EXPERIMENTAL STUDY OF CHEMICAL COMPOSITION OF DENTAL ENAMEL DURING PROFESSIONAL WHITENING USING HYDROGEN PEROXIDE

Teeth whitening is a way to restore the natural colour of teeth with applying a chemical agent that oxidizes the organic pigments of the hard dental tissues. Teeth whitening has become one of the most frequently requested dental procedures among the population. The public demands whiter, more perfect smiles, and many teeth whitening options have been made in response. To assess the changes occurring in the hard dental tissues, and, in particular, in the enamel, it is necessary to study the chemical structure of the teeth and determine the number of elements in the enamel to predict the whitening procedure outcomes and make adjustments in post-procedural care. The aim of this study was to investigate the changes in the chemical composition of the dental enamel surface after the procedure of professional hygiene and the use of 35% hydrogen peroxide for teeth whitening as the main chemical component of the whitening system. To study the trace element composition of the dental enamel, the tooth surface was segmented into areas for microanalysis. The peculiarity consisted in that the studied areas differed from the right and left sides of the tooth, because the left side in the studied teeth was the control area, and the right side allowed us to compare and contrast the chemical component of enamel in each tooth separately, by comparing the findings. The results obtained have demonstrated that there is a change in the chemical composition of the enamel in the studied teeth. The change in chemical composition indicators significantly affects the change in clinical indicators, and the strength of clinical manifestations will depend on the features of functional and structural resistance of the dental enamel. We can state that changing in the number of elements can lead to increased sensitivity during the rehabilitation period throughout which the chemical composition of the dental enamel restores.

Photodegradation of atmospheric chromophores: changes in oxidation state and photochemical reactivity

Atmospheric chromophoric organic matter (COM) plays a fundamental role in photochemistry and aerosol aging. However, the effects of photodegradation on chemical components and photochemical reactivity of COM remain unresolved. Here, we report the potential effects of photodegradation on carbon contents, optical properties, fluorophore components and photochemical reactivity in aerosol. After 7 d of photodegradation, fluorescent intensity and the absorption coefficient of COM decrease by 71.4 % and 32.0 %, respectively. Photodegradation makes a difference to the chemical component of chromophore and the degree of aerosol aging. Low-oxidation humic-like substance (HULIS) is converted into high-oxidation HULIS due to photooxidation. Photodegradation also changes the photochemical reactivity. The generation of triplet-state COM (3COM*) decreases slightly in ambient particulate matter (ambient PM) but increases in primary organic aerosol (POA) following photodegradation. The results highlight that the opposite effect of photodegradation on photochemical reactivity in POA and ambient PM. However, the generation of singlet-oxygen (1O2) decreases obviously in POA and ambient PM, which could be attributed to photodegradation of precursors of 1O2. The combination of optical property, chemical component and reactive oxygen species has an important impact on the air quality. The new insights on COM photodegradation in aerosol reinforce the importance of studying dissolved organic matter (DOM) related with the photochemistry and aerosol aging.