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PubMedDate not supplied

New die design for dimensional accuracy assessment of crown castings.

PURPOSE: The aim of this study was to introduce a newly designed die for ceramometal restoration, and to compare the dimensional accuracy with the traditional complete-crown design. Two methods of dimensional accuracy assessment, vertical axial discrepancy and transverse diametral percentage, were compared. MATERIALS AND METHODS: Patterns were prepared from two different die designs--complete crown and ceramometal. Two investments available for titanium crown casting were used, Titavest CB and T-invest C & B. Titanium castings were made from each investment with a high-pressure casting machine. Vertical axial discrepancy of casting was determined by measuring the discrepancy for each set of wax patterns and their castings on the same die under a traveling microscope. Dimensional accuracy was expressed as vertical axial discrepancy and by transforming the vertical axial discrepancy into transverse diametral percentage. RESULTS: Both dies produced undersized castings with T-invest C & B and oversized castings with Titavest CB. Dimensional accuracy assessment of the two different types of crown casting design showed no significant difference in vertical axial discrepancy. CONCLUSION: Compared to the traditional transverse diametral percentage calculation, the vertical axial discrepancy assessment is independent of the die's dimensions. The two types of investment materials studied resulted in castings with different dimensional accuracies.

Crowns↗
PubMed1989

[Casting of pure titanium and high fusing dental alloys by experimental casting machine. 7. Casting procedure for pure titanium denture frame].

The pure titanium cast frameworks were made using an arc-melting pressure and vacuum casting apparatus invented by Sato, and an experimental investment material. The salient features of the method and the cast frameworks were as follows: 1. The casting apparatus used was capable of making both complete and partial denture frameworks with pure titanium. It reduced casting errors and the interaction between titanium and the casting mold, producing less porous casted frameworks with a smooth surface. 2. The experimental investment material made a firm heat-resistant investment model with a smooth surface. It showed appropriate expansion and also excellent strength at room temperature after the burn out of the wax pattern. 3. The titanium casted frameworks fitted to the model and the oral cavity closely, and yielded satisfactory clinical results in more than 15 patients.

Dental Casting Investment↗
PubMed1994

Post-and-core assemblies made with an accelerated pattern elimination technique.

PURPOSE: Accelerated pattern elimination has the potential for increasing productivity. This study evaluated the accelerated pattern elimination technique using three commonly used phosphate-bonded investments. MATERIALS AND METHODS: Part one of this study determined the mean time interval from start of mixing to the maximum exothermic setting reaction temperature for each investment. A chromel/alumel thermocouple was placed at the heat center of a methylcellulose lined casting ring, using wet or dry ring liner. Investments were vacuum mixed at the recommended ratio for the accelerated technique. Colloidal silica solution and ddH2O were combined at a 50:50 ratio to meet the manufacturer's recommended liquid volume. Part two determined the dimensional reproduction of a standardized pattern and its casting using both casting techniques. Mixing ratios were the same as in part one for the accelerated technique and 75% colloidal silica to 25% double-distilled water (ddH2O) for the conventional technique. The accelerated technique used the mean setting time established in part one followed by a 15-minute furnace holding time at 725 degrees C (1350 degrees F). The conventional technique used a 1-hour bench setting time, followed by placing the mold into a cold furnace. A controlled rate of climb to a maximum temperature of 725 degrees C (1350 degrees F) was used with a 1-hour soak time. Each pattern and its casting were measured at four sites: (1) Length of the post-and-core assembly, (2) maximum core diameter, (3) post diameter at the core base, and (4) post diameter at its apex. RESULTS: A significant difference was found between the time interval to maximum exothermic setting reaction temperature for all the investments (P < .01). The accelerated technique produced castings with a relative dimensional increase of 0.11% to 4.80%. The conventional technique ranged from a 0.04% decrease in size to an increase of 3.65%. Castings made with the accelerated technique were significantly different than those made with the conventional technique (P < .01). CONCLUSIONS: Differences in the time interval to maximum exothermic setting reaction temperature indicate that each phosphate investment should have a recommended setting time before introduction into the furnace. The carbon-containing investment showed the least relative change of the three investments evaluated for both casting techniques.

Analysis of Variance↗
PubMed1992

Use of plastic bar molded casting in the modification of variably expanding investment to compensate for casting shrinkage of nickel-chromium alloy.

Trial plastic bar molded castings were compared for accuracy with cast crowns by means of a nickel-chromium alloy, which was used to establish the liquid density of variably expanding investments. The plastic bars were invested to evaluate the change of expansion rate in a wide range of six liquid densities from 0% to 100%, and the distances between the sections were measured before and after casting. Wax crowns were cast to obtain a more detailed relation around 0% expansion at seven liquid densities, and the gaps between the base of the die and the margin of the crown were measured before and after casting. The expansion rates of both castings were calculated and thus were proportional to the liquid density; both regression curves indicated high correlation coefficients. As a result of the statistics of the Student's t-test, the difference between the two methods was not significant. The trial plastic bar was useful in establishing the variably expanding investment for precise casting of artificial crowns.

Chromium Alloys↗
PubMed1993

Influence of mold materials and heat treatment on tensile properties of Ni-Ti alloy castings.

The influence of mold materials and heat treatment on the tensile properties and the transformation temperatures of Ni-Ti alloy castings was investigated by tensile test and differential scanning calorimetry (DSC) in order to apply the special properties of the alloy to dental field. The compositions of the two alloys examined were 49.0 and 49.2 at % Ti. A silica investment and a magnesia investment were used as the mold materials. Heat treatment at 440 degrees C for 1.8 ks was performed. Apparent proof strength decreased in both compositions, and residual strain increased in Ni-49.2Ti by the heat treatment. Elongation increased in Ni-49.0Ti with use of the magnesia mold or by the heat treatment. The transformation temperatures of Ni-49.2Ti increased with use of the magnesia mold. The change by the heat treatment suggested a structural change. The development of a suitable method for the casting of the alloy is expected to bring about the development of new devices and therapy in dentistry.

Calorimetry, Differential Scanning↗
PubMed1983

Casting accuracy of base metal alloys.

The effect of investment material on the casting accuracy of five base metal alloys was evaluated. Overall, the fit of the test castings was poor. Individual alloy-investment interaction appears to be significant. Although marketed for use with base metal alloys, it appears that investment manufacturers' recommended techniques require alteration to enhance the fit of base metal restorations.

Dental Alloys↗
PubMed1980

Evaluation of three variables affecting the casting of base metal alloys.

All the vented samples with sprue widths of 2 mm or more were defect free, whereas the corresponding unvented samples had extensive voids and porosity in all but one casting. All castings with a sprue width of 1 mm were defective regardless of whether or not vents were used. The thickness of the investment above the pattern had no effect on casting results.

Dental Alloys↗
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↗
PubMed1991

Dimensional accuracy of small gold alloy castings. Part 1. A brief history and the behaviour of inlay waxes.

Part 1 reviews published studies which relate to materials and techniques contributing to the dimensional accuracy of small dental castings. A brief history of the cire perdue or lost-wax method of casting alloys and the development of modern dental casting materials and techniques are presented. Data on the behaviour of inlay wax, in particular its contraction and distortion, are reviewed as is the extensive literature about the casting shrinkage of gold alloys (Part 2) and the setting and thermal expansion of investments under both laboratory and practical conditions (Part 3). Part 4 discusses the role of the casting ring and its asbestos liner. Asbestos as a liner has now largely been replaced by two alternative materials, one based on cellulose and the other on ceramic fibres. The limited literature on the effect of these newer materials on casting accuracy is also reviewed, as their introduction may require significant changes in the traditional technology of dental casting.

Dental Casting Investment↗