Properties Of Dental Resin Composites Research Articles

Preparation of Al-doped mesoporous silica spheres (Al-MSSs) for the improvement of mechanical properties and aging resistance of dental resin composites

ObjectiveThe purpose of this study was to synthesize Al-doped mesoporous silica spheres (Al-MSSs) and evaluate the effect of them as functional fillers on the mechanical properties and aging resistance of dental resin composites. MethodsAl-MSSs were prepared by a two-step method. The effect of Al-MSSs on the performance of the composites was evaluated using neat resin matrix, commercial composites 3M Z350XT and samples containing mesoporous silica spheres (MSSs) and nonporous silica spheres (NSSs) as control. The neat resin matrix consisted of resin monomer (Bisphenol A glycerolate dimethacrylate/triethylene glycol dimethacrylate, 49.5/49.5, wt%) and photoinitiator (camphor quinone/Ethyl-4-dimethylaminobenzoate, 0.2/0.8, wt%). The mechanical properties (flexural strength, flexural modulus, compressive strength and microhardness) of them were evaluated by a universal testing machine and microhardness tester. The mechanical stabilities of the prepared composites in wet environment were evaluated by immersing them in deionized water at 37 °C. In addition, we evaluated the effect of Al-MSSs on other properties of the dental resin composites such as polymerization shrinkage, degree of conversion, curing depth, contact angle, water sorption and solubility according to ISO 4049: 2019. ResultsThe synthesized Al-MSSs possessed good dispersibility with an average particle size of about 505 ± 16 nm. The mechanical properties of resin composites gradually increased with the increase of the loading amounts of inorganic fillers. The reinforcing effect of Al-MSSs was similar to that of MSSs and better than that of the NSSs groups at the same filler loading. After aging in deionized water at 37 °C for 30 days, the mechanical properties of all resin composites decreased. However, the decrease percentage of the composites filled with Al-MSSs was significantly lower than the other groups, indicating that the stability of the dental composites in wet environments was significantly improved by the Al-MSSs fillers. Furthermore, Al-MSSs had no obvious influence on the biocompatibility and other properties of dental resins. SignificanceThe prepared Al-MSSs could effectively improve the mechanical properties and aging resistance without sacrificing other physic-chemical properties of dental resin composites.

Comparative analysis of self-cure and dual cure-dental composites on their physico-mechanical behaviour.

Clinical practitioners may have become familiar with the rapid transformation of dental composites. However, they may not scientifically understand the factors influencing the mechanical and physical properties. Scientific knowledge of filler-resin interaction can significantly improve clinical understanding of resin composites. Several independent studies have examined the mechanical and physico-mechanical properties of dental resin composites; however, no comprehensive study has examined the influence of fillers and resin materials on the physico-mechanical properties of both self-cure and dual-cure composites. This study performed investigations on the physico-mechanical behaviour of four commercially available dual-cure dental composites (Bioactive, Fill Up!, Surefil One, Cention N) and two commercially available self-cure dental composites (Stela Capsule and Stela Automix). Test specimens for flexural and compressive strength, microhardness, fracture toughness, and hydrolytic behaviour were prepared and tested as per respective standards. The data sets were statistically analysed using one-way ANOVA and Tukey's post-hoc comparison. There was a substantial variation in flexural strength and modulus values in this study, ranging from 32.0 to 113.4 MPa and 2.36 to 12.07 GPa, respectively. Similarly, there were significant differences in compressive strength between the materials in this study, ranging from 119.3 to 223.5 MPa. The highest fracture toughness value was found to be 1.41 MPa.m0.5, while the lowest value was 0.43 MPa.m0.5. Variations in surface microhardness were significant (24.11-68.0 N/mm2), which correlated with the filler content. Water sorption and solubility demonstrated high variations among materials, with Surefil One exceeding ISO 4049 thresholds significantly. A linear correlation can be established between surface microhardness (HV) and flexural and compressive moduli, as well as filler content (wt.%). However, both flexural and compressive strengths are impacted by the resin's constituent monomers and the resin-filler matrix's cross-linking capability. Additionally, factors such as filler size, shape, and the cross-linking ability of the resin-filler matrix play a crucial role in fracture toughness and the propagation of cracks within the restoration. Also, resin monomers and filler particle size affect the hydrolytic degradation characteristics of composites, which can also affect their mechanical properties. © 2023 Australian Dental Association.

ON THE POSSIBILITIES AND STRATEGIES FOR INCORPORATION ANTIMICROBIAL AGENTS INTO RESIN COMPOSITE DENTAL MATERIALS – A NARRATIVE REVIEW

Because of the high frequency of recurrent caries following composite resin restorative treatment, as well as the large number of cariogenic microorganisms present in the oral cavity, which represent a potential risk factor for the development of new carious lesions, the antimicrobial effects of composite resins are receiving increasing attention. Recently, attempts have been made to include specific antimicrobial compounds in restorative materials, mainly GJCs and composites, in addition to fluorides. Conventional composites’ lack of antibacterial qualities implies a lack of an inhibitory impact against plaque accumulation on their surface, allowing bacteria such as mutans streptococci to grow freely. As a result, the antibacterial properties of dental resin composites are crucial to their therapeutic applications. The present study demonstrates the methods and possibilities for incorporating antimicrobial chemicals, both leachable and non-leachable, into the resin matrix or filler of composite resins.

Synthesis of Pore-Size-Tunable Porous Silica Particles and Their Effects on Dental Resin Composites.

The filler/resin matrix interface interaction plays a vital role in the properties of dental resin composites (DRCs). Porous particles are promising fillers due to their potential in constructing micromechanical interlocking at filler/resin matrix interfaces, therefore improving the properties of the resulting DRCs, where the pore size is significantly important. However, how to control the pore size of porous particles via a simple synthesis method is still a challenge, and how their pore sizes affect the properties of resulting DRCs has not been studied. In this study, porous silica (DPS) with a dendritic structure and an adjustable pore size was synthesized by changing the amounts of catalyst in the initial microemulsion. These synthesized DPS particles were directly used as unimodal fillers and mixed with a resin matrix to formulate DRCs. The results showed that the DPS pore size affects the properties of DRCs, especially the mechanical property. Among various DPS particles with different pore sizes, DPS6 resulted in 19.5% and 31.4% improvement in flexural strength, and 24.4% and 30.7% enhancement in compression strength, respectively, compared to DPS1 and DPS9. These DPS particles could help to design novel dental restorative materials and have promising applications in biomedicine, catalysis, and adsorption.

A Comparative Study on the Microscale and Macroscale Mechanical Properties of Dental Resin Composites.

Dental resin composites are universal restorative materials, and various kinds of fillers are used to reinforce their mechanical properties. However, a combined study on the microscale and macroscale mechanical properties of dental resin composites is missing, and the reinforcing mechanism of the composites is still not fully clarified. In this work, the effects of the nano-silica particle on the mechanical properties of dental resin composites were studied by combined dynamic nanoindentation tests and macroscale tensile tests. The reinforcing mechanism of the composites was explored by combining near-infrared spectroscopy, scanning electron microscope, and atomic force microscope characterizations. It was found that the tensile modulus increased from 2.47 GPa to 3.17 GPa, and the ultimate tensile strength increased from 36.22 MPa to 51.75 MPa, with the particle contents increasing from 0% to 10%. From the nanoindentation tests, the storage modulus and hardness of the composites increased by 36.27% and 40.90%, respectively. The storage modulus and hardness were also found to increase by 44.11% and 46.46% when the testing frequency increased from 1 Hz to 210 Hz. Moreover, based on a modulus mapping technique, we found a boundary layer in which the modulus gradually decreased from the edge of the nanoparticle to the resin matrix. Finite element modeling was adopted to illustrate the role of this gradient boundary layer in alleviating the shear stress concentration on the filler-matrix interface. The present study validates mechanical reinforcement and provides a potential new insight for understanding the reinforcing mechanism of dental resin composites.

Low shrinkage bulk-filled dental resin composites with non-estrogenic dimethacrylate.

This study synthesized and characterized different proportions of nonestrogenic di(meth)acrylate 9,9-bis[4-((2-(2-methacryloyloxy)ethyl-carbamate)ethoxy)phenyl] fluorine (Bis-EFMA)-based resin composite systems to study their physical, chemical, optical and biological characteristics, and adhesive properties after bonding to a tooth. The estrogenic activity of raw materials was evaluated and compared with estrogen and commercial bisphenol A. After photopolymerization, all resin composite systems were prepared, and their properties were systematically investigated. Notably, the nonestrogenic di(meth)acrylate Bis-EFMA exhibited a more suitable refractive index, excellent biocompatibility, low marginal microleakage and improved bonding strength. Except for the pure UDMA and Bis-EFMA groups, the depth of cure and Vickers microhardness ratios of all the other groups met the requirements of bulk filling (one-time curing depth of more than 4 mm). Bis-EFMA resin systems exhibited lower volumetric polymerization shrinkage (about 3-5%), higher curing depth (>6 mm in specific proportions), mechanical properties (flexural strength of 120-130 MPa, etc.), and microtensile bonding strength (>27.8 MPa), which were comparable or superior to Bis-GMA or commercial composites. Herein, we believe that the novel nonestrogenic di(meth)acrylate (Bis-EFMA) has a wide application prospect as an alternative to Bis-GMA.

Isobornyl methacrylate as diluent co‐monomer on physical‐mechanical properties of dental resin composites

AbstractThe aim of this study was to evaluate the effects of isobornyl methacrylate (IBOMA) as a diluent co‐monomer on the physical properties of experimental resins. Blends of bisphenol glycidyl methacrylate (Bis‐GMA) were formulated with triethylene glycol dimethacrylate (TEGDMA) and IBOMA in different wt%. The degree of conversion, flexural strength, elastic modulus, and ultimate tensile strength were determined. Immediate and 24 h volumetric shrinkage were calculated. Data were submitted to ANOVA and Tukey's tests (α = 0.05). Blends of Bis‐GMA and IBOMA showed the lowest ultimate tensile strength, flexural strength, elastic modulus, degree of conversion, and immediate and 24 h volumetric shrinkage results. However, when IBOMA was used together with TEGDMA in blends of Bis‐GMA, the resin composites showed best curing performance and high physical‐mechanical properties. Thus, the IBOMA is as diluent co‐monomer that can be used in dental resin composites to reduce the volumetric shrinkage.

Antibacterial activity and reinforcing effect of SiO2-ZnO complex cluster fillers for dental resin composites.

The accumulation of bacteria at the margin of dental resin composites is the main reason for secondary caries, which may further cause failure of prosthodontics. Therefore, antibacterial activity is highly required. However, the addition of antibacterial agents or fillers weakens the mechanical or aesthetic properties of composites. In this work, regular-shaped SiO2-ZnO complex clusters (CCs) constructed by spray-drying technology can enhance the antibacterial activity while maintaining the mechanical and aesthetic properties of dental resin composites. The results show that the regular shape and closely packed structure of nanoparticle clusters were not corrupted by the introduction of ZnO particles. As compared to resin composites filled with SiO2 nanoparticle clusters, the comprehensive performances of composites containing SiO2-ZnO CCs were further improved, and the composites filled with 70 wt% Si66Zn4 (CCs composed of 66/70 SiO2 and 4/70 of ZnO) exhibited superior antibacterial capability (antibacterial ratio >99.9%) and acceptable depth of cure, degree of conversion, and biocompatibility. The cooperation of different fillers is highly essential for resin composites to achieve enhanced multifunctional performance.

Does the Addition of Zinc Oxide Nanoparticles Improve the Antibacterial Properties of Direct Dental Composite Resins? A Systematic Review.

A promising approach to improve the poor antibacterial properties of dental composite resins has been the addition of metal oxide nanoparticles into the resin matrix. This systematic review aimed to determine whether the addition of zinc oxide nanoparticles (ZnO-NPs) improves the antibacterial properties of direct dental composite resins. This review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and registered with the PROSPERO database: CRD42019131383. A systematic literature search was conducted using the following databases: Medline (Ovid), the Cochrane Library, SCOPUS, CINAHL, Web of Science, Trove, Google Scholar, World Cat, and OpenGrey. The initial search retrieved 3178 results, which were then screened against inclusion and exclusion criteria, resulting in a total of four studies that were eligible for qualitative synthesis within this review. All the included studies were in vitro non-randomized post-test design experimental studies. A lack of congruity in the results obtained from these studies that used different tests to evaluate antibacterial activity was evident. Although some studies demonstrated a significant improvement of antibacterial properties in composites containing at least 1% ZnO-NPs (wt %), they are unlikely to present any clear clinical advantage due to the short lifetime of observed antibacterial properties.

Comparative Effectiveness of Two Light Curing Units on the Properties of Dental Resin Composites

Background: Setting of conventional glass ionomers cement and dental resin composites as filling materials is predominantly through polymerization reaction, which is usually induced by light. The objective of this study was to assess the temperature changes, light intensities, sorption and solubility capability and comparative micro hardness in Dental Resin Composites (DRC) by using two different light curing units that is Quartz Tungsten Halogen (QTH) and Light Emitting Diodes (LED). Methods: This analytical, experimental, in-vitro study was spanned over one month, conducted in the laboratory of Dental Materials, Dr. Ishrat-ul-Ibad Khan Institute of Oral Health Sciences. Through non-probability, convenient sampling, 60 samples of DRCs was prepared as 10mm in diameter and 2mm in thickness in the steel moulds by a single trained operator. Effect of heat generation, light intensities, sorption and solubility and micro hardness during polymerization of DRCs were all measured. Statistical analysis was done using SPSS with descriptive statistics and two sample independent t-tests. The p-value of <0.05 was considered significant at 95 % confidence level. Results: Mean surface micro hardness of DRC was found to be 15.48±0.46 and 18.26±0.53 when QTH and LED lamps were employed respectively. Whereas, mean light intensity of QTH and LED lamps were found to be 434 and 925mW/cm2. No significant difference in temperature change during polymerization reaction (p=0.128) and in sorption and solubility capability (p=0.001) of DRC was observed. Conclusion: Light-emitting diodes were evaluated to be more effective than Quartz Tungsten Halogen Light in achieving increased surface micro hardness of DRC. Keywords: Light; Glass Ionomer Cements; Tungsten; Hardness.

Application of Antimicrobial Polymers in the Development of Dental Resin Composite

Dental resin composites have been widely used in a variety of direct and indirect dental restorations due to their aesthetic properties compared to amalgams and similar metals. Despite the fact that dental resin composites can contribute similar mechanical properties, they are more likely to have microbial accumulations leading to secondary caries. Therefore, the effective and long-lasting antimicrobial properties of dental resin composites are of great significance to their clinical applications. The approaches of ascribing antimicrobial properties to the resin composites may be divided into two types: The filler-type and the resin-type. In this review, the resin-type approaches were highlighted. Focusing on the antimicrobial polymers used in dental resin composites, their chemical structures, mechanical properties, antimicrobial effectiveness, releasing profile, and biocompatibility were included, and challenges, as well as future perspectives, were also discussed.

Surface Modification of ZrO2 Nanoparticles and Its Effects on the Properties of Dental Resin Composites.

Endowing dental resin composites (DRCs) with suitable radiopacity is necessary for clinical diagnosis during treatment of caries. To reach this effect, ZrO2 nanoparticles were introduced into the DRCs in this work after modification with two different methods, one modified with 3-methacryloxypropyltrimethoxysilane (ZrO2@γ-MPS) and the other coated with mesoporous SiO2 and then modified with γ-MPS (ZrO2@m-SiO2@γ-MPS). These ZrO2 nanoparticles were used as functional additives, and the SiO2 nanoparticles were used as the fundamental filler in the preparation of DRCs to study the effects of the surface modification of ZrO2 nanoparticles and the amount of particles added (0, 3, 5, and 7 wt %) on the properties of the DRCs. The DRC containing ZrO2@m-SiO2@γ-MPS showed a higher transmittance, which may be attributed to the fact that the SiO2 coating reduced the refractive index of the nanoparticles and thus decreased the scattering of light within the DRC. The silane polymer film on the surface of ZrO2@γ-MPS nanoparticles acted as a lubricant and decreased the viscosity of DRC, but the DRC containing ZrO2@m-SiO2@γ-MPS showed a higher viscosity due to the presence of a mesoporous structure. The radiopacity value of the DRCs containing the functional additives was close to 1 mm Al, much higher than that of the DRC filled with SiO2 nanoparticles alone (0.74 ± 0.07 mm Al), meeting the requirement of ISO 4049:2009. The surface modification of ZrO2 nanoparticles had no significant influence on the mechanical properties, radiopacity, and cytotoxicity of DRCs (p > 0.05). This study provides useful insight into the design and development of radiopaque DRCs with excellent physical and mechanical properties.

Synthesis and characterization of cellulose/hydroxyapatite based dental restorative composites

The aim of this study was an in-situ synthesis of hydroxyapatite (HA) on cellulose fibers to be used as a new reinforcing agent for dental restorations. The microwave irradiation method was used for synthesis and the materials were characterized with analytical techniques. The prepared dental resin composites were mechanically tested by a universal testing machine and electrodynamic fatigue testing system. FTIR, XRD, SEM/EDS analysis confirmed the successful synthesis of HA on cellulose fibers. The Alamar blue biocompatibility assay showed more than 90% cell viability for the prepared cellulose/HA. The mechanical properties of resin composites improved with cellulose content from 30 wt.% to 50 wt.% in the polymer matrix. Substantially, increasing the cellulose/HA content from 40% to 50% improved the mechanical properties. The results suggested that HA could be successfully synthesized on cellulose fibers using microwave irradiation and contributed to improving the mechanical properties of dental resin composites.

Preparation of Zn doped mesoporous silica nanoparticles (Zn-MSNs) for the improvement of mechanical and antibacterial properties of dental resin composites

ObjectiveThe purpose of this work was to explore the enhancement effect of zinc doped mesoporous silica nanoparticles (Zn-MSNs), which could form micromechanical interlocking with resin matrix and sustainably release Zn2+, on the mechanical and antibacterial properties of the dental resin composites. MethodsZn-MSNs were prepared by a sol–gel method, and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 adsorption/desorption. The mechanical properties of the dental composites reinforced by Zn-MSNs were measured by a universal mechanical testing machine. Antibacterial activities of dental composites were evaluated by both qualitative and quantitative analysis using Streptococcus mutans (S. mutans). The cytotoxicity of the Zn-MSNs filled dental composites was investigated by osteoblasts (OBs). ResultsThe synthesized Zn-MSNs possessed good monodispersity with an average particle size of about 138nm. The mechanical properties of the composites gradually increased with the increase of the content of Zn-MSNs. The flexural strength, flexural modulus, compressive strength and micro-hardness of the composites containing 15wt% Zn-MSNs were 31.21%, 50.47%, 53.83% and 26.79% higher than the samples with no Zn-MSNs, respectively. The antibacterial performance was significantly improved by the addition of Zn-MSNs and the antibacterial rate of the composite with 15wt% of Zn-MSNs reached 100%. Cytotoxicity tests revealed that all the composites were biocompatible during OBs incubation. SignificanceThe prepared Zn-MSNs can effectively improve the mechanical and antibacterial properties of the dental resin composites.

Effect of Type and Concentration of Nanoclay on the Mechanical and Physicochemical Properties of Bis-GMA/TTEGDMA Dental Resins.

Bis-GMA/TTEGDMA-based resin composites were prepared with two different types of nanoclays: an organically modified laminar clay (Cloisite® 30B, montmorillonite, MMT) and a microfibrous clay (palygorskite, PLG). Their physicochemical and mechanical properties were then determined. Both MMT and PLG nanoclays were added into monomer mixture (1:1 ratio) at different loading levels (0, 2, 4, 6, 8 and 10 wt.%), and the resulting composites were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and mechanical testing (bending and compressive properties). Thermal properties, depth of cure and water absorption were not greatly affected by the type of nanoclay, while the mechanical properties of dental resin composites depended on both the variety and concentration of nanoclay. In this regard, composites containing MMT displayed higher mechanical strength (both flexural and compression) than those resins prepared with PLG due to a poor nanoclay dispersion as revealed by SEM. Solubility of the composites was dependent not only on nanoclay-type but also the mineral concentration. Dental composites fulfilled the minimum depth cure and solubility criteria set by the ISO 4049 standard. In contrast, the minimum bending strength (50 MPa) established by the international standard was only satisfied by the dental resins containing MMT. Based on these results, composites containing either MMT or PLG (at low filler contents) are potentially suitable for use in dental restorative resins, although those prepared with MMT displayed better results.

The properties of dental resin composites reinforced with silica colloidal nanoparticle clusters: Effects of heat treatment and filler composition

Resin composites have been frequently applied in dental restoration due to their distinguished overall performance. The size, structure and composition of inorganic fillers have significant effects on the properties of dental resin composites (DRCs). The aim of our research is to strengthen the structure of spray-dried silica colloidal nanoparticle clusters (SCNCs) by means of a calcination process, and achieve the excellent comprehensive performance of DRCs by the combined use with different fillers. The results indicate that the SCNCs calcined at 500 °C has a significant strengthening effect on the flexural properties and hardness of DRCs except the decrease of compressive strength in comparison to the uncalcined SCNCs. To overcome this problem, the SiO2 nanoparticles (NPs) as building blocks for SCNCs and the SCNCs were further adopted as co-fillers of the calcined SCNCs (CSCNCs). It can be found that the strengthening effect of SCNCs is better than that of the NPs at the same filling ratio. The DRCs filled with 60 wt% CSCNCs and 10 wt% SCNCs have a greatly enhanced compressive strength, reaching the same level with the DRCs filled with 70 wt% SCNCs. More importantly, the corresponding flexural strength (143.5 ± 8.3 MPa), flexural modulus (8.91 ± 0.48 GPa) and hardness (70.7 ± 1.4 HV) still have an improvement of 14%, 23% and 48% in comparison with those of the counterpart, respectively.

Efficient Construction of SiO2 Colloidal Nanoparticle Clusters as Novel Fillers by a Spray-Drying Process for Dental Composites

The size and structure of inorganic fillers have a significant effect on the mechanical properties of dental resin composites. In this work, we report the use of spray-drying for the efficient cons...

Efficacy of light-emitting diode light polymerization units used in private practices in Toronto, Ontario, Canada

Efficacy of light-emitting diode light polymerization units used in private practices in Toronto, Ontario, Canada

Development of mechanical properties in dental resin composite: Effect of filler size and filler aggregation state

The aim of this work was to study the effect of filler size and filler aggregation state on the mechanical properties of dental resin composites evaluated at filler loadings between 20 wt% and up to 76.5 wt%. Non-aggregated silica nanoparticles (SiNPMPS) (80 nm), doughnut-shaped silica nanoclusters obtained by spray drying (SDSiNPMPS) (3.5 μm) and amorphous barium-alumina borosilicate microparticles (BaAlBoSiMPS) (1.0 μm), functionalized by 3-methacryloxypropyl trimethoxysilane (MPS), were the fillers incorporated into resin matrix dental composites composed of triethylene glycoldimethacrylate (TEGDMA), urethane dimethylacrylate (UDMA), bisphenol A polyethylene glycol diether dimethacrylate (Bis EMA), and bisphenol A glycidyl methacrylate (BisGMA) (0.3:0.7:1:1 weight ratio, respectively). The mechanical properties developed in the resin composites were correlated with the formation of percolated-like particle networks, as observed by scanning electron microscopy (SEM), and volume fraction percolation thresholds (ϕc) calculated from a percolation model. Resin composites with non-aggregated SiNPMPS showed an apparent percolation threshold ϕc = 0.15 (i.e. 27 wt%); above this filler concentration and up to a volume fraction of particles (ϕP) of 0.24 (i.e. 40 wt%) there was an increase in the flexural modulus and the compressive strength of the resin composite. However, a further increase in filler concentration diminished all its mechanical properties due to a decrease in the particle-matrix adhesion strength, demonstrated by the increase in surface roughness and fracture steps as observed by SEM images. On the other hand, a resin composite filled with doughnut-shaped silica nanoclusters (SDSiNPMPS) showed an apparent percolation threshold ϕc = 0.41 (i.e. 60 wt%); increasing filler loading over this concentration generated an improvement in its mechanical properties, except the flexural strength also due to a decrease in the particle-matrix adhesion strength. The resin composites obtained with amorphous individual BaAlBoSiMPS microparticles (1.0 μm) and BaAlBoSiMPS microparticle aggregates (ca. 40.0 μm) showed an apparent percolation threshold ϕc = 0.41 (i.e. 64 wt%) that promoted an improvement in all their mechanical properties. SEM image of BaAlBoSiMPS resin composite at high filler loading (≥ 60 wt%) showed a decrease in fracture steps and no presence of voids, indicating a better adhesion between amorphous BaAlBoSiMPS particles and the polymeric matrix, which explains the improvement of mechanical properties. Resin composites filled exclusively with silica doughnut-shape nanoclusters or amorphous BaAlBoSiMPS microparticles could develop mechanical properties similar to or even better than those obtained by mixing nanofillers with spherical nanoclusters, which are commonly used in commercial resin composites.

Reinforcement of dental resin composite via zirconium hydroxide coating and phosphate ester monomer conditioning of nano-zirconia fillers

ObjectivesThe present study aimed to evaluate effects of conditioning with the phosphate ester monomer 10-methacryloyloxydecyl dihydrogen phosphate (MDP), with and without precoating with zirconium hydroxide for nano-size zirconia fillers, on mechanical properties of dental resin composites. Materials and methodsNano-zirconia fillers coated with or without zirconium hydroxide [Zr(OH)4] were prepared. Transmission electron microscopy (TEM), Fourier infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to observe the coating and to characterize Zr(OH)4 coating on the zirconia filler surface. Zirconia fillers with or without Zr(OH)4 coating were conditioned with MDP and were subsequently used to prepare experimental resin composites. XPS was used to analyze the Zr-O-P bonds on the filler surface after MDP conditioning. Moreover, three-point bending strength and elastic modulus of prepared resin composites were measured, and Weibull analysis was performed. Resin composites without addition of zirconia fillers and the ones with addition of untreated or silane conditioned-zirconia fillers were set as controls. Cell counting kit (CCK)-8 was used to test cell cytotoxicity of these zirconia fillers-containing experimental resin composites. ResultsNano-zirconia fillers were coated with Zr(OH)4 through chemical deposition. FTIR and XPS analysis confirmed the increase of hydroxyl groups after Zr(OH)4 coating. XPS detected the highest contents of Zr-O-P bonds on MDP-conditioned zirconia fillers with pre-Zr(OH)4 coating, followed by MDP-conditioned zirconia fillers. Resin composite with added MDP-conditioned zirconia fillers with and without Zr(OH)4 coating exhibited greater three-point bending strength, elastic modulus values, and Weibull moduli. According to the cytotoxicity classification, resin composites containing experimental zirconia fillers were considered to have no significant cell cytotoxicity. ConclusionNano-zirconia fillers conditioned with MDP, with or without precoating with Zr(OH)4, improve the mechanical properties of resin composites, and are potentially safe for clinical use.