ABSTRACT
An apatitic calcium phosphate cement was developed from calcium bis-dihydro-genophosphate monohydrate (or monocalcium phosphate monohydrate, MCPM) and calcium oxide (CaO). The powder had a Ca/P molar ratio of 1.67, and the liquid was either pure water or 0.25 M-1 M sodium phosphate buffer, pH 7.4. The influence of the powder-to-liquid (P/L) ratio on the setting time and the mechanical strength were studied. The best results were obtained for the 1 M phosphate buffer with a P/L ratio of 1.53; the setting time was 7 min and the compressive strength was 25 MPa after 24 h and 33 MPa after 11 d. The mechanism and kinetics of the setting reaction were investigated by X-ray diffraction, differential scanning calorimetry, 31P magic angle spinning-nuclear magnetic resonance and infrared spectrometry. The setting reaction was found to be biphasic: in the first step, during the mixing time, MCPM reacted with CaO immediately to give calcium hydrogenophosphate dihydrate (or dicalcium phosphate dihydrate, DCPD) which, in the second step, reacted more slowly with the remaining CaO to give hydroxyapatite. The conversion of the starting materials to hydroxyapatite was complete within 24 h when the liquid was water, but was slower and incomplete with the phosphate buffers. Of the starting materials, 30% remained after 3 d.
ABSTRACT
The chemical composition of zinc polycarboxylate dental cements aged in vivo was studied. Thirty samples aged from one to 17 years were investigated using X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and differential scanning calorimetry. Evidence for the presence of zinc oxide, amorphous zinc polycarboxylate and water of hydration was found. No correlation with age concerning either the chemical structure of the components or their relative amounts was found. Zinc polycarboxylate dental cements show very good chemical stability on long-term use.
ABSTRACT
The behaviour of zinc polycarboxylate cements in contact with dilute aqueous solutions of organic acids at concentrations close to those existing in buccal medium, was studied. The organic acids were acetic, citric, tartaric and lactic acids, at 0.01 M and 0.001 M. The elution of zinc and magnesium was 10-1000 times greater in acid than in pure water, and correlated with the concentrations and the dissociation constants, pK1, of the acids tested. In all cases, important water losses were observed. In the 0.01 M acids, the cement structure collapsed to form a viscous, compact and homogeneous layer on the cement surface. In this layer, the polymeric carboxylic chains were regenerated from the zinc and magnesium polycarboxylate cement. Comparison with pure water showed that even the smallest concentration of the weak acids greatly modified the cement behaviour. This could explain the well-known differences in erosion processes between theoretical erosion predicted by standard specification tests and the in vivo situation.
ABSTRACT
The authors have observed 2 new cases of splenic rupture due to pancreatic pseudocyst and have made a review of the literature on the subject (40 cases). The clinical, diagnostic and therapeutic approaches of this rare but sometimes dramatic complication of chronic pancreatitis have been analyzed. Diagnosis should be suspected in the case of abdominal pain, mass and anemia in the male subject with previously known chronic pancreatic or alcoholic disease. Sonography completed by either angiography or CT scan if time permits are the best diagnostic methods. Ideal management should include treatment (excision or drainage) of the pseudocyst and splenectomy.
