Zirconia Use in Dentistry - Manufacturing and Properties.

Several types of metal-free ceramics have been developed to meet the patients demand for natural looking appearance restorations. Owing to their biocompatibility and good mechanical properties zirconia has been successfully used in recent years as a dental biomaterial. Due to its high opacity zirconia cores are generally covered with ceramic veneers that provide a more natural appearance but have frequent incidence of chipping. As an alternative to veneered zirconia full-contour zirconia restorations become more widely used nowadays. The paper reviews the current knowledge and scientific data of the zirconia use in dentistry in order to compare the zirconia based dental restorations with the metal-ceramic ones and also the two types of dental restoration based on zirconia, veneered or monolithic zirconia.

Local structure at Mn2+ ions in vacuum annealed small cubic ZnS nanocrystals self-assembled into a mesoporous structure.

A mesoporous structure of self-assembled nanocrystals of cubic ZnS doped with Mn2+ ions with a homogeneous distribution of pores of similar size was synthesized at room temperature by a surfactant-assisted liquid-liquid reaction. The component nanocrystals exhibit a high crystallinity and a tight size distribution centered at 2 nm, as well as the narrowest Electron Paramagnetic Resonance (EPR) spectra linewidth and the best resolution reported so-far, effects attributed to self-assembling. The observed EPR spectra consist of lines from the substitutional Mn2+(I) and surface Mn2+(II) and Mn2+(III) centers. Here we show that, in contrast with previous reports, our EPR spectra are highly sensitive to structural changes during pulse annealing in vacuum up to 500 degrees C. The changes are related to the transformation of the surface Mn2+ centers in new Mn2+ centers, attributed to an oxidation process in which the thermal decomposition of the Tween 20 additive, also observed by EPR, seems to be involved. We have also been able to observe, for the first time by EPR spectroscopy, the formation of the ZnO phase and the nanocrystals size increase, which occur during annealing up to 500 degrees C, structural changes confirmed by XRD and TEM observations on the samples previously investigated by EPR.

Localization of Mn2+ ions in mesoporous NnS.

Nanocrystalline cubic ZnS doped with 0.2% mol manganese, exhibiting a stable mesoporous structure, was synthesized at room temperature by a non toxic surfactant-assisted liquid-liquid reaction. The X-ray diffraction measurements demonstrate the formation of a sponge-like mesoporous material built from cubic ZnS nanocrystals of 1.8 nm average sizes, with a tight distribution of pores of 1.8 nm mean diameter. The transmission electron microscopy images confirm the formation of the mesoporous structure with walls of 3.1 nm mean thickness built from cubic ZnS nanocrystallites of 2.1 nm average size. The resulting tight distribution of crystallites and pores yields a well resolved Electron Paramagnetic Resonance spectrum, with the narrowest reported component lines attributed to three types of isolated Mn2+ centers, called Mn2+(I), Mn2+(II) and Mn2+(III). From the analysis of the spin Hamiltonian parameters it is shown that in the Mn2+(I) centers the paramagnetic ion is situated at substitutional Zn sites in the ZnS nanocrystals, being also subjected to a small axial distortion. The relative concentration changes under thermal treatment experiments strongly suggest that in both Mn2+(II) and Mn2+(III) centers the Mn2+ ion is localized on the surface of the ZnS nanocrystallites, being bond to an oxygen ion in the first case and to an additional water molecule in the second case.

Organic photovoltaic cells based on ZnO thin film electrodes.

Due to its wide band-gap (ca. 3.4 eV), ZnO is a possible candidate material to be used as transparent electrode for a new class of photovoltaic (PV) cells. Also, an increased interest for the photovoltaic properties of several organic monomers and polymers (merocyanines, phthalocyanines and porphyrins) was noticed, because of their high optical absorption in the visible region of the spectrum allowing them to be used as potential inexpensive materials for solar cells. Preparation and properties of CuPc (copper phthalocyanine) based photovoltaic cells using ZnO thin films as transparent conductor electrodes are presented in this paper. ZnO layers are grown by pulsed laser deposition, while the organic layers are obtained by thermal evaporation. Structural characterization is performed by electron microscopy. Optical and transport properties of the mutilayered structures are obtained by electrical and spectro-photometric measurements. The influence of the ZnO-polymer interface on the external quantum efficiency (EQE) of the photovoltaic cell is clearly evidenced by our measurements.

Advances and problems with TEM characterization of Cr/CrN multilayer coatings.

Multilayer Cr/CrN/Cr/Cr(N,C) and Cr/CrN with 8 and 32 layer coatings were deposited on austenite substrates using pulsed laser deposition (PLD) technique. The microstructure observations were performed using Philips CM20trade mark, TECNAI G(2) F20 - TWINtrade mark and JEOL EX4000trade mark transmission microscopes. The performed experiments indicated that lowering the argon flow from 60 to 30 cm(3)/s during chromium ablation changes buffer layers microstructure from nearly amorphous to nano-crystalline. The nitride or carbo-nitride layers turned out to be less sensitive to changes in nitrogen flow during deposition. The columnar microstructure of Cr layers is coarser than those in CrN ones under the same deposition condition. This observation proved also that relying on PLD technique as thin as 30 nm layers might be formed within multilayer Cr/CrN coatings.

Stability of the Birmingham hip resurfacing arthroplasty at two years. A radiostereophotogrammetric analysis study.

The Birmingham hip resurfacing metal-on-metal arthroplasty was introduced in 1997 and has shown promising short- to mid-term results. We used radiostereophotogrammetric analysis (RSA) to study the stability of 20 resurfacing arthroplasties over a follow-up period of 24 months. Radiological examinations for RSA were performed immediately after surgery and at two, six, 12 and 24 months after operation. Precision and detection of migration thresholds (non-zero movement) were calculated. All the results corresponded well to those found in similar experimental arrangements with standard hip prostheses. Migration of the cup and vertical and mediolateral migration of the head were calculated. The values were low at two years compared with those of earlier studies of cemented femoral components in conventional total hip replacements indicating that there was no evidence of excessive early migration or loosening of the components.

Clinical and etiopathogenetic profile of heart failure in the First Medical Clinic of Cluj-Napoca. A study of 5 years.

The authors analysed the main etiopathogenetic conditions and the clinical and evolutional profile of 1586 patients with heart failure (HF), admitted to the First Medical Clinic of Cluj-Napoca between 1990 and 1994. Ischemic heart disease was found in 1,236 patients (78%), followed by chronic cor pulmonale, valvulopathies and congenital heart diseases. Among the precipitating and/or aggravating factors of HF, the most important were infections in 434 patients (33.10%), and arrhythmias, especially atrial fibrillation, in 332 patients (25.39%). In decreased order of frequency there were also failure to observe prescribed therapy, uncontrolled arterial hypertension, anemias, dyselectrolytemias, dysproteinemias. HF had a chronic evolution in 1,450 patients (91.40%), and an acute one in 136 (8.6%). In conditions of complex therapy including cardiotonics, diuretics, plus, more recently, conversion enzyme inhibitors, the clinical evolution was favourable in 1,432 patients (90.20%), which had a lower functional class on discharge from hospital.

In vivo measurements of relative motion between an uncemented femoral total hip component and the femur by roentgen stereophotogrammetric analysis.

Roentgen stereophotogrammetric analysis (RSA) was used to study rotation and subsidence of an uncemented polyethylene-coated femoral component for total hip arthroplasty in ten patients younger than 55 years of age. Three years postoperatively, the total subsidence averaged 2.44 mm and the internal rotation was 7.4 degrees. The rate of subsidence decreased between the observation periods, whereas the rate of rotation, after an initial significant decrease, became almost constant. One patient, who was a clinical failure and required revision arthroplasty, had a significantly higher rate of migration after six months. The pattern of subsidence in the absence of pain might be the normal reaction of bone to an uncemented prosthesis, but the continuing rotation suggests the potential for failure of the arthroplasty. The type of analysis made possible in RSA may allow early prediction of the success of arthroplasties and significantly speed the design cycle for arthroplasty components.

A technique for measurements of plantar flexion torque with the Cybex II dynamometer.

A standard procedure for measurements of calf muscle strength with an isokinetic dynamometer is presented. The method is based on recordings in supine position, with a straight knee joint and a firm fixation of the foot in a new device. The reproducibility was studied by a test-retest procedure in ten testing subjects. The methodological error varied between 5 and 10% and the coefficient of reliability varied between 0.94 and 0.98. The coefficient of variation when measuring one testing subject at ten different occasions was smaller at isokinetic than at isometric measurements.

Surgical and non-surgical treatment of Achilles Tendon rupture. A prospective randomized study.

One hundred and five consecutive patients with a closed acute rupture of the tendo achillis were assigned randomly for surgical or non-surgical treatment. After treatment, the patients were evaluated clinically and with static and dynamic measurements of plantar flexion strength. Only minor differences were noted between the final results in the two groups. Non-surgical treatment had the advantages of shorter morbidity and no hospital stay. The frequency of major complications was about the same in both groups of patients: two re-ruptures and two deep infections in patients who had operations as compared with five re-ruptures in the conservatively treated patients. I concluded that non-surgical treatment offers advantages over surgical treatment.

Strength of plantar flexion and function after resection of various parts of the triceps surae muscle.

Nine patients who had undergone resection of various well defined parts of the triceps surae muscle because of tumour were examined. The function was estimated from the patient's history and the muscle strength was measured statically and dynamically using a Cybex II dynamometer. Two patients reported slight symptoms. The loss of strength was less than one might expect from theoretical calculations. The strength of the operated limb showed a particular pattern depending on the part resected. From this pattern it was concluded that the soleus is more active when the foot is dorsiflexed and the gastrocnemius more active when the foot is in plantar flexion, and that the gastrocnemius is most important in quick movements of the foot.

Calorimetric absorption coefficient measurements using pulsed CO(2) lasers.

An experimental arrangement is devised by which the absorption coefficient of low-loss materials can be measured by calorimetry using pulsed CO(2) lasers. The values obtained for long rod KCl samples are compared with those inferred when a cw CO(2) laser was used as radiation source. The values measured in the pulsed regime are little affected by the quality of the end sample surfaces and are close to the values corresponding to bulk absorption. Such behavior is explained as due to the essential role of the radiation process in dissipating the surface absorbed heat.