Remineralization effectiveness of the PAMAM dendrimer with different terminal groups on artificial initial enamel caries in vitro

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.

Promotion of Dentin Biomimetic Mineralization and Bonding Efficacy by Interfacial Control of an Experimental Citric Acid Dental Etching Agent

Resin-bonded restorations are the most important caries treatment method in clinical practice. Thus, improving the durability of dentin bonding remains a pressing issue. As a promising solution, guided tissue remineralization can induce the formation of apatite nanocrystals to repair defects in the dentin bonding interface. In this study, we present an experimental 20 wt % citric acid (CA) dental etching agent that removes the smear layer. After CA-etching, approximately 3.55 wt % residual CA formed a strong bond with collagen fibrils, reducing the interfacial energy between the remineralizing solution and dentin. CA helped achieve almost complete intrafibrillar and extrafibrillar mineralization after 24 h of mineralization. CA also significantly promoted poly(amidoamine)-induced dentin biomimetic mineralization. The elastic modulus and microhardness of remineralized dentin were restored to that of sound dentin. The remineralized interface reduced microleakage and provided a stronger, longer-lasting bond than conventional phosphate acid-etching. The newly developed CA dental etching agents promoted rapid dentin biomimetic mineralization and improved bonding efficacy through interfacial control, representing a new approach with clinical practice implications.

Characterization of a Novel TiF4 Inclusion Complex and in vitro Evaluation of Its Effect on Inhibiting Enamel Demineralization

INTRODUCTION

Titanium tetrafluoride (TiF4) is an anticariogenic agent with high remineralizing potential. However, the acidic pH of TiF4 solution can limit its clinical application. The present study aimed to prepare and characterize a new TiF4-dendrimer inclusion complex and evaluate its ability to inhibit enamel demineralization under pH cycling conditions.

METHODS

PEG-citrate dendrimer and TiF4-dendrimer inclusion complex were synthesized and their molecular structures were evaluated using Fourier-transform Infrared Spectroscopy (FTIR), Hydrogen Nuclear Magnetic Resonance (HNMR), and Liquid Chromatography-Mass Spectrometry (LC-MS) tests. Forty-eight enamel samples were prepared and randomly divided into four groups: distilled water (negative control), TiF4 solution (T), dendrimer solution (D), and TiF4-dendrimer solution (TD). The microhardness of the samples was measured initially. Next, the samples underwent pH cycling, were exposed to the solutions, the microhardness was measured again, and microhardness loss was calculated. EDX analysis was performed on the surface and cross-sectional segments of the samples.

RESULTS

The microhardness loss was significantly higher in control (-65.1 ± 6.0) compared to other groups. No significant difference was observed between T (-47.9 ± 5.6) and D (-41.7 ± 12.0) and also D and TD (-40.5 ± 9.4) in this regard. Microhardness loss was significantly higher in T compared to TD group. The TD samples showed similar fluoride and titanium content in both surface and subsurface regions, while the T group had higher concentrations in the surface region. Moreover, the TD solution had a higher pH of 3.4 compared to the T solution's pH of 1.1.

CONCLUSION

No significant difference was observed between the efficacy of TiF4-dendrimer and TiF4 solution in inhibiting demineralization while TiF4-dendrimer solution had the added advantage of having a higher pH.

Remineralization effects of enamel binding peptide, WGNYAYK, on enamel subsurface demineralization in vitro. Enamel binding peptide, WGNYAYK effect remineralization of enamel

Objectives: We investigated remineralization effects of enamel binding peptide (EBP), WGNYAYK, on enamel subsurface demineralization in vitro.Methods: Bovine lower incisor crowns were used as subsurface enamel demineralization samples, and changes of EBP binding, remineraliztion rate, hardness and microstructure were investigated. Binding of EBP, remineralization rate, hardness and structural changes were investigated. Fluorescein isothiocyatate (FITC)-labeled EBPs (0.4 mM, 4.0 mM, and 7.0 mM) were applied to the samples for 30 min at 37 °C, with sample surfaces and cross-sections observed by confocal laser scanning microscope (CLSM). Mineralization analysis samples were divided into 4 experimental groups; distilled water (DW), EBP 0.4 mM, EBP 4.0 mM, and EBP 7.0 mM. Mineral density changes were measured by micro-CT with hardness measured by nano-indentation. Samples were also observed by scanning electron microscope (SEM) for surface and longitudinal microstructure.

Results

CLSM images indicated that increased fluorescence was observed in the surface layer and up to about 20 μm below the surface layer. The remineralization rate was significantly higher for EBP 7.0 mM compared to DW (p = 0.008). Enamel surface hardness was significantly higher in all EBP groups compared to DW (p < 0.05) and was highest in the 7.0 mM group. SEM images showed obscuring of the superficial columnar structure in the 7.0 mM EBP group, indicating subsurface crystalline structure recovery.

Conclusion

The results of this study suggest that EBP binds to demineralized enamel and promotes remineralization.

Novel bioactive dental restorations to inhibit secondary caries in enamel and dentin under oral biofilms

OBJECTIVE

To provide the first review on cutting-edge research on the development of new bioactive restorations to inhibit secondary caries in enamel and dentin under biofilms. State-of-the-art bioactive and therapeutic materials design, structure-property relationships, performance and efficacies in oral biofilm models.

DATA, SOURCES AND STUDY SELECTION

Researches on development and assessment new secondary caries inhibition restorations via in vitro and in vivo biofilm-based secondary caries models were included. The search of articles was carried out in Web of Science, PubMed, Medline and Scopus.

CONCLUSIONS

Based on the found articles, novel bioactive materials are divided into different categories according to their remineralization and antibacterial biofunctions. In vitro and in vivo biofilm-based secondary caries models are effective way of evaluating the materials efficacies. However, new intelligent and pH-responsive materials were still urgent need. And the materials evaluation should be performed via more clinical relevant biofilm-based secondary caries models.

CLINICAL SIGNIFICANCE

Secondary caries is a primary reason for dental restoration failures. Biofilms produce acids, causing demineralization and secondary caries. To inhibit dental caries and improve the health and quality of life for millions of people, it is necessary to summarize the present state of technologies and new advances in dental biomaterials for preventing secondary caries and protecting tooth structures against oral biofilm attacks. In addition, suggestions for future studies are provided.

May carriers at nanoscale improve the Endodontic's future?

Nanocarriers (NCs) are dynamic nanovehicles used to transport bioactive derivatives like therapeutical formulations, drugs and/or dyes. The current review assists in understanding the mechanism of action of several recent developed NCs with antimicrobial purposes. Here, nine NCs varieties are portrayed with focus on nineteen approaches that are fulfil described based on outcomes obtained from in vitro antimicrobial assays. All approaches have previously been verified and we underline the biochemical challenges of all NCs, expecting that the present data may encourage the application of NCs in endodontic antimicrobial basic research. Methodological limitations and the evident base gaps made not possible to draw a definite conclusion about the best NCs for achieving efficient antimicrobial outcomes in endodontic studies. Due to the lack of pre-clinical trials and the scarce number of clinical trials in this emergent area, there is still much room for improvement on several fronts.

Dendritic Polymers in Tissue Engineering: Contributions of PAMAM, PPI PEG and PEI to Injury Restoration and Bioactive Scaffold Evolution

The capability of radially polymerized bio-dendrimers and hyperbranched polymers for medical applications is well established. Perhaps the most important implementations are those that involve interactions with the regenerative mechanisms of cells. In general, they are non-toxic or exhibit very low toxicity. Thus, they allow unhindered and, in many cases, faster cell proliferation, a property that renders them ideal materials for tissue engineering scaffolds. Their resemblance to proteins permits the synthesis of derivatives that mimic collagen and elastin or are capable of biomimetic hydroxy apatite production. Due to their distinctive architecture (core, internal branches, terminal groups), dendritic polymers may play many roles. The internal cavities may host cell differentiation genes and antimicrobial protection drugs. Suitable terminal groups may modify the surface chemistry of cells and modulate the external membrane charge promoting cell adhesion and tissue assembly. They may also induce polymer cross-linking for healing implementation in the eyes, skin, and internal organ wounds. The review highlights all the different categories of hard and soft tissues that may be remediated with their contribution. The reader will also be exposed to the incorporation of methods for establishment of biomaterials, functionalization strategies, and the synthetic paths for organizing assemblies from biocompatible building blocks and natural metabolites.

Effect of an aqueous 4% titanium tetrafluoride solution on preventing caries in orthodontic patients: a controlled clinical trial

INTRODUCTION

Titanium tetrafluoride (TiF4) is a fluoride compound that, when is applied over enamel, promotes a protection against demineralization through a titanium dioxide (TiO2) acid-resistant coat.

OBJECTIVES

This study sought to verify the hypothesis that a single application of 4% TiF4 increases the resistance of enamel to dental demineralization in orthodontic patients.

MATERIALS AND METHODS

This controlled clinical trial followed CONSORT guidelines and investigated the prevention of enamel demineralization, fluoride retention, and the presence of a Ti layer after TiF4 application on banded teeth exposed to clinical cariogenic biofilm. Forty premolars were divided into a control group (CG; n = 20) and a test group (TG; n = 20). Teeth from both groups received prophylaxis and orthodontic bands with a cariogenic locus. In the TG, all teeth additionally underwent aqueous 4% TiF4 solution application after prophylaxis before being banded. After one month, teeth from both groups were extracted and prepared to assess the microhardness, fluoride retention, and evaluation of the Ti coating over the enamel surface. All data were analyzed with a paired Student's t-test (p<0.05).

RESULTS

Enamel microhardness and fluoride uptake were higher in TG than in CG, while the Ti layer could be seen over TG teeth that received TiF4 application.

CONCLUSION

Under clinical circumstances, the 4% aqueous TiF4 solution was effective in preventing enamel mineral loss through increasing the enamel resistance to dental demineralization, enhancing its microhardness and fluoride uptake, and forming a Ti coat.

A novel amelogenesis-inspired hydrogel composite for the remineralization of enamel non-cavitated lesions

Enamel non-cavitated lesions (NCLs) are subsurface enamel porosity from carious demineralization. The developed enamel cannot repair itself once NCLs occurs. The regeneration of mineral crystals in a biomimetic environment is an effective way to repair enamel subsurface defects. Previously, an amelogenin-derived peptide named QP5 was proven to repair demineralized enamel. In this work, inspired by amelogenesis, a novel biomimetic hydrogel composite containing the QP5 peptide and bioactive glass (BG) was designed, in which QP5 could promote enamel remineralization by guiding the calcium and phosphorus ions provided by BG. Also, BG could adjust the mineralization micro-environment to alkalinity, simulating the pH regulation of ameloblasts during enamel maturity. The BQ hydrogel composite showed biosafety and possessed capacity for enamel binding, ion release and pH buffering. Enamel NCLs treated with the BQ hydrogel composite showed a higher reduction in lesion depth and mineral loss both in vitro and in vivo. Moreover, compared to the hydrogels containing only BG or QP5, groups treated with the BQ hydrogel composite attained more surface microhardness recovery and color recovery, exhibiting resistance to erosion and abrasion of the remineralization layer. We envision that the BQ hydrogel composite can provide a biomimetic micro-environment to favor enamel remineralization, thus reducing the lesion depth and increasing the mineral content as a promising biomimetic material for enamel NCLs.

Nano-hydroxyapatite-induced remineralization of artificial white spot lesions after bleaching treatment with 10% carbamide peroxide

OBJECTIVE

To assessed in vitro the effect of nanohydroxyapatite (n-HA) to improve the aesthetic appearance and microhardness of white spot lesions (WSL) when associated with a low-concentration bleaching agent (carbamide peroxide-CP10%).

MATERIAL AND METHODS

Enamel/dentin specimens (n = 60) of 5 × 5 × 2.2 mm were prepared, of these, 48 were submitted to pH-cycling to create artificial WSL. Subsequently, these were allocated into five groups (n = 12): n-HA; n-HA + CP10%; CP10%; WSL control (WSL_C ); sound control (Sound). The color was assessed at baseline, pre-treatment, and post-treatment using a spectrophotometer, and the color (ΔE/ΔE₀₀ ) and whiteness index (ΔWID) alterations were determined. The enamel cross-sectional microhardness (CSMH) was evaluated (post-treatment) with a Knoop indenter, 25gf/5 s, 20-200 μm. The data was analyzed through generalized linear models (α = 5%).

RESULTS

ΔE and ΔE₀₀ were significantly higher for the bleached groups (n-HA + CP10% and CP10%), and the n-HA was higher than the WSL_C group (p < 0.05). ΔWID was significantly higher for the bleached groups (p < 0.05). The CSMH values were significantly higher in the sound group than in the n-HA, CP10%, and WSL_C groups (p < 0.05). The WSL_C had lower microhardness than the n-HA + CP10% and sound groups (p < 0.05).

CONCLUSION

n-HA is suitable to remineralize and recover the color of the WSL. However, its association with CP10% maintains the esthetical outcome while increasing its in-depth remineralizing effect.

CLINICAL SIGNIFICANCE

Considering the aesthetic and functional repercussions of the WSL persistence, treatments that tend to improve its physical appearance and reinforce its weakened substructure in a non-invasive way are ideal. For this associating low-concentration, bleaching agents to the remineralizing treatments is promising to treat this type of lesions.

Advanced materials for enamel remineralization

Dental caries, a chronic and irreversible disease caused by caries-causing bacteria, has been listed as one of the three major human diseases to be prevented and treated. Therefore, it is critical to effectively stop the development of enamel caries. Remineralization treatment can control the progression of caries by inhibiting and reversing enamel demineralization at an early stage. In this process, functional materials guide the deposition of minerals on the damaged enamel, and the structure and hardness of the enamel are then restored. These remineralization materials have great potential for clinical application. In this review, advanced materials for enamel remineralization were briefly summarized, furthermore, an outlook on the perspective of remineralization materials were addressed.

A Dentin Biomimetic Remineralization Material with an Ability to Stabilize Collagen

The integrity of collagen matrix structure is a prerequisite for effectively inducing biomimetic remineralization. Repeated low pH stimulation activates matrix metalloproteinases (MMPs) in dental caries. Activated MMPs cause the breakdown of collagen fibrils. Collagen stabilization is a major obstacle to the clinical application of remineralization templates. Here, galardin-loaded poly(amido amine) (PAMAM)-NGV (PAMAM-NGV@galardin, PNG) is constructed to induce collagen stabilization and dentin biomimetic remineralization simultaneously, in order to combat early caries in dentin. PAMAM acts in the role of nucleation template for dentin remineralization, while galardin acts as the role of MMPs inhibitor. NGV peptides modified on the surface of dendrimer core can form small clusters with synergistic movement in short range, and those short-range clusters can form domain areas with different properties on the surface of PAMAM core and restrict the movement of collagen, favoring collagen crosslinking, which can be explained through the computational simulation analysis results. NGV peptides and galardin show a dual collagen-protective effect, laying the foundation for the dentin remineralization effect induced by PAMAM. PNG induces dentin remineralization in an environment with collagenase, meanwhile showsing anti-dentin caries efficacy in vivo. These findings indicate that PNG has great potential to combat early dentin caries for future clinical application.

Comparison of calcium-based technologies to remineralise enamel subsurface lesions using microradiography and microhardness

Assessment of enamel subsurface lesion remineralisation is essential for the evaluation of novel remineralisation technologies. The gold standard to assess subsurface mineral gain of enamel lesions is transverse microradiography (TMR). However, some studies have utilised surface microhardness (SMH) to evaluate efficacy of remineralisation agents. The aim of this study was to assess remineralisation of enamel subsurface lesions using TMR and SMH after in vitro treatment with calcium-containing technologies, and to test correlation between the TMR and SMH measurements. The parameters obtained from the TMR and SMH analyses of enamel subsurface remineralisation were not significantly correlated. Furthermore, the enamel subsurface remineralisation as measured by TMR was significantly correlated with the water-soluble calcium concentration of the remineralisation products. Scanning electron microscopy revealed surface precipitates formed by specific remineralisation treatments obfuscated accurate assessment of remineralisation by SMH. It was concluded that TMR is a more appropriate method for analysis of enamel subsurface remineralisation, and that SMH values of remineralised enamel should be interpreted with caution. Using TMR the level of remineralisation (%R) by the different technologies was CPP-ACP/F (31.3 ± 1.4%); CPP-ACP (24.2 ± 1.4%); CaSO₄/K₂HPO₄/F (21.3 ± 1.4%); f-TCP/F (20.9 ± 1.0%); Nano-HA/F (16.3 ± 0.3%); Nano-HA (15.3 ± 0.6%) and F alone control (15.4 ± 1.3%).

Novel trends, challenges and new perspectives for enamel repair and regeneration to treat dental defects

Dental enamel is the hardest tissue in the human body, providing external protection for the tooth against masticatory forces, temperature changes and chemical stimuli. Once enamel is damaged/altered by genetic defects, dental caries, trauma, and/or dental wear, it cannot repair itself due to the loss of enamel producing cells following the tooth eruption. The current restorative dental materials are unable to replicate physico-mechanical, esthetic features and crystal structures of the native enamel. Thus, development of alternative approaches to repair and regenerate enamel defects is much needed but remains challenging due to the structural and functional complexities involved. This review paper summarizes the clinical aspects to be taken into consideration for the development of optimal therapeutic approaches to tackle dental enamel defects. It also provides a comprehensive overview of the emerging acellular and cellular approaches proposed for enamel remineralization and regeneration. Acellular approaches aim to artificially synthesize or re-mineralize enamel, whereas cell-based strategies aim to mimic the natural process of enamel development given that epithelial cells can be stimulated to produce enamel postnatally during the adult life. The key issues and current challenges are also discussed here, along with new perspectives for future research to advance the field of regenerative dentistry.

Efficacy of a Novel Bioactive Glass-Polymer Composite for Enamel Remineralization following Erosive Challenge

Introduction

Dental caries is the most common cause of tooth loss. However, it can be stopped by enhancing remineralization. Fluoride and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) are among the most important remineralizing agents. Recent studies have used bioactive glass as a remineralizing agent in different forms. This study aimed to assess the efficacy of a composite paste (prepared by mixing urethane polypropylene glycol oligomer with bioactive glass powder for easier application).

Materials and Methods

Enamel disks were cut out of the buccal surface of extracted sound third molars. The samples were randomly divided into 3 groups of 15 and underwent Vickers microhardness test. X-ray diffraction (XRD) and field emission scanning electron microscopy/energy dispersive X-ray spectroscopy (FESEM/EDS) were performed. All samples were immersed in a demineralizing solution for 14 days. The tests were then repeated. Next, bioactive glass paste, fluoride, and CPP-ACP were applied on the surface of the samples and they were then stored in an artificial saliva for 14 days. The tests were repeated again. The microhardness values were analyzed using repeated measures ANOVA followed by one-way ANOVA and Tukey's post hoc test (P < 0.05).

Results

The microhardness of the bioactive glass group was significantly higher than that of other groups (P < 0.05). XRD revealed an enamel structure more similar to sound enamel in the bioactive glass and CPP-ACP groups compared with the fluoride group. FESEM/EDS revealed higher hydroxyapatite deposition in the bioactive glass group than in the other two groups.

Conclusions

All three remineralizing agents caused remineralization, but bioactive glass paste had a greater efficacy.

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.

Polyzwitterion Manipulates Remineralization and Antibiofilm Functions against Dental Demineralization

Biomineralization technology has become a trend for the arrest and prevention of dental caries. In particular, the bioactivity and ability to release large amounts of Ca²⁺ and PO₄^3- ions make amorphous calcium phosphate (ACP) for hard tissue remineralization are highly desired. However, the instability of ACP limits its clinical application. Under continuous bacterial challenge in the oral cavity, the currently developed ACP-based remineralization system lacks the ability to inhibit bacterial adhesion and biofilm formation. Here, a dual-functional nanocomposite with antibiofilm and remineralization properties was designed by combining zwitterionic poly(carboxybetaine acrylamide) (PCBAA) and ACP. The resulting nanocomposite was stable in solution for at least 3 days without any aggregation. The PCBAA/ACP nanocomposite exerted a significant inhibitory effect on the adhesion and biofilm formation of Streptococcus mutans and exhibited bactericidal activities under acidic conditions resulting from bacteria. Moreover, compared with fluoride, this nanocomposite demonstrated superior effects in promoting the remineralization of demineralized enamel and the occlusion of exposed dentinal tubules in vivo and in vitro. The present work provides a theoretical and experimental basis for the use of the PCBAA/ACP nanocomposite as a potential dual-functional agent for arresting and preventing caries.

The power of weak ion-exchange resins assisted by amelogenin for natural remineralization of dental enamel: an in vitro study

This study aims to develop an innovative dental product to remineralize dental enamel by a proper combination of ion-exchange resins as controlled release of mineral ions that form dental enamel, in the presence of amelogenin to guide the appropriate crystal growth. The novel product proposed consists of a combination of ion-exchange resins (weak acid and weak base) individually loaded with the remineralizing ions: Ca²⁺, PO₄^3- and F^-, also including Zn²⁺ in a minor amount as antibacterial, together with the protein amelogenin. Such cocktail provides onsite controlled release of the ions necessary for enamel remineralization due to the weak character of the resins and at the same time, a guiding tool for related crystal growth by the indicated protein. Amelogenin protein is involved in the structural development of natural enamel and takes a key role in controlling the crystal growth morphology and alignment at the enamel surface. Bovine teeth were treated by applying the resins and protein together with artificial saliva. Treated teeth were evaluated with nanoindentation, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The innovative material induces the dental remineralization creating a fluorapatite layer with a hardness equivalent to sound enamel, with the appropriate alignment of corresponding nanocrystals, being the fluorapatite more acid resistant than the original mineral. Our results suggest that the new product shows potential for promoting long-term remineralization leading to the inhibition of caries and protection of dental structures.

Advances in biomineralization-inspired materials for hard tissue repair

Biomineralization is the process by which organisms form mineralized tissues with hierarchical structures and excellent properties, including the bones and teeth in vertebrates. The underlying mechanisms and pathways of biomineralization provide inspiration for designing and constructing materials to repair hard tissues. In particular, the formation processes of minerals can be partly replicated by utilizing bioinspired artificial materials to mimic the functions of biomolecules or stabilize intermediate mineral phases involved in biomineralization. Here, we review recent advances in biomineralization-inspired materials developed for hard tissue repair. Biomineralization-inspired materials are categorized into different types based on their specific applications, which include bone repair, dentin remineralization, and enamel remineralization. Finally, the advantages and limitations of these materials are summarized, and several perspectives on future directions are discussed.

A novel anticaries agent, honokiol-loaded poly(amido amine) dendrimer, for simultaneous long-term antibacterial treatment and remineralization of demineralized enamel

OBJECTIVE

Existing agents to induce enamel self-repair and inhibit the progression of dental caries in the early stage have been proven to be inadequate and far from satisfactory. In this study, a honokiol-loaded poly(amido amine) (PAMAM) dendrimer (PAMH) was constructed to combat early caries lesions in enamel.

METHODS

PAMH was prepared via a codissolution method. Computational simulation analysis was used to explore the mechanism of honokiol release. The cytotoxicity of PAMH was tested. The antibacterial effects of PAMH were tested by planktonic growth assays and biofilm formation inhibition assays. The remineralization effect of PAMH was examined via transverse microradiography and scanning electron microscopy after a pH cycling model. The in vivo anti-caries effect of PAMH was carried out in a rat model.

RESULTS

Honokiol released from PAMH was slower but more durable in a cariogenic pH environment than in a neutral pH environment, which could be explained through the computational simulation analysis results. Under electrostatic action, P3 beads with the same charge repelled each other and extended outwards, resulting in the rapid expansion of the PAMAM dendrimer and accelerating the release of the drug. At a low pH of 5.5, the protonated P3 beads were not charged and the protonated P1 beads were positively charged. However, the electrostatic repulsive interaction between protonated P1 beads was restricted by the P3 beads in the outermost layer of the PAMAM dendrimer, so the swelling rate was relatively slow, resulting in the slow release of drug molecules in the acidic environment. The cytotoxicity demonstration and the biocompatibility experiment in animal study showed that PAMH is biologically safe. PAMH showed excellent enamel remineralizing ability after pH cycling and showed a long-term antibacterial effect in vitro. Meanwhile, PAMH showed long-term anticaries efficacy in vivo.

SIGNIFICANCE

Our findings indicated that PAMH had great potential to combat early caries lesions in enamel for future clinical application.

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.

Remineralization effectiveness of adhesive containing amorphous calcium phosphate nanoparticles on artificial initial enamel caries in a biofilm-challenged environment

OBJECTIVES

Dental caries is closely associated with acid-producing bacteria, and Streptococcus mutans is one of the primary etiological agents. Bacterial accumulation and dental demineralization lead to destruction of bonding interface, thus limiting the longevity of composite. The present study investigated remineralization effectiveness of adhesive containing nanoparticles of amorphous calcium phosphate (NACP) in a stimulated oral biofilm environment.

METHODS

The enamel blocks were immersed in demineralization solution for 72 h to imitate artificial initial carious lesion and then subjected to a Streptococcus mutans biofilm for 24 h. All the samples then underwent 4-h demineralization in brain heart infusion broth with sucrose (BHIS) and 20-h remineralization in artificial saliva (AS) for 7 days. The daily pH of BHIS after 4-h incubation, lactic acid production, colony-forming unit (CFU) count, and content of calcium (Ca) and phosphate (P) in biofilm were evaluated. Meanwhile, the remineralization effectiveness of enamel was analyzed by X-ray diffraction (XRD), surface microhardness testing, transverse microradiography (TMR) and scanning electron microscopy (SEM).

RESULTS

The NACP adhesive released abundant Ca and P, achieved acid neutralization, reduced lactic acid production, and lowered CFU count (P < 0.05). Enamel treated with NACP adhesive demonstrated the best remineralization effectiveness with remineralization value of 52.29 ± 4.79% according to TMR. Better microhardness recovery of cross sections and ample mineral deposits were also observed in NACP group.

CONCLUSIONS

The NACP adhesive exhibited good performance in remineralizing initial enamel lesion with cariogenic biofilm.

SIGNIFICANCE

The NACP adhesive is promising to be applied for the protection of bonding interface, prevention of secondary caries, and longevity prolonging of the restoration.

[Application of biomimetic restoration in oral-maxillofacial hard tissue repair]

Oral-maxillofacial hard tissue is the support of maxillofacial structure and appearance, and lays the foundation for functions of oral and maxillofacial system. Once the defect occurs, it will not only affect the physiological functions such as chewing and pronunciation, but also have a significant impact on the psychological and social life of patients. However, the self-repairing capability of the oral-maxillofacial hard tissue is pretty limited, in which case, substitute materials are required for tissue repair. A huge gap exists between the physical, chemical, structural characteristics of conventional substitute materials and those of human hard tissues, resulting in poor repair effect. Based on this, scholars simulated the process of biomineralization in the development of hard tissues, to improve the structure and function of materials through biomimetic mineralization technology and enhance the repair performance of materials. The current understanding of biomineralization theory and the construction of biomimetic repair technology is still in the stage of rapid development. In recent years, a mass of innovative studies are keeping emerging. In this review, the representative advances in the repair of oral-maxillofacial hard tissues of the past five years are reviewed.

Rechargeable adhesive with calcium phosphate nanoparticles inhibited long-term dentin demineralization in a biofilm-challenged environment

OBJECTIVES

This study aims to investigate the long-term demineralization-inhibition capability of a rechargeable adhesive with nanoparticles of amorphous calcium phosphate (NACP) on dentin in a biofilm-challenged environment.

METHODS

The NACP adhesive was immersed in a pH 4 solution to exhaust calcium (Ca) and phosphate (P) ions and then recharged with Ca and P ions. Dentin samples were demineralized underStreptococcus mutans biofilms for 24 h and randomly divided into two groups: (1) dentin control, (2) dentin with recharged NACP adhesives. Each day, all the samples were immersed in brain heart infusion broth with 1% sucrose (BHIS) for 4 h, and then in artificial saliva (AS) for 20 h. This cycle was repeated for 10 days. The pH of BHIS, the Ca and P ions content of the BHIS and AS were measured daily. After 10 days, the lactic acid production and colony-forming units of the biofilms were tested. The changes of remineralization/demineralization were also analyzed.

RESULTS

Dentin in the control group showed further demineralization. The recharged NACP adhesive neutralized acids, increasing the pH to above 5, and released large amounts of Ca and P ions each day. The recharged NACP adhesive decreased the production of lactic acid (P < 0.05), inhibited dentin demineralization and sustained the dentin hardness in the biofilm-challenged environment, showing an excellent long-term demineralization-inhibition capability.

CONCLUSIONS

The NACP adhesive could continuously inhibit dentin demineralization in a biofilm-challenged environment by recharging with Ca and P ions.

SIGNIFICANCE

The rechargeable NACP adhesive could provide long-term dentin bond protection.

Tooth Formation: Are the Hardest Tissues of Human Body Hard to Regenerate?

With increasing life expectancy, demands for dental tissue and whole-tooth regeneration are becoming more significant. Despite great progress in medicine, including regenerative therapies, the complex structure of dental tissues introduces several challenges to the field of regenerative dentistry. Interdisciplinary efforts from cellular biologists, material scientists, and clinical odontologists are being made to establish strategies and find the solutions for dental tissue regeneration and/or whole-tooth regeneration. In recent years, many significant discoveries were done regarding signaling pathways and factors shaping calcified tissue genesis, including those of tooth. Novel biocompatible scaffolds and polymer-based drug release systems are under development and may soon result in clinically applicable biomaterials with the potential to modulate signaling cascades involved in dental tissue genesis and regeneration. Approaches for whole-tooth regeneration utilizing adult stem cells, induced pluripotent stem cells, or tooth germ cells transplantation are emerging as promising alternatives to overcome existing in vitro tissue generation hurdles. In this interdisciplinary review, most recent advances in cellular signaling guiding dental tissue genesis, novel functionalized scaffolds and drug release material, various odontogenic cell sources, and methods for tooth regeneration are discussed thus providing a multi-faceted, up-to-date, and illustrative overview on the tooth regeneration matter, alongside hints for future directions in the challenging field of regenerative dentistry.