Long-term stability of dental adhesive incorporated by boron nitride nanotubes

Development of a Boron Nitride-Filled Dental Adhesive System

There is a dearth of adhesive systems capable of forming stable bonds between restorative materials and tooth surfaces. To address the concern, this study determined the effects of using methacrylate-functionalized boron nitride nanosheets (BNNSs) in a polymeric dental adhesive system. The bisphenol A glycidyl dimethacrylate (BisGMA):2 hydroxyethyl methacrylate (HEMA) (60:40) adhesive monomer blend with a photoinitiator was filled with 0 wt% (control), 0.1 wt%, and 1 wt% BNNSs and light cured. Fourier transform infrared spectroscopy was performed to determine the conversion degree of monomer double bonds (DoC). Water absorption and solubility were measured. Flexural strength and Youngs's modulus were evaluated to determine the mechanical properties of the composite adhesive system. Finally, dentin bond strength degradation and fracture mode were quantified with a microtensile bond test to confirm the bonding ability of the developed adhesive system. Results showed that the incorporation of BNNSs increased DoC (9.8% and 5.4% for 0.1 and 1 wt%, respectively), but it did not affect water sorption (101.9-119.72 (µg/mm3)), solubility (2.62-5.54 (µg/mm3)), Young's modulus (529.1-1716.1 MPa), or microtensile bond strength (46.66-54.72 MPa). Further studies are needed with varying BNNS loading percentages from 0.1 wt% to 1 wt% in order to more comprehensively determine the effect of BNNSs on dental adhesives.

In Vitro and In Vivo Cytotoxicity of Boron Nitride Nanotubes: A Systematic Review

Boron nitride nanotubes (BNNTs) are an exciting class of nanomaterials due to their unique chemical and physical characteristics. In recent decades, BNNTs have gained huge attention in research and development for various applications, including as nano-fillers for composites, semiconductor devices, hydrogen storage, and as an emerging material in biomedical and tissue engineering applications. However, the toxicity of BNNTs is not clear, and the biocompatibility is not proven yet. In this review, the role of BNNTs in biocompatibility studies is assessed in terms of their characteristics: cell viability, proliferation, therapeutic outcomes, and genotoxicity, which are vital elements for their prospective use in biomedical applications. A systematic review was conducted utilising the databases Scopus and Web of Science (WOS) (2008-2022). Additional findings were discovered manually by snowballing the reference lists of appropriate reviews. Only English-language articles were included. Finally, the significant analysis and discussion of the chosen articles are presented.

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.

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

The limited durability of dentin bonding harshly shortens the lifespan of resin composites restorations. The controlled, dynamic movement of materials through non-contacting forces provides exciting opportunities in adhesive dentistry. We, herein, describe comprehensive investigations of a new dental adhesive with superparamagnetic iron oxide nanoparticles (SPIONs) sensitive to magnetic fields for bonding optimization. This contribution outlines a roadmap of (1) designing and tuning of an adhesive formulation containing SPIONs to enhance penetrability into etched dentin guided by magnetic-field; (2) employing a clinically relevant model of simulated hydrostatic pulpal pressure on the microtensile bond to dentin; and (3) investigating a potential antibacterial effect of the formulated adhesives, and their biocompatibility. SPION-concentration-dependency chemical and mechanical behavior was shown via the degree of conversion, ultimate tensile strength, and micro shear bond strength to dentin. The effects of SPIONs carried on a dental adhesive on the bonding strength to dentin are studied in depth by combining experiments with in vitro simulated model. The results show that under the guided magnetic field, 0.07 wt.% of SPIONs-doped adhesive increased the bond strength that surpasses the reduction caused by hydrostatic pulpal pressure. Using a magnetic guide workflow during the bonding procedures, SPIONs-doped adhesives improved dentin's adhesion without changing adhesives' physicochemical properties. This outcome addresses the key challenge of poor resin infiltration of dentin's conventional total etching during the bonding procedure. The real-time magnetic motion of dental adhesives may open new paths to enhance resin-based restorations' longevity. STATEMENT OF SIGNIFICANCE: In this study, dental adhesives containing superparamagnetic iron oxide nanoparticles (SPIONs) were developed to enhance penetrability into dentin guided by a magnetic field. The adhesives were screened for physical, chemical, antibacterial properties, and cytotoxicity. For the first time, simulated pulpal pressure was used concurrently with the magnetic field to simulate a clinical setting. This approach showed that it is feasible to overcome pulpal pressure jeopardization on bond strength when SPIONs and a magnetic field are applied. The magnetic-responsive adhesives had great potential to improve bond strength, opening new paths to enhance resin-based restorations' longevity without affecting adhesives' biological properties. The use of magnetic-responsive particles and magnetically assisted motion is a promising strategy to improve the sealing ability of dental adhesives.

Titanium dioxide nanotubes with triazine-methacrylate monomer to improve physicochemical and biological properties of adhesives

OBJECTIVE

Formulate experimental adhesives containing titanium dioxide nanotubes (nt-TiO₂) or titanium dioxide nanotubes with a triazine-methacrylate monomer (nt-TiO₂:TAT) and evaluate the effect of these fillers on the physical, chemical, and biological properties of the adhesives.

METHODS

First, nt-TiO₂ were synthesized via a hydrothermal method. The nt-TiO₂ were mixed with a triazine-methacrylate monomer (TAT) to formulate nt-TiO₂:TAT, which were characterized by transmission electron microscopy (TEM). The nt-TiO₂, TAT, and nt-TiO₂:TAT were evaluated via Fourier Transform Infrared, Ultraviolet-visible, and micro-Raman spectroscopies. An experimental adhesive resin was formulated with bisphenol A glycerolate dimethacrylates, 2-hydroxyethyl methacrylate, and photoinitiator/co-initiator system. nt-TiO₂ or nt-TiO₂:TAT were incorporated at 2.5 wt.% and 5 wt.% in the adhesive. The base resin without nt-TiO₂ or nt-TiO₂:TAT was used as a control group. The adhesives were evaluated for antibacterial activity, cytotoxicity, polymerization kinetics, degree of conversion (DC), Knoop hardness, softening in solvent (ΔKHN%), ultimate tensile strength (UTS), 24 h- and 1 year- microtensile bond strength (μ-TBS).

RESULTS

TEM confirmed the nanotubular morphology of TiO₂. FTIR, UV-vis, and micro-Raman analyses showed the characteristic peaks of each material, indicating the impregnation of TAT in the nt-TiO₂. Adhesives with nt-TiO₂:TAT showed antimicrobial activity against biofilm formation compared to control (p < 0.05), without differences in the viability of planktonic bacteria (p > 0.05). All groups showed high percentages of pulp cell viability. The polymerization kinetics varied among groups, but all presented DC above 50%. The addition of 5 wt.% of nt-TiO₂ and both groups containing nt-TiO₂:TAT showed higher values ​​of Knoop hardness compared to the control (p < 0.05). The groups with nt-TiO₂:TAT presented lower ΔKHN% (p < 0.05) and higher UTS (p < 0.05) than the control group. After one year, the group with 5 wt.% of nt-TiO₂, as well as both groups containing nt-TiO₂:TAT, showed higher μ-TBS than the control (p < 0.05).

SIGNIFICANCE

The mixing of a triazine-methacrylate monomer with the nt-TiO₂ generated a filler that improved the physicochemical properties of the adhesive resins and provided antibacterial activity, which could assist in preventing carious lesions around tooth-resin interfaces. The set of physical, chemical, and biological properties of the formulated polymer, together with the greater stability of the bond strength over time, make nt-TiO₂:TAT a promising filler for dental adhesive resins.

Wollastonite as filler of an experimental dental adhesive

OBJECTIVE

The aim of this study was to formulate experimental dental adhesives with wollastonite and evaluate the physical, chemical, and bioactivity properties of the resins.

METHODS

Wollastonite was characterized by Fourier transform infrared spectroscopy, X-ray and laser diffraction analyses, and scanning electronic microscopy. An experimental adhesive resin was formulated, and wollastonite was used as filler at 0 (control group), 0.5, 1, or 2 wt.%. Radiopacity, degree of conversion (DC%), microhardness, softening in solvent, ultimate tensile strength (UTS), 24 h- and 1 year- microtensile bond strength (μTBS), mineral deposition, and color of the adhesives were evaluated.

RESULTS

Wollastonite particles showed a needle-like shape, a mean diameter of 70 (± 30) μm, characteristic chemical peaks, and pure crystalline β-CaSiO₃ phase. There were no significant differences (p > 0.05) for radiopacity, softening in solvent, and color change. The group with 2 wt.% of wollastonite showed higher microhardness and UTS in comparison to the control group (p < 0.05). After one year, the control group showed reduced μTBS compared to the immediate value (p < 0.05). The groups with wollastonite presented stable μTBS after one year in comparison to the immediate μTBS (p > 0.05). Wollastonite induced mineral deposition on the adhesive surface over the time of storage in simulated body fluid.

CONCLUSION

The addition of wollastonite improved the mechanical behavior of the adhesive without changing the analyzed chemical properties. The adhesives with this filler presented mineral deposition and acceptable clinical color. Moreover, dentin treated with wollastonite-doped adhesives showed higher bonding stability after one year of aging.

CLINICAL SIGNIFICANCE

Wollastonite, a silicate-based material, provided bioactivity for the adhesives, which assists in producing therapeutic tooth-restoration interfaces. Moreover, the incorporation of this mineral improOfiller to improve the biological properties of adhesives and assist in dentin-restoration stability.

Dual modified nanosilica particles as reinforcing fillers for dental adhesives: Synthesis, characterization, and properties

A facile procedure has been devised to develop a novel dentin bonding system containing poly (acrylic acid)-grafted-silanized fumed silica particles as reinforcing filler, with high stability of nanoparticle dispersion and enhanced bond strength and mechanical properties. In the first step, the silanization of fumed silica nanoparticles was performed in the following conditions: (i) ethanol-water solution with a pH of 5 and (ii) cyclohexane with a pH of 9 using trimethoxysilylpropyl methacrylate (γ-MPS) as a reactive silane coupling agent. FTIR and TGA analyses confirmed the presence of silane in the resultant structure and enhanced dispersion stability of modified particles was proved by a separation analyzer and also zeta potential analyses. In the second step, free radical polymerization of acrylic acid monomers in the presence of silanized nanoparticles was carried out and poly (acrylic acid) -grafted- silanized fumed silica were acquired. The flexural strength and fracture toughness of the adhesive containing 0.2 wt.% of the dual modified filler reached maximum of 70.4 MPa and 1.34 MPa m^1/2, respectively, showing average improvements of 74% and 179%, respectively, in comparison with the adhesive without filler. Flexural modulus values did not significantly change with increasing the filler content except the adhesive containing 5 wt.% having the lowest flexural modulus. The highest microtensile bond strength was also observed at 0.2 wt.% filler content showing the average improvements of 197% as compared with the neat adhesive. Energy dispersive X-ray (EDX) mapping confirmed a homogenous and uniform distribution of the fillers in the adhesive matrix containing 0.2 wt.% and 0.5 wt.% of filler while incorporation of 5 wt.% led to large particle aggregates. SEM images of the fracture surface of the adhesive with different filler contents subjected to fracture toughness test showed rougher surface and longer crack path by increasing filler concentration. The adhesive containing 0.2 wt.% of filler perfectly penetrated into the dentin tubules proved by the SEM micrographs in microtensile bond strength test.

Dental Composition Modified with Aryloxyphosphazene Containing Carboxyl Groups

A modifier consisting of the mixture of cyclotriphosphazenes containing 4-allyl-2-methoxyphenoxy and β-carboxyethenylphenoxy moieties was developed for administration with acrylate dental restorative compositions. The synthesized compounds were characterized by ¹H and ¹³C NMR spectroscopy and MALDI-TOF mass spectrometry. The optimal conditions to combine the modifier with the starting dental mixture consisting of bis-GMA and TGM-3 were revealed by differential scanning calorimetry (DSC) method. Properties of the cured modified compositions were evaluated for the compliance with requirements of ISO 4049:2019. It was found that these compositions possess the increased adhesion to dental tissues and cure depth and the decreased water sorption and water solubility. The values of elastic modules, destructive compressive stress and microhardness were also increasing along with the increased content of the modifier in the composition.

Chlorhexidine-modified nanotubes and their effects on the polymerization and bonding performance of a dental adhesive

OBJECTIVES

The purpose of this study was to synthesize chlorhexidine (CHX)-encapsulated aluminosilicate clay nanotubes (Halloysite®, HNTs) and to incorporate them into the primer/adhesive components of an etch-and-rinse adhesive system (SBMP; Scotchbond Multipurpose, 3M ESPE) and to test their effects on degree of conversion, viscosity, immediate and long-term bonding to dentin.

METHODS

CHX-modified HNTs were synthesized using 10% or 20% CHX solutions. The primer and the adhesive components of SBMP were incorporated with 15wt.% of the CHX-encapsulated HNTs. Degree of conversion (DC) and viscosity analyses were performed to characterize the modified primers/adhesives. For bond strength testing, acid-etched dentin was treated with one of the following: SBMP (control); 0.2%CHX solution before SBMP; CHX-modified primers+SBMP adhesive; SBMP primer+CHX-modified adhesives; and SBMP primer+CHX-free HNT-modified adhesive. The microtensile bond strength test was performed after immediate (24h) and long-term (6 months) of water storage. Data were analyzed using ANOVA and Tukey (α=5%) and the Weibull analysis.

RESULTS

DC was greater for the CHX-free HNT-modified adhesive, whereas the other experimental adhesives showed similar DC as compared with the control. Primers were less viscous than the adhesives, without significant differences within the respective materials. At 24h, all groups showed similar bonding performance and structural reliability; whereas at the 6-month period, groups treated with the 0.2%CHX solution prior bonding or with the CHX-modified primers resulted in greater bond strength than the control and superior reliability.

SIGNIFICANCE

The modification of a primer or adhesive with CHX-encapsulated HNTs was an advantageous approach that did not impair the polymerization, viscosity and bonding performance of the materials, showing a promising long-term effect on resin-dentin bonds.

Boron Nitride Nanotubes as Filler for Resin-Based Dental Sealants

The aim of this study was to evaluate the influence of boron-nitride nanotubes (BNNTs) on the properties of resin-based light-curing dental sealants (RBSs) when incorporated at different concentration. RBSs were formulated using methacrylate monomers (90 wt.% TEGDMA, 10 wt.% Bis-GMA). BNNTs were added to the resin blend at 0.1 wt.% and 0.2 wt.%. A Control group without filler was also designed. Degree of conversion, ultimate tensile strength, contact angle, surface free energy, surface roughness and color of the RBSs were evaluated for the tested materials. Their cytotoxicity and mineral deposition ability (Bioactivity) were also assessed. A suitable degree of conversion, no effect in mechanical properties and no cytotoxic effect was observed for the experimental materials. Moreover, the surface free energy and the surface roughness decreased with the addition of BNNTs. While the color analysis showed no difference between specimens containing BNNTs and the control group. Mineral deposition occurred in all specimens containing BNNTs after 7d. In conclusion, the incorporation of BNNTs may provide bioactivity to resin-based dental sealants and reduce their surface free energy.

Assessing size-dependent cytotoxicity of boron nitride nanotubes using a novel cardiomyocyte AFM assay

As boron nitride nanotubes (BNNTs) find increased use in numerous applications, potential adverse health effects of BNNT exposure are a growing concern. Current in vitro cytotoxicity studies on BNNTs are inconsistent and even contradictory, likely due to the lack of reference materials, standardized characterization methods and measurement protocols. New approaches, particularly with the potential to reliably relate in vitro to in vivo studies, are critically needed. This work introduces a novel atomic force microscopy (AFM)-based cardiomyocyte assay that reliably assesses the cytotoxicity of a well-characterized boron nitride nanotube reference material, code named BNNT-1. High energy probe sonication was used to modify and control the length of BNNT-1. The polymer polyethylenimine (PEI) was used concurrently with sonication to produce stable, aqueous dispersions of BNNT-1. These dispersions were used to perform a systematic analysis on both the length and height of BNNT-1 via a correlated characterization approach of dynamic light scattering (DLS) and AFM. Cytotoxicity studies using the novel cardiomyocyte AFM model were in agreement with traditional colorimetric cell metabolic assays, both revealing a correlation between tube length and cytotoxicity with longer tubes having higher cytotoxicity. In addition to the size-dependent cytotoxicity, it was found that BNNT-1 exhibits concentration and cell-line dependent cytotoxic effects.

Antibacterial and Remineralizing Fillers in Experimental Orthodontic Adhesives

Orthodontic adhesives with antimicrobial and remineralizing properties may be an alternative to control white spot lesions around brackets. The aim of this study is to develop an experimental orthodontic adhesive containing boron nitride nanotubes (BNNT) and alkyl trimethyl ammonium bromide (ATAB). Methacrylate (BisGMA and TEGDMA) monomers were used to formulate the adhesives. Four experimental groups were produced with the addition of 0.1 wt.% BNNT (G_BNNT); 0.1 wt.% ATAB (G_ATAB); and 0.2 wt.% BNNT with ATAB (G_BNNT/ATAB); in the control group, no fillers were added (G_Ctrl). The degree of conversion, cytotoxicity, softening in solvent, contact angle and free surface energy, antibacterial activity, shear bond strength, and mineral deposition were evaluated. Adhesives achieved degree of conversion higher than 50% and cell viability higher than 90%. G_BNNT and G_ATAB adhesives exhibited reduced softening in solvent. Mean free surface energy was decreased in the G_BNNT adhesive. Significant reduction in bacterial growth was observed in the G_BNNT/ATAB. No statistical difference was found for shear bond strength. Mineral deposition was found in G_BNNT, G_ATAB, and G_BNNT/ATAB groups after 14 and 28 days. The addition of 0.2% BNNT/ATAB to an experimental orthodontic adhesive inhibited bacterial growth and induced mineral deposition without affecting the properties of the material.