RESUMO
This study details the differences in real-time hydration between pure tricalcium aluminate (cubic C(3)A or 3CaO·Al(2)O(3)) and Na-doped tricalcium aluminate (orthorhombic C(3)A or Na(2)Ca(8)Al(6)O(18)), in aqueous solutions containing sulfate ions. Pure phases were synthesized in the laboratory to develop an independent benchmark for the reactions, meaning that their reactions during hydration in a simulated early age cement pore solution (saturated with respect to gypsum and lime) were able to be isolated. Because the rate of this reaction is extremely rapid, most microscopy methods are not adequate to study the early phases of the reactions in the early stages. Here, a high-resolution full-field soft X-ray imaging technique operating in the X-ray water window, combined with solution analysis by (27)Al nuclear magnetic resonance (NMR) spectroscopy, was used to capture information regarding the mechanism of C(3)A hydration during the early stages. There are differences in the hydration mechanism between the two types of C(3)A, which are also dependent on the concentration of sulfate ions in the solution. The reactions with cubic C(3)A (pure) seem to be more influenced by higher concentrations of sulfate ions, forming smaller ettringite needles at a slower pace than the orthorhombic C(3)A (Na-doped) sample. The rate of release of aluminate species into the solution phase is also accelerated by Na doping.
RESUMO
Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) have been used to study the microstructural changes and phase development that take place during the hydration of cubic (pure) and orthorhombic (Na-doped) tricalcium aluminate (C3A) and gypsum in the absence and presence of lime. The results demonstrate that important differences occur in the hydration of each C3A polymorph and gypsum when no lime is added; orthorhombic C3A reacts faster with gypsum than the cubic phase, forming longer ettringite needles; however, the presence of lime slows down the formation of ettringite in the orthorhombic sample. Additional rheometric tests showed the possible effects on the setting time in these cementitious mixes.
RESUMO
AIM: The aim of the present study was to investigate knowledge, practices, and opinions on tobacco and oral health among dentists of the Berlin Dental Association using a questionnaire. MATERIALS AND METHODS: Questions focussed on smoking habits, knowledge about oral malignancies and premalignancies and practical approaches to screening for oral mucosal diseases and other associations of tobacco with oral changes. The questions related to risk factors and behavioural counselling for patients and associated constraints. RESULTS: Of a total of 4000 questionnaires sent, 483 were received for evaluation (12.1%). Of respondents 9.5% were regular smokers. The median number of oral malignancies observed was 3. Knowledge about some associations of oral changes such as wound healing was adequate. A total of 93.1% of respondents would refer patients with oral lesions. Only 35% take a regular history of both tobacco and alcohol consumption and 26.6% explain the side effects of tobacco. Some 73.4% believed that the dentist could play a role in anti-tobacco counselling. Limiting factors were lack of training and of competence in anti-tobacco counselling. CONCLUSIONS: This study shows that there still is a considerable need for improvement of knowledge and for provision with effective anti-tobacco teaching material. Since most of the respondents thought that the dentist should play a role in anti-tobacco counselling, adequate programmes in Germany should be inititated and followed up.
