The normal IVU: a trap for the unwary

Intravenous urography (IVU) is considered to be a reliable means of investigating the urinary tract for renal pathology. We present two cases of patients who were investigated for loin pains. In both patients the IVU appearances were normal but the final diagnosis, as obtained by ultrasound, was renal cell carcinoma of the upper pole of the right kidney.

Uptake of 99mTc-DTPA by a renal oncocytoma

In a patient with a large vascular renal mass, a preoperative DTPA scan showed retention of the activity within the tumour. On histology, the tumour proved to be an oncocytoma.

Dimensional changes of a high-tin content amalgam

Amalgam made with Brewster Alloy (62% Ag, 33% Sn, 5% Cu, and 0.2% Zn) had little or no dimensional change during 24 h at 23 degrees C. Brewster amalgam stored for five yr in air expanded 186, 68, and 14 microns/cm at 60, 37, and 23 degrees C, respectively. Nearly "stable" conditions were approached at about 50 mo.

Copper-free amalgams: dimensional change after approximately five years at 60, 37, and 23 degrees C

Two copper-free amalgams expanded excessively after storage in air at 60 degrees C for about five yr. One expanded significantly at 37 degrees C and slightly at 23 degrees C. High silver content, absence of copper, and presence of small amounts of zinc, or all three, seemed to promote very high expansions at 60 degrees C.

Effect of residual mercury content on creep in dental amalgams

For most of the tested amalgams, the increased mercury content caused by delayed compaction increases the flow or creep. The amalgams that had high creep values when packed early were decidedly affected by the increase in mercury content caused by delay in compaction. Amalgams made with Dispersalloy, Tytin, Sybraloy, and New True Dentalloy are not as sensitive to the mercury content as are some of the others tested. Tests for creep may be related more to clinical practice if they are performed on specimens compacted three minutes after trituration rather than on specimens compacted immediately (a half minute) after trituration. In clinical practice, small amounts of amalgam should be mixed and used immediately after trituration. If the delay between trituration and compaction is longer than three minutes, additional mixes are required. We therefore conclude that, in making a large amalgam restoration, many small mixes have superior results over one large mix.

Linear dimensional change of copper-rich dental amalgam

Copper-rich amalgams made from alloy mixtures have large expansions in air at 105 +/- 2 weeks that range from 100 to 194 micrometers/cm at 60 C, from 36 to 101 micrometers/cm at 37 C, and from 14 to 44 micrometers/cm at 23 C on unrestricted 8- x 4-mm cylinders (Dispersalloy, Micro II, and Optaloy II). Other copper-rich amalgams made from one alloy usually had a slight shrinkages at the three temperatures with an exception, a slight expansion of 12 micrometers/cm at 60 C (Aristaloy CR, Indilogy non-zinc, Sybraloy, and Tytin). Dimensional changes during hardening ranged,on the average, from -3 to +19 micrometers/cm when measured by ADA Specification methods and from -2 to +25 micrometers/cm when measured by an indirect method. The clinical significance of the foregoing findings is unknown; nor is a relationship known among dimensional change of unrestricted specimens, dimensional change of restricted specimens, creep value, and clinical behavior of amalgams generally. In specific instances, however, a relationship is sometimes shown.

Dimensional change of dental amalgam and a suggested correlation between marginal integrity and creep

Discussion of a possible correlation of marginal integrity and degree of creep resulting from relative resistance of amalgams to deformation caused by expansion is included in this study of the effect of phase changes on the dimensional stability of amalgams.

Thermodynamic solubility product of human tooth enamel: powdered sample

Solubility of human dental enamel in H3PO4 was studied in the pH range of 4.5 to 7.6. Thermodynamic solubility of the enamel mineral was calculated in terms of the ion activity product, (Ca2+)5(PO43-)3(OH-), for hydroxyapatite. The solubility product varied from 7.2 times 10(-53) to 6.4 times 10(-58) mol9 liter-9 depending on the cumulative amount of the dissolution of the solid in a series of repetitive sequences of solubility experiments.

Formation of Ca HPO4-2H2O from enamel mineral and its relationship to caries mechanism

Tooth enamel, when treated with dilute H3P94 solutions, dissolved incongruently with formation of large CaHPO4-2HO2O crystals. Equilibrated solutions were saturated with respect to Ca5(PO4)3OH, probably an impure, defective apatite. The CaHPO4-2H2O crystals formed at considerably higher pH values than expected becuase of enhanced solubility of the apatitic phase in enamel. Pyolysis of carious enamel revealed the presence of acidic calcium phosphate presumed to be CaHPO4-2H2O.

Solubility of CaHPO4 · 2H2O in the Quaternary System Ca(OH)2 - H3PO4 - NaCl - H2O at 25 °C

Solubility of CaHPO4 · 2H2O was determined in the quaternary system Ca(OH)2 - H3PO4 - NaCl - H2O at 25 °C in the pH range 4.39-6.38; ionic strengths of the saturated solutions varied from 0.00485 to 0.545, Satisfactory constancy in the solubility product, (K sp = [ Ca 2 + ] ⋅ [ HPO 4 2 - ] ⋅ γ Ca 2 + ⋅ γ HPO 4 2 - = 2.49 ± 0.05 × 10 - 7   mol 2 × 1 - 2 ) was obtained when (i) the ion activity coefficients, γ i , were calculated with the Debye-Hückel equation, log   γ i = - A Z i 2 I / ( 1 + B α i I ) + 0.0626   I ; the value 0.0626 for the coefficient in the linear term was derived from the solubility data by utilizing a statistical procedure, and (ii) formation of an ion pairNaHPO 4 - was taken into account; a statistically derived value for the stability constant of this ion pair is 7.0 ± 2.4 1 × mol-1. The ion pairNaHPO 4 - appears to have significant concentrations in physiological fluids.

Ionization of Hydrofluoric Acid at 25 °C

The ionization constant, K 1, for the reaction HF⇄H+ + F- was calculated on the basis of potentiometric measurements in the cell Ag; AgCl, Cl-, F-∥LaF3∥NaF, HCl, H2O∣KCl(Satd.), Hg2Cl2; Hg at 25 °C. A least squares procedure was applied to the experimental data yielding a best estimate for K 1 of 5.85 × 10-4 with a standard error of 0.03 × 10-4.

Isothermal Diffusion in the Dilute Range of the System Ca(OH)2 - H3PO4 - H2O: Theory

The equations describing isothermal diffusion in the dilute range of the ternary system Ca(OH)2 - H3PO4 - H2O are derived in two ways, first, assuming that the components are electroneutral species and, second, considering the actual ionic species present in solution. It is shown that the two models are thermodynamically equivalent. The theory permits the calculation of the four fundamental diffusion coefficients (phenomenological coefficients) in the concentration range where the Debye-Hückel theory suffices for the calculation of ionic activity coefficients. The equations can be used to test the Onsager reciprocal relations for the diffusion process in the above system. The ionic model was used to calculate practical diffusion coefficients for the electroneutral components from the limiting equivalent conductances of the ions in solutions saturated with respect to hydroxyapatite, Ca10(OH)2(PO4)6. Large diffusion interferences, as revealed by relatively large values for the cross-terms in D ij , are predicted even for solutions with total molarity in the order of 10-5. Therefore, diffusion models based on independent fluxes of the components appear to be invalid.

Quantitation of enamel demineralization mechanisms. 3. A critical examination of the hydroxyapatite model

A physical model which assumes that hydroxyapatite is the thermodynamic governing phase for the acid dissolution-rate behavior of enamel has been critically examined theoretically and experimentally. Both enamel powder and synthetic hydroxyapatite initial dissolution-rate experiments were conducted under various conditions of acid-buffer type and concentration, pH, and common ion concentrations.

Calculation of Diffusion Coefficients in Ternary Systems from Diaphragm Cell Experiments

Using a generalized least square procedure, a method is developed to estimate diffusion coefficients, D _ij , from concentration measurements made in a set of experiments of varying duration but with the same initial conditions. The method requires neither approximations nor restrictions in the flow equations. The D _ij and their errors are calculated simultaneously with the adjustment of the weighted observables - concentrations of the two solute components and time. A procedure is described to insure convergence in a given experimental set. The effect of the duration of the longest experiment, and errors in the observables on the estimated values of D _ij and their errors, are investigated. Application of the method to available data yielded values for D _ij in agreement with those previously calculated by more involved procedures.