Glass ionomer cements with enhanced mechanical and remineralizing properties containing 45S5 bioglass-ceramic particles

Effects of novel additives on the mechanical and Biological properties of glass ionomer cement: An in vitro study

Aim

To evaluate the efficacy of incorporated novel additives in Glass Ionomer Cement to ameliorate biocompatibility and mechanical properties.

Introduction

Though Glass Ionomer Cement (GIC) has multiple advantages, it is not strong enough for medical applications, and its biocompatibility is questionable. To improve biocompatibility and its mechanical properties, a study was performed to investigate the potential benefits of adding graphene, carbon nanotubes, hydroxyapatite, and bioactive glass to GIC. The objective was to enhance both the mechanical properties and biocompatibility of GIC.

Material and Method

Modified Glass Ionomer Cement was prepared by creating five groups. Hydroxyapatite, multi-walled carbon nanotubes, graphene, and bioactive glass were incorporated in a 10:1 weight ratio, respectively. Group 5 was designated as the control group and used Fuji Type II GIC. After preparing 90 samples, they were kept in deionized water for a day and then evaluated their compressive strength, microhardness, and diametral tensile strength, and also checked their in vitro cytotoxicity by direct contact with L929 mammalian fibroblast cells.

Statistical Analysis

The data were examined using mean and standard deviation descriptive statistics. The comparative evaluation was done via Tukey HSD test and one-way ANOVA using S.P.S.S. software.

Result

It showed that Group 3 had better results in compressive strength (144.478+- 3.989), diametral tensile strength (20.29+- 0.8601), and microhardness (131+-3.536) when compared with other groups while in the biocompatibility (viability %) Group 1 [82.55], Group 3 [76.49], Group 4 [87.63], while Group 2[58.02].

Conclusion

Group 3 has better physical properties in microhardness, diametral tensile strength, and compressive strength, than the other groups. In Biocompatibility, Group 1, Group 3, Group 4, and Group 5 were noncytotoxic at the same time multi-walled carbon nanotubes group (Group 2) had cytotoxic potential.

Assessment of Mechanical/Chemical Properties and Cytotoxicity of Resin-Modified Glass Ionomer Cements Containing Sr/F-Bioactive Glass Nanoparticles and Methacrylate Functionalized Polyacids

This study prepared low-toxicity, elemental-releasing resin-modified glass ionomer cements (RMGICs). The effect of 2-hydroxyethyl methacrylate (HEMA, 0 or 5 wt%) and Sr/F-bioactive glass nanoparticles (Sr/F-BGNPs, 5 or 10 wt%) on chemical/mechanical properties and cytotoxicity were examined. Commercial RMGIC (Vitrebond, VB) and calcium silicate cement (Theracal LC, TC) were used as comparisons. Adding HEMA and increasing Sr/F-BGNPs concentration decreased monomer conversion and enhanced elemental release but without significant effect on cytotoxicity. Rising Sr/F-BGNPs reduced the strength of the materials. The degree of monomer conversion of VB (96%) was much higher than that of the experimental RMGICs (21-51%) and TC (28%). The highest biaxial flexural strength of experimental materials (31 MPa) was significantly lower than VB (46 MPa) (p < 0.01) but higher than TC (24 MPa). The RMGICs with 5 wt% HEMA showed higher cumulative fluoride release (137 ppm) than VB (88 ppm) (p < 0.01). Unlike VB, all experimental RMGICs showed Ca, P, and Sr release. Cell viability in the presence of extracts from experimental RMGICs (89-98%) and TC (93%) was significantly higher than for VB (4%). Experimental RMGICs showed desirable physical/mechanical properties with lower toxicity than the commercial material.

Mechanical Properties of Poly(Alkenoate) Cement Modified with Propolis as an Antiseptic

Background: We assessed the effect of propolis on the antibacterial, mechanical, and adhesive properties of a commercial poly(alkenoate) cement. Methods: The cement was modified with various concentrations of propolis, and antibacterial assays were performed against S. mutans by both MTT assays and agar diffusion tests. The compressive, flexural, and adhesive properties were also evaluated. Results: the modified cement showed activity against S. mutans in both assays, although reductions in compressive (from 211.21 to 59.3 MPa) and flexural strength (from 11.1 to 6.2 MPa) were noted with the addition of propolis, while adhesive strength (shear bond strength and a novel pull-out method) showed a statistical difference (p < 0.05). Conclusion: the antiseptic potential of modified material against S. mutans will allow this material to be used in cases in which low mechanical resistance is required (in addition to its anti-inflammatory properties) when using atraumatic restorative techniques, especially in deep cavities.

Mechanical Properties and Antibacterial Effect on Mono-Strain of Streptococcus mutans of Orthodontic Cements Reinforced with Chlorhexidine-Modified Nanotubes

Recently, several studies have introduced nanotechnology into the area of dental materials with the aim of improving their properties. The objective of this study is to determine the antibacterial and mechanical properties of type I glass ionomers reinforced with halloysite nanotubes modified with 2% chlorhexidine at concentrations of 5% and 10% relative to the total weight of the powder used to construct each sample. Regarding antibacterial effect, 200 samples were established and distributed into four experimental groups and six control groups (4 +ve and 2 -ve), with 20 samples each. The mechanical properties were evaluated in 270 samples, assessing microhardness (30 samples), compressive strength (120 samples), and setting time (120 samples). The groups were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy, and the antibacterial activity of the ionomers was evaluated on Streptococcus mutans for 24 h. The control and positive control groups showed no antibacterial effect, while the experimental group with 5% concentration showed a zone of growth inhibition between 11.35 mm and 11.45 mm, and the group with 10% concentration showed a zone of growth inhibition between 12.50 mm and 13.20 mm. Statistical differences were observed between the experimental groups with 5% and 10% nanotubes. Regarding the mechanical properties, microhardness, and setting time, no statistical difference was found when compared with control groups, while compressive strength showed higher significant values, with ionomers modified with 10% concentration of nanotubes resulting in better compressive strength values. The incorporation of nanotubes at concentrations of 5% and 10% effectively inhibited the presence of S. mutans, particularly when the dose-response relationship was taken into account, with the advantage of maintaining and improving their mechanical properties.

Experimental borosilicate bioactive glasses: pulp cells cytocompatibility and mechanical characterisation

AIM

To assess in vitro the effect of two novel phase separated borosilicate glasses (PSBS) in the system SiO₂ -B₂ O₃ -K₂ O-CaO-Al₂ O₃ on dental pulp cells; and to compare their bioactivity and mechanical properties to a conventional fluoroaluminosilicate glass namely FUJI IX.

METHODOLOGY

The cytocompatibility assessment of the two novel borosilicate glasses, one without alumina (PSBS8) and one containing alumina (PSBS16), was performed on cultured primary human pulp cells (hDPCs). Alamar blue assay was used to assess cell metabolic activity and cell morphology was evaluated by confocal imaging. The bioactivity in Stimulated Body Fluid was also evaluated after 1 and 3 weeks of immersion using SEM-EDX analysis. Vickers microhardness and flexural strength were assessed after incorporating the glass particles into a commercial glass ionomer cement liquid containing both polyacrylic and polybasic carboxylic acid.

RESULTS

The data revealed that the two borosilicate glasses enhanced cell viability ratios at all-time points in both direct and indirect contact assays. After 3 days of contact, PSBS8 without alumina showed higher viability rate (152%) compared to the PSBS16 containing alumina (145%) and the conventional glass ionomer particles (117%). EDX analysis confirmed an initial Ca/P ratio of 2.1 for 45S5K and 2.08 for PSBS8 without alumina after 3 weeks of immersion. The cement prepared using PSBS8 showed significantly higher Vickers hardness values (p=0.001) than that prepared using PSBS16 (46.6 vs 36.7 MPa). After 24 hours of maturation, PSBS8 (without alumina) exhibited a flexural strength of 12.9 MPa compared to a value of 16.4 MPa for the commercial control. PSBS8 without alumina had a higher strength than PSBS16 with alumina, after 1 and 7 days of maturation (p=0.001).

CONCLUSIONS

The present in vitro results demonstrated that the borosilicate bioactive glass without alumina enhanced pulp cell viability, spreading and acellular bioactivity better than the conventional glass ionomer cement and the experimental borosilicate glass containing alumina.

Aluminum-free glass ionomer cements containing 45S5 Bioglass® and its bioglass-ceramic

Although the incorporation of bioactive glasses into glass ionomer cements (GICs) has led to promising results, using a bioactive glass as the only solid component of GICs has never been investigated. In this study, we developed an Al-free GIC with standard compressive strength using various combinations of 45S5 Bioglass® and its glass-ceramic as the solid component. The glass-ceramic particles with 74% crystallinity were used for this purpose as they can best act as both remineralizing and reinforcing agents. Strengthening mechanisms including crack deflection and crack-tip shielding were activated for the GICs containing 50-50 wt% bioglass and bioglass-ceramic as the optimum ratio. The progression of the GIC setting reaction at its early stages was also monitored and verified. We also discussed that our bimodal particle size distribution containing both micron- and nanosized particles may enhance the packing density and integrity of the structure of the cements after setting. In such GICs produced in this study, the toxic effects of Al are avoided while chemical bonds are expected to form between the cement and the surrounding hard tissue(s) through interfacial biomineralization and adhesion.

Polymer-Induced Liquid Precursor (PILP) remineralization of artificial and natural dentin carious lesions evaluated by nanoindentation and microcomputed tomography

OBJECTIVES

The study evaluates the efficacy to remineralize artificial and natural dentin lesions through restorative dental procedures that include the Polymer-Induced Liquid Precursor (PILP) method comprising polyaspartic acid (pAsp).

METHODS

Novel ionomeric cement compositions based on bioglass 45S5 and pAsp mixtures, as well as conditioning solutions (conditioner) containing 5 mg/mL pAsp, were developed and tested on demineralized dentin blocks (3-4 mm thick) on shallow and deep lesions with the thickness of 140 μm ± 50 and 700 μm ± 50, respectively. In the first treatment group, 20 μL of conditioner was applied to demineralized shallow (n = 3) and deep (n = 3) lesion specimens for 20 s before restoration with glass ionomer cement (RMGIC). For the PILP cement treatment group, cement was applied onto the wet surface of the demineralized specimen for both shallow (n = 3) and deep (n = 3) artificial lesions after the application of the conditioner and before the final restoration. Sample groups were compared to RMGIC restoration, for both shallow and deep lesions (n = 3 each) and treatments in PILP-solution (n = 3 for deep lesions) without restoration for 4 weeks. All of the restored specimens were immersed in simulated body fluid (SBF) solution for 2 weeks and 4 weeks for shallow and deep lesions respectively to allow for remineralization. The artificial lesion specimens were evaluated for changes in the nanomechanical profile (E-modulus and hardness) using nanoindentation. Shallow lesions were analyzed by SEM under vacuum for changes in morphology caused by PILP treatments. Also, a pilot study on human third molars with moderate lesions in dentin (n = 3) was initiated to test the efficacy of treatments in natural lesions based on mineral densities using microcomputed tomography (μCT) at 0, 1, and 3 months.

RESULTS

This study showed that functional remineralization of artificial lesions using PILP-releasing restoratives occurred, indicated by an increase of the elastic modulus in shallow lesions and in the middle zone of deep artificial lesions. The mechanical improvement was significant when compared to RMGIC restoration without pAsp (P < 0.05). Nonetheless, recovery across artificial lesions was most significant when specimens were immersed into PILP-solution with restorative (P < 0.01). Furthermore, natural lesions increased in mineral volume content to a higher degree when the restorative treatment included the PILP-method (P < 0.05). However, none of the natural lesions recovered to full mineral degree regardless of the treatments.

CLINICAL SIGNIFICANCE/CONCLUSION

These findings indicate the benefit of PILP applications in the functional repair of dentin caries and illustrate the challenge to integrate the PILP-method into a restorative approach in minimally invasive dental procedures.

Pulsed Laser Deposition Derived Bioactive Glass-Ceramic Coatings for Enhancing the Biocompatibility of Scaffolding Materials

The purpose of this work was to propose and evaluate a new composition for a bioactive glass-ceramic starting from the well-known 45S5 commercial product. Thus, we developed a modified version, including MgO, an oxide that turned out to induce superior mechanical properties and improved biological response. This had the following molar percentages: 46.1% SiO₂, 2.6% P₂O₅, 16.9% CaO, 10.0% MgO, and 24.4% Na₂O. The precursor alkoxides and nitrates were processed by a standard sol-gel technique, resulting in a glass-ceramic target, suitable for laser ablation experiments. Combeite (Na₂Ca₂Si₃O₉) was identified as a main crystalline phase within the calcined sol-gel powder, as well as in the case of the target sintered at 900 °C. The thin films were deposited on silicon substrates, at room temperature or 300 °C, being subsequently characterized from the material point of view, as well as in terms of bioactivity in simulated conditions and biocompatibility in relation to human fibroblast BJ cells. The investigations revealed the deposition of nanostructured glassy layers with a low proportion of crystalline domains; it was shown that a higher substrate temperature promoted the formation of surfaces with less irregularities, as a consequence of material arrangement into a shell with better morphological homogeneity. The complex elemental composition of the target was successfully transferred to the coatings, which ensured pronounced mineralization and a stimulating environment for the cell cultures. Thereby, both samples were covered with a thick layer of apatite after immersion in simulated body fluid for 28 days, and the one processed at room temperature was qualified to be the best in relation to the cells.