dialysis patients mainly focused on total protein. Individual proteins have hardly been studied. We determined serum and effluent concentrations of four individual proteins with a wide molecular weight range routinely in the standardised peritoneal permeability analysis performed yearly in all participating patients. These include β2-microglobulin, albumin, immunoglobulin G and α2-macroglobulin. The dependency of transport of these proteins on their molecular weight and diffusion coefficient led to the development of the peritoneal protein restriction coefficient (PPRC), which is the slope of the relation between the peritoneal clearances of these proteins and their free diffusion coefficients in water, when plotted on a double logarithmic scale. The higher the PPRC, the more size restriction to transport. In this review, we discuss the results obtained on the PPRC under various conditions, such as effects of various osmotic agents, vasoactive drugs, peritonitis and the hydrostatic pressure gradient. Long-term follow-up of patients shows an increase of the PPRC, the possible causes of which are discussed. Venous vasculopathy of the peritoneal microcirculation is the most likely explanation.

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.

Progress on Biomimetic Mineralization and Materials for Hard Tissue Regeneration

Biomineralization is a process in which natural organisms regulate the crystal growth of inorganic minerals, resulting in hierarchical structured biominerals with excellent properties. Typical biominerals in the human body are the bones and teeth, and damage to these hard tissues directly affect our daily lives. The repair of bones and teeth in a biomimetic way, either by using a biomimetic mineralization strategy or biomimetic materials, is the key for hard tissue regeneration. In this review, we briefly introduce the structure of bone and tooth, and highlight the fundamental role of collagen mineralization in tissue repair. The recent progress on intra-/extrafibrillar collagen mineralization by a biomimetic strategy or materials is presented, and their potential for tissue regeneration is discussed. Then, recent achievements on bone and tooth repair are summarized, and these works are discussed in the view of materials science and biological science, providing a broader vision for the future research of hard tissue repair techniques. Lastly, recent progress on hard tissue regeneration is concluded, and existing problems and future directions are prospected.

Enzymatic Approach in Calcium Phosphate Biomineralization: A Contribution to Reconcile the Physicochemical with the Physiological View

Biomineralization is the process by which organisms produce hard inorganic matter from soft tissues with outstanding control of mineral deposition in time and space. For this purpose, organisms deploy a sophisticated "toolkit" that has resulted in significant evolutionary innovations, for which calcium phosphate (CaP) is the biomineral selected for the skeleton of vertebrates. While CaP mineral formation in aqueous media can be investigated by studying thermodynamics and kinetics of phase transitions in supersaturated solutions, biogenic mineralization requires coping with the inherent complexity of biological systems. This mainly includes compartmentalization and homeostatic processes used by organisms to regulate key physiological factors, including temperature, pH and ion concentration. A detailed analysis of the literature shows the emergence of two main views describing the mechanism of CaP biomineralization. The first one, more dedicated to the study of in vivo systems and supported by researchers in physiology, often involves matrix vesicles (MVs). The second one, more investigated by the physicochemistry community, involves collagen intrafibrillar mineralization particularly through in vitro acellular models. Herein, we show that there is an obvious need in the biological systems to control both where and when the mineral forms through an in-depth survey of the mechanism of CaP mineralization. This necessity could gather both communities of physiologists and physicochemists under a common interest for an enzymatic approach to better describe CaP biomineralization. Both homogeneous and heterogeneous enzymatic catalyses are conceivable for these systems, and a few preliminary promising results on CaP mineralization for both types of enzymatic catalysis are reported in this work. Through them, we aim to describe the relevance of our point of view and the likely findings that could be obtained when adding an enzymatic approach to the already rich and creative research field dealing with CaP mineralization. This complementary approach could lead to a better understanding of the biomineralization mechanism and inspire the biomimetic design of new materials.

Effects of bioactive glass with high phosphorus content on mineralization of type I collagen fibrils

PURPOSE

To study effects of bioactive glass with high phosphorus content (10.8% P₂O₅, 54.2% SiO₂, 35% CaO, mol%, named PSC) on mineralization of type I collagen fibrils.

METHODS

(1) PSC, and PSC combining 0.1 mg/mL, 0.5 mg/mL, or 1.0 mg/mL polyacrylic acid (PAA), were used to induce the mineralization of self-assembled type I collagen fibrils. After 3 and 7 days of mineralization, collagen fibrils were observed by transmission electron microscopy (TEM) and selected area electron diffraction (SAED). (2) PSC suspension was dialyzed in simulated body fluid (SBF), or in SBF containing 0.1 mg/mL, 0.5 mg/mL, or 1.0 mg/mL PAA, to form amorphous calcium phosphate (ACP), then observed by TEM.

RESULTS

(1) PSC and PSC combining 0.1 mg/mL or 0.5 mg/mL PAA induced mainly extrafibrillar mineralization. PSC combining 1.0 mg/mL PAA induced both extrafibrillar and intrafibrillar mineralization. (2) The ACP induced by PSC or PSC combining 0.1 mg/mL PAA partly formed lattice structure after 24 h. The particle size of the ACP induced by PSC combining 0.5 mg/mL PAA was 100-150 nm, and that induced by PSC combining 1.0 mg/mL PAA was 30-50 nm.

CONCLUSION

PSC induced mainly extrafibrillar mineralization, and PSC combining an appropriate concentration (1.0 mg/mL) of PAA induced both extrafibrillar and intrafibrillar mineralization.

Growth of mineralized collagen films by oriented calcium fluoride nanocrystal assembly with enhanced cell proliferation

Bone is a highly calcified tissue with 60 wt% inorganic components. It is made up of mineralized collagen fibrils, where the platelet-like hydroxyapatite nanocrystals deposit within the collagen fibrils in an oriented manner. Inspired by the special structure and biological activity of bone, we realize the intrafibrillar mineralization of collagen films with oriented calcium fluoride nanocrystals in vitro. Amorphous calcium fluoride (ACF) precursors are generated by polyacrylic acid through polymer-induced liquid precursor processes. The precursors are ready to infiltrate and fill the gap zones laterally and then diffuse to occupy the whole space inside the collagen longitudinally. Finally, the fully mineralized collagen fibrils exhibit a single-crystal-like structure after transforming precursors to co-oriented nanocrystals under the influence of arranged collagen molecules. Expanding the collagen mineralization from 1D fibrils to 2D films, the growth of mineralized areas on the films with a reaction-limited behavior is found. The kinetic rate of growth is around 0.2-0.3 μm min^-1, which depends on the pH of the solution. Furthermore, the mineralized collagen films exhibit an enhanced ability of cell proliferation over the pure collagen matrices. Understanding the mineralization of artificial collagen-based scaffolds may have broad promising potentials for bone tissue regeneration and repair in the future.

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.

In Vitro Mineralization of Collagen

Collagen mineralization is a biological process in many skeletal elements in the animal kingdom. Examples of these collagen-based skeletons are the siliceous spicules of glass sponges or the intrafibrillar hydroxyapatite platelets in vertebrates. The mineralization of collagen in vitro has gained interest for two reasons: understanding the processes behind bone formation and the synthesis of scaffolds for tissue engineering. In this paper, the efforts toward collagen mineralization in vitro are reviewed. First, general introduction toward collagen type I, the main component of the extracellular matrix in animals, is provided, followed by a brief overview of collagenous skeletons. Then, the in vitro mineralization of collagen is critically reviewed. Due to their biological abundance, hydroxyapatite and silica are the focus of this review. To a much lesser extent, also some efforts with other minerals are outlined. Combining all minerals and the suggested mechanisms for each mineral, a general mechanism for the intrafibrillar mineralization of collagen is proposed. This review concludes with an outlook for further improvement of collagen-based tissue engineering scaffolds.

Use of phosphorylated PAMAM and carboxyled PAMAM to induce dentin biomimetic remineralization and dentinal tubule occlusion

It is crucial to emphasize the biomineralization therapeutic method to repair etched dentin in clinic. Non-collagenous proteins (NCPs) play critical role in the biomineralization of dentine. In this paper, we synthesized the phosphate-terminated polyamidoamine dendrimer (PAMAM-PO₃H₂) by one-step modification successfully and examined by Fourier-transform infrared spectroscopy (FTIR) and ¹H-nuclear Magnetic Resonance (¹H-NMR) to characterize the structure of PAMAM-PO₃H₂. PAMAM-PO₃H₂ and carboxylterminated dendrimers (PAMAM-COOH) were applied as the dual biomimetic analogs of NCPs. Through the characterization of FT-IR, field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), the surfaces of human dentin were covered with regenerated crystals and the dentinal tubules were occluded by PAMAM-PO₃H₂ and PAMAM-COOH. In summary, the combination of PAMAM-PO₃H₂ and PAMAM-COOH may be another feasible therapeutic method for the treatment of dentin caries and dentin hypersensitivity.

A novel dentin bonding scheme based on extrafibrillar demineralization combined with covalent adhesion using a dry-bonding technique

Dentin bonding is a dynamic process that involves the penetration of adhesive resin monomers into the extrafibrillar and intrafibrillar demineralized collagen matrix using a wet-bonding technique. However, adhesive resin monomers lack the capacity to infiltrate the intrafibrillar space, and the excess water that is introduced by the wet-bonding technique remains at the bonding interface. This imperfectly bonded interface is inclined to hydrolytic degradation, severely jeopardizing the longevity of bonded clinical restorations. The present study introduces a dentin bonding scheme based on a dry-bonding technique, combined with the use of extrafibrillar demineralization and a collagen-reactive monomer (CRM)-based adhesive (CBA). Selective extrafibrillar demineralization was achieved using 1-wt% high-molecular weight (MW) carboxymethyl chitosan (CMCS) within a clinically acceptable timeframe to create a less aggressive bonding substance for dentin bonding due to its selectively extrafibrillar demineralization capacity. CMCS demineralization decreased the activation of in situ collagenase, improved the shrinking resistance of demineralized collagen, and thus provided stronger and more durable bonding than traditional phosphoric acid etching. The new dentin bonding scheme that contained CMCS and CBA and used a dry-bonding technique achieved an encouraging dentin bonding strength and durability with low technical sensitivity. This bonding scheme can be used to improve the stability of the resin-dentin interface and foster the longevity of bonded clinical restorations.

A matched irrigation and obturation strategy for root canal therapy

In root canal therapy, irrigating solutions are employed to eliminate the bacterial load and also prepare dentin for sealer interaction. The aim of this research was to assess how irrigating solutions employed on their own or in sequence affected the tooth structure. The best way to prepare the tooth for obturation using hydraulic calcium silicate cement (HCSC) sealers and gutta-percha, thus guiding clinicians on a matched irrigation-obturation strategy for optimized root canal treatment was investigated. The effect of irrigating solutions on dentine was investigated by assessing changes in dentin microhardness, ultrastructure and mineral content, organic/inorganic matter, surface roughness and Young’s modulus. The interaction of four root canal sealers with the dentin was analysed by assessing the changes in microhardness of the dentin after sealer placement and also the sealer to dentin interface by scanning electron and confocal laser microscopy. The irrigating solutions damaged the dentin irreversibly both when used on their own and in combination. The best sequence involved sodium hypochlorite followed by chelator and a final rinse with sodium hypochlorite and obturation using HCSC sealers that enabled the restoration of dentin properties. The HCSC sealers did not rely on chelator irrigating solutions for a good material adaptation to dentin.

Non-equilibrium growth and twist of cross-linked collagen fibrils

The lysyl oxidase (LOX) enzyme that catalyses cross-link formation during the assembly of collagen fibrils in vivo is too large to diffuse within assembled fibrils, and so is incompatible with a fully equilibrium mechanism for fibril formation. We propose that enzymatic cross-links are formed at the fibril surface during the growth of collagen fibrils; as a consequence no significant reorientation of previously cross-linked collagen molecules occurs inside collagen fibrils during fibril growth in vivo. By imposing local equilibrium only at the fibril surface, we develop a coarse-grained quantitative model of in vivo fibril structure that incorporates a double-twist orientation of collagen molecules and a periodic D-band density modulation along the fibril axis. Radial growth is controlled by the concentration of available collagen molecules outside the fibril. In contrast with earlier equilibrium models of fibril structure, we find that all fibrils can exhibit a core-shell structure that is controlled only by the fibril radius. At small radii a core is developed with a linear double-twist structure as a function of radius. Within the core the double-twist structure is largely independent of the D-band. Within the shell at larger radii, the structure approaches a constant twist configuration that is strongly coupled with the D-band. We suggest a stable radius control mechanism that corneal fibrils can exploit near the edge of the linear core regime; while larger tendon fibrils use a cruder version of growth control that does not select a preferred radius.

The effect of prime-and-rinse approach using MDP micellar solutions on extrafibrillar demineralization and dentin bond performance

OBJECTIVE

This study investigated the effects of prime-and-rinse approach using 10-methacryloyloxydecyl dihydrogen phosphate (MDP) micellar solutions on extrafibrillar demineralization and dentin bond performance of etch-and-rinse adhesive.

METHODS

The micellar solutions were prepared by adding 15% MDP in two ethanol-aqueous (75:25, 55:45 V/V%) solutions, referring to MDP/EtOH₇₅ and MDP/EtOH₅₅. After mid-coronal dentin surfaces were either etched (control) or conditioned with MDP/EtOH₇₅ and MDP/EtOH₅₅ and rinsed, they were applied with adhesive (Adpter Single Bond 2) in dry- or wet-bonding mode and placed with composite resin (Filtek Z350 XT). They were prepared into multiple micro-beams for micro-tensile bond strengths (MTBS) testing after storage in water for 24 h or subjecting to thermocycling. The other pretreated dentin surfaces were analyzed by TF-XRD, ATR-FTIR, HRTEM, FE-SEM, contact angle measurement and nanoindentation testing. The MTBS data was analyzed with two-way ANOVA followed by LSD post-hoc test.

RESULTS

MDP/EtOH₇₅ produced significantly greater MTBS values than MDP/EtOH₅₅ and control after thermocycling aging in dry- or wet-bonding mode (P < 0.05). The ATR-FTIR spectrums shows that ratios of phosphate/monomer (1,034 cm^-1/1,716 cm^-1) on MDP/EtOH₇₅-, MDP/EtOH₅₅-treated dentin surfaces are 0.51 and 0.23, respectively. This is confirmed by HRTEM images and SAED pattern that intrafibrillar minerals were mostly preserved after treatment with MDP/EtOH₇₅. MDP/EtOH₇₅ produced significantly higher elastic modulus and nanohardness on pretreated dentin surface than MDP/EtOH₅₅ (P < 0.05). TF-XRD pattern shows some MDP-Ca salts remained on the primed dentin surface.

SIGNIFICANCE

Prime-and-rinse approach using MDP/EtOH₇₅ micellar solution could produce mostly extrafibrillar demineralization, and greatly increase dentin bond durability in dry- or wet-bonding mode.

Biomineralization of Collagen-Based Materials for Hard Tissue Repair

Hydroxyapatite (HA) reinforced collagen fibrils serve as the basic building blocks of natural bone and dentin. Mineralization of collagen fibrils play an essential role in ensuring the structural and mechanical functionalities of hard tissues such as bone and dentin. Biomineralization of collagen can be divided into intrafibrillar and extrafibrillar mineralization in terms of HA distribution relative to collagen fibrils. Intrafibrillar mineralization is termed when HA minerals are incorporated within the gap zone of collagen fibrils, while extrafibrillar mineralization refers to the minerals that are formed on the surface of collagen fibrils. However, the mechanisms resulting in these two types of mineralization still remain debatable. In this review, the evolution of both classical and non-classical biomineralization theories is summarized. Different intrafibrillar mineralization mechanisms, including polymer induced liquid precursor (PILP), capillary action, electrostatic attraction, size exclusion, Gibbs-Donnan equilibrium, and interfacial energy guided theories, are discussed. Exemplary strategies to induce biomimetic intrafibrillar mineralization using non-collagenous proteins (NCPs), polymer analogs, small molecules, and fluidic shear stress are discussed, and recent applications of mineralized collagen fibers for bone regeneration and dentin repair are included. Finally, conclusions are drawn on these proposed mechanisms, and the future trend of collagen-based materials for bone regeneration and tooth repair is speculated.

Role of emerging vitamin K‑dependent proteins: Growth arrest‑specific protein 6, Gla‑rich protein and periostin (Review)

Vitamin K-dependent proteins (VKDPs) are a group of proteins that need vitamin K to conduct carboxylation. Thus far, scholars have identified a total of 17 VKDPs in the human body. In this review, we summarize three important emerging VKDPs: Growth arrest-specific protein 6 (Gas 6), Gla-rich protein (GRP) and periostin in terms of their functions in physiological and pathological conditions. As examples, carboxylated Gas 6 and GRP effectively protect blood vessels from calcification, Gas 6 protects from acute kidney injury and is involved in chronic kidney disease, GRP contributes to bone homeostasis and delays the progression of osteoarthritis, and periostin is involved in all phases of fracture healing and assists myocardial regeneration in the early stages of myocardial infarction. However, periostin participates in the progression of cardiac fibrosis, idiopathic pulmonary fibrosis and airway remodeling of asthma. In addition, we discuss the relationship between vitamin K, VKDPs and cancer, and particularly the carboxylation state of VKDPs in cancer.

Polyelectrolyte-calcium complexes as a pre-precursor induce biomimetic mineralization of collagen

Polyelectrolytes such as polyaspartic acid (PAsp) are critical in biomimetic mineralization as stabilizers of amorphous calcium phosphate (ACP) precursors and as nucleation inhibitors similar to non-collagenous proteins (NCPs). Nevertheless, the application of polyelectrolyte-calcium complexes as a pre-precursor, such as PAsp-Ca complexes, in the mineralization of collagen is unexplored. Herein, we propose a polyelectrolyte-Ca complex pre-precursor (PCCP) process for collagen mineralization. By combining three-dimensional (3D) STORM, potential measurements, and cryogenic transmission electron microscopy with molecular dynamics simulations, we show that liquid-like electropositive PAsp-Ca complexes along with free calcium ions infiltrate electronegative collagen fibrils. The PAsp-Ca complexes are immobilized within the fibrils via chelation and hydrogen bonds, and outward movement of free calcium ions is prevented while phosphate and hydroxide are recruited through electrostatic attractions. Afterwards, ACP instantly forms and gradually crystallizes. The PCCP process not only unites two distinct crystallization pathways (classical (free Ca/P ions) and non-classical (polyelectrolyte-Ca complexes)), but also provides a novel strategy for rapid biomimetic mineralization of collagen.

Piezoelectric Heterogeneity in Collagen Type I Fibrils Quantitatively Characterized by Piezoresponse Force Microscopy

Piezoelectricity of Type I collagen can provide the stress-generated potential that is considered to be one of the candidate mechanisms to explain bone's adaptation to loading. However, it is still challenging to quantify piezoelectricity because of its heterogeneity and small magnitude. In this study, resonance-enhanced piezoresponse force microscopy (PFM) was utilized to amplify a weak piezoresponse of a single collagen fibril with a carefully calibrated cantilever. The quantitative PFM, combined with a dual-frequency resonance-tracking method, successfully identified the anisotropic and heterogenous nature of the piezoelectric properties in the collagen fibril. The profile of shear piezoelectric coefficient (d₁₅) was obtained to be periodic along the collagen fibril, with a larger value in the gap zone (0.51 pm/V) compared to the value in the overlap zone (0.29 pm/V). Interestingly, this piezoelectric profile corresponds to the periodic profile of mechanical stiffness in a mineralized collagen fibril having a higher stiffness in the gap zone. Considering that apatite crystals are nucleated at the gap zone and subsequently grown along the collagen fibril, the heterogeneous and anisotropic nature of piezoelectric properties highlights the physiological importance of the collagen piezoelectricity in bone mineralization.

Doping bioactive elements into a collagen scaffold based on synchronous self-assembly/mineralization for bone tissue engineering

Pure collagen is biocompatible but lacks inherent osteoinductive, osteoimmunomodulatory and antibacterial activities. To obtain collagen with these characteristics, we developed a novel methodology of doping bioactive elements into collagen through the synchronous self-assembly/mineralization (SSM) of collagen. In the SSM model, amorphous mineral nanoparticles (AMN) (amorphous SrCO3, amorphous Ag3PO4, etc.) stabilized by the polyampholyte, carboxymethyl chitosan (CMC), and collagen molecules were the primary components under acidic conditions. As the pH gradually increased, intrafibrillar mineralization occurred via the self-adaptive interaction between the AMNs and the collagen microfibrils, which were self-assembling; the AMNs wrapped around the microfibrils became situated in the gap zones of collagen and finally transformed into crystals. Sr-doped collagen scaffolds (Sr-CS) promoted in vitro cell proliferation and osteogenic differentiation of rat bone marrow mesenchymal stromal cells (rBMSCs) and synergistically improved osteogenesis of rBMSCs by altering the macrophage response. Ag-doped collagen scaffolds (Ag-CS) exhibited in vitro antibacterial effects on S. aureus, as well as cell/tissue compatibility. Moreover, Sr-CS implanted into the calvarial defect of a rat resulted in improved bone regeneration. Therefore, the SSM model is a de novo synthetic strategy for doping bioactive elements into collagen, and can be used to fabricate multifunctional collagen scaffolds to meet the clinical challenges of encouraging osteogenesis, boosting the immune response and fighting severe infection in bone defects.

The effects of sequential and continuous chelation on dentin

OBJECTIVE

Proteolytic and demineralizing agents have a profound influence on the dentin ultrastructure, which plays a key role in the mechanical integrity of the tooth and integrity of dentin-biomaterial interfaces. In-depth characterization of dentin treated with a novel root canal irrigation protocol comprising sodium hypochlorite (NaOCl) and etidronate (HEDP) is lacking. This study comprehensively characterized and compared the effects of the continuous chelation (NaOCl/HEDP) and sequential chelation (NaOCl/EDTA) protocols on dentin.

METHODS

Dentin blocks, dentin powder and root canals of mandibular premolars were distributed into Group 1, Saline (control); Group 2, NaOCl/EDTA; and Group 3, NaOCl/HEDP. Ultrastructural characteristics of the treated dentin were investigated using electron microscopy and light microscopy, while the surface roughness was analyzed using atomic force microscopy. Chemical compositional changes were characterized using Fourier transform infrared spectroscopy (FTIR) and energy-dispersive-X-ray spectroscopy (EDS), while collagen degradation was determined using ninhydrin assay. Data were statistically analyzed using multiple-factor one-way ANOVA and Tukey HSD tests (P = 0.05).

RESULTS

NaOCl/HEDP resulted in partially degraded, yet mineralized collagen fibers, with minimal alteration to the subsurface matrix. Conversely, NaOCl/EDTA dissolved the hydroxyapaptite encapsulation, exposing collagen fibre bundles. There was no significant difference in the surface roughness between the two protocols (P > 0.05). NaOCl/HEDP resulted in homogenous distribution of organic and inorganic components on the treated surface.

SIGNIFICANCE

This study highlighted that continuous chelation (NaOCl/HEDP) resulted in a frail surface collagen layer while sequential chelation (NaOCl/EDTA) exposed bare collagen fibres. These surface and sub-surface effects potentially contribute to structural failures of dentin and/or dentin-biomaterial interfacial failures.

[Effect of bioactive glass pretreatment on the durability of dentin bonding interface]

OBJECTIVE

To study the effect of bioactive glass (BG) on the dentin bond strength and the microleakage of hybrid layer.

METHODS

In the study, 30 dentin planes were prepared from the third molars with no caries and equally assigned to the control group, BG group, and sodium trimetaphosphate (STMP)-polyacrylic acid (PAA)-BG group (S-P-BG group), randomly. After etched with 35% phosphoric acid, the dentin planes of BG group were pretreated with 0.5 g/L BG, and the dentin planes of S-P-BG group were pretreated with 5% STMP, 5% PAA and 0.5 g/L BG. No additional pretreatment was done to the dentin planes of control group. Then the dentin planes were bonded using 3M Single Bond 2 adhesive to 3M Z350XT composite resin, and cut into 0.9 mm×0.9 mm column samples, which were stored at 37 ℃ artificial saliva (AS). After 24 hours, 1 month, and 3 months, the microtensile bond strength test was performed. The data were analyzed using one-way ANOVA and LSD method. The morphology of the bond fracture interface was observed with scanning electron microscope. Other 27 teeth were collected and the enamel layer and roots cut off, with the pulp chamber exposed. 0.1% rhodamine B was added to the 3M Single Bond 2 adhesive, and then the adhesive was applied to complete the bonding procedures as above. The teeth were stored in 37 ℃ AS for 24 hours, 1 month, 3 months, and then 0.1% sodium fluorescein solution was placed in the chambers and stained for 1 hour. Confocal laser scanning microscopy was used to observe the interface morphology and microleakage of the hybrid layer.

RESULTS

At the end of 24 hours and 1 month, there was no significant difference in the microtensile bond strength among the three groups (P>0.05). After 3 months of soaking, the S-P-BG group [(36.91±7.07) MPa] had significantly higher microtensile bond strength than the control group [(32.73±8.06) MPa] (P=0.026); For the control group and the BG group, the microtensile bond strength significantly decreased at the end of 3 months compared with 24 hours (control group: P=0.017, BG group: P=0.01); The microtensile bond strength of S-P-BG group af the end of 3 months had no significant difference in compared with 24 hours [(37.99±7.98) MPa] (P>0.05). Observation of the fracture surface at the 24 hours showed no obvious mineralization in all the three groups. After 1 and 3 months, mineral formation was observed in BG group and S-P-BG group, and no obvious collagen exposure was observed in S-P-BG group. Confocal laser scanning microscopy revealed no obvious differences in the morphology and quantity of the resin tag in the control group, BG group and S-P-BG group. At the end of 24 hours, leakage was found in all the three groups. The microleakage of the control group increased at the end of 3 months, while the microleakage of the BG and S-P-BG groups decreased.

CONCLUSION

BG pretreatment of dentin bonding interface can induce mineralization at the bonding interface and reduce the microleakage of the hybrid layer; pretreating the dentin bonding interface with STMP, PAA and BG may enhance the maintaining of the dentin bonding durability.