Effects of experimental bleaching agents on the mineral content of sound and demineralized enamels

Abstract High concentrations of hydrogen peroxide can cause adverse effects on composition and structure of teeth. However, the addition of calcium and fluoride in bleaching agents may reduce enamel demineralization. Objective: To evaluate chemical changes of sound and demineralized enamels submitted to high concentrations of hydrogen peroxide containing fluoride (F) or calcium (Ca). Material and Methods: Enamel blocks of bovine incisors with standard dimensions were obtained and half of them were submitted to pH-cycling to promote initial enamel caries lesions. Sound and demineralized enamel samples were divided into (n=10): (C) Control (no whitening treatment); (HP) 35% hydrogen peroxide; and two experimental groups: (HPF) 35% HP+0.2% F and (HPC) 35% HP+0.2% Ca. Experimental groups were submitted to two in-office bleaching sessions and agents were applied 3 times for 15 min to each session. The control group was kept in remineralizing solution at 37°C during the bleaching treatment. The surface mineral content of sound and demineralized enamels was determined through Fourier Transform Raman spectroscopy (FT-Raman), Energy dispersive Micro X-ray fluorescence spectroscopy (μ-EDXRF); and the subsurface, through cross-sectional microhardness (CSMH). In addition, polarized light microscopy (PLM) images of enamel subsurface were observed. Results: According to three-way (FT-Raman and μ-EDXRF analyses) or two-way analysis of variance (ANOVA) (CSMH) and Tukey test (α=5%), the calcium or fluoride added to high-concentrated bleaching agents increased phosphate and carbonate concentrations on sound and demineralized enamels (p<0.05). However, HPC and HPF were unable to completely reverse the subsurface mineral loss promoted by bleaching on sound and demineralized enamels. The calcium/ phosphate (Ca/P) ratio of sound enamel decreased after HP treatment (p<0.001). Conclusion: Even though experimental bleaching agents with Ca or F reduced mineral loss for both sound and demineralized enamel surfaces, these agents were unable to reverse the enamel subsurface demineralization.

Alveolar bone repair with strontium- containing nanostructured carbonated hydroxyapatite

ABSTRACT Objective: This study aimed to evaluate bone repair in rat dental sockets after implanting nanostructured carbonated hydroxyapatite/sodium alginate (CHA) and nanostructured carbonated hydroxyapatite/sodium alginate containing 5% strontium microspheres (SrCHA) as bone substitute materials. Methods: Twenty male Wistar rats were randomly divided into two experimental groups: CHA and SrCHA (n=5/period/group). After one and 6 weeks of extraction of the right maxillary central incisor and biomaterial implantation, 5 μm bone blocks were obtained for histomorphometric evaluation. The parameters evaluated were remaining biomaterial, loose connective tissue and newly formed bone in a standard area. Statistical analysis was performed by Mann-Withney and and Wilcoxon tests at 95% level of significance. Results: The histomorphometric results showed that the microspheres showed similar fragmentation and bio-absorbation (p>0.05). We observed the formation of new bones in both groups during the same experimental periods; however, the new bone formation differed significantly between the weeks 1 and 6 (p=0.0039) in both groups. Conclusion: The CHA and SrCHA biomaterials were biocompatible, osteoconductive and bioabsorbable, indicating their great potential for clinical use as bone substitutes.

Physicochemical, surface and catalytic properties of Co3O4/Mn2O3 and Mn2O3/Co3O4 systems

The two catalytic systems were prepared using equimolar proportions of cobalt nitrate and manganese carbonate [Co3O4/Mn2O3] and manganese carbonate and cobalt nitrate Mn2O3/Co3O4]. The mixed solids were subjected to heating at 500, 700, and 900°C. The solid - solid interactions taking place in the two catalytic systems were followed up using XRD investigation. Their specific surface areas were determined from nitrogen - adsorption isotherms carried out at - 196°C. Their catalytic activities were studied via following up the kinetics of CO oxidation by O2 at 125-400°C using a static method. The results obtained revealed that solid - solid interaction took place between cobalt and manganese oxides at 500 - 900°C yielding cobalt manganite and manganese cobaltite. In Co3O4/Mn2O3 system, a complete conversion of cobalt and manganese oxides took place at 900°C to yield cobalt manganite. In the other system, however, a partial conversion of Mn2O3/Co3O4 took place at 900°C. The specific surface areas of the two investigated systems are close to each other and decrease by increasing their calcinations temperature within 500 - 900°C.The decrease was, however, more pronounced by increasing the calcinations temperature from 700 to 900°C. The catalytic activity of Mn2O3/Co3O4 is smaller than that measured for the other system calcined at 500 °C. Opposite results were observed for the solids calcined at 700°C and 900°C. The catalytic reaction proceeds via almost the same mechanism in contact with different solids

Dynamics of lead (Pb) in different soil conditions.

Four soil samples were collected from various locations having wider range of pH and EC for incubation experiment. These soil samples were added with Pb (NO3)2 salts, and samples were taken on 1st, 35th, 45thand 60th day. Soils samples were fractioned by sequential extraction to estimate the concentration of lead in different fractions viz, water soluble, exchangeable +adsorbed, organic, carbonate and residual fraction. The result reveals that concentration of organic and carbonate bound-Pb was high in waterlogged condition and soil pH has been comprehensively identified as the single most important soil factor controlling the availability of lead (Pb) in soil. Low content of Pb in exchangeable + adsorbed (KNO3) and water soluble (H2O) fraction in all soils (except in S1) could signify low availability of Pb to plants. Bioavailable fractions, viz. water soluble and exchangeable + adsorbed, were low in all soils (except S1) well below critical limits, which may not pose any toxicity in the food chain.

Effects of home bleaching products on different tooth colored restorative materials

In this study, the effects of two commercial bleaching gels on color and surface roughness of hybrid composite, compomer, and hybrid ionomer respectively were evaluated. Test specimens were exposed to both bleaching gels for 312 hours at 37°C at 100% relative humidity. Color change value and surface roughness values were calculated before and after exposure to the gels. All the specimens of tested materials showed change in color. The hybrid ionomer had the highest mean change in color and the compomer showed the lowest mean change in color with both gels and this difference was significant. All specimens of tested materials showed a high mean percentage of change in surface roughness, while the compomer showed the lowest value and this difference was significant. Nupro Gold gel showed a significant increase in mean percentage of change in surface roughness. There was no correlation between change in color and change in surface roughness