Sol–gel-derived bioactive glass nanoparticle-incorporated glass ionomer cement with or without chitosan for enhanced mechanical and biomineralization properties
Graphical abstract
Introduction
Glass ionomer cement (GIC) is a tooth-colored material introduced by Wilson and Kent [1] in the late 1960s. GIC is set based on a reaction between a fluoroaluminosilicate-based glass powder and an acidic liquid primarily composed of polyacrylic acid. These substances bond chemically to the tooth structure via a carboxyl (from GIC)-calcium (from enamel or dentin) interaction and release fluoride ions for a relatively long period, which is a beneficial anticariogenic property [2], [3]. Along with the above advantages, GIC has been used as luting cement, a restorative material or a base and liner before a final direct or indirect restoration.
Although GIC has a high compressive strength after setting, it is vulnerable to tension and shear force and consequently shows lower flexural and diametral tensile strength [4]. Therefore, increasing its mechanical properties using additives has been investigated. Metal alloy (i.e., silver–tin or silver–palladium/titanium) has been successfully incorporated into glass powder to enhance the mechanical properties, but the bioactivity was compromised with a change of color to an unaesthetic metal color [5], [6].
In 1969, Hench [7] reported that certain degradable glass compositions (Bioglass 45S5) were able to form chemical bonds with bone due to released ions such as Na+, Si4+ and Ca2+. These materials are referred to as bioactive glasses and have been used as regenerative biomaterials for damaged hard tissues, including teeth. In dentistry, bioactive glass has been widely investigated as a bone graft material or additive to restorative materials, cement and bonding agents for enhancing bioactivity [8], [9], [10], [11], [12], [13]. In terms of its application in GIC (including GIC derivatives), commercially available bioactive glasses (NovaBone and S53P4) containing (10–20%) GIC or air abrasion with bioactive glass (45S5) before resin-modified GIC application have been reported to exhibit enhanced bioactivity in simulated body fluid and bonding durability, thus enabling re-mineralization of human dentin [14], [15], [16]. However, the addition of bioactive glass into GIC decreased its compressive strength, flexural strength and surface hardness [15], [17]. Thus, developing bioactive GIC without decreasing its mechanical properties remains a challenge.
Due to their high surface area, nanoparticles are of special interest for applications to dental materials including GIC to enhance the mechanical properties of the matrix and enhance communication with dental tissue-derived cells to aid their regeneration [18], [19], [20], [21]. In addition to many nanoadditives (i.e., hydroxy(or fluoro)apatite, titanium oxide, zirconia, resin, and their combinations) that have been incorporated into conventional GIC, one of the promising nanoparticulates for use in GIC is bioactive glass nanoparticles (BGNs) [22], [23], [24].
BGNs increase the surface area and bioactivity when combined with the matrix in GIC and thereby provide a greater enhancement of mechanical/biological properties as an additive per particle weight than conventional micro-sized bioactive glass particles [25], [26]. Since BGNs were first produced using the sol–gel method with the development of nanotechnology, the application of BGNs has been diversified to overall dentistry due to their enhanced bioactivity and mechanical properties as a nanocomposite [26]. However, no studies have evaluated the effect of BGNs incorporated into GIC on the GIC’s mechanical properties (i.e., compressive, flexural and diametral tensile strength) and biological effects (i.e., cytotoxicity and biomineralization).
Chitosan, a linear polysaccharide composed of randomly distributed β-(1-4)-linked d-glucosamine and N-acetyl-d-glucosamine, has been used in the dental (or biomedical) field due to its natural adhesive properties, biocompatibility, antibacterial properties, and pH-sensitive solubility [20], [27]. Chitosan has also been incorporated into GIC to enhance its mechanical properties by acting as a physical or chemical binder between the glass filler and matrix in GIC [28], [29], [30] or to induce antibacterial effects [29], depending on the concentration of chitosan in GIC.
In the present study, the mechanical and biological properties of BGN (ϕ = ∼42 nm)-incorporated GIC with or without chitosan were investigated in vitro study (immortalized human dental pulp stem cells (ihDPSCs)) to support further study in vivo. The null hypothesis is that there is no significant difference in the mechanical and biological properties of GIC with or without BGNs or chitosan.
Section snippets
Fabrication of bioactive glass nanoparticle
Tetraethyl orthosilane (TEOS), calcium nitrate tetrahydrate (Ca(NO3)2·4H2O), ammonia solution (28%) and Pluronic 123 (P123) were used as precursors for the synthesis of BGNs (85% SiO2–15% CaO). All chemicals were purchased from Sigma–Aldrich unless otherwise stated. Spherical bioglass nanoparticles containing 85SiO2/15CaO (mol%) were synthesized via a base-catalyzed sol–gel approach in the presence of templates according to our previously reported method [31]. In a 150-mL solution that
Characterization of bioactive glass nanoparticles
BGNs were sol–gel synthesized to diameters of 42 ± 5 nm (Fig. 1A) with a spherical morphology from TEM images (insert in Fig. 1a). The EDS results confirmed that the composition of BGNs matched well with those initially designed (Fig. 1B, 85:15 as atomic ratio of Si:Ca). The XRD patterns from as-prepared BGNs (Fig. 1C, down) exhibited a broad amorphous peak between 2θ = 15° and 35°, a typical characteristic of amorphous bioactive glasses. The density of BGNs was 2.51 ± 0.02 g/cm3, while that commercial
Discussion
GIC has been widely used as a provisional or permanent restorative material due to its high compressive strength, anticaries fluoride ion release, biocompatibility and chemically bonding ability to the tooth structure [2], [3]. However, this material is vulnerable to tension and shear force and its biomineralization ability to pulp tissue was not sufficient for the regeneration of damaged dentin–pulp complex when the extract contacts the pulp tissue via open dentinal tubules [4]. Therefore, an
Conclusion
Within the limitations of this study, BGNs were successfully incorporated into GIC for enhancing its mechanical properties and in vitro chemical or biomineralization capacities with compliance with the net setting time in the ISO standard. Chitosan was used as a bio-binder between BGN and fluorosilicate glass in GIC, and it was successful in enhancing the mechanical and (bio)mineralization properties compared to those of the control but failed to enhance the (bio)mineralization compared to its
Acknowledgments
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT& Future Planning (NRF-2015R1C1A1A01052127 and NRF-2015R1A2A2A01007567).
Current address of two authors are shown: Dong-Ae Kim (Department of Dental Hygiene, Kyungwoon University) and Soo-Kyung Jun (Department of Dental Hygiene, Kyungdong University).
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