Comparison of Fracture Load of the Four Translucent Zirconia Crowns

Recently, translucent zirconia has become the most prevalent material used as a restorative material. This study aimed to compare the crown fracture load of the four most common different translucent zirconia brands available in the market at 1.5 mm thickness. Standardized tooth preparations for a full ceramic crown were designed digitally with software (AutoCAD) by placing a 1.0 mm chamfer margin and 1.5 mm occluso-cervical curvature for the crown sample manufacturing. Stylized crowns were chosen to control the thickness of the crown. The axial and occlusal thickness were standardized to 1.5 mm thickness except at the central pit, which was 1.3 mm thick. The STL file for the tooth dies was prepared using software (3Shape TRIOS^® Patient Monitoring, Copenhagen, Denmark). The tooth dies were printed with a resin material (NextDent Model 2.0, Vertex-Dental B.V., Soesterberg, The Netherlands) using a 3D printing software (3D Sprint^® Client Version 3.0.0.2494) from a 3D printer (NextDent™ 5100, Vertex-Dental B.V., Soesterberg, The Netherlands). The printing layer thickness was 50 µm. Then, a total of twenty-eight (N = 28) stylized crowns were milled out of AmannGirrbach (Amann Girrbach GmbH, Pforzheim, Germany) (n = 7), Cercon HT (Dentsply Sirona, Bensheim, Germany) (n = 7), Cercon XT (Dentsply Sirona, Bensheim, Germany) (n = 7), and Vita YZ XT (Zahnfabrik, Bäd Sackingen, Germany) (n = 7). Following sintering the crowns, sandblasting was performed and they were bonded to the tooth dies with the resin cement (RelyX U-200, 3M ESPE, Seefeld, Germany) and permitted to self-cure under finger pressure for 6 min. The crowns were loaded on the occlusal surface in a universal testing machine (MTS Centurion) with a stainless-steel ball indenter (7 mm radius) with a loading rate of 1 mm/min to contact the stylized crowns on each of the four cusps until failure. A rubber sheet (1.5 mm thickness) was positioned between the crown and indenter, which helped with the load distribution. Statistical analysis was done using SPSS version 20 (IBM Company, Chicago, USA). The fracture loads were analyzed using Dunnett’s T3 test, and the number of cracks was analyzed using the Mann–Whitney U test among the groups. The significant level was set at p value = 0.05. The mean fracture loads were 3086.54 ± 441.74 N, 4804.94 ± 70.12 N, 3317.76 ± 199.80 N, and 2921.87 ± 349.67 N for AmannGirrbac, Cercon HT, Cercon XT, and Vita YZ XT, respectively. The mean fracture loads for the surfaces with the greatest number of cracks (excluding the occlusal surfaces) were on the lingual surface for AmannGirrbach and Cercon HT, on the distal and mesial for Cercon XT, and on the buccal for Vita YZ XT. We found that the AmannGirrbach had the most overall cracks. Cercon XT had the greatest number of occlusal cracks and appeared to be the most shattered. Cercon HT had the least number of cracks. In conclusion, Cercon HT presented the best strength properties, the highest fracture load, and no visible cracks. AmannGirrbach presented the lowest strength properties.     

Multi-element preconcentration of heavy metal ions from aqueous solution by APDC impregnated activated carbon

Ammonium pyrrolidinedithiocarbamate impregnated activated carbon (APDC-AC) has been used for the preconcentration of Cd(II), Cu(II), Ni(II), and Zn(II) from aqueous solution by column solid phase extraction (SPE) technique. Trace metal ions in aqueous solution were quantitatively sorbed onto APDC-AC packed in a SPE column at pH 5.0 with a flow rate of 1.0 mL min⁻¹. The sorbed metals were eluted with 1 M nitric acid in acetone solution at a flow rate of 0.6 mL min⁻¹ and analyzed by flame atomic absorption spectrometry. The effects of sample volume, amount of APDC-AC, volume of eluent and ionic strength of working solution on metal ion recovery have been investigated. The present methodology gave recoveries from 90 to 106% and R.S.D. from 0.6 to 5.5%.     

Bulk optode sensors for batch and flow-through determinations of lead ion in water samples

A sensitive optode consisting of highly lead-selective ionophore (Lead IV), proton-selective chromoionophore (ETH 5294) and lipophilic anionic sites (KTpClPB) in plasticized polyvinyl chloride (PVC) membrane was fabricated. The optode membranes were used for determination of Pb²⁺ by absorption spectrophotometry in batch and flow-through systems. The influence parameters such as pH, type of buffer solution, response time and concentration of regenerating solution were optimized. The membrane responded to Pb²⁺ by changing its color from blue to pinkish purple in Tris buffer containing different concentration of Pb²⁺ at pH 7.0. The optode provided the response range of 3.16 × 10⁻⁸ to 5.00 × 10⁻⁵ mol L⁻¹ Pb²⁺ with the detection limit of 2.49 × 10⁻⁸ mol L⁻¹ in the batch system within the response time of 30 min. The dynamic range of 1.26 × 10⁻⁸ to 3.16 × 10⁻⁵ mol L⁻¹ Pb²⁺ with detection limit of 8.97 × 10⁻⁹ mol L⁻¹ were obtained in the flow-through system within the response time of 15 min. Moreover, the proposed optode sensors showed good selectivity towards Pb²⁺ over Na⁺, K⁺, Mg²⁺, Cd²⁺, Hg²⁺ and Ag⁺. It was successfully applied to determine Pb²⁺ in real water samples and the results were compared with well-established inductively coupled plasma optical emission spectrometry (ICP-OES). No significant different value (t_critical = 4.30 > t_exp = 1.00-3.42, n = 3 at 95% of confidence level) was found.     

Investigation of Gold Quantum Dot Enhanced Organic Thin Film Solar Cells

Gold quantum dots (AuQDs) are employed as photosensitizers in organic thin‐film solar cells (OSCs) to improve their photoelectric conversion properties. Three types of AuQDs with different fluorescence emission wavelengths are used: blue (B‐AuQDs), green (G‐AuQDs), and red (R‐AuQDs). AuQDs are loaded into the poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) thin‐film layer of OSCs. UV–vis spectra, atomic force microscope images, current density–voltage characteristics, and impedance spectra of the fabricated devices are measured for the three aforementioned types of AuQDs. All types of AuQDs improve the photoelectric conversion properties, and the G‐AuQD‐loaded OSCs exhibit the best improvement, exhibiting an efficiency increase of 10% compared with OSCs without the AuQDs. The fluorescence/photosensitization of the AuQDs plays an important role in the enhancement of the OSCs. Finite‐difference time‐domain simulations indicate increased electric field intensity due to a small degree of AuQDs aggregation.