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At least 37 records · Page 2Linked to original sources
PubMed1977

[Studies on the contract of the casting. (II) Influence of core inside the cast (author's transl)].

A alloy has its constant coefficient of casting shrinkage, but its value is changed by casting conditions. This time, we studied with effect of core which exist inside the cast. The results obtained were as follows: 1. The more the strength of core material increases, the smaller the coefficient of casting shrinkage becomes. 2. The smaller the thermal expansion coefficient of core material in solid state, the smaller the casting shrinkage. 3. In case of Silver-Palladium-Gold casting alloy, its actual casting shrinkage (y) has a multiple correlation with the compressive strength (x1) of core material in high temperature, and with the difference (x2) of the original casting shrinkage of the alloy from the casting shrinkage of core material, that is, y = -0.0023x1 + 0.0087x2 + 1.4927 4. Silver-Indium casting alloy is hard to be influenced by the quality of core material, for the alloy has a small shrinkage force.

Dental Alloys↗
PubMed1990

[Determination of copper alloy hardness, in original form and after casting as a function of casting techniques].

It was evaluated the Vickers hardness of five high-copper casting alloys, in their original package form and after casting, according to the casting method used. That way, ten ingots, supplied by the manufacturers of each alloy, were included in self-curing acrylic resin, polished, numerated and submitted to Vickers hardness test at load of 200 g during 30 seconds. Afterwards the numerated ingots were removed from the acrylic resin and five of those were cast in an electrical casting machine and the other five in a centrifugal casting machine with an air/gas torch. The specimens obtained were included in self-curing acrylic resin, polished and submitted to Vickers hardness test. As a result it was verified that there is a variation of hardness among the alloys tested, and the use of the electrical casting machine produced lower hardness values than those produced when used the centrifugal casting machine with an air/gas torch. Also, there is a decrease of hardness of the cast alloys when they are tested in their original form and after casting.

Copper↗
PubMed2002

Laser digitization of casts to determine the effect of tray selection and cast formation technique on accuracy.

UNLABELLED: STATEMENT OF PROBLEM; Several studies have attempted to determine the ideal combination of dental materials and laboratory techniques to produce the most accurate dental cast. Most have made use of 2-dimensional manual measuring devices, which neglect to account for the dimensional changes that exist along a 3-dimensional surface. PURPOSE: The purpose of this study was to determine the effect of impression tray selection and cast formation techniques on the dimensional change of a dental cast with the use of new, 3-dimensional optical digitizing technology. MATERIAL AND METHODS: Multiple impressions of a machined steel die that resembled a dental arch were made with custom and stock impression trays and vinyl polysiloxane impression material. The impressions were poured in type V artificial dental stone and allowed to set with the tray inverted or noninverted. The steel master die and stone casts were digitized with the Steinbichler Comet 100 Optical Digitizer, which was developed at the Minnesota Dental Research Center for Biomaterials and Biomechanics. Three-dimensional images of the stone casts were aligned to the 3-dimensional image of the master die and analyzed with AnSur-NT software. Multiple measurements of the master die and stone casts were analyzed to determine the accuracy of the 3-dimensional technology and of the impression and cast fabrication techniques. Planar distances between the center of each crown preparation were measured, as were crown heights. Data were analyzed with analysis of variance (P<.05), and root mean square error values were determined. RESULTS: Casts were compared with a total of 45 significance tests, of which only 4 yielded P<.05. There was no pattern to these results, which suggests that they were false-positive findings. CONCLUSION: Results obtained with the use of new optical digitizing technology indicated that neither impression tray type nor cast formation technique affected the accuracy of final casts.

Analysis of Variance↗
PubMed2002

Cast articulation accuracy using rigid cast stabilization.

PURPOSE: This study evaluated the positional accuracy of casts articulated on a semi-adjustable articulator, with and without rigid cast stabilization using either laboratory plaster or mounting plaster. MATERIALS AND METHODS: A reference articulation of melamine casts in maximum articulation was established and recorded in the horizontal and vertical dimensions using a verification device. The same casts were subsequently remounted 24 times using either laboratory plaster or mounting plaster. Half of the articulations from each group were stabilized using detachable mounting rods and sticky wax, and half were hand-articulated without stabilization, for a total of 6 articulations in each of 4 test groups. The resulting spatial positions established on the articulator were compared to the initial reference position on the verification device grid. Means and standard deviations of the absolute values of the horizontal and vertical displacement for each group were determined separately and compared using a one-way anaylsis of variance. Significant differences (p <0.05) were identified using Tukey's honestly significant difference multiple comparison test. RESULTS: Mean vertical mandibular cast displacement ranged from 0.26 +/-0.21mm for stabilized casts mounted with laboratory plaster to 1.58 +/-0.32 mm for unstabilized casts mounted with mounting plaster. For each mounting material, significantly less vertical displacement (p <0.001) was observed with the mandibular cast stabilized before mounting. The cast mounted with laboratory plaster exhibited horizontal displacement (0.87 +/-0.29 mm) that was significantly greater than the remaining groups (p <0.001), which did not differ from each other. CONCLUSIONS: Rigid stabilization of the mandibular to maxillary cast during mounting with laboratory and mounting plaster improved articulation accuracy.

Analysis of Variance↗
PubMed1995

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.

Alloys↗
PubMed2001

Titanium casting: the surface reaction layer of castings obtained using ultra-low-temperature molds.

To examine whether the surface reaction layer of titanium castings can be reduced by lowering the mold temperature during casting, we cast titanium at three mold temperatures, including an ultra-low temperature produced by cooling the mold with liquid nitrogen, then measured the tensile strength and elongation of the castings. The titanium was cast using a centrifugal casting machine, and the molds were incinerated according to the manufacturers' instructions. Castings were then made with the molds at 200 degrees C, 600 degrees C, and an ultra-low temperature (-196 degrees C). The castability of titanium cast in the mold at the ultra-low temperature was good. The Vickers hardness near the surface layer of castings decreased as the mold temperature decreased.

Cold Temperature↗
PubMed1981

Inner surface roughness of complete cast crowns made by centrifugal casting machines.

Six variables that could affect the surface roughness of a casting were investigated. The variables were (1) type of alloy, (2) mold temperature, (3) metal casting temperature, (4) casting machine, (5) sandblasting, and (6) location of each section. It was determined that the training portion of a complete cast crown had rougher surfaces than the leading portion. Higher mold and casting temperatures produced rougher castings, and this effect was more pronounced in the case of the base metal alloy. Sandblasting reduced the roughness, but produced scratched surfaces. Sandblasting had a more pronounced affect on the surface roughness of the base metal alloy cast either at a higher mold temperature or metal casting temperature. The morphology and the roughness profile of the original cast surface differed considerably with the type of alloy used.

Crowns↗
PubMed1976

[Studies on the contract of the casting. (I). Influence of casting condition (author's transl)].

A study was made of the contraction of the Silver-Indium alloy due to the difference of the casting condition, by mean of the quartz pipe, whose thermal-expansion coefficient was very small. The results were as follows. 1) The higher the mold temperature, the smaller the casting shrinkage. 2) When the casting pressure was extremely low the casting shrinkage was great. But if the casting pressure was over 0.16 kg/cm2, the casting shrinkage didn't change. 3) The bigger the sprue size, the smaller the casting shrinkage. 4) The casting temperature of the alloy, the cooling system, the amount of the metal and the form of the wax pattern showed that the casting shrinkage remain the same.

Dental Alloys↗
PubMed1996

The accuracy of implant verification casts compared with casts produced from a rigid transfer coping technique.

PURPOSE: Prosthodontic techniques for implant-supported prostheses continue to evolve in an effort to facilitate treatment and minimize costs. Because research has shown no impression transfer technique to be without error, some clinicians have attempted to control the fit of prosthetic frameworks by reorienting sections of patterns or frameworks intraorally, fabricating a verification cast, and completing the prosthesis to fit such a cast. One manufacturer has attempted to meet both impression-making and verification-cast objectives by providing metallic impression copings (MICS) with extensions that allow contact between the copings for rigid fixation with acrylic resin before impression making. The purpose of this study was to determine the accuracy of casts produced from the MICS transfer process compared with casts produced from sectioned frameworks, where both techniques used a low-polymerization-shrinkage acrylic resin polymer to rigidly join the sections. MATERIALS AND METHODS: Using stainless steel measurement spheres as a reference point on each implant analog, the distances between analogs on the experimental casts were compared with the distances measured on the master cast. Seven casts were produced for each group and measured with a machinist's microscope at a 4-micron level of precision. RESULTS: The results revealed that the MICS transfer exhibited a mean error of 41 microns, which was significantly less than the verification-cast group mean error of 57 microns (p < .01, Student's t test). CONCLUSIONS: Given these results, clinicians can consider the rigid transfer technique as provided in the MICS transfer to be more accurate than the verification technique as outlined in this study.

Analysis of Variance↗
PubMed1982

[The cushion ability of lining materials for the setting and heating expansion of plaster bonded investment in casting ring. Part I: For casting mold cavity of inlay type (author's transl)].

We measured the dimensional change of mold cavity in casting ring and casting accuracy for inlay type casting using two kinds of lining materials in various conditions. These lining materials were asbestos ribbon and ceramic fiber. In the comparison of cushion ability for the expansion of investment in casting ring of these two lining materials, following results were obtained. 1. Compressibility of ceramic fiber was twice as much as asbestos. And, two sheets of ceramic fiber ribbons had enough ability for free expansion of investment in casting ring. 2. More than two sheets of asbestos ribbons in dry state had the ability of compensation for casting shrinkage in heating process. 3. Asbestos ribbon in wet state made a setting expansion of investment larger, but had not any ability of cushion for heating expansion of investment. 4. If the cushion ability of lining materials was not enough, the mold cavity shrank. The order of this shrinking inclination were no lining material state, two sheets, one sheet of wet asbestos, and one sheet of dry asbestos. 5. This shrinking inclination of smaller cavity was greater than that of larger cavity. That meant that the larger thickness of investment in ring made this shrinking inclination greater. 6. In case of without mold cavity, the heating expansion of the investment toward the casting ring were same value at any position in casting ring.

Chemical Phenomena↗
PubMed1989

Dental casting of titanium and Ni-Ti alloys by a new casting machine.

The purpose of this study was to develop a new casting machine for titanium and Ni-Ti alloys. Properties of cast pure titanium and Ni-Ti alloys were studied by means of the tensile and casting tests. As gas in the mold was removed by the mold being heated under a high vacuum, the reaction between the molten metal and the mold decreased. The new control system and the two types of crucibles developed proved very useful for prevention of internal macro-defects in castings and for improvement of castability. Mechanical properties and castability of pure titanium were improved. Ni-Ti alloys could be cast without loss of their shape-memory effect or super-elasticity characteristics. The new casting machine is thought to be promising for the casting of titanium and Ni-Ti alloys. Furthermore, we can cast these alloys using conventional techniques and investments.

Dental Alloys↗
PubMed1996

Analysis of cryotherapy penetration: a comparison of the plaster cast, synthetic cast, Ace wrap dressing, and Robert-Jones dressing.

Four groups were studied to determine the cooling effect at skin level of ice application over common ankle bandages and casts. The plaster cast, synthetic cast, and Ace wrap dressing groups had 18 participants and the Robert-Jones dressing group had four participants. In a standardized fashion, ice bags were applied over each bandage or cast and skin temperatures were measured with a thermocouple over a 90-min period. The average final skin temperature was 16.5 degrees in the plaster cast, 18.8 degrees in the synthetic cast, 21.2 degrees in the Ace wrap dressing, and 28.7 degrees in the Robert-Jones dressing. The temperature curves showed that ice application effectively decreased skin temperatures through the plaster cast, synthetic cast, and Ace wrap dressing. The cooler temperature did not adequately penetrate the Robert-Jones dressing.

Adult↗
PubMed1992

Evaluation of the dermal effects of cast padding in coaptation casts on dogs.

Three configurations of cast padding and no cast padding were evaluated for their effects on skin in dogs. Padding was placed over bony prominences, between bony prominences, and over both areas for full-length padding under short-limb walking casts applied to 1 pelvic limb of Greyhounds. Evaluations were performed by pressure measurement over the calcaneal tuberosity, measurement of skin thromboxane B2 (TxB2) concentrations in skin over bony prominences, and measurement of plasma TxB2 concentrations. Pressure studies were performed to evaluate cutaneous pressures related to no cast padding and various configurations of cast padding. Concentrations of TxB2 in the skin were determined to evaluate the skin inflammatory effects of no padding and the padding configurations, and TxB2 concentrations in the plasma were analyzed to ascertain whether they could be used to predict impending dermal pressure lesions. Flexion of casted limbs revealed the greatest pressure over the calcaneal tuberosity with full-length cast padding. This was followed in decreasing order by no cast padding, padding over the prominences, and padding between the prominences. Compared with all other bony prominences and padding configurations, TxB2 skin concentrations were significantly higher over the calcaneal tuberosity when no padding was used and over the lateral base of metatarsal V when padding was placed between the prominences. Over the calcaneal tuberosity, this was attributed to the sharpness of the prominence and its potential for movement. This high TxB2 concentration corresponded to the high pressure found in the pressure studies. Over the lateral base of metatarsal V, the increase in TxB2 concentration was related to the mass of the prominence and the tendency for localized padding to settle around the area.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

In vitro determination of equine third metacarpal bone unloading, using a full limb cast and a walking cast.

OBJECTIVE: To improve fracture treatment, in vitro experiments were performed to study the influence of a full limb cast and a walking cast on the loading regimen of bones in the distal portion of the equine forelimb. ANIMALS: 6 forelimbs of 6 Shetland ponies. PROCEDURE: Loading of the third metacarpal bone was considered a representative measure for distal limb loading. Electrical resistance rosette strain gauges were attached to the dorsal, palmar, medial, and lateral surfaces of the midshaft of this bone in 6 forelimbs of 6 Shetland ponies. The limbs were tested in a pneumatic loading device to a maximal load of 1,500 N. RESULTS: Both casts decreased the amount of compressive forces acting on the metacarpal bone. Application of a full limb cast resulted in a variable and eccentric decrease, remaining strains ranging from 84 to 7% of the baseline value. A walking cast was superior in that it gave a centric and more uniform reduction of compressive loading to < 11% of the baseline value. Moreover, a walking cast neutralized the bending and torsion components of the loading. CONCLUSION: This study confirmed the clinical experience that a walking cast creates more reliable and favorable conditions for healing of fractures than does a full limb cast.

Animals↗