Synthesis and characterization of a dental cement based on bioactive glass/zinc oxide modified with organic resin as a novel pulp capping agent.

This study aimed to synthesize and characterize a novel dental pulp capping cement containing bioactive glass (BG)/zinc oxide modified with an organic resin. BG (45S5) with or without ZnO (Zn) and hemaphosphate (HP) combined with a liquid consisting of polyacrylic and itaconic acids (AA) were synthesized and the structural, physical, and mechanical properties were assessed. Hydroxyapatite formation was evaluated by immersion in simulated body fluid. Biological analysis including methyl thiazolyl tetrazolium assay, alizarin red staining, alkaline phosphatase (ALP) activity, and gene expression of odontogenic markers were performed to evaluate the cytotoxic effect and biomineralization potential of the cements on human dental pulp stem cells (hDPSCs). A commercial mineral trioxide aggregate (MTA) served as control. The highest compressive strength value and the shortest setting time were belonged to the BG + HP + AA and BG + AA groups, respectively. The shear bond strength to dentin was the highest for the BG + HP + AA cement. Scanning electron microscope showed only scarce deposits of calcium phosphate formation on the surface of the synthesized cements. BG + HP + AA and BG + HP + Zn + AA groups had significantly lower cytotoxicity than MTA. The mineralization potential of hDPSCs after stimulation by the novel cements increased. Quantitative reverse-transcription-polymerase chain reaction showed higher odontogenic marker expression in hDPSCs exposed to the BG + HP + Zn + AA cement compared to other synthesized cements, although it was higher in MTA group. Based on the obtained results, the novel synthesized cements can be used as appropriate capping agents in the treatment of dental pulp.

Effect of Helium Plasma Exposure on Wettability and Shear Bond Strength between the Zirconia Core and Feldspathic Veneering Ceramic: An In Vitro Study.

Introduction: The present study aimed to evaluate the effect of helium plasma treatment on the wettability of zirconia surface and on the shear bond strength between the dental zirconia core and feldspathic veneering ceramic. Methods: 128 zirconia specimens were prepared, polished, and then divided into four groups: control, Zr, FC, and Zr/FC. In Zr and Zr/FC groups, the zirconia blocks were treated by helium plasma for 60 s. In FC and Zr/FC, the feldspathic ceramic powder received 60 s of plasma treatment. Then, the feldspathic powder was applied on the zirconia blocks. Half of the specimens in each group were sintered in a tube furnace, and the contact angle between the zirconia core and feldspathic ceramic was measured at different time intervals. The other half were sintered in a ceramic furnace and then subjected to thermocycling. The shear bond strength was measured using a universal testing machine. The failure mode was assessed using a stereomicroscope. Data were analyzed by one-way ANOVA test, and the statistical significance was considered less than 0.05. Results: There was no significant difference in the mean contact angle and the shear bond strength values of the experimental groups (P > 0.05). The mean contact angle decreased significantly in all groups over time (P < 0.001). The modes of failure were predominantly mixed in all groups. Conclusion: The helium plasma applied on either dental zirconia core or feldspathic ceramic powder could not improve the zirconia surface wettability and the shear bond strength between the two ceramics.

Comparative evaluation of fiber-reinforced, bulk-fill and conventional dental composites: Physical characteristics and polymerization properties.

BACKGROUND: Resin composites have various applications. At the same time, they have some drawbacks, such as polymerization shrinkage. Conventional composites are polymerized in 2-mm thick layers. However, in posterior restoration, the 2-mm depth of cure is not satisfactory. To find a solution, resin composites have been vastly improved in terms of fillers, matrix and initiators. OBJECTIVES: To evaluate polymerization properties and physical characteristics of fiber-reinforced composites and compare them with bulk-fill composites that are designed for large posterior restorations. MATERIAL AND METHODS: Samples were prepared from each resin composite. The 3-point bending test was performed to evaluate the flexural strength of all composites. The depth of cure of the composite from 1 mm to 4 mm of depth was analyzed using Vickers hardness test (VHN). To analyze the degree of conversion, Fourier-transform infrared spectroscopy (FTIR) of the top and bottom surfaces of the samples with 4-mm thickness was calculated. The data were analyzed using one-way analysis of variance (ANOVA) test followed by post hoc test (95% confidence interval (95% CI)). RESULTS: The Filtek showed the highest flexural strength followed by everX and X-tra fil. At 1-mm depth, X-tra fil had the highest and Gradia had the lowest microhardness. At the 4-mm depth, the microhardness trend was as follows: everX > Filtek > X-tra fil > Gradia > Beautifil. The everX composite had the lowest reduction of the degree of conversion at 4-mm thickness, which showed a significant difference in comparison with Filtek, Gradia and X-tra fil composites. CONCLUSIONS: Based on the results of our study, it can be concluded that the fiber-reinforced composite everX showed more favorable results regarding polymerization properties, such as the degree of conversion and the depth of cure. However, the flexural strength results in Filtek were better than those in everX.

Repairability of aged dimethacrylate-free ORMOCER-based dental composite resins with different surface roughening methods and intermediate materials.

STATEMENT OF PROBLEM: The repair of damaged composite resin restorations has been recommended as a conservative treatment option. However, a reliable protocol for repairing ORMOCER-based restorations is lacking. PURPOSE: The purpose of this in vitro study was to investigate the effect of different surface roughening methods, repair composite resins, and intermediate materials on the repair bond strength of a dimethacrylate-free ORMOCER-based composite resin. MATERIAL AND METHODS: Cylindrical composite resin specimens (Admira Fusion) were roughened by using hydrofluoric acid (HF) or a diamond rotary instrument. In both groups, 4 types of intermediate materials were used (Monobond-S, Clearfil SE bond [second bottle], Clearfil Universal bond, GC Composite Primer), and then half of the specimens were repaired with a similar composite resin, and the other half with dimethacrylate composite resin (Clearfil-APX). The specimens (n=20) were then subjected to repair bond strength and failure mode evaluation. The data were analyzed by using the Weibull test, 3-way and 1-way ANOVA, and the Tukey honestly significant difference (HSD) test (α=.05). RESULTS: All variables, including the surface roughening method, intermediate material, and repair composite resin, had a significant effect on repair bond strength (P<.001). The lowest repair bond strength values were obtained in the group roughened with HF, prepared with Monobond-S, and repaired with Admira Fusion, and the highest values were obtained in the group roughened with a rotary instrument, prepared with GC Composite Primer, and repaired with Clearfil APX (P<.05). All experimental groups had a lower bond strength than the cohesive and control groups (P<.05). In all experimental groups, the predominant failure modes were adhesive and mixed. CONCLUSIONS: The use of a diamond rotary instrument was a more reliable method of creating roughness, and different intermediate materials based on the clinical situation can be used to repair dimethacrylate-free ORMOCER-based composite resin with similar or different composite resins. However, in general, the highest repair bond strengths were achieved with Clearfil APX-repaired specimens.

Effect of Different Cavity Lining Techniques on Marginal Sealing of Class II Resin Composite Restorations In Vitro.

This study investigated the effect of different cavity lining techniques on the marginal sealing of Class II composite restorations. A total of 36 human molar teeth, free of caries and fillings, were each prepared with two proximal Class II boxes mesially and distally. In mesial boxes, cavity liners were applied as follows: in group 1, separately cured flowable composite; in group 2, co-cured flowable composite; and in group 3, resin-modified glass ionomer (RMGI). The remaining cavities were filled incrementally with a universal restorative composite. The distal boxes were filled with no liner as controls. After thermocycling, the specimens were immersed in a silver nitrate solution and the microleakage was evaluated. Analysis of variance showed that the degree of microleakage for group 3 was significantly lower than that of the other groups. Based on the results, it was concluded that the use of RMGI as a cavity liner under composite restorations showed the least microleakage. Flowable composites, whether co-cured or separately cured, had no influence on the marginal sealing.

Effect of Laser-assisted and Conventional In-office Bleaching on Monomer Release from Microhybrid and Nanohybrid Composite.

BACKGROUND AND AIMS: Bleaching might affect structural properties of composite materials, and lead to monomer release. This study aimed to evaluate the effect of Laser-assisted and conventional in-office bleaching on the release of BIS-GMA, TEGDMA, and UDMA monomers from a nanohybrid and a microhybrid BIS-GMA based composite. MATERIALS AND METHODS: 32 samples of each composite, were divided into 4 subgroups; subgroup 1: Conventional in-office bleaching (CIB) with the Opalescence Boost PF 38% gel, subgroup 2: Laser-assisted bleaching (LBO) with the Opalescence Boost PF 38% gel, subgroup 3: Laser-assisted bleaching (LBH) with the JW Power bleaching gel, subgroup 4: (CO) control without bleaching. All the samples were immersed in tubes of 2cc Ethanol 75% medium. The released monomers were analyzed using the high performance liquid chromatography (HPLC) method 24 h, 7, and 28 days. Data's were analyzed by Univariate Analysis of Variance test followed by Tukeys HSD. RESULTS: The amount of TEGDMA monomer released was not significant. However, nanohybrid composites showed significantly more monomer release than microhybrid composites (P < 0.05). For UDMA the interaction was significant only after 1 week. In microhybrid composites, the CO subgroup showed more monomer release than LBH and LBO. In nanohybrid composites, LBH showed more monomer release than CIB and CO subgroups. For BIS-GMA monomers the interaction was significant at all time periods and the LBH subgroup of nanohybrid composite had significantly more BIS_GMA release in comparison to other subgroups. CONCLUSION: Bleaching by laser with JW Power Bleaching gel led to more monomer release in nanohybrid composite.