Improved performance of Bis-GMA/TEGDMA dental composites by net-like structures formed from SiO2 nanofiber fillers

Zr-doped mesoporous silica (Zr-MSS) for improved mechanical stability and biocompatibility of dental composite resins

Mesoporous silica particles are of great interest in the field of dental composites as functional inorganic fillers due to their unique interconnected pores which can form micromechanical interlocking at the filler-resin interfaces. However, the degradation of mesoporous silica is fast in wet environments, leading to the poor mechanical stability of dental composites. Here, we synthesized Zr-doped mesoporous silica spheres (Zr-MSS) to increase the chemical stability of the particles. The particles were formulated with dental resins (Bisphenol A glycerolate dimethacrylate/triethylene glycol dimethacrylate, 50/50, wt%) to evaluate the performance of dental composites. Dental composites filled with different amount of Zr-MSS (15, 20, 25 and 30 wt%) and their bimodal fillers with nonporous silica spheres (NSS) at a total filler loading of 60 wt% (mass ratios of Zr-MSS: NSS = 10:50) were prepared. Neat resin matrix and samples filled with mesoporous silica spheres (MSS) were used as control. The results showed that the decrease percentage of flexural strength of dental resins with Zr-MSS was the lowest, which was between 3.4 and 6.8%. It was between 20.8 and 35.5% for those with MSS. Further studies revealed that the incorporation of Zr into mesoporous fillers did not affect their light curing ability of dental composites. Not only that, cell proliferation on the dental composites with Zr-MSS was promoted, suggesting improved biocompatibility of the restorations. These indicated that the prepared Zr-MSS would be promising functional fillers for dental composite resins.

Evolution of Dental Resin Adhesives-A Comprehensive Review

This comprehensive review of dental resin adhesives explores their historical development, key components, recent innovations, and potential future directions, highlighting a dynamic and continually advancing field. From Buonocore's breakthrough acid-etching technique and Bowen's pioneering dental resin invention, successive generations of clinicians and scientists have pushed forward the technological and materials development for secure bonding, while preserving dental tissues. The review discusses the substantial advances in improving adhesive reliability, enabling more conservative treatment approaches. It also delves into enhancing fundamental adhesive components and their synergistic combinations. Recent innovations, including biostable and functional resins, nanotechnology, and bioactive components, address persistent challenges such as durability, antimicrobial efficacy, and therapeutic functionality. Emerging technologies, such as digital dentistry, artificial intelligence, and bioinspired adhesives, portend an exciting and promising future for dental adhesives. This review underscores the critical role of ongoing research in developing biocompatible, multifunctional, and durable adhesives. It aims to support dental professionals and researchers by providing a comprehensive understanding of the dynamic progression of dental adhesives, inspiring continued innovation and excellence in restorative dentistry.

Physicochemical and biological properties of dental materials and formulations with silica nanoparticles: A narrative review

OBJECTIVE

Silica nanoparticles (SNPs) have been extensively studied and used in different dental applications to promote improved physicochemical properties, high substance loading efficiency, in addition to sustained delivery of substances for therapeutic or preventive purposes. Therefore, this study aimed to review the SNPs applications in nanomaterials and nanoformulations in dentistry, discussing their effect on physicochemical properties, biocompatibility and ability to nanocarry bioactive substances.

DATA RESOURCES

Literature searches were conducted on PubMed, Web of Science, and Scopus databases to identify studies examining the physicochemical and biological properties of dental materials and formulations containing SNPs. Data extraction was performed by one reviewer and verified by another STUDY SELECTION: A total of 50 were reviewed. In vitro studies reveal that SNPs improved the general properties of dental materials and formulations, such as microhardness, fracture toughness, flexural strength, elastic modulus and surface roughness, in addition to acting as efficient nanocarriers of substances, such as antimicrobial, osteogenic and remineralizing substances, and showed biocompatibility CONCLUSIONS: SNPs are biocompatible, improve properties of dental materials and serve as effective carriers for bioactive substances CLINICAL SIGNIFICANCE: Overall, SNPs are a promising drug delivery system that can improve dental materials biological and physicochemical and aesthetic properties, increasing their longevity and clinical performance. However, more studies are needed to elucidate SNPs short- and long-term effects in the oral cavity, mainly on in vivo and clinical studies, to prove their effectiveness and safety.

Characterization of dental light-curing resin composites incorporating multiple modified low-shrink monomers

OBJECTIVE

Polymerization shrinkage poses a significant challenge in dental resin composites. The objective of this study is to introduce spiroorthocarbonate monomer 3,9-dimethylene-1,3,5,7-tetraoxa-spiro[5,5]undecane (BMSOC) and epoxy resin monomer 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (ECHM-ECHC) into bisphenol-S-bis(3-methacrylato-2-hydroxy propyl)ether (BisS-GMA) based resin composites to develop composites with reduced shrinkage properties.

METHODS

BMSOC and BisS-GMA were synthesized and thoroughly mixed with ECHM-ECHC, followed by inorganic fillers and photoinitiators. Based on the composition of the resin matrix, five groups of experimental composites were prepared, with traditional bisphenol A-dimethacrylate glycidyl ester (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) based composite serving as the control. The polymerization properties, including degree of conversion (DC) and polymerization shrinkage (PS), as well as marginal microleakage, wettability, flexural strength (FS), flexural modulus (FM), and biocompatibility were evaluated.

RESULTS

The results demonstrated that compared with the control group, the PS of BisS-GMA based composites containing BMSOC and ECHM-ECHC were significantly reduced (P < 0.05), and the lowest PS (0.96 ± 0.08 %) was observed when the ratio of BisS-GMA: (Epoxy + BMSOC) was 4:6. Additionally, the experimental composites also exhibited improved DC, minimal microleakage, low hydrophilicity, enhanced mechanical properties, qualified in vivo biocompatibility, and slight/moderate in vitro biocompatibility.

SIGNIFICANCE

The resin composites incorporating multiple modified low-shrink monomers are promising for dental applications to prevent various clinical problems caused by PS and extend restoration longevity.

Niobium oxyhydroxide as a bioactive agent and reinforcement to a high-viscosity bulk-fill resin composite

OBJECTIVE

The present in vitro study incorporated niobium oxyhydroxide fillers into an experimental high-viscosity bulk-fill resin composite to improve its mechanical performance and provide it a bioactive potential.

METHODOLOGY

Scanning electron microscopy synthesized and characterized 0.5% niobium oxyhydroxide fillers, demonstrating a homogeneous morphology that represented a reinforcement for the feature. Fillers were weighed, gradually added to the experimental resin composite, and homogenized for one minute, forming three groups: BF (experimental high-viscosity bulk-fill resin composite; control), BF0.5 (experimental high-viscosity bulk-fill resin composite modified with 0.5% niobium oxyhydroxide fillers), and BFC (commercial bulk-fill resin composite Beautifil Bulk U, Shofu; positive control). In total, 10 specimens/groups (8 × 2 × 2 mm) underwent flexural strength (FS) tests in a universal testing machine (Instron) (500N). Resin composites were also assessed for Knoop hardness (KH), depth of cure (DoC), degree of conversion (DC), elastic modulus (E), and degree of color change (ΔE). The bioactive potential of the developed resin composite was evaluated after immersing the specimens into a simulated body fluid in vitro solution and assessing them using a Fourier-transformed infrared spectroscope with an attenuated total reflectance accessory. One-way ANOVA, followed by the Tukey's test (p<0.05), determined FS, DC, KH, and ΔE. For DoC, ANOVA was performed, which demonstrated no significant difference between groups (p<0.05).

CONCLUSIONS

The high-viscosity bulk-fill resin composite with 0.5% niobium oxyhydroxide fillers showed promising outcomes as reinforcement agents and performed well for bioactive potential, although less predictable than the commercial resin composite with Giomer technology.

Effect of nanofibers as reinforcement on resin-based dental materials: A systematic review of in vitro studies

This systematic review provides an update on the effect of nanofibers as reinforcement on resin-based dental materials. A bibliographic search was conducted in MEDLINEPubMed, Embase, Web of Science, Scopus, BVS (LILACS, BBO e IBECS), Cochrane, LIVIVO, and gray literature (BDTD) to identify relevant articles up to May 2021. In vitro studies that evaluated and compared the mechanical properties of nanofibers resin-based composite materials, were eligible. No publication year or language restriction was applied, and methodological quality was assessed using two methods. In a total of 6100 potentially eligible studies, 81 were selected for full-text analysis and 35 were included for qualitative analysis. Of the 35 included studies, a total of 29 studies evaluated the flexural strength (FS) of the materials. These groups were distinguished according to the resin-based materials tested and nanofiber types. Most of the studies evaluated materials composed of glass fibers and demonstrated higher values of FS when compared to resin-based materials without nanofibers. The incorporation of nanofibers into resin-based dental materials improved the mechanical properties compared to resin-based materials without nanofibers, suggesting better performance of these materials in high-stressbearing application areas. Further clinical studies are required to confirm the efficacy of resin-based materials with nanofibers.

Glass-Ceramic Fillers Based on Zinc Oxide-Silica Systems for Dental Composite Resins: Effect on Mechanical Properties

The potential of glass ceramics as applicable materials in various fields including fillers for dental restorations is our guide to present a new procedure for improvements of the mechanical properties of dental composites. This work aims to use Zn2SiO4 and SiO2-ZnO nano-materials as fillers to improve the mechanical properties of Bis-GMA/TEGDMA mixed dental resins. Zn2SiO4 and SiO2-ZnO samples were prepared and characterized by using XRD, FE-SEM, EDX, and FT-IR techniques. The XRD pattern of the SiO2-ZnO sample shows that ZnO crystallized in a hexagonal phase, while the SiO2 phase was amorphous. Similarly, the Zn2SiO4 sample crystallized in a rhombohedral crystal system. The prepared samples were used as fillers for the improvement of the mechanical properties of Bis-GMA/TEGDMA mixed dental resins. Five samples of dental composites composed of Bis-GMA/TEGDMA mixed resins were filled with 2, 5, 8, 10, and 15 wt% of SiO2-ZnO, and similarly, five samples were filled with Zn2SiO4 samples (2, 5, 8, 10, and 15 wt%). All of the 10 samples (A1-A10) were characterized by using different techniques including FT-IR, FE-SEM, EDX, and TGA analyses. According to the TGA analysis, all samples were thermally stable up to 200 °C, and the thermal stability increased with the filler percent. Next, the mechanical properties of the samples including the flexural strength (FS), flexural modulus (FM), diameter tensile strength (DTS), and compressive strength (CS) were investigated. The obtained results revealed that the samples filled with 8 wt% of SiO2-ZnO and 10 wt% of Zn2SiO4 had higher FS values of 123.4 and 136.6 MPa, respectively. Moreover, 8 wt% of both fillers displayed higher values of the FM, DTS, and CS parameters. These values were 8.6 GPa, 34.2 MPa, and 183.8 MPa for SiO2-ZnO and 11.3 GPa, 41.2 MPa, and 190.5 MPa for the Zn2SiO4 filler. Inexpensive silica-based materials enhance polymeric mechanics. Silica-metal oxide nanocomposites improve dental composite properties effectively.

Evaluation of contact angle and mechanical properties of resin monomers filled with graphene oxide nanofibers

This in vitro study synthesized hybrid nanofibers embedded in graphene oxide (GO) and incorporated them into experimental resin composite monomers to evaluate their physical-mechanical properties. Inorganic-organic hybrid nanofibers were produced with precursor solutions of 1% wt. GO-filled Poly (d,l-lactide, PLA) fibers and scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) characterized the morphology and chemical composition of the spun fibers. Resin composite monomers were developed and a total of 5% nanofibers were incorporated into the experimental materials. Three groups were developed: G1 (control resin monomers), G2 (resin monomers/PLA nanofibers), and G3 (resin monomers/inorganic-organic hybrid nanofibers). Contact angle (n=3), flexural strength (n=22), elastic modulus (n=22), and Knoop hardness (n=6) were evaluated. The mean of the three indentations was obtained for each sample. The normality of data was assessed by QQ Plot with simulated envelopes and analyzed by Welch's method (p<0.05). Overall, SEM images showed the regular shape of nanofibers but were non-aligned. Compositional analysis from EDS (n=6) revealed the presence of carbon and oxygen (present in GO composition) and Si from the functionalization process. The results of contact angle (°) and hardness (Kg/mm2) for each group were as follow, respectively: G1 (59.65±2.90; 37.48±1.86a), G2 (67.99±3.93; 50.56±1.03b) and G3 (62.52±7.40; 67.83±1.01c). The group G3 showed the highest Knoop hardness values (67.83 kg/mm2), and the flexural strength of all groups was adversely affected. The experimental resin composite composed of hybrid nanofibers with GO presented increased hardness values and hydrophilic behavior.

Effect of monodisperse mesoporous bioactive glass spheres (MBGs) on the mechanical properties and bioactivity of dental composites

Secondary caries is one of the main reasons for the failure of dental resin composites, and adding bioactive fillers such as bioactive glass and amorphous calcium phosphate to the resin composites has been proved to be an effective solution for this problem. In the present study, we investigated the effect of monodisperse mesoporous bioactive glass spheres (MBGs) we prepared on the mechanical properties and bioactivity of dental resins. The results revealed that compared with traditional bioactive glass (BG), MBGs fillers significantly enhanced the mechanical properties of the dental resin composites, whether they were added alone or as functional fillers together with nonporous silica particles. The dental resins filled with bimodal fillers (mass ratio of MBGs: nonporous silica = 10:50, total filler loading 60 wt%) exhibited the best mechanical performance. Their flexural strength was 37.66% higher than the samples with BG at the same filling proportion. Furthermore, the prepared MBGs possessed excellent monodispersity and sufficient apatite formation performance, and the biocompatibility of the composites were also improved by MBGs fillers. These suggest the potential use of the prepared MBGs as multifunctional fillers for the improvement of the performance of dental resins.

Developing a Novel Enamel Adhesive with Amorphous Calcium Phosphate and Silver Nanoparticles to Prevent Demineralization during Orthodontic Treatment

During fixed orthodontic treatment, white spot lesions are prevalent issues associated with cariogenic bacteria. This study aims to construct an orthodontic adhesive containing nanoparticles of amorphous calcium phosphate-polydopamine-Ag (NPA) fillers to combat white spot lesions. The NPA fillers were prepared and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The biocompatibility of the fillers was evaluated. A colony counting test evaluated the antibacterial property of the fillers against Streptococcus mutans (S. mutans). NPA fillers were mixed with orthodontic adhesive (Transbond XT) at different weight ratios (0, 0.1, 0.2, 0.3, and 0.5 wt.%). The shear bond strength and antibacterial properties were then further investigated. The results showed that NPA was prepared successfully, with good antibacterial properties. The cell survival rate of all groups of fillers was higher than 70%, showing good biocompatibility. Moreover, the shear bond strength of the orthodontic adhesive with 0.2 wt.% NPA fillers was 11.89 ± 1.27 MPa, meeting the minimal clinical bond strength requirements of 7.8 MPa. Furthermore, the orthodontic adhesive resin blocks and the extract displayed good antibacterial properties, with the number of colonies decreasing significantly (p < 0.001). Taken together, we think that an orthodontic adhesive with NPA may have a good application potential for the prevention and treatment of white spot lesions.

A Bibliometric Analysis of Electrospun Nanofibers for Dentistry

Electrospun nanofibers have been widely used in dentistry due to their excellent properties, such as high surface area and high porosity, this bibliometric study aimed to review the application fields, research status, and development trends of electrospun nanofibers in different fields of dentistry in recent years. All of the data were obtained from the Web of Science from 2004 to 2021. Origin, Microsoft Excel, VOSviewer, and Carrot² were used to process, analyze, and evaluate the publication year, countries/region, affiliations, authors, citations, keywords, and journal data. After being refined by the year of publication, document types and research fields, a total of 378 publications were included in this study, and an increasing number of publications was evident. Through linear regression calculations, it is predicted that the number of published articles in 2022 will be 66. The most published journal about electrospun dental materials is Materials Science & Engineering C-Materials for Biological Applications, among the six core journals identified, the percent of journals with Journal Citation Reports (JCR) Q1 was 60%. A total of 17.60% of the publications originated from China, and the most productive institution was the University of Sheffield. Among all the 1949 authors, the most productive author was Marco C. Bottino. Most electrospun dental nanofibers are used in periodontal regeneration, and Polycaprolactone (PCL) is the most frequently used material in all studies. With the global upsurge in research on electrospun dental materials, bone regeneration, tissue regeneration, and cell differentiation and proliferation will still be the research hotspots of electrospun dental materials in recent years. Extensive collaboration and citations among authors, institutions and countries will also reach a new level.

Impact of Nanoparticles Additions on the Strength of Dental Composite Resin

Objective

This study aimed to evaluate the effect of nanoparticles, zirconium dioxide (ZrO₂), titanium dioxide (TiO₂), and silicon dioxide (SiO₂), on flexural strength (FS), hardness, and wear resistance of light cured dental composite resin.

Materials and Methods

210 rectangular and disc-shaped composite resin specimens were fabricated with dimensions (25 × 2 × 2 ± 0.03 mm) and (6×4 ± 0.03 mm) for FS, hardness, and wear resistance, respectively (70/test). Specimens of each test were divided according to nanofillers into four groups, unmodified as control, ZrO₂ (Z), TiO₂ (T), and SiO₂ (S) groups; each one was further subdivided into two subgroups according to nanoparticles concentration, 3wt.% and 7wt.% (Z3, Z7, T3, T7, S3, and S7), 10 specimens of each subgroup. A3-point bending test and Vickers hardness test were used for FS and hardness measurements, respectively. Wear resistance was evaluated by the differences in surface roughness of tested specimens before and after wear test. Two-way and 1-way ANOVA and Bonferroni's post hoc tests were done for data analysis (α = 0.05).

Results

Two-way ANOVA for FS and wear resistance showed that there was a significant interaction between type of nanoparticles and concentration of nanoparticles (p < 0.001) while two-way ANOVA for hardness showed that both type of nanoparticles and concentration of nanoparticles had a significant effect (p < 0.001), while the effect of their interaction was not statistically significant (p=0.142). 1-way-ANOVA test showed significant increase in FS and wear resistance for all tested groups (p < 0.001 and p < 0.001, respectively) except T7 and S7. Also, there was a significant enhancement in hardness for all tested groups (p < 0.001).

Conclusion

Modification of light cured composite resin with certain amounts of nanoparticles (3% and 7% of ZrO₂ and 3% of TiO₂ and SiO₂) can be beneficial in improving flexural strength and wear resistance while hardness of composite resin was increased with all NPs additions.

Effects of hybrid inorganic-organic nanofibers on the properties of enamel resin infiltrants - An in vitro study

This in vitro study aimed to evaluate the overall mechanical properties of resin infiltrants doped with bioactive nanofibers and their ability in inhibiting enamel demineralization or achieving remineralization of the adjacent enamel to white spots. A commercial resin infiltrant (ICON, DMG) was doped with hybrid inorganic-organic nanofibers and analyzed for degree of conversion (DC, n = 3) and surface hardness (SH, n = 6). Subsequently, enamel specimens (6 × 4 × 2 mm³) were prepared and submitted to a demineralizing/remineralizing process to produce a subsurface caries-like lesion. The specimens were treated with one of the following materials: ICON infiltrant, DMG (control); ICON + nanofibers of poly-lactic acid (PLA)-filled with silica (PLA-SiO₂); ICON + nanofibers of (PLA)-filled with calcium incorporated into a silica network (SiO₂-CaP). Then, the specimens were subjected to a pH-cycling demineralizing/remineralizing model for 7 days at 37 °C. The %ΔSH change (after treatment), %SH loss and %SH recovery (after pH-cycling regimen) were calculated after SH evaluation (n = 9/group). The Ca/P weight ratio before and after pH-cycling regimen was evaluated through SEM/EDX. The results of DC were analyzed through the T-test (p < 0.05). ANOVA followed by Tukey's test (p < 0.05) was performed for hardness and EDX. A significant SH increase was observed in the ICON/SiO₂CaP group (p < 0.05). The ICON/PLA-SiO₂ presented higher DC values than the control group (p = 0.043). All groups presented significant difference in %ΔSH (p < 0.05), although the specimens treated with ICON/SiO₂CaP presented greater values. Regarding the %SHL and %SHR, the ICON/SiO₂CaP and ICON/PLA-SiO₂ were significantly different compared to the control group (p < 0.001). However, no difference was observed between the ICON/SiO₂CaP and ICON/PLA-SiO_2. The Ca/P ratio showed that the ICON/SiO₂CaP and ICON/PLA-SiO₂ after the pH-cycling regimen differed from sound enamel and modified infiltrants before pH-cycling. In conclusion, tailored hybrid nanofibers may be incorporated into enamel resin infiltrants without compromise the mechanical properties of such experimental materials. These latter can inhibit the demineralization of enamel and increase its hardness during pH-clycling challange.

Monomer Elution from Three Resin Composites at Two Different Time Interval Using High Performance Liquid Chromatography-An In-Vitro Study

Esthetics, improved colour stability and ease of contour have made photo-activated resin based restorative materials being widely used in routine dental clinical practice. Perhaps improper and inadequate polymerization of resin based composite material might lead to elution of monomer. Thus, the aim of the current study was to quantify the monomer elution from three resin composites. The intended analysis was made using high performance liquid chromatography (HPLC) at two different time periods. Three different materials that were investigated in the current study included Swiss Tech resin composite (Group A), Ceram X (Group B) and Beautifil Injectable composite (Group C). Ten cylindrical samples were fabricated in each study group. In 75% wt of ethanol, the samples were ingressed immediately and stored at room temperature. A 0.5 mL of the samples was assessed at pre-defined time intervals at 24 h and 7th day. Later, assessment of the samples was performed with HPLC and the data was analyzed using statistical test. Bisphenol A-glycidyl methacrylate (Bis-GMA), Triethylene glycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA) and Urethane dimethacrylate (UDMA) were quantified in the samples. When analyzing the release monomer, it was found that at the end of 24 h Bis-GMA was eluted more in the injectable resin composite whereas, TEGDMA was eluted from Swiss Tech and Ceram X resin composites. At the end of the 7th day it was evident that Bis-GMA was eluted maximum in all the three resin composites. Thus, monomer release was found to be evident among all three resin composites and it is of utmost important to be assessed in routine clinical practice.

The Development of Filler Morphology in Dental Resin Composites: A Review

Dental resin composites (DRCs) with diverse fillers added are widely-used restorative materials to repair tooth defects. The addition of fillers brings an improvement in the mechanical properties of DRCs. In the past decade, diverse fillers have emerged. However, the change of emerging fillers mainly focuses on the chemical composition, while the morphologic characteristics changes are often ignored. The fillers with new morphologies not only have the advantages of traditional fillers (particles, fibrous filler, etc.), but also endow some additional functional characteristics (stronger bonding ability to resin matrix, polymerization resistance, and wear resistance, drug release control ability, etc.). Moreover, some new morphologies are closely related to the improvement of traditional fillers, porous filler vs. glass particles, core-sheath fibrous vs. fibrous, etc. Some other new morphology fillers are combinations of traditional fillers, UHA vs. HA particles and fibrous, tetrapod-like whisker vs. whisker and fibrous filler, mesoporous silica vs. porous and silica particles. In this review, we give an overall description and a preliminary summary of the fillers, as well as our perspectives on the future direction of the development of novel fillers for next-generation DRCs.

Molecular dynamics investigation of structural and mechanical properties of silica nanorod reinforced dental resin composites

In this work, molecular dynamics simulations are conducted to investigate the structural and mechanical properties of dental materials, i.e., the silica nanorod reinforced Bis-GMA/TEGDMA resin composite. The effects of loading content and size of the silica nanorods on the composite stiffness were performed by examining resin chain conformation, hydrogen bonds and matrix/filler binding energy. It is revealed that the presence of the silica nanorod causes polymer chain expansion, endowing the resins with higher stiffness. Moreover, the volumetric hydrogen bonds and binding energy increase considerably with the loading content, but decrease gradually with the diameter or show almost independence of the length. Furthermore, the composite moduli were quantified by the micromechanics models and the transverse moduli were well predicted by the Counto model, signifying a perfect bonding between the matrix and nanorod. The chain expansion and energetic matrix/filler interactions are believed to contribute to the significant mechanical reinforcement of the composites with the loading content. However, the length of the nanorod has a little effect on the composite moduli due to the unaltered interfacial interaction. In contrast, a smaller diameter is supposed to give a larger modulus, and this is not observed in this work due to the synergic effects of improved matrix/filler interaction and actual reduced filler volume fraction. The mechanical enhancement by the rod-like structures is more influenced by the loading content, but less so by the size of the nanorod, and it also exhibits superior mechanical performance as compared to nanoparticles. The findings thus extend the current understanding of the nanostructure and mechanical properties of silica nanorod reinforced dental resin composites from an atomic/molecular perspective.

Effect of the incorporation of silica blow spun nanofibers containing silver nanoparticles (SiO2/Ag) on the mechanical, physicochemical, and biological properties of a low-viscosity bulk-fill composite resin

OBJECTIVE

This work aimed at producing silica-blow-spun nanofibers containing silver nanoparticles (SiO₂/Ag) and investigating the effect of their incorporation in different proportions, with or without pre-treatment with a silane coupling agent, on the mechanical, physicochemical, and biological properties of a commercial composite low-viscosity bulk-fill resin.

METHODS

The production of SiO₂/Ag nanofibers was confirmed by transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). A portion of the produced nanofibers was silanized. Scanning electronic microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), contact angle measurements, and agar diffusion tests against Streptococcus mutans were used to verify the differences between silanized and non-silanized nanofibers. Different proportions (0.5 wt% and 1 wt%) of silanized (SiO₂/Ag-0.5S and SiO₂/Ag-1S) and non-silanized (SiO₂/Ag-0.5NS and SiO₂/Ag-1NS) nanofibers were incorporated into the bulk-fill composite (Opus Bulk Fill Flow, FGM). A commercial composite was used as the control. Evaluation of the color parameters (L*, a*, and b*), radiopacity, contact angle, antimicrobial activity, Vickers microhardness, surface roughness (Sa and Sq), flexural strength, and SEM of the fractured surfaces were performed. The data were analyzed using the Mann-Whitney U test (fiber morphology), Kruskal-Wallis tests, with Dunn's post hoc test (antimicrobial activity of the specimen against S. mutans), Student's t-test (disk diffusion), one-way ANOVA and Tukey (color, radiopacity, and contact angle), and two-way ANOVA and Tukey (microhardness, surface roughness, and flexural strength) tests. All statistical analyses were performed at a significance level of 1% (α = 0.01).

RESULTS

Porous nanometric SiO₂/Ag fibers were successfully produced. The silanization process, confirmed by FTIR, increased the diameter and contact angle and reduced the growth inhibition halos of the nanofibers (p < 0.01). After the incorporation of nanofibers into the dental composite, all color parameters were altered in all the experimental groups (p < 0.01). All the groups presented adequate radiopacity values. No statistical difference was observed in the contact angles of the experimental composites (p > 0.01). The lowest microbial counts were obtained in the SiO₂/Ag-0.5S group; although no significant difference was observed with the control group (p < 0.01). The SiO₂/Ag-1S, SiO₂/Ag-0.5S, and SiO₂/Ag-0.5NS groups exhibited higher microhardness after 30 d of immersion in water (p < 0.01). The surface roughness (Sa-μm) resembled that of the control at baseline, except for the SiO₂/Ag-1NS group. For the baseline evaluation of flexural strength, all the experimental groups exhibited lower values than the control, except for SiO₂/Ag-0.5NS and SiO₂/Ag-0.5S, but after 30 d of immersion in water, there was no difference (p < 0.01).

SIGNIFICANCE

The incorporation of 0.5% wt. of silanized nanofibers in the commercial composite (SiO₂/Ag-0.5S) seemed to be promising, especially for its greater inhibition of S. mutans, adequate roughness, and flexural strength, in addition to high hardness, even after aging in water.

Hydrophobically Modified Isosorbide Dimethacrylates as a Bisphenol-A (BPA)-Free Dental Filling Material

A series of bio-based hydrophobically modified isosorbide dimethacrylates, with para-, meta-, and ortho- benzoate aromatic spacers (ISBGBMA), are synthesized, characterized, and evaluated as potential dental restorative resins. The new monomers, isosorbide 2,5-bis(4-glyceryloxybenzoate) dimethacrylate (ISB4GBMA), isosorbide 2,5-bis(3-glyceryloxybenzoate) dimethacrylate (ISB3GBMA), and isosorbide 2,5-bis(2-glyceryloxybenzoate) dimethacrylate (ISB2GBMA), are mixed with triethylene glycol dimethacrylate (TEGDMA) and photopolymerized. The resulting polymers are evaluated for the degree of monomeric conversion, polymerization shrinkage, water sorption, glass transition temperature, and flexural strength. Isosorbide glycerolate dimethacrylate (ISDGMA) is synthesized, and Bisphenol A glycerolate dimethacrylate (BisGMA) is prepared, and both are evaluated as a reference. Poly(ISBGBMA/TEGDMA) series shows lower water sorption (39-44 µg/mm³) over Poly(ISDGMA/TEGDMA) (73 µg/mm³) but higher than Poly(BisGMA/TEGDMA) (26 µg/mm³). Flexural strength is higher for Poly(ISBGBMA/TEGDMA) series (37-45 MPa) over Poly(ISDGMA/TEGDMA) (10 MPa) and less than Poly(BisGMA/TEGDMA) (53 MPa) after immersion in phosphate-buffered saline (DPBS) for 24 h. Poly(ISB2GBMA/TEGDMA) has the highest glass transition temperature at 85 °C, and its monomeric mixture has the lowest viscosity at 0.62 Pa·s, among the (ISBGBMA/TEGDMA) polymers and monomer mixtures. Collectively, this data suggests that the ortho ISBGBMA monomer is a potential bio-based, BPA-free replacement for BisGMA, and could be the focus for future study.

The incorporation of phosphorylated chitosan/amorphous calcium phosphate nanocomplex into an experimental composite resin

This study evaluated the effect of incorporating phosphorylated chitosan/amorphous calcium phosphate nanocomplex (Pchi/ACP) into an experimental light-cure composite resin on mechanical-chemical properties and human dentin remineralization. The results showed that the mechanical strength and contact angles of the resins decreased with the increase incorporation of Pchi/ACP. Release concentrations of calcium in saline solution were measured at different time points, showing the incorporation of Pchi/ACP significantly increased calcium release within 14 days, and kept steady thereafter. Finally, the demineralized dentin slabs treated with our resins for four weeks were characterized by SEM-EDS. Various amounts of apatite were formed on the dentin slabs which were treated with the resins containing Pchi/ACP, whereas no apatite was formed without Pchi/ACP. In conclusion, the Pchi/ACP-incorporating composite resin can be a promising dental material due to its favorable mechanical and remineralization properties.

Review of nano-technology applications in resin-based restorative materials

OBJECTIVE

Nanotechnology has progressed significantly and particles as small as 3 nm are being employed in resin-based restorative materials to improve clinical performance. The goal of this review is to report the progress of nanotechnology in Restorative Dentistry by reviewing the advantages, limitations, and applications of resin-based restorative materials with nanoparticles.

MATERIALS AND METHODS

A literature review was conducted using PubMed/Medline, Scopus and Embase databases. In vitro, in vivo and in situ research studies published in English between 1999 and 2020, and which focused on the analysis of resin-based restorative materials containing nanoparticles were included.

RESULTS

A total of 140 studies were included in this review. Studies reported the effect of incorporating different types of nanoparticles on adhesive systems or resin composites. Mechanical, physical, and anti-bacterial properties were described. The clinical performance of resin-based restorative materials with nanoparticles was also reported.

CONCLUSIONS

The high surface area of nanoparticles exponentially increases the bioactivity of materials using bioactive nanofillers. However, the tendency of nanoparticles to agglomerate, the chemical instability of the developed materials and the decline of rheological properties when high ratios of nanoparticles are employed are some of the obstacles to overcome in the near future.

CLINICAL SIGNIFICANCE

In spite of the recent advancements of nanotechnology in resin-based restorative materials, some challenges need to be overcome before new nano-based restorative materials are considered permanent solutions to clinical problems.

Farnesal-loaded pH-sensitive polymeric micelles provided effective prevention and treatment on dental caries

BACKGROUND

Farnesol is a sesquiterpene from propolis and citrus fruit that shows promising anti-bacterial activity for caries treatment and prevention, but its hydrophobicity limits the clinical application. We aimed to develop the novel polymeric micelles (PMs) containing a kind of derivative of farnesol and a ligand of pyrophosphate (PPi) that mediated PMs to adhere tightly with the tooth enamel.

RESULTS

Farnesal (Far) was derived from farnesol and successfully linked to PEG via an acid-labile hydrazone bond to form PEG-hyd-Far, which was then conjugated to PPi and loaded into PMs to form the aimed novel drug delivery system, PPi-Far-PMs. The in vitro test about the binding of PPi-Far-PMs to hydroxyapatite showed that PPi-Far-PMs could bind rapidly to hydroxyapatite and quickly release Far under the acidic conditions. Results from the mechanical testing and the micro-computed tomography indicated that PPi-Far-PMs could restore the microarchitecture of teeth with caries. Moreover, PPi-Far-PMs diminished the incidence and severity of smooth and sulcal surface caries in rats that were infected with Streptococcus mutans while being fed with a high-sucrose diet. The anti-caries efficacy of free Far can be improved significantly by PPi-Far-PMs through the effective binding of it with tooth enamel via PPi.

CONCLUSIONS

This novel drug-delivery system may be useful for the treatment and prevention of dental caries as well as the targeting therapy of anti-bacterial drugs in the oral disease.

Triethyleneglycol dimethacrylate addition improves the 3D-printability and construct properties of a GelMA-nHA composite system towards tissue engineering applications

In tissue engineering, there is a growing interest in the development of 3D printable bone tissue-inspired nanocomposites. However, most such nanocomposites have poor mechanical properties, owing to poor dispersion of the mineral phase (e.g. nano-hydroxyapatite, nHA) within the organic phase (e.g. methacrylated gelatin, GelMA) and low volume fractions of each phase. Triethyleneglycol dimethacrylate (TEGDMA) is commonly added to dental resin-based composites to improve the properties of the dental resin. Here, the effects of substituting a portion of the water phase in a GelMA-nHA composite with TEGDMA were evaluated. TEGDMA improved the dispersion of nHA within the highly-concentrated GelMA-based composite ink, as well as increased the ink's shear yield strength and reduced the critical energy for ink cure. As a result, the printability of the composite ink was greatly improved upon TEGDMA inclusion. Lastly, while the swelling of the cast composite in 37 °C water increased slightly, the mechanical properties (tensile strength, toughness, and stiffness) of the cast composite increased by at least an order of magnitude upon TEGDMA addition, and all composites demonstrated MSC cytocompatibility after 24 h. Overall, TEGDMA shows promise as an additive to tune properties of the GelMA-nHA system towards use in tissue engineering applications.

Composite resin reinforced with fluorescent europium-doped hydroxyapatite nanowires for in-situ characterization

OBJECTIVE

The object is to find an easy but efficient way to illustrate the in-situ dispersion of nano-scaled one-dimensional fillers in composite resins, and to correlate their dispersion status with the properties of composite resins.

METHODS

Fluorescent europium-doped hydroxyapatite nanowires (HANW:Eu) were synthesized via the hydrothermal method. The HANW:Eu was mixed into Bis-GMA/TEGDMA (60/40, w/w) at different contents (1-5wt.%), and different processing methods (kneading, grinding, stirring) were tested to achieve good dispersion of HANW:Eu with the aid of fluorescent imaging system. Then, the mixtures of HANW:Eu and barium glass powder (BaGP) were kneaded into resin at a fixed content (70wt.%) while at different mixing ratios. In addition to the 3D fluorescent imaging, characterizations were carried out on mechanical properties, fractured surface, wear resistance and polymerization shrinkage, to correlate the composite properties of with the dispersion status of the incorporated HANW:Eu.

RESULTS

By doping calcium with 5mol.% of europium, the obtained HANW:Eu displayed strong fluorescence, which made the illustration of its in-situ dispersion status within composites being possible. And this helped to judge that kneading was more efficient to homogeneously disperse HANW:Eu than grinding and stirring. However, it was illustrated vividly that HANW:Eu aggregated severely when it was co-incorporated with BaGP into composites at the total content of 70wt.%, which had not been previously revealed by other microscope observations. In comparison with composites containing 70wt.% of BaGP, improvements in the mechanical properties of resulting composites were identified for the cases containing 3wt.% of HANW and 67wt.% of BaGP, however, their wear volume loss and the polymerization shrinkage did not decrease as expected due to the HANW aggregations.

SIGNIFICANCE

The fluorescent filler prepared in this study provides a feasible strategy to illustrate the in-situ dispersion status of inorganic fillers, which provides guidance for the processing of composite resins.

Improved mechanical performance of self-adhesive resin cement filled with hybrid nanofibers-embedded with niobium pentoxide

OBJECTIVES

In this study hybrid nanofibers embedded with niobium pentoxide (Nb₂O₅) were synthesized, incorporated in self-adhesive resin cement, and their influence on physical-properties was evaluated.

METHODS

Poly(D,L-lactide), PDLLA cotton-wool-like nanofibers with and without silica-based sol-gel precursors were formulated and spun into submicron fibers via solution blow spinning, a rapid fiber forming technology. The morphology, chemical composition and thermal properties of the spun fibers were characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC), respectively. Produced fibers were combined with a self-adhesive resin cement (RelyX U200, 3M ESPE) in four formulations: (1) U200 resin cement (control); (2) U200+1wt.% PDLLA fibers; (3) U200+1wt.% Nb₂O₅-filled PDLLA composite fibers and (4) U200+1wt.% Nb₂O₅/SiO₂-filled PDLLA inorganic-organic hybrid fibers. Physical properties were assessed in flexure by 3-point bending (n=10), Knoop microhardness (n=5) and degree of conversion (n=3). Data were analyzed with One-way ANOVA and Tukey's HSD (α=5%).

RESULTS

Composite fibers formed of PDLLA-Nb₂O₅ exhibited an average diameter of ∼250nm, and hybrid PDLLA+Nb₂O₅/SiO₂ fibers were slightly larger, ∼300nm in diameter. There were significant differences among formulations for hardness and flexural strength (p<0.05). Degree of conversion of resin cement was not affected for all groups, except for Group 4 (p<0.05).

SIGNIFICANCE

Hybrid reinforcement nanofibers are promising as fillers for dental materials. The self-adhesive resin cement with PDLLA+Nb₂O₅ and PDLLA+Nb₂O₅/SiO₂ presented superior mechanical performance than the control group.

The Effect of Thermocycling on Surface Layer Properties of Light Cured Polymer Matrix Ceramic Composites (PMCCs) Used in Sliding Friction Pair

This paper discusses the problem of thermocycling effect of light-curing polymer–ceramic composites. Cyclic thermal shocks were simulated in laboratory conditions. As a rule, these loads were supposed to reproduce the actual conditions of biomaterials exploitation. Periodically variable stresses occurring in dental restorations are associated with the wear of cold and hot foods and beverages. They lead to changes in the properties of composites, including the properties of the surface layer. The aim of the work was to assess the impact of cyclic hydrothermal interactions on the properties of the surface layer of composites relevant to the operational quality. Two commercial materials manufactured by the world’s leading producer (3M ESPE)—Filtek Z550, Filtek Flow and two experimental, micro-hybrid and flow type composites marked Ex-mhyb(P) and Ex-flow(P), respectively. All tests were carried out before and after hydro-thermal cycles (flowing water thermocycling). Micro-hardness test using the Vickers method, indentation hardness, and resistance to tribological wear in a ball–disc system in sliding friction conditions were performed. In addition, observations of the surface layer of composites on the SEM (scanning electron microscope) were carried out. It was noticed that semi-liquid composites, containing a smaller amount of filler, retain higher stability of mechanical and tribological properties of the surface layer under cyclic hydro-thermal loads. Coefficient of friction of samples after hydro-thermal cycles increased for micro-hybrid materials and Filtek Flow (FFlow) composite. In the case of Ex-flow(P) material, the coefficient of friction decreased. The microhardness of composites also changed, the variability of this size depended on the type of material. Composites with a higher content of filler particles were characterized by greater variability of microhardness under the influence of thermocycles. The resistance to tribological wear also changed in a similar way. Composites containing higher volume fraction of inorganic filler showed higher tribological wear after thermocycling. The wear resistance of flow composites changed to a lesser extent, after thermocycling increased. The paper also showed that, in real kinematic nodes, the surface layer of light-curing ceramic–polymer composites is exposed to significant non-tribological (erosive, thermal, and chemical) defects that synergize with tribological ones. In slip pairs loaded dynamically, under mixed friction conditions, tribological wear of PMCCs (polymer matrix ceramic composites) is manifested by spalling (spalling of the material flakes, in particular the polymer phase) and pitting (crushing wear caused by wear products, in particular large filler particles or clusters, previously adhesively extracted).

TiO2 and PEEK Reinforced 3D Printing PMMA Composite Resin for Dental Denture Base Applications

The future of manufacturing applications in three-dimensional (3D) printing depends on the improvement and the development of materials suitable for 3D printing technology. This study aims to develop an applicable and convenient protocol for light-curing resin used in 3D industry, which could enhance antibacterial and mechanical properties of polymethyl methacrylate (PMMA) resin through the combination of nano-fillers of surface modified titanium dioxide (TiO₂) and micro-fillers of polyetheretherketone (PEEK). PMMA-based composite resins with various additions of TiO₂ and PEEK were prepared and submitted to characterizations including mechanical properties, distribution of the fillers (TiO₂ or/and PEEK) on the fractured surface, cytotoxicity, antibacterial activity, and blood compatibility assessment. These results indicated that the reinforced composite resins of PMMA (TiO₂-1%-PEEK-1%) possessed the most optimized properties compared to the other groups. In addition, we found the addition of 1% of TiO₂ would be an effective amount to enhance both mechanical and antibacterial properties for PMMA composite resin. Furthermore, the model printed by PMMA (TiO₂-1%-PEEK-1%) composite resin showed a smooth surface and a precise resolution, indicating this functional dental restoration material would be a suitable light-curing resin in 3D industry.

Wear Characteristics of Dental Ceramic CAD/CAM Materials Opposing Various Dental Composite Resins

The aim of this study was to evaluate the wear properties of opposed dental ceramic restorative CAD/CAM materials and several posterior direct restorative composite resins. Three kinds of dental ceramics CAD/CAM materials (monolithic zirconia, lithium disilicate, leucite) and four dental composite resins—that is, MI Gracefil, Gradia Direct P, Estelite Σ Quick, and Filtek Supreme Ultra—were used in this study. For each of the 12 groups (three ceramics × four composite resins), five each of a canine-shaped ceramic specimen and a cuboidal shape opposing composite resin were prepared. All of the specimens were tested in a thermomechanical loading machine (50 N, 100,000 cycles, 5/55 °C). Wear losses of ceramic specimens and composite resin specimens were evaluated using a three-dimensional profiling system and an electronic scale, respectively. Statistical analyses were performed using the Kruskal–Wallis test and Mann–Whitney U test with Bonferroni’s correction. Zirconia showed significantly less volumetric loss than lithium disilicate or leucite regardless of composite resin type (p > 0.05/3 = 0.017), and that Estelite Σ Quick showed significantly more weight loss than Filtek Supreme Ultra, MI Gracefil, or Gradia Direct P regardless of ceramic type (p > 0.05/6 = 0.083). Zirconia showed less volumetric loss than lithium disilicate or leucite. Some composite resins opposing ceramics showed considerable weight loss.

Physicochemical and Microbiological Assessment of an Experimental Composite Doped with Triclosan-Loaded Halloysite Nanotubes

This study is aimed at evaluating the effects of triclosan-encapsulated halloysite nanotubes (HNT/TCN) on the physicochemical and microbiological properties of an experimental dental composite. A resin composite doped with HNT/TCN (8% w/w), a control resin composite without nanotubes (HNT/TCN-0%) and a commercial nanofilled resin (CN) were assessed for degree of conversion (DC), flexural strength (FS), flexural modulus (FM), polymerization stress (PS), dynamic thermomechanical (DMA) and thermogravimetric analysis (TGA). The antibacterial properties (M) were also evaluated using a 5-day biofilm assay (CFU/mL). Data was submitted to one-way ANOVA and Tukey tests. There was no significant statistical difference in DC, FM and RU between the tested composites (p > 0.05). The FS and CN values attained with the HNT/TCN composite were higher (p < 0.05) than those obtained with the HNT/TCN-0%. The DMA analysis showed significant differences in the TAN δ (p = 0.006) and Tg (p = 0) between the groups. TGA curves showed significant differences between the groups in terms of degradation (p = 0.046) and weight loss (p = 0.317). The addition of HNT/TCN induced higher PS, although no significant antimicrobial effect was observed (p = 0.977) between the groups for CFUs and (p = 0.557) dry weight. The incorporation of HNT/TCN showed improvements in physicochemical and mechanical properties of resin composites. Such material may represent an alternative choice for therapeutic restorative treatments, although no significance was found in terms of antibacterial properties. However, it is possible that current antibacterial tests, as the one used in this laboratory study, may not be totally appropriate for the evaluation of resin composites, unless accompanied with aging protocols (e.g., thermocycling and load cycling) that allow the release of therapeutic agents incorporated in such materials.

Composite resin reinforced with silver nanoparticles-laden hydroxyapatite nanowires for dental application

OBJECTIVE

The object is to find a functional one-dimensional nanofibrous filler for composite resin, which is able to provide both efficient reinforcement and high antibacterial activity.

METHODS

Hydroxyapatite (HA) nanowires were synthesized via hydrothermal technique using calcium oleate as the precursor. Polydopamine (PDA)-coated HA (HA-PDA) nanowires were prepared by soaking HA nanowires in dopamine (DA) aqueous solution. Silver nanoparticles (AgNPs)-laden HA (HA-PDA-Ag) nanowires were prepared via reduction reaction by adding silver nitrate and glucose into HA-PDA suspensions in DI water. The resulted HA-PDA-Ag nanowires were then mixed into Bis-GMA/TEGDMA (50/50, w/w) at 4-10wt.%, thermal-cured, and submitted to characterizations including mechanical properties, interfacial adhesion between filler and resin matrix, distribution of HA nanowires and AgNPs, as well as silver ion release, cytotoxicity and antibacterial activity.

RESULTS

HA-PDA-Ag nanowires were readily obtained and the loading amounts of AgNPs could be controlled by adjusting the feeding doses of silver nitrate and HA-PDA nanowires. Benefiting from the PDA surface layer, HA-PDA-Ag nanowires could disperse well in composite resin and form good interfacial adhesion with the resin matrix. In comparison with neat resin, significant increases in flexural strength and modulus of cured composites were achieved at the addition amounts of HA-PDA-Ag nanowires being 6-8wt.%. The distribution of AgNPs was homogeneous throughout the resin matrix in all designs, which endowed the composites with high antibacterial activity against streptococcus mutans. Continuous silver ion release from composites was detected, however, it was determined the composites would have insignificant cytotoxicity based on the proliferation of L929 fibroblasts in extracts of HA-PDA-Ag nanowires.

SIGNIFICANCE

The finding proved that HA-PDA-Ag nanowires could serve as functional nanofillers for composite resins, which should help much in developing materials for satisfactory long-term clinical restorations.

Improved mechanical properties and thermal degradation of low-temperature hydrogenated acrylonitrile butadiene rubber composites with poly(sodium methacrylate) nanowires

Complex phase structures including a lot of poly(sodium methacrylate) nanowires improved the mechanical properties and thermal stability of LTG-HNBR composites.