Evaluation of titanium in oral conditions and its electrochemical corrosion behaviour

Due to its excellent biocompatibility and good mechanical properties, titanium has been used successfully in dentistry for many years. In this study, complete dentures with titanium palatal plates were applied to 10 patients who were in need of upper dentures. The clinical performance of cast titanium palatal plates was determined over a period of 6 months. No increase in accumulation of denture plaque nor mucosa irritation was observed. After the above period, the electrochemical corrosion behaviour of cast titanium and chromium-cobalt palatal plates were compared with the titanium plates that were not left in an oral environment after casting. For the electrochemical corrosion tests, a corrosion cell was designed and artificial saliva with lactic acid was used, with the temperature during the tests being about 37 degrees C. The potential difference between the test sample and the saturated calomel electrode was measured, and after the determination of the rest potentials, the anodic potentiodynamic polarization curves were traced at a rate of 1 mV/s. From the standpoint of corrosion, the titanium plates used by the patients for a 6-month period corroded more than the titanium not used by the patients. This may be due to the casting and processing conditions and the effect of the oral environment.     

Effects of different surface treatment methods on the bond strength of composite resin to porcelain

In this study failures of composite resin/ porcelain interfaces under shear loading were examined. Porcelain firing were made onto metal cylinders and porcelain surfaces were roughened with burrs or treated with hydrofloric acid gel and/ or sandblasted with a Microetcher. Two silane coupling agents were used in five groups, each of which had 22 samples. All of the treated samples were restored with a hybrid-type composite resin. Then each group was divided into two subgroups according to storage times of 24 h and 30 days. After thermocyling the samples which were stored for 30 days, all of the groups were subjected to shear force at the composite resin/porcelain interface until fracture occurred. The results showed that there were differences both in the 24-h and 30-day storage period bond strengths between the various surface treatment methods. The samples treated with all three of the Microetcher, hydrofloric acid and silane exhibited the highest shear bond values after 24 h storage, followed by the microetched/silane and the hydrofluoric acid/silane groups (F: 570.31, P: 0.00). After 30 days, the highest mean shear bond strength values were again with samples treated by all three processes. The storage period and thermocycling decreased the bond strength of samples, however, there was a significant difference among groups (F: 1388-55, P: 0.00). Silane pre-treatment of porcelain was important as the mean bond strength of sandblasted/etched specimens were significantly lower than the other groups which were treated mechanically, in 24 h. Sandblasting seems to have little effect on the bonding. The comparison of 24-h and 30-day samples have also significant difference (F: 91.4376, P: 0.00).     

Modelling of alternating-current machines having multiple rotorcircuits

The modeling of a synchronous or an asynchronous machine forms the basis of simulation investigations made with high-powered computers. Many phenomena and processes require corresponding refinement of the models used, and an increase in input in the form of fictive rotor circuits. A method is presented which has been tested out over a relatively long period of time. The general equations contain none of the usual approximations, and can be programmed quite readily. Numerical examples are given as an aid in applying the procedures     

Effect of root canal sealers on the push-out bond strengths of tooth-colored posts to root dentine

Objectives: This study evaluated the effect of different root canal sealers on the push-out bond strength of tooth-colored posts to root dentin. Material and methods: Eighty human mandibular premolar teeth with single roots were decoronated and randomly divided into two groups according to post material: G1–G5: Cytec blanco; G6–G10: Cosmopost. In each group, the specimens were further subgrouped according to the filling material plus sealer (n = 8): G1, G6: Gutta-percha + AH Plus; G2, G7: Resilon + Epiphany SE; G3, G8: Gutta-percha + Sealite; G4, G9: Gutta-percha + iRoot SP; and G5, G10: control (unobturated). Cytec blanco and Cosmopost of 1.4 mm diameter were adhesively luted to samples using Variolink II. Push-out test was performed in a universal testing machine, and failure modes were examined under stereomicroscope. Data were analyzed with the two-way ANOVA and post hoc Tukey’s tests. Statistical significance was set to 0.05. Results: Roots obturated with AH Plus (3.48 ± 1.41 MPa), Sealite (3.47 ± 0.65 MPa), and Resilon (3.36 ± 1.23 MPa) had the lowest bond strength (p < 0.005). iRoot SP and control group samples showed the highest bond strength values (7.38 ± 0.89 MPa and 6.43 ± 1.16 MPa, respectively) (p < 0.05). Significant differences were observed among tooth-colored posts and sealers (p < 0.05). Adhesive failures were predominant in all groups (48%). Conclusions: When the resin cement Variolink II was used, the types of root canal filling materials and sealers could affect the retentions of the fiber/zirconium posts; the fiber post revealed the higher bond values than the zirconium post; and the calcium silicate-based sealer (iRoot SP) revealed the highest bond strengths.     

Phase transition temperature in the Zr-rich corner of Zr–Nb–Sn–Fe alloys

The influence of small composition changes on the phase transformation temperature of Zr–1Nb–1Sn–0.2(0.7)Fe alloys was studied in the present work, by electrical resistivity measurements and metallographic techniques. For the alloy with 0.2 at.% Fe we have determined T_↔+β=741°C and T_+β↔β=973°C, and for the 0.7 at.% Fe the transformation temperatures were T_↔+β=712°C and T_+β↔β=961°C. We have verified that the addition of Sn stabilized the β phase.     

Determination of the model parameters of machines from thereactance operators xd(p), xq(p) (evaluation of standstill frequency response test)

A method is presented for determining the characteristic quantities and model parameters from the given frequency responses x _d(js), x_q(js). The curves of values measured on a large turbogenerator at standstill are used as an example. The characteristic values and model parameters are determined for various models (with four, three, and two rotor circuits in each axis) and are compared with the results of short-circuit tests and with advanced calculations     

Delayed current zeros due to out-of-phase synchronizing [ofturbogenerators]

Out-of-phase synchronizing occasionally occurs in power stations. The resulting fault current may exhibit delayed current zeros. These delayed current zeros have totally different causes and are quite dissimilar in comparison with the well-known delayed current zeros associated with generator terminal faults. The rapid movement of the rotor from initial out-of-phase angle δ₀ to δ=0 results in a very small AC component and a dominant DC component when δ=0 is reached. The various parameters influencing the extent of the delayed current zeros have been analyzed and are discussed. The most influential parameter is the initial out-of-phase angle δ₀ . Other important parameters are inertia constant of the turbogenerator set and initial deviation from synchronous speed. The influence of incorrect generator modelling on the result has also been demonstrated. The effect of circuit-breaker arc voltages on delayed current zeros has been examined and a comparison made between generator voltage and HV-side circuit-breakers. From this comparison, it follows that while circuit-breakers on both sides of the step-up transformer are necessary from a protection point of view, the generator circuit-breaker should preferably be used for synchronizing operations     

Effect of muscle relaxation splint therapy on the electromyographic activities of masseter and anterior temporalis muscles

The purpose of this study was to compare the effectiveness of splint therapy on the electromyographic activity of masticatory muscles (anterior temporalis and masseter) before and after the application of a muscle relaxation splint. Electromyography recordings from the masseter and anterior temporalis muscles were analyzed quantitatively during maximal biting in the intercuspal position both before and after treatment without a splint. Fourteen patients whose chief complaint was masticatory muscle pain were selected for the study. After the initial evaluations muscle relaxation splints were applied, and the patients were instructed to use the splints for 6 weeks. Surface electromyographic recordings were taken from each patient before the beginning of clinical therapy and after 6 weeks of wearing the splints. The data obtained were analyzed through paired sample t tests and Wilcoxon's signed rank tests. The results of the study were as follows: (1) the electromyographic activity of the two muscles during maximal biting was not markedly changed after the muscle relaxation splint was used; and (2) the changes observed in electromyographic activity of the involved and noninvolved sides were insignificant as well.     

Allgemeine Theorie der Synchron- und Asynchronmaschinen in der Operator-Matrix-Darstellung

Inhaltsübersicht 1. Einleitung-2. Allgemeines über die Rechnungsart und die Voraussetzungen-3. Grundgleichungen der beiden Achsen-4. Ersatzschemata derd-undq-Achsen-5. Allgemeiner Zusammenhang zwischen den Achsengrößen im Bildbereich derLaplace-Transformation-6. Zusammenhang zwischen den Strom-Spannungssystemen im Bildbereich derLaplace-Transformation (Admittanz-Operator-Matrizen im Bildbereich)-7. Zusammenhang zwischen den Strom-und Spannungssystemen im Originalbereich derLaplace-Transformation (Admittanz-Operator-Matrizen im Orginalbereich)-8. Drehmoment-9. Beispiele: 9.1. Stationärer Synchronbetrieb am symmetrischen Netz; 9.2. Stationärer Asynchronbetrieb am symmetrischen Netz; 9.3. Dreisträngiger Kurzschluß anschließend an stationäre Belastung; 9.4. Drehmoment einer Synchronmaschine bei plötzlicher Änderung der Spannung-10. Zusammenfassung-Anhang I-Anhang II-Literatur.Mit 6 Textabbildungen