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Objective: The purpose of this study is to develop a mathematical model for efficient prediction of the packing density of different filler formulations in dental resin composites (DRCs), and to study properties of DRCs at the maximum filler loading (MFL), thereby providing an effective guidance for the design of filler formulations in DRCs to obtain excellent properties., Methods: The packing density data generated by discrete element model (DEM) simulation were used to re-derive the parameters of 3-parameter model. The modifier effect was also induced to modify the 3-parameter model. DRCs with 10 filler formulations were selected to test properties at the MFL. The packing densities of binary and ternary mixes in DRCs were calculated by 3-parameter model to explore the regularity of composite packing., Results: The predicted packing density was validated by simulation and experimental results, and the prediction error is within 1.40 vol%. The optimization of filler compositions to obtain a higher packing density is beneficial to enhancing the mechanical properties and reducing the polymerization shrinkage of DRCs. In binary mixes, the maximum packing density occurs when the volume fraction of small fillers is 0.35-0.45, and becomes higher with the reduction of particle size ratio. In ternary mixes, the packing density can reach the maximum value when the volume fractions of large and small fillers are in the 0.5-0.75 and 0.15-0.4 ranges, respectively., Significance: The modified 3-parameter model can provide an effective method to design the multi-level filler formulations of DRCs, thereby improving the performance of the materials., (Copyright © 2021 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.)

Objective: The inorganic fillers in dental resin composites can enhance their mechanical properties and reduce polymerization shrinkage. When the usage amount of inorganic fillers is closed to maximum filler loading (MFL), the composites will usually achieve optimal performances. This study aims to develop a method that can predict the MFL of dental resin composites for the optimization of filler formulations., Methods: A method based on discrete element method (DEM) simulations and experiments was firstly developed to predict the MFL of spherical silica particles for single-level and multi-level filling., Results: The results indicate that the presence of modifier can increase the MFL, and the MFL increment can be exponentially changed with the content of the modifier. Compared with the single-level filling, the addition of secondary fillers is beneficial to increase the MFL, and the increment can be affected by the particle size and size ratio. The prediction results show a good agreement with the experiment results., Significance: The accuracy of prediction results indicates a great potential of DEM simulations as a numerical experimental method in studying the MFL, and provides an effective method for the optimization of filler formulations., (Copyright © 2020 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.)

Nanocomposites have been used in various industries due to their excellent properties. For some of them, high filler content (over 50 wt%) is beneficial to improving their performances. This study aims to explore the network model construction and properties of high filler content dental resin composites (DRCs). An improved multistep dynamic cross-linking procedure was proposed and firstly applied to construct the reasonable molecular model of high filler content DRCs. The predicted elastic modulus and stress–strain results of DRCs with different nanofiller contents show that the DRCs with a 70 wt% filler content have the most excellent mechanical properties. Furthermore, the dynamic property study indicates that the diffusion coefficient of matrices firstly decreased and then increased with the nanofiller content increasing from 0 to 80 wt%, reaching the lowest value at 70 wt%. The migration of resin matrices can be limited by nanofillers at the content within 70 wt%. However, when the filler content is excessively high (80 wt%), the stability of matrices is destroyed and the fractional free volume of DRCs sharply increases, resulting in a decrease of mechanical properties of DRCs. The findings of this study deepen the understanding of structures and properties of DRCs at the atomic/molecular scales. [ABSTRACT FROM AUTHOR]

The good mechanical performances and caries inhibition of resin composites (RCs) are of great importance in dental restoration. Generally, the addition of SiO2 can improve the mechanical properties of RCs, while the introduction of fluoride (F) ions is capable of preventing caries. In this work, we first report the use of CaF2/SiO2 core–shell nanoparticles (CaF2/SiO2 NPs) as novel fillers for developing RCs with excellent mechanical properties and sustained F release. The results show that the superior performances of RCs can be obtained by filling 50 wt.% CaF2/50%SiO2 NPs, where the flexural strength, flexural modulus, compressive strength, and hardness were, respectively, increased by 111.5%, 41.4%, 61.7% and 66.8%, compared with the RCs filled with CaF2 nanoparticles. In addition, the initial F-release rate of RCs containing 50 wt.% CaF2/50%SiO2 NPs was 2.5 ± 0.4 μg/(h cm2), while the sustained release rate and the F release ratio were 0.96 ± 0.15 μg/h·cm2 and 5.22‰ after 1632 h (68 days), respectively. It was much more stable and sustained compared with the counterpart filled with CaF2 NPs. Therefore, it could be envisioned that CaF2/SiO2 NPs have a great potential as inorganic fillers in dental RCs. [ABSTRACT FROM AUTHOR]

Dental resin-based composites have been used for more than 50 years. The size and the structure of inorganic filler have a great effect on the mechanical properties of the composite resin. In this study, novel micro-sized clusters of hydroxyapatite nanorods (MCHN) were designed and conveniently fabricated by spray drying combined with heat treatment. The effects of the aspect ratio of primary hydroxyapatite nanorods (HN), suspension concentration for spray drying and heat treatment temperature were explored. The results indicated that HN with a lower aspect ratio of 2 (HN-2) and a heat treatment temperature of 500 °C were beneficial to the construction of high-performance MCHN (MCHN-2). As compared to HN-2, MCHN-2 had a further increased filling amount by 10%. More importantly, the flexural strength, flexural modulus and compressive strength of the composite resin were greatly improved by 36.3%, 11.4% and 56.6%, respectively. Therefore, it could be envisioned that MCHN could have a great potential in dental restorative application. [ABSTRACT FROM AUTHOR]

In dental resin composites (DRCs), the structure of fillers has a great impact on the mechanical behavior. The purpose of this study is to gain an in-depth understanding of the reinforcement mechanism and mechanical behavior of DRCs with nanoparticle clusters (NCs) fillers, thereby providing a guidance for the optimal design of filler structures for DRCs. This work pioneers the use of discrete element method (DEM) simulations combined with experiments to study the mechanical behavior and reinforcement mechanism of DRCs with NCs fillers. The uniaxial compressive strength (UCS) of NCs-reinforced DRCs have an improvement of 9.58 % and 15.02 % in comparison with nanoparticles (NPs) and microparticles (MPs), respectively, because of the ability of NCs to deflect cracks and absorb stress through gradual fracturing. By using NCs and NPs as co-fillers, the internal defects of DRCs can be reduced, resulting in a further improvement of UCS of DRCs by 6.21 %. Furthermore, the mechanical properties of DRCs can be effectively improved by increasing the strength of NCs or reducing the size of NCs. This study deepens the understanding of relationship between filler structure and mechanical behavior in DRCs at the mesoscale and provides an avenue for the application of DEM simulations in composite materials. [ABSTRACT FROM AUTHOR]

The objective of this study is to develop novel CaF 2 /SiO 2 nanoclusters (NCs) fillers, which can endow the dental resin composites (DRCs) with excellent mechanical properties, stable and sustained fluoride ion release, and good antibacterial activity. The CaF 2 /SiO 2 NCs were efficiently fabricated by assembling CaF 2 /SiO 2 nanoparticles (NPs) as building blocks with a spray-drying technology. CaF 2 /SiO 2 NCs with different SiO 2 coating amounts (20 wt%, 50 wt% and 80 wt%) were incorporated into the DRCs at the filler content of 55 wt% for the measurement of mechanical properties including flexural strength, flexural modulus, compressive strength, and hardness. The effect of the filling amount of CaF 2 /50SiO 2 NCs (50 represents 50 wt% SiO 2 coating amount) in the DRCs was investigated, while CaF 2 /50SiO 2 NPs were adopted as comparison group. The fluoride ion release and antibacterial activity of the DRCs with the optimal mechanical performances were evaluated. Furthermore, the statistical analyses were performed for mechanical properties. Spherical CaF 2 /50SiO 2 NCs with an average size of 2.4 µm were obtained at the feed rate of 7.4 mL/min and the CaF 2 /50SiO 2 NPs solid content of 2 wt% in the suspension. The optimum comprehensive performances of the DRCs can be achieved by filling 55 wt% CaF 2 /50SiO 2 NCs. Compared with CaF 2 /50SiO 2 NPs, the filling amount of CaF 2 /50SiO 2 NCs was increased by 5 wt% (50–55 wt%), and under the same filling amount of 50 wt%, the flexural strength, flexural modulus, compressive strength, and hardness of the DRCs containing CaF 2 /50SiO 2 NCs were improved by 9.8%, 17.7%, 7.5% and 69.8%, respectively. Furthermore, the DRCs filled with 50 wt% CaF 2 /50SiO 2 NCs exhibited more cumulative F-release by 126% and more stable F-release rate than the counterpart filled with 50 wt% CaF 2 /50SiO 2 NPs after immersed for 1800 h. And 55 wt% CaF 2 /50SiO 2 NCs filled DRCs could inhibit the growth of S. mutans, reaching an antibacterial ratio of 93%. The spray-dried CaF 2 /50SiO 2 NCs are promising fillers for the development of high-performance multifunctional DRCs. [ABSTRACT FROM AUTHOR]

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 SiO 2 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. [ABSTRACT FROM AUTHOR]