Effect of laser irradiation on root canal walls after final irrigation with 17% EDTA or BioPure MTAD: X-ray diffraction and SEM analysis.

OBJECTIVE: To evaluate the effect of diode laser irradiation on crystallographic and morphologic characteristics of root canal walls after final irrigation with either 17% EDTA or BioPure MTAD. METHOD AND MATERIALS: Root canals in 60 single-rooted teeth were instrumented using a rotary Ni-Ti system. The teeth were randomly divided into three groups (n = 20) based on the final irrigants: group 1, saline; group 2, 17% EDTA; and group 3, MTAD. Each group was further divided into two subgroups (n = 10). Subgroup A received diode laser irradiation at a wavelength of 810 nm and an output power of 2 W for 5 × 5 seconds, while subgroup B received no irradiation. A paired t test was used to compare mean dentinal erosion before and after irradiation in each group. Specimens were analyzed using SEM and x-ray diffractometery. One-way ANOVA and a post hoc Tukey test were used to evaluate dentinal erosion between groups. Kruskal-Wallis and Mann-Whitney U tests were used to evaluate any significant differences in the amount of dentin erosion between the groups. RESULTS: SEM micrographs showed closed dentinal tubules in the control group, while in unlased BioPure MTAD and EDTA groups, clean root canal walls were evident. Erosion was mostly seen in EDTA-treated teeth, while an increase of erosion degree was noted on root canal walls after additional laser irradiations. After irrigation and laser irradiation, the XRD spectrums indicated sharper peaks of EDTA, which showed a slight crystallographic change compared with the other groups. EDTA made changes in the mineralization of dentin due to its higher accumulation on the dentinal wall surface and produced significant degrees of erosion in comparison with MTAD by changing the physical properties of the root canal wall surface. These undesirable changes can be enhanced by further laser irradiation. CONCLUSION: Results confirm that a diode laser in combination with BioPure MTAD have minimum effect on the chemical properties of root canal dentin while having good smear layer removal properties. The results of the present study indicated that a diode laser in combination with Biopure MTAD might be suggested as a final management of the root canal system prior to canal obturation.

A Comparative Study of MTA Solubility in Various Media.

INTRODUCTION: Solubility of root filling materials is heavily influenced by the environment they are in contact with. This study compared the solubility of ProRoot MTA in deionized water and synthetic tissue fluid. MATERIALS AND METHODS: Forty specimens of prepared MTA were immersed in deionized water and synthetic tissue fluid (20 samples each). The solubility was assessed after 7 and 28 days. Scanning electron microscope observation was also performed. The mean weight loss was evaluated using a digital scale. Data were analyzed using one-way ANOVA. Tukey test was performed for multiple comparisons. RESULTS: MTA solubility in synthetic tissue fluid was significantly lower than deionized water after 7 and 28 days (P<0.05). Secondary electron detectors revealed the presence of lumps and platelets on the surfaces of both specimens. Also, more voids were observed in specimen stored in deionized water. CONCLUSION: MTA dissolved faster in deionized water than synthetic tissue fluid. Despite this, the solubility of this material in both media was acceptable.

Investigation of C-H...O=C and N-H...OC hydrogen-bonding interactions in crystalline thymine by DFT calculations of O-17, N-14 and H-2 NQR parameters.

A computational study at the level of density functional theory (DFT) was carried out to investigate C-H...O=C and N-H...O=C hydrogen-bonding interactions (HBs) in the real crystalline cluster of thymine by O-17, N-14 and H-2 calculated nuclear quadrupole resonance (NQR) parameters. To perform the calculations, a hydrogen-bonded pentameric cluster of thymine was created using X-ray coordinates where the hydrogen atoms positions are optimized and the electric field gradient (EFG) tensors were calculated for the target molecule. Additional EFG calculations were also performed for crystalline monomer and an optimized isolated gas-phase thymine. The calculated EFG tensors at the level of B3LYP and B3PW91 DFT methods and 6-311++G**and CC-pVTZ basis sets were converted to those experimentally measurable NQR parameters, quadrupole coupling constants and asymmetry parameters. The results reveal that because of strong contribution to N-H...O=C HBs, NQR parameters of O2, N1 and N3 undergo significant changes from monomer to the target molecule in cluster. Furthermore, the NQR parameters of O2 also undergo some changes because of non-classical C-H...O=C HBs.