Magnetic motion of superparamagnetic iron oxide nanoparticles- loaded dental adhesives: physicochemical/biological properties, and dentin bonding performance studied through the tooth pulpal pressure model

Surface modifications of short quartz fibers and their influence on the physicochemical properties and in vitro cell viability of dental composites

OBJECTIVE

Although glass fibers are more common, quartz fibers (QFs) are also considered as the ideal reinforcing material in dentistry, due to their superior mechanical strength, high purity, and good photoconductive properties. However, the relatively inert surfaces limit their further applications. Therefore, the aim of this study is to modify the fiber surface properties to improve the interfacial interactions with polymeric resins.

METHODS

In this study, we systematically introduced four different surface modification strategies onto short quartz fibers (SQFs) for the preparation of dental composites. Particularly, the acid etching was a facile way to create mechanical interlocking structures. In addition, the silanization process, the sol-gel treatment, and the polymer grafting were further proposed to increase the surface roughness and the reactive sites. The effect of surface modifications on the fiber surface morphological changes, mechanical properties, water stability, and in vitro cell viability of dental composites were investigated.

RESULTS

Among all surface-modified SQFs, SQFs-POSS (SQFs modified with methacrylate-POSS) exhibited the roughest surface morphology and highest grafting rates compared with other three materials. Furthermore, all these SQFs were applied as reinforcements to make dimethacrylate-based dental resin composites. Of all fillers, SQFs-POSS demonstrated the best reinforcing effect, providing significantly higher improvements of 55.7 %, 114.3 %, and 164.7 % for flexural strength, flexural modulus, and breaking energy, respectively, over those of SQFs-filled composite. The related reinforcing mechanism was further investigated. The SQFs-POSS-filled composite also exhibited the best water stability performance and in vitro cell viability.

SIGNIFICANCE

This work provided valuable insights into the optimization of filler-matrix interaction through fiber surface modifications. Specifically, SQFs-POSS markedly outperformed other formulations in terms of the physicochemical performance and in vitro cytotoxicity, which offers possibilities for developing high-performance dental composites for clinical applications in restorative dentistry.

Ionic Liquid-Based Silane for SiO2 Nanoparticles: A Versatile Coupling Agent for Dental Resins

The current longevity of dental resins intraorally is limited by susceptibility to acidic attacks from bacterial metabolic byproducts and vulnerability to enzymatic or hydrolytic degradation. Here, we demonstrate synthesizing an ionic liquid-based antibiofilm silane effective against Streptococcus mutans, a major caries pathogen. Furthermore, we incorporate this silane into dental resins, creating antibiofilm- and degradation-resistant materials applicable across resin types. FTIR, UV-vis, and NMR spectroscopy confirmed the synthesis of the expected ionic liquid-based silane. The characterization of SiO2 after the silanization indicated the presence of the silane and how it interacted with the oxide. All groups achieved a degree of conversion similar to that found for commercial resin composites immediately and after two months of storage in water. The minimum of 2.5 wt % of silane led to lower softening in solvent than the control group (GCTRL) (p < 0.05). While the flexural strength indicated a lower value from 1 wt % of silane compared to GCTRL (p < 0.05), the ultimate tensile strength did not indicate differences among groups (p > 0.05). There was no difference within groups between the immediate and long-term tests of flexural strength (p > 0.05) or ultimate tensile strength (p > 0.05). The addition of at least 5 wt % of silane reduced the viability of S. mutans compared to GCTRL (p < 0.05). The fluorescence microscopy analysis suggested that the higher the silane concentration, the higher the amount of bacteria with membrane defects. There was no difference among groups in the cytotoxicity test (p > 0.05). Therefore, the developed dental resins displayed biocompatibility, proper degree of conversion, improved resistance against softening in solvent, and stability after 6 months of storage in water. This material could be further developed to produce polymeric antimicrobial layers for different surfaces, supporting various potential avenues in developing novel biomaterials with enhanced therapeutic characteristics using ionic liquid-based materials.

Multifunctional Dental Adhesives Formulated with Silane-Coated Magnetic Fe3O4@m-SiO2 Core-Shell Particles to Counteract Adhesive Interfacial Breakdown

The process of bonding to dentin is complex and dynamic, greatly impacting the longevity of dental restorations. The tooth/dental material interface is degraded by bacterial acids, matrix metalloproteinases (MMPs), and hydrolysis. As a result, bonded dental restorations face reduced longevity due to adhesive interfacial breakdown, leading to leakage, tooth pain, recurrent caries, and costly restoration replacements. To address this issue, we synthesized and characterized a multifunctional magnetic platform, CHX@SiQuac@Fe3O4@m-SiO2, to provide several beneficial functions. The platform comprises Fe3O4 microparticles and chlorhexidine (CHX) encapsulated within mesoporous silica, which was silanized by an antibacterial quaternary ammonium silane (SiQuac). This platform simultaneously targets bacterial inhibition, stability of the hybrid layer, and enhanced filler infiltration by magnetic motion. Comprehensive experiments include X-ray diffraction, FT-IR, VSM, EDS, N2 adsorption-desorption (BET), transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, and UV-vis spectroscopy. Then, CHX@SiQuac@Fe3O4@m-SiO2 was incorporated into an experimental adhesive resin for dental bonding restorations, followed by immediate and long-term antibacterial assessment, cytotoxicity evaluation, and mechanical and bonding performance. The results confirmed the multifunctional nature of CHX@SiQuac@Fe3O4@m-SiO2. This work outlined a roadmap for (1) designing and tuning an adhesive formulation containing the new platform CHX@SiQuac@Fe3O4@m-SiO2; (2) assessing microtensile bond strength to dentin using a clinically relevant model of simulated hydrostatic pulpal pressure; and (3) investigating the antibacterial outcome performance of the particles when embedded into the formulated adhesives over time. The results showed that at 4 wt % of CHX@SiQuac@Fe3O4@m-SiO2-doped adhesive under the guided magnetic field, the bond strength increased by 28%. CHX@SiQuac@Fe3O4@m-SiO2 enhanced dentin adhesion in the magnetic guide bonding process without altering adhesive properties or causing cytotoxicity. This finding presents a promising method for strengthening the tooth/dental material interface's stability and extending the bonded restorations' lifespan.

Recurrent caries models to assess dental restorations: A scoping review

OBJECTIVES

To review the literature on recurrent caries models used to evaluate restorative materials, compare reported methodology and parameters, and devise specific recommendations to be considered in future investigations.

DATA

The following were extracted: study design, sample characteristics, source of teeth, name of restorations compared including controls, recurrent caries model type, type of demineralizing and remineralizing solutions, type of biofilm used, methods to detect recurrent caries.

SOURCES

Literature searches were performed in OVID Medline, EMBASE, SCOPUS, and Cochrane Library.

STUDY SELECTION

For a study to be included, it had to examine dental materials for tooth restoration purposes only with a valid control group and evaluate restorative dental materials regardless of the form of the teeth caries model used or nature of the tooth structure used. A total of 91 studies were included. Most of the studies presented were in vitro. Human teeth were the main source of specimens utilized. Around 88% of the studies used specimens without an artificial gap, and 44% used a chemical model. S. mutans was the main bacterial species used in microbial caries models.

CONCLUSION

The findings of this review provided an insight into the performance of available dental materials assessed using different recurrent caries models, yet this review cannot be used as a guideline for material selection. Selecting the appropriate restorative material relies on several patient-related factors such as microbiota, occlusion, and diet that are not comprehensively taken into consideration in recurrent caries models and thus hinder reliable comparison.

CLINICAL SIGNIFICANCE

Due to the heterogenicity of variables among studies on the performance of dental restorative materials, this scoping review aimed to provide insights for dental researchers concerning the available recurrent caries models, testing methods used, and aspects of comparison between these materials including their characteristics and limitations.

Smart dental materials for antimicrobial applications

Smart biomaterials can sense and react to physiological or external environmental stimuli (e.g., mechanical, chemical, electrical, or magnetic signals). The last decades have seen exponential growth in the use and development of smart dental biomaterials for antimicrobial applications in dentistry. These biomaterial systems offer improved efficacy and controllable bio-functionalities to prevent infections and extend the longevity of dental devices. This review article presents the current state-of-the-art of design, evaluation, advantages, and limitations of bioactive and stimuli-responsive and autonomous dental materials for antimicrobial applications. First, the importance and classification of smart biomaterials are discussed. Second, the categories of bioresponsive antibacterial dental materials are systematically itemized based on different stimuli, including pH, enzymes, light, magnetic field, and vibrations. For each category, their antimicrobial mechanism, applications, and examples are discussed. Finally, we examined the limitations and obstacles required to develop clinically relevant applications of these appealing technologies.

Enhancing bioactivity and stability of polymer-based material-tissue interface through coupling multiscale interfacial interactions with atomic-thin TiO2 nanosheets

Stable and bioactive material-tissue interface (MTF) basically determines the clinical applications of biomaterials in wound healing, sustained drug release, and tissue engineering. Although many inorganic nanomaterials have been widely explored to enhance the stability and bioactivity of polymer-based biomaterials, most are still restricted by their stability and biocompatibility. Here we demonstrate the enhanced bioactivity and stability of polymer-matrix bio-composite through coupling multiscale material-tissue interfacial interactions with atomically thin TiO2 nanosheets. Resin modified with TiO2 nanosheets displays improved mechanical properties, hydrophilicity, and stability. Also, we confirm that this resin can effectively stimulate the adhesion, proliferation, and differentiation into osteogenic and odontogenic lineages of human dental pulp stem cells using in vitro cell-resin interface model. TiO2 nanosheets can also enhance the interaction between demineralized dentinal collagen and resin. Our results suggest an approach to effectively up-regulate the stability and bioactivity of MTFs by designing biocompatible materials at the sub-nanoscale.

Electronic Supplementary Material

Supplementary material (further details of fabrication and characterization of TiO2 NSs and TiO2-ARCs, the bioactivity evaluation of TiO2-ARCs on hDPSCs, and the measurement of interaction with demineralized dentin collagen) is available in the online version of this article at 10.1007/s12274-022-5153-1.

Metal Oxide Nanoparticles and Nanotubes: Ultrasmall Nanostructures to Engineer Antibacterial and Improved Dental Adhesives and Composites

Advances in nanotechnology have unlocked exclusive and relevant capabilities that are being applied to develop new dental restorative materials. Metal oxide nanoparticles and nanotubes perform functions relevant to a range of dental purposes beyond the traditional role of filler reinforcement-they can release ions from their inorganic compounds damaging oral pathogens, deliver calcium phosphate compounds, provide contrast during imaging, protect dental tissues during a bacterial acid attack, and improve the mineral content of the bonding interface. These capabilities make metal oxide nanoparticles and nanotubes useful for dental adhesives and composites, as these materials are the most used restorative materials in daily dental practice for tooth restorations. Secondary caries and material fractures have been recognized as the most common routes for the failure of composite restorations and bonding interface in the clinical setting. This review covers the significant capabilities of metal oxide nanoparticles and nanotubes incorporated into dental adhesives and composites, focusing on the novel benefits of antibacterial properties and how they relate to their translational applications in restorative dentistry. We pay close attention to how the development of contemporary antibacterial dental materials requires extensive interdisciplinary collaboration to accomplish particular and complex biological tasks to tackle secondary caries. We complement our discussion of dental adhesives and composites containing metal oxide nanoparticles and nanotubes with considerations needed for clinical application. We anticipate that readers will gain a complete picture of the expansive possibilities of using metal oxide nanoparticles and nanotubes to develop new dental materials and inspire further interdisciplinary development in this area.