Third-order NLO properties and optical limiting behavior of p-toluidinium 2,4-dichlorobenzoate organic single crystal

This research work focuses on the synthesis and characterization of p-toluidinium 2,4-dichlorobenzoate (PTDA), organic non-linear optical crystal grown at room temperature. Single crystal X-ray diffraction (SCXRD) analysis was used to analyze the lattice parameters under the centrosymmetric space group of P121/c1 with a monoclinic crystal system. The crystalline nature and phase identification of the sample was analyzed by powder X-ray diffraction (PXRD) analysis. FT-IR and 1H NMR were used to identify the functional groups and various vibrations present in the grown crystal. The cut-off wavelength was observed at 284 nm from the transmittance spectrum, and the optical bandgap value (4.06 eV) was also determined from UV-visible analysis. TG-DTA analysis was carried out to understand its thermal properties. The mechanical strength of the material plays an important role in fabricating devices. Open-aperture Z-scan analysis was taken in order to get its third-order nonlinearity using Nd: YAG nanopulsed laser. PTDA crystal exhibits reverse saturable absorption and shows two-photon absorption- induced optical limiting behavior. Theoretical calculations were done by using Gaussian 09 software with a basic set of B3LYP/6-311G++ (d, p) to provide optimized molecular geometry, Frontier Molecular Orbital (FMO), and NBO analysis.

Evaluation of shear bond strength and enamel remineralizing effect of experimental orthodontic composite containing nano-hydroxyapatite: An in vitro study

OBJECTIVE

The purpose of this study was to prepare an orthodontic composite containing hydroxyapatite nanoparticles to prevent demineralization and create a suitable environment for mineral deposition around orthodontic brackets, and to investigate the mechanical and remineralizing properties of the experimental adhesive composite.

METHODS

Experimental orthodontic composite were formulated using varying percentages of nano-hydroxyapatite particles. Assessments were based on four groups: a control group (3M™ Transbond™ XT) and experimental composites containing 2% (HA2), 5% (HA5) and 10% (HA10) hydroxyapatite. Vickers Microhardness test was performed to investigate the remineralizing effect in 3 stages: initial stage, after demineralization and after 4 weeks of exposure to artificial saliva. Scanning electron microscopy with energy dispersive X-ray spectroscopy analyser (SEM/EDAX) was used to evaluate hydroxyapatite precipitation and elemental composition of enamel surface. Shear Bond Strength tests were carried out using a universal testing machine and the debonding pattern was assessed using Adhesive Remnant Index (ARI).

RESULTS

All groups showed clinically acceptable SBS values. The highest SBS was achieved in the HA2 group, followed by Transbond™ XT, HA5 and HA10. There was no significant difference in the ARI scores. In terms of microhardness properties, HA5 and HA10 demonstrated a significant increase after 4 weeks. The results of SEM analysis showed the precipitation of hydroxyapatite crystals and EDAX analysis indicated the increase of calcium and phosphate ion peaks compared to the demineralized sample. The data were analysed using one-way ANOVA and Tukey's Post-hoc test.

CONCLUSIONS

Addition of hydroxyapatite nanoparticles to orthodontic composite can increase the mineral content and microhardness of the adjacent enamel. However, increasing the amount of nanoparticles reduces shear bond strength in a decreasing trend. The above-mentioned findings showed that incremental increase of nanoparticles of HA can be incorporated in composite to a certain extent and limitations are determined by mechanical properties (SBS) required for bracket bonding.

Influence of Immediate Coronal Restoration on Microhardness of CEM Cement: An In Vitro Study

Introduction

Coronal restoration could affect the setting reaction of the underlying CEM cement. The aim of the present study was to evaluate the effect of immediate coronal restoration placement on the subsurface microhardness of CEM cement.

Methods and Materials

In 50 extracted human mandibular molars, access cavities were prepared and CEM cement was placed in the pulp chamber at a 3-mm thickness. Samples were divided into ten groups (n=5). CEM cement was placed and after 10 min, two groups were restored with Zonalin temporary restoration and eight groups were restored with glass ionomer cement (GIC), resin modified glass ionomer (RMGI), resin based composite and amalgam respectively. Vickers microhardness number (VHN) of CEM cement was measured in two time intervals (7- and 21-days). Data was analyzed with SPSS and two-way analysis of variance and Bonferroni tests. Level of significance was set at the 5%.

Results

The mean VHN of CEM cement showed statistically significant differences only between Zonalin and amalgam groups (P=0.021). There were also significant differences considering the effect of time (P=0.042) and material (P=0.046). Although the effect of time-material on the microhardness values showed no statistically significant differences (P=0.636).

Conclusion

Based on the results of the present study, immediate placement of final restorations affects the setting reaction in underlying CEM cement. Therefore, sufficient moist curing and hydration should be guaranteed before placement of the coronal restoration.