Abdominal and pelvic splenosis: atypical findings, pitfalls, and mimics.

Splenosis is an acquired form of ectopic splenic tissue that typically arises after trauma or splenectomy. It is often an incidental image finding in an otherwise asymptomatic patient, but the spectrum of symptoms varies based on the site of implantation. Radiologists should be familiar with the imaging features of splenosis to avoid mistaking it for malignancy. Splenosis has identical imaging features to that of the native spleen on US, CT, MRI, and nuclear medicine examinations. Therefore, when the radiologic findings support the diagnosis of splenosis, the patient can be spared invasive procedures for tissue sampling.

Stress relaxation in titanium-ceramic beams during veneering.

Spalling of a ceramic from the metallic substrate is related to stress at the metallo-ceramic interface of crowns. The purpose of this study is to (1) establish a method for recording the bending radius of metallo-ceramic strips during cooling, (2) calculate the stress in the metal adjacent to the metallo-ceramic interface based on the recorded bending and (3) compare this stress with that calculated from the mismatch between measurements of the coefficients of thermal expansion, alpha, of the ceramic and titan. Metallo-ceramic specimens (n = 9) were made by firing a 0.6 mm thick layer of ceramic on (11.3 x 3.2 x 0.6) mm Ti-substrates. The opaque material of three commercial porcelains for titanium were applied: Titankeram (Vita), TiBond (DeTrey/Dentsply) and Duceratin (Ducera). The Ti-side of the specimens rested on two quartz supports of a jig in an apparatus for thermo-mechanical analysis (TMA). The vertical, mid-span movements of a quartz flexure probe resting on the ceramic-side of the metallo-ceramic specimen were continuously recorded during heating and cooling in the temperature range 20-600 degrees C. The cooling rate was 6 degrees C min(-1) from 600 degrees C, to below the glass transition temperature, Tg. The bending radii recorded continuously during cooling were reproducible. The thermal expansions, alpha(cer), lay in the range 23-47 x 10(-6) K(-1) above Tg compared to 7.9-9.8 x 10(-6) K(-1) (alpha(cer, 20-400 degrees C)) below Tg. For Ti, the coefficient of thermal expansion was found to be 9.7 x 10(-6) K(-1) (alpha(Ti, 20-600 degrees C)). The calculated stresses above Tg based on the thermal mismatch were much higher than those calculated from the flexure movement. The observed differences are attributed to stress relaxations in the ceramic above Tg.

Corrosion and biocompatibility testing of palladium alloy castings.

OBJECTIVE: The biocompatibility of palladium-copper alloys has been questioned in the literature. The intention of the present work was to study: (a) the release of ions in an immersion test from a copper-containing alloy, Option((R)) (79% Pd, 10% Cu, 9% Ga, 2% Au), compared with an alloy without Cu, IS85 (82% Pd, 6% Ga, 3.5% Sn, 3.5% In, 2.5% Ag, 2.5% Au); (b) the effect of oxide films produced by preoxidation on corrosion resistance; and (c) the possibility of biologically synergetic effects of ions released. METHODS: Specimens of both alloys were cast, rubbed and ultrasonically cleaned. Metallographic specimens were prepared after (a) casting and (b) preoxidizing treatment at approximately 1000 degrees C and studied by SEM and EDS. Immersion tests were carried out in a solution of 0.1mol/l of NaCl and 0.1mol/l of lactic acid at 37 degrees C for 7 days. The alloy specimens were tested in the following three steps: (1) as preoxidized; (2) after subsequent removal of a 0.1mm thick layer by grinding; and (3) after an additional removal of approximately 0.1mm by grinding. The test solutions were analyzed by means of ICP to record the amounts of ions that had leached out from the alloy specimens. The biocompatibility was studied by cell culture tests and the HET-CAM method. Test solutions were prepared by dissolving PdCl(2) and CuCl(2) to appropriate concentrations. RESULTS: The metallographic investigations revealed moderate segregations in interdendritic regions and grain boundaries. After preoxidation in air a zone of oxidation from 25 up to 200 microm thickness for Option and from 5 to 10 microm for IS85 was found. Oxidation was observed along a rim for both alloys and for Option also along interdendritic positions. The oxides were seen as small, dark spots <1 microm in a metallic matrix. These results indicate that: (1) the oxidation of the copper-containing palladium alloy is far more severe than that of the alloy with no copper; and (2) the elemental release from these oxides is substantially larger than that from the corrosion of the metallic structure. The results of the cell culture testing showed that Cu was most toxic, followed by Cu(2+)+Pd(2+) (1:2), based on the determination of the concentration that caused 50% cytotoxicity. The HET-CAM testing showed Cu(2+)+Pd(2+) (1:2) to have the highest irritation score. SIGNIFICANCE: The copper-containing Pd alloy developed a 0.1mm thick rim with small oxide particles in a metallic matrix during preoxidation. If this rim is not completely removed, significantly more Cu, Ga and Pd ions have been shown to leach into the test solution than from the alloy structure. No synergetic effect of Cu and Pd ions was observed in cultured cells, while the mixture Pd(2+)+Cu(2+) (1:2) was most irritating to mucous membrane as evaluated by the HET-CAM method.

Hot isostatic pressing-processed hydroxyapatite-coated titanium implants: light microscopic and scanning electron microscopy investigations.

Hot isostatic pressing (HIP) was used in a new procedure to produce hydroxyapatite (HA) coatings on a commercially pure titanium (cpTi) substrate for osseous implantation. Eighteen HIP-processed HA-coated implants were placed in the inferior border of the mandibles in 2 Labrador retriever dogs and left submerged for 3 months. As control specimens, 12 sandblasted cpTi implants were placed in the same mandibles and, to compare the bone reaction, 2 additional plasma-sprayed HA-coated implants (Integral) were placed. Tissue reactions at the bony interfaces of the implants were studied in ground sections with the implants in situ, using ordinary, fluorescent, and polarized light microscopy and scanning electron microscopy (SEM). The HIP-processed HA coatings displayed an increased density in light microscopy and SEM as compared to plasma-sprayed coatings. Direct bone-implant contact was found in all 3 types of surfaces. However, the production of new bone was far more abundant for the HA-coated implants than for sandblasted cpTi implants. The presence of bone-forming and bone-resorbing cells indicated active bone remodeling in the interface area at 3 months after implant placement. The present results support the view that epitaxial bone growth may occur from the HA-coated implant surface. It was concluded that the increased density of the present HIP-processed HA material does not reduce the bioactive properties of the coatings.

Corrosion of gallium alloys in vivo.

The aim of this work was to study the corrosion of gallium alloys in vivo. Three gallium alloys were tested: GF alloy, Galloy and an experimental GaIn alloy. An amalgam was applied as a control. After ageing for a minimum of two weeks, one disc of each of these alloys was mounted with the polished side up in the buccal surfaces of 17 acrylic dentures. Eight sets of the specimens were retrieved after exposure to the oral cavity for 2-4 months, and another seven were retrieved after 6-9 months. Corrosion of the polished cross-sections of the specimens was studied using scanning electron microscopy (SEM). Only the CuGa2 phase was found to corrode substantially in all three of the alloys investigated, leaving behind holes up to 20 microm deep. This is consistent with the corrosion reported after immersion tests in a solution of 0.1 mol lactic acid and 0.1 mol NaCl for 7 days. Such in vitro tests are also reported to cause distinct corrosion of the Sn phase in the gallium alloys. However, a salient feature of the corrosion in vivo was the lack of detectable dissolution of this phase. Thus, for gallium alloys, the accelerated in vitro immersion method produced results which did not agree with clinical observations. Large variations in the corrosion of the CuGa2 were observed from patient to patient. The amount of corrosion on the Galloy specimens appeared to be less and on a finer scale than on specimens of the two other alloys. The depth of corrosion was thus shallower than for this alloy. This finding indicates that there is room for further improvement of the corrosion resistance by modifying the microstructures. Less overall corrosion was found for the amalgam control than for the gallium alloys.

Dental gallium alloy composites studied by SEM and TEM.

Analytical scanning and transmission electron microscopy (SEM and TEM) studies of dental gallium alloys have been carried out. The Ga alloys were made by triturating a LU powder (Ag-Sn-Cu rich alloy powder) and a GF powder (Ag-Sn-Cu-Pd rich alloy powder) with a liquid Ga alloy containing Ga, In and Sn. The dental materials were found to be composites consisting of remaining, undissolved particles from the Ag-based alloy powders in a matrix of reaction products with the Ga alloy. SEM studies have been carried out to give an overview of the composites. The distribution of the elements was found by the X-ray mapping technique. The phases in the matrix and the remaining alloy particles have been identified by electron diffraction, high-resolution electron microscopy and energy-dispersive X-ray spectroscopy. The following phases were identified in the LU alloy: orthorhombic Ag3Sn, cubic Ag9In4, tetragonal beta-Sn and hexagonal Ag2Ga. In addition to these well-known phases Ga-rich regions were observed consisting of an intergrowth of tetragonal CuGa2 and one of the cubic gamma-Cu9Ga4 phases. In addition to these phases cubic Ga7Pd3 was found in the GF alloy. The anomalous setting expansion of the GF alloy may be explained by the presence of Ga7Pd3.

Structure of dental gallium alloys.

The interest in gallium alloys as a replacement for amalgam has increased in recent years due to the risk of environmental pollution from amalgam. Alloy powders with compositions close to those for alloys of amalgam are mixed with a liquid gallium alloy. The mix is condensed into a prepared cavity in much the same way as for amalgam. The aim of the present work was to study the structure of: (1) two commercial alloy powders containing mainly silver, tin and copper, and (2) the phases formed by mixing these powders with a liquid alloy of gallium, indium and tin. One of the alloy powders contained 9 wt% palladium. Cross-sections of cylindrical specimens made by these gallium mixes were investigated by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Discrete grains of the following phases were found to be present in both gallium alloys: hexagonal Ag2Ga, tetragonal Cu(Pd)Ga2, cubic Ag9In4 and tetragonal beta-Sn. Indications of hexagonal or orthorhombic Ag2Sn were found in the remaining, unreacted alloy particles. In the palladium-containing alloy the X-ray reflections indicate a minor fraction of cubic Cu9Ga4 in addition to the Cu(Pd)Ga2 phase. Particles of beta-Sn are probably precipitated because Sn-Ga phases cannot be formed according to the binary phase diagram.

Solubility of hydroxyapatite/mica composites.

The solubility of some inorganic materials was studied. It was found that Ca dissolution was high in calcium phosphates with Ca/P ratios 1.67-2.0. Dissolution of P was moderate compared with dissolution of Ca. The composites, HA content 70 wt-%, and HA showed to be corrosion resistant. Dissolution of alumina in the mineral muscovite, used as a filler material, was found to be neglectable and dependent on the density of the composite.

Bonding capacity in bone of HIP-processed HA-coated titanium: mechanical and histological investigations.

The main problems using plasma-sprayed hydroxyapatite (HA) as a coating material on metallic implants are its porosity, low fatigue strength, and weak adherence to the metallic substrate. To overcome these problems a new technique using hot isostatic pressing (HIP) has been developed for producing HA-coated titanium (Ti) implants. Specimens produced at a maximum temperature of 850 degrees C and a maximum pressure of 720 bar displayed a dense, glassy, 25-microns thick coating with small amounts of porosity and a mean surface roughness of 0.7 microns, as compared with 1.6 microns for sandblasted Ti. Twenty conical HA-coated (720 and 100 bar pressure) and 10 noncoated Ti implants were inserted through the cortex of the lower margin of the mandibles of sheep and allowed to heal for 60 days. Push-out tests for implants processed at 720 bar pressure showed substantially higher bone/implant bonding values than for sandblasted Ti implants. Histological studies indicated a direct contact and probably chemical bonding between bone tissue and the HA coatings. The area of contact was almost 3 times as large as for the Ti implants. The adherence of the 100-bar coating to the Ti surface was inferior to the 720-bar coating, as shown by the loosening of the coatings in several areas.

Casting of Ti-6Al-4V alloy compared with pure Ti in an Ar-arc casting machine.

Dental prostheses of Ti are normally cast in pure Ti. Some appliances, however, require higher yield strength. Casting of Ti alloys is of interest in such cases. The objective of the present work was to study the quality of castings made of Ti-6Al-4V compared with those made of pure Ti. Casting was made into a mold kept at room temperature using a MgO-Al2O3 investment. A standardized five-unit bridge was cast, consisting of two cylindrical crowns with sharp margins and three pontics. The overall mold filling was satisfactory. The margins of the casting alloys were, however, more rugged and incomplete than those of pure Ti. The most likely reason for this difference is the increased formation of dendrites in the alloy and thus more resistance to fluid flow. Furthermore, the sprue of the alloy was also found to contain some spherical, internal pores. Such pores were rare in the pure Ti castings. The surface reactions were found to be minimal for both of the materials. Increased casting deficiencies observed in the cast bridges of the Ti-6Al-4V alloy, compared with pure Ti, were: 1) the margins of the crowns in the bridge were less complete and 2) there was a tendency to an increased internal porosity, particularly in the sprues.

Amalgams made from liquid Hg-In.

The addition of indium to amalgam appears to reduce the mercury vapour above fillings during setting. In the present work the structure and the physical properties of amalgams with In additions to the mercury up to 30 vol.% have been investigated. No new phase or undissolved in could be detected by X-ray diffraction and scanning electron microscopy studies. Energy dispersive spectroscopy measured 4 at.% In in the gamma 1-phase of an amalgam with 20 vol.% In added to the mercury. At the same time, the Ag/Hg ratio was substantially increased compared with amalgam having no In addition. The compression strength decreased with increasing In content, and for amalgam with as much as 30 vol.% In added to the mercury, it fell below the minimum requirement of ISO 1559 (Alloys for dental amalgam, International Organization for Standardization, Geneva, 1986). An abrupt drop of the load at the onset of failure and cracks running through the gamma 1-phase, as well as the eta-phase, indicates embrittlement of these phases with increasing In content.

Mold filling of Ti castings using investments with different gas permeability.

OBJECTIVES: The aim of this work was to study mold filling during casting of standardized five-unit Ti bridges vs. the gas permeability of the investments. METHODS: An Ar arc casting machine with a separate melting and mold chamber was used. Both chambers were evacuated before Ar was introduced into the melting chamber. A rubber sealer was inserted between the top of the steel ring of the mold and the steel floor between the two chambers. The mold cavity required the same Ar pressure as the melting chamber prior to casting. Four different investments for Ti casting were investigated: 1) Bellavest T (BEGO), 2) Rematitan Plus (Dentaurum), 3) Titavest CB (Morita) and 4) Titanium Vest (Ohara Co.). Three castings were made with each investment. The molds were fired according to the manufacturers' instructions and cooled to room temperature. The Ar gas pressures in the two chambers were recorded during casting, and the mold filling was evaluated initially by visual inspection and subsequently by studying the margins of the crowns in a microscope. RESULTS: In the melting and molding chambers, the Ar pressure was found to be: 1) Bellavest T: 400 and 1 torr; 2) Rematitan Plus: 600 and 85 torr; 3) Titavest CB:600 and 150 torr; and 4) Titanium Vest: 600 and 85 torr, respectively. This indicates substantial differences in the gas permeability of the molds. Bellavest T produced poorly filled molds, Rematitan Plus and Titanium Vest resulted in poor margins and Titavest CB produced complete castings. SIGNIFICANCE: Proper mold filling is promoted by investments with a high gas permeability, so the gases in the mold cavity can escape through the investment to the mold chamber.

Hydroxyapatite coatings on Ti produced by hot isostatic pressing.

Plasma spraying is a technique currently used in the production of HA-coated titanium implants. These coatings have been shown to be porous; they dissolve and have a weak bond to the substrate. The long-term interface strength has been questioned in particular. The aim of the present work was to produce HA coatings without the shortcomings of those produced by plasma spraying. Hot isostatic pressing (HIP) at 850 degrees C and 1000 bar with no holding time was applied for this purpose. Initially, the HA powder was mixed with water and air sprayed on the Ti substrate. The Ti specimens were then cold-pressed, enclosed by a protective Pt foil, and encapsulated in an evacuated glass ampulla. Subsequent to HIP, the glass and the Pt foil were removed. These coatings were denser than those produced by plasma spraying. The bonding was measured to be > 62 MPa, which is considered to be satisfactory. The structure of the coating was checked by X-ray diffraction and IR spectroscopy, and was found to correspond to that of HA. Some cracks were observed in the coating running predominantly vertical to the surface. Whether these are acceptable has to be verified by in vivo experiments.

Mechanical properties of hydroxyapatite/mica composite.

Bend specimens of the inorganic synthetic materials hydroxyapatite (HA) and a composite of hydroxyapatite/muscovite mica have been prepared and tested mechanically. Sintering followed by hot isostatic pressing (HIP) without encapsulation gave an increased strength for HA alone, but no significant increase in strength compared with sintering alone for HA/mica composites. The bend strength of the HA/mica composite was inferior to that of HA alone, the reason being inadequate bonding between HA and mica. HIP in glass capsules and an increased cold compaction pressure tended to improve the bend strength of the composite. Corrosion in tris for 7 d did not affect the bend strength of the investigated materials significantly.

Mold filling and porosity in castings of titanium.

The present study focused on the effects of argon pressure, mold venting, and investment permeability on the mold filling of titanium and the soundness of titanium castings. Casting soundness was determined by density measurement and x-ray radiography. To achieve complete filling of molds made from a relatively impermeable investment, the molds were vented. Regardless of the presence or absence of vents, all of the molds made from a highly permeable refractory material filled completely. The soundness of castings made under an argon pressure of 50 torr was significantly greater than that of castings made under a pressure of 400 torr. The non-vented molds of the highly permeable refractory material yielded the soundest castings (mean density = 4.45 g/cm3).

Bond strength of porcelain on cast vs. wrought titanium.

The bond strength of porcelain fused to cast and wrought titanium surfaces was calculated from fracture loads in a 4-point bending test. Two different porcelain were applied (O'Hara and Duceratin). The surface of Ti-cast specimens was treated in two different ways to produce variations in the impurity level before porcelain veneering. Microhardness measurements as well as scanning electron microscopy with EDX analysis were conducted. The results showed no significant difference in bond strength between the two porcelains. Nor was any difference in bond capacity found between thoroughly blasted castings and wrought titanium. Significantly lower bond strengths were observed for lightly blasted specimens and for specimens treated with Gold bonding agent. Impurities in the surface region of the castings were found to be due to contact with the investment during solidification. This indicates that a thin surface layer (50-100 microns) of the casting should be removed before firing of the porcelain.

Fracture toughness measurements of some dental core ceramics: a methodologic study.

Fracture toughness is regarded as an important property of dental ceramics. The most widely used methods for fracture toughness (KIc) determination are based on assessment of cracks created by hardness indentations. Different formulas have been developed for KIc calculations and all these methods and formulas include empirical factors based on pure ceramics, i.e. non-composite ceramics. These factors may, however, vary for a specified method for materials with different and complex structure. An important question is whether the various proposed methods and formulas lead to approximately the same numerical KIc values or at least to the same ranking of materials. The aim of this work was to compare two indentation methods and various formulas for calculation of KIc values when used on four commercial composite dental ceramics. The two applied methods and the different formulas showed substantial differences in the obtained values for one and the same material and a different ranking of various materials. It is unknown which method gives the most correct KIc values for these ceramic materials.

Effect of vacuum and supertemperature on mold filling during casting.

A comparison of the effect on mold filling of using vacuum vs. a protective gas of Ar during casting has been carried out. A conventional gold casting alloy and a NiCr-alloy without Be have been cast at three temperatures into two different mold patterns: a mesh screen and a cylindrical crown with a 30 degrees sharp margin. In all cases the application of vacuum rather than a protective gas of Ar was found to be beneficial for the mold filling. A reduction of the back pressure due to the trapped gases in the last part of the mold to be filled with metal was assumed to be the major reason for this effect. A reduced surface tension of the melt may also contribute. An improved mold filling was also observed for both nets and crown margins with increasing supertemperature of the melt. Physical reasons for this effect have been suggested.

Effects of In and Zn on properties of low noble metal alloys.

Four low noble metal alloys with high In and Zn contents were investigated with regard to porosity in castings, structure, tarnish, hardening mechanism and cytotoxicity. Fumes were observed above the melt, due to the high Zn content and low boiling point of this metal. This Zn evaporation during melting created a small amount of porosity in the castings. This porosity diminished when the Zn content was reduced from 4 to 2%. Scanning electronmicroscopy, microprobe analyses and X-ray diffraction analyses revealed a face-centred cubic (fcc) matrix enriched in Au and Ag and a body-centred cubic (bcc) phase enriched in Pd, In and Zn which had a yellow gold-like appearance. After immersion in a 2% Na2S solution for 72 h, no tarnish attack was observed on the PdlnZn-rich phase. The matrix phase was found to be slightly tarnished. The alloys remained yellow by visual inspection. The agar overlay technique displayed a very slight cytotoxic effect of a sandblasted specimen and no cytotoxic effect of a polished specimen.

Effect of casting atmosphere on the quality of Ti-crowns.

Ti has a strong affinity to elements like O, N, and C. During melting a non-reacting crucible and vacuum and/or Ar-gas protection therefore have to be used. If the impurity content becomes too high, the material turns hard and brittle. In the present work vacuum/Ar-pressure casting of crowns has been carried out at different air pressure levels. Recording of hardness on cross-sections of the castings and the degree of mold filling show that an air pressure level less than 1 torr in the melting chamber and less than 10 torr in the mold chamber is sufficient to obtain sound castings of a small size like a crown.