Enhancing Stability and Tooth Bleaching Activity of Carbamide Peroxide by Electrospun Nanofibrous Film

Carbamide peroxide (CP) possesses a strong tooth bleaching activity, however, its clinical application is limited because of its instability in aqueous formulations. This study explores the improvement of CP stability and bleaching activity by loading CP in electrospun nanofibrous film (ENF). Polyvinylalcohol, polyvinylpyrrolidone, and silica were used as components for core-based nanofibers of ENF. Electrospinning feed aqueous solutions (EFASs) were developed for preparing CP loaded ENF (CP-ENF). Stability of CP in EFASs is significantly higher than in pure water. The highest stability of CP is found in PPS-CP3, composed of 0.5% CP, 5.5% polyvinylalcohol, 3% polyvinylpyrrolidone, and 1% silica. The results from X-ray diffraction indicate that CP is dispersed as a non-crystalline form in CP-ENFs. CP and the compositions of EFASs play a major role on characteristics and bleaching efficiency of CP-ENFs. Drug release of CP-ENFs is the first order kinetics. CP-ENF obtained from PPS-CP3 shows the highest drug entrapment efficiency, high adhesion, and suitable sustained release. Drug release mechanism is along with anomalous transport according to Korsmeyer–Peppas model. In an ex vivo study using human teeth, it shows the highest bleaching efficiency among the others. Therefore, CP-ENF obtained from PPS-CP3 is a promising ENF for clinical use.

Characterization, Acid Activation, and Bleaching Performance of Ibeshe Clay, Lagos, Nigeria

This paper investigated the possibility of using clay characterization as a major tool to predict its suitability for bleaching of vegetable oil, namely, palm oil. The clay sample collected from Ibeshe deposit was characterized by X-ray diffraction (XRD). The results of the XRD showed that the clay is composed of dioctahedral kaolinite and dickite, silica, ilmenite, and merlinite. The compositional analysis using atomic absorption spectroscopy (AAS) showed that the Na2O : CaO ratio is 0.22, a value less than one and indicative of the absence of bentonite which presence, just like montmorillonite, confers bleaching activity to clays. Furthermore, the SiO2 : Al2O3 ratio of 1.12 (greater than one) is suggestive of a clay suitable not for bleaching but for zeolite development. Actual laboratory tests for bleaching performance evaluation confirmed the prediction above that the clay indeed has poor bleaching action as shown by percent colour reduction. The colour reduction for natural clay was 9.1%. This value only increased to 27.3% after 3M HCl activation, a value still very low for effective bleaching.

Synthesis and Bleaching Activity of 1-Ethyl-and 1 -Propy 1-5-Substituted Imidazoles

Twenty-eight 1-ethyl-and 1-propyl-5 -substituted imidazoles were synthesized an d their bleaching activity was evaluated by using the lettuce seedling test. 5-Phenyl-1-propylim idazole (1) caused distinct chlorosis, while none of the c ompounds with various alkenyl groups at the 5-position o the imidazole ring show ed this bleaching activity. Introduction of a bromo, chloro, fluoro, methyl or trifluoromethyl groupa t the 4-position on the benzene ring of com­pound 1 increased the activity in comparison with that of compound 1. 5-[4-(3-Chlorobenzyl-oxy)phenyl]-l-ethylimidazole (15) an d l-ethyl-5-[4-(3-methylbenzyloxy)phenyl]imidazole (21), analogs with a large substituent at the 4 -position on the benzene ring, also caused pronounced chlorosis in the lettuce seedlings. Both compounds 1 and 15 a t 30 ppm decreased total c arot­enoid content in the lettuce seedlings to less than 40% of that in the control, and the reduction of total carotenoid content correlated well with treatment dose.