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At least 37 records · Page 2Linked to original sources
PubMed1994

[Variables effecting casting accuracy of quick heating casting investments].

Recently, several new products of investments for "quick heating" have been put on the Japanese market. The total casting procedure time for this quick heating method involves only one hour; 30-minutes waiting after the start of mixing before placing the mold directly into the 700 degrees C furnace and 30-minutes heating in the furnace. The purpose of this study was to evaluate two variables effecting casting accuracy using these new investments. The effect of thickness of the casting liner inside the casting ring and the effect of waiting time before placing the mold into the 700 degrees C furnace were evaluated. A stainless-steel die with a convergence angle of 8 degrees was employed. Marginal discrepancies of the crown between the wax patterns and castings were measured. The size of the cast crown became larger when the thickness of the ring liner was thick and when the waiting time before placing the mold into the furnace was long. These results suggest that these new investments have the advantage of providing sound castings using short-time casting procedures. However, it is necessary to pay careful attention to the casting conditions for obtaining reproducible castings.

Dental Casting Investment↗
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↗
PubMed2004

Upper extremity pain seen with fly-casting technique: a survey of fly-casting instructors.

OBJECTIVE: To identify the prevalence of upper extremity pain symptoms in fly-casting instructors and examine the association between pain and casting style and equipment. METHODS: We used a cross-sectional survey of a randomly selected group of 577 fly-casting instructor mailing-list members and recorded equipment; casting styles; pain symptoms; and Disability of the Arm, Shoulder, and Hand inventory. We used univariate statistical tests to examine the associations between pain and casters' equipment and styles. RESULTS: In 292 usable surveys, pain was reported in the shoulder (50%), elbow (39%), and wrist (36%) of those surveyed and was characterized as moderate-to-severe by 25% of all respondents. Overhead casting was associated with less frequent wrist and elbow pain than was sidearm or elliptical casting. Respondents who used multiple casting styles had significantly less elbow pain than did single-style casters (7% vs 38% overhead, P = .04: 45% sidearm, P = .02; 71% elliptical, P = .003). Pain was significantly more frequent in those who cast with a haul (75% vs 33%, P = .04), used shooting heads (79% vs 66%, P = .04), or added weight to sinking flies (78% vs 60%, P = .01). Moderate-to-severe pain was more frequent in fishers of heavy saltwater fish. CONCLUSIONS: Upper extremity pain was frequent, but not often severe, in this group of fly-casting instructors. Increased weight on the line and "haul" technique appeared to increase pain symptoms. Modifications in casting style and equipment may help in avoiding or reducing pain.

Animals↗
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↗
PubMed2004

Porosity of cpTi casting with four different casting machines.

STATEMENT OF PROBLEM: Porosity is a well-known problem in dental titanium casting, resulting in inferior mechanical properties of dental restorations. PURPOSE: The aim of this study was to evaluate the porosity of cpTi castings produced with different casting machines. MATERIAL AND METHODS: Four groups of 20 rectangular (30 x 3 x 0.5 mm) wax patterns were fabricated. Group CyII was cast in a CyclarcII casting machine, Group DAM in a Dor-A-Matic, Group TiF in a Titec 201F, and Group ETi in an EasyTi with cpTi, according to manufacturers' instructions. Groups CyII, DAM and TiF were invested with magnesia based Titavest CB and Group ETi with Ticoat S+L silica based investment. The percentage porosity of each specimen was determined using standardized digital radiographs and calculated by quantitative image analysis procedure. The results were statistically analyzed by nonparametric Kruskal-Wallis test (alpha=.05). RESULTS: No statistical differences were found among the groups tested; nevertheless, pore distribution among the specimens of the same group was inhomogeneous. The results show that the casting machines tested produced nonuniform porosity. CONCLUSIONS: Under the conditions of the present study, the type of casting machine does not significantly influence the internal porosity in cpTi castings.

Argon↗
PubMed2003

Serial casting vs combined intervention with botulinum toxin A and serial casting in the treatment of spastic equinus in children.

PURPOSE: Serial casting has been an effective tool used by physical therapists to increase ankle dorsiflexion range of motion and improve functional gait. The purpose of this retrospective study was to determine whether injection with botulinum toxin type A (BtA) before serial casting vs serial casting alone was associated with any changes in (1) the number of weeks necessary to reach the desired dorsiflexion range of motion and (2) the number of degrees of dorsiflexion range of motion gained per week of casting. METHOD: Data were obtained through review of records maintained on patients undergoing serial casting. Thirty subjects comprised the two groups of 15 patients each. One group had received BtA before serial casting while the other group had received no BtA before serial casting. Data were analyzed using two t tests to determine whether there were significant differences, and the appropriate statistical adjustment (Bonferroni) was applied. RESULTS: Fewer weeks were required to reach the goal of 15 to 20 degrees of ankle dorsiflexion (or plateau) for the group receiving BtA than for the group that did not receive BtA. Results also indicated that the group receiving BtA had a significantly greater increase in range of motion per week than the group that received no BtA. CONCLUSIONS: Using serial casting in conjunction with BtA may achieve range of motion goals in less time than serial casting alone.

Journal Article↗
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↗