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At least 109 records · Page 6Linked to original sources
PubMed1997

Stabilization investment template for direct casting connection of implant framework segments.

This article presents a procedure whereby a template made of casting investment is used to stabilize a sectioned implant framework that has been adapted in a passive relationship to the implant analogs in a corrected master cast. The joints in the sectioned framework are filled with wax, sprues attached, and the template and sectioned framework are invested in a casting ring. When the casting procedure is completed, the framework will be reconnected by direct metal casting.

Dental Casting Investment↗
PubMed1989

Layered structure of cast titanium surface.

The present study concerns the surface layered structure of the cast Ti. A commercial Ti was cast into a mold which was made of a phosphate-bonded Al2O3/SiO2 investment. Elemental analyses of the interfacial zone of the casting were made under an electron probe micro-analyzer. The interfacial zone was composed of four layers: the outermost reaction or casting burn layer, the second layer of an O-and Al-stabilized alpha case, the third layer in which Si, P, O, and C were inhomogeneously concentrated, and the fourth layer which consisted of acicular or plate-like crystals. It was observed that the larger the cast volume and the higher the mold temperature, the thicker became each layer and the coarser became the acicular grains. Probably, the layered structure was formed through decomposition of reducible species in the burnout investment and diffusion of the resulting elements into the casting.

Dental Casting Investment↗
PubMed1998

Stress-strain and thermal expansion characteristics of a phosphate-bonded investment mould material for dental super plastic forming.

OBJECTIVES: The stress-strain and thermal expansion characteristics of a phosphate-bonded investment material were measured to determine its suitability as a die material for superplastic forming of dental appliances. Titanium alloy denture bases and implant superstructures have been fabricated successfully using this investment material, but a greater understanding of its properties was sought to optimize the forming technique before exploitation could proceed. The effect of a boron nitride powder on the properties of phosphate-bonded investment was also investigated. METHODS: Three-point bend test specimens were cast in the phosphate-bonded investment material. Four groups of test samples were produced at specified water-to-powder ratios (w/p ratios). For one group 5 wt.% boron nitride powder was added to the investment powder before mixing with water. For stress-strain measurements specimens were heated to 920 degrees C and held for 30 min prior to the application of load. For thermal expansion measurements specimen length was measured for the entire heating and cooling cycle. RESULTS: Curves of stress versus strain and thermal expansion were recorded for all four test groups. For increasing initial w/p ratio failure stress decreased with lowest failure stresses for specimens containing boron nitride. Strain to failure also decreased with increasing initial w/p ratio, except for the group containing boron nitride which showed relatively large elongations to fracture. Specimen surfaces with higher initial w/p ratios were observed to have larger surface porosity. Thermal expansion curves for three groups were very similar, but differed considerably from the group containing boron nitride. CONCLUSIONS: The lowest initial w/p ratio should be used for highest hot strength. Hot deformation of phosphate-bonded investment dies for superplastic forming is an issue that requires further investigation because of potential die deformation and the resulting loss of fit between the superplastic superstructure and implant components. Boron nitride could be used in phosphate-bonded investment to decrease thermal expansion, but the consequences of reduced hot strength and increased strain to failure may make the modified material unsuitable as a die for superplastic forming.

Alloys↗
PubMed1990

[Comparison of investment expansion methods aspect of porosity].

Currently, the use of non-precious metal alloys in fixed prosthetic restorations has warranted review of the work done sofar using precious metal alloys. One of the parameters exhibiting the success of castings done using non-precious metal alloys is porosity, which is evaluated through such methods as rod forms, waxing heat, to investing and other castability methods. The porosity ratios of cats similarly done employing different investment expansion methods have been evaluated. While there is no statistical difference due to different methods, the hygroscopic expansion method noted successful results.

Dental Alloys↗
PubMed2002

Titanium casting into phosphate bonded investment with zirconite.

OBJECTIVE: Reaction layer structure of the titanium castings surface was investigated when a new centrifuge-vacuum-pressure cast titanium machine and a zirconite inner investment was used. METHODS: The micro-hardness of titanium castings was measured using a Knoop's hardness tester. The structure of reaction layers and the distribution of elements on the surfaces of titanium castings were analysed by SEM and EDS, respectively, when zirconite was used as the inner investment for cast titanium. RESULTS: Knoop's micro-hardness at distances of 50 and 75 microm from the titanium casting surfaces made directly in phosphate investment molds had significantly harder surfaces than those made in zirconite coating molds. The thickness of the reaction layer on the surface of titanium castings was <35 microm with zirconite coating and was >50 microm without zirconite coating. The structure of reaction layer was divided into four layers from the outer surface to the inner including: sintering layer, alpha-Case, Si-rich layer, acicular crystal structure. The distribution of elements was different on each layer. SIGNIFICANCE: The thickness of the cast titanium reaction layer was reduced when the wax patterns were coated with zirconite. The surface of the titanium castings was smooth and without cracks, and the investment on the surface of titanium castings was easily removed.

Dental Casting Investment↗
PubMed1992

The fit of gold-alloy full-crown castings made with pre-wetted casting ring liners.

Measurements were made of the fit of full-crown gold-alloy castings produced with two types of pre-wetted ring liner (asbestos and cellulose) and a typical gypsum-bonded investment (Cristobalite Inlay, Sybron/Kerr Products, Romulus, MI; W/P = 0.40). Laboratory measurements were made of the effects of the liners on potential investment expansion, and properties of the lining materials considered relevant to casting accuracy were also measured. There was a wide variation in values for mean dimensional inaccuracy. One liner produced a series of castings all of whose inaccuracies lay within the range +/- 0.1%, with a mean value of + 0.01%. With the other five liners, all or most castings were undersize. With three, all or most castings showed inaccuracies worse than -0.2%. The values for casting inaccuracy with the various liners showed a probable correlation with potential investment expansion (p < 0.05); however, no correlation was found between casting inaccuracy and any apparently relevant liner properties, alone or in combination. In casting techniques which use a pre-wetted ring liner, the choice of a specific lining material is an important factor which has a significant effect on casting inaccuracy. With at least three of the six liners tested, a higher investment expansion was needed for accurate full-crown castings to be ensured.

Absorption↗
PubMed2003

[The study of compressive strength of phosphate-bonded investment materials].

OBJECTIVE: The purpose of this study was to compare the compressive strength of phosphate-bonded investments. METHODS: The three sorts of investments were mixed according to manufacturer's recommendation before poured in the molds. After heated up to 900 degrees C, every sample was mounted on a universal experimental machine to test its compressive strength in ambient. RESULTS: Significant differences were found between the four groups(P < 0.01). CONCLUSION: From the data above it is concluded that the compressive strength of X-20 Chrome Investment mixed with the special liquid was the highest.

Compressive Strength↗
PubMed1992

The fit of gold-alloy full-crown castings made with ceramic casting ring liners.

Measurements were made of the fit of gold-alloy full-crown castings produced with dry ceramic ring liners. When used with vacuum investing, these liners absorb relatively large amounts of water from the investment mix (thereby reducing its original W/P ratio) and then function as wet liners, thus increasing the investment's potential expansion and giving castings which are consistently larger than when air investing is used. With four of the five liners tested, investing in air produced many castings which were unacceptably undersized (inaccuracy worse than -0.2%). The fifth liner, an industrial material 2 mm thick, gave only one casting out of 12 which was outside this limit, although all castings were undersized to a lesser extent. Vacuum investing gave improved casting accuracy; with four of the five liners, the improvement was highly significant (p < 0.001), and with the fifth, probably significant (p < 0.05). Even with vacuum investing, however, with only two of the liners did all castings show inaccuracies within +/- 0.2%. With the other three liners, some castings (ranging from 2/10 to 7/9) had inaccuracies worse than -0.2%. With both air and vacuum investing, changing from one liner to another caused changes in relative casting accuracy which were often significant (p < 0.01) or highly significant (p < 0.001). In casting techniques where a ceramic ring liner is used, the choice of specific lining material and the choice between investing in air or under vacuum are important factors which can have a major effect on the fit of castings.

Absorption↗
PubMed2000

Study of resin-bonded calcia investment: Part 1. Setting time and compressive strength.

This study was carried out to develop a new titanium casting investment consisting of calcia as the refractory material and a cold-curing resin system as the binder. The setting time of the investment was investigated under different N,N-dimethyl-p-toluidine (DMPT) contents in methyl methacrylate monomer (MMA) and benzoyl peroxide (BPO) contents in calcia without any sintering agent. The effects of the sintering agents, which were calcium fluoride (CaF2) and calcium chloride (CaCl2), on the compressive strength of the investments were investigated at room temperature before and after heating to two different temperatures. The shortest setting time (68 minutes) of the investment was obtained at 0.37 DMPT/BPO (1.5 vol% /1.0 mass%) ratio by mass. The highest strength (16.5 MPa) was obtained from the investment which contained 2 mass% CaF2 and was heated to 1,100 degrees C. It was found that the developed calcia investment containing 2 mass% CaF2 has a possibility for use in titanium castings.

Alloys↗
PubMed2004

Study of resin-bonded calcia investment. Part 3: Hardness of titanium castings.

The Vickers hardness of the cross-sectioned area of titanium castings made from an experimental resin-bonded calcia investment and three commercial investments was evaluated. The microstructure and element distribution of the surface zone were analyzed using an EPMA. The results showed that the high hardness of the casting surface could be decreased using the experimental investment. The hardness of the castings made from the experimental investment at a 25-50 microm depth was lower than those from the other investments, and the thickness of the hardened casting surface was 125 microm. Layered structures with fewer layers were formed on the surfaces of the castings made from the experimental investment. The layered structures were influenced by both the investment components and the mold temperature at casting. The less contaminating nature of the experimental investment components and the technology of the room temperature mold contributed to the improved surface properties of the resulting castings.

Calcium Compounds↗
PubMed1982

Effect of casting methods on accuracy of peridental restorations.

The present study has shown that the accuracy of peridental gold alloy castings depends 1) on the type of casting machine used, 2) on the diameter of the casting sprue, and 3) on the strength properties of the investment material. The dependence between the accuracy and the three factors mentioned is based on erosion of the investment mold by the inflow of the liquid casting alloy. The vacuum casting technique proved to be a more gentle casting method than centrifugal and vacuum/pressure techniques.

Chemical Phenomena↗
PubMed2002

Effect of a new tension system, used in acrylic resin flasking, on the dimensional stability of denture bases.

STATEMENT OF PROBLEM: The pressure of final closure may be released when the flask is removed from the mechanical or pneumatic press and placed in the spring clamp. This release in pressure may result in dimensional changes that distort the denture base. PURPOSE: The purpose of this study was to investigate differences between the dimensional stability of standardized simulated denture bases processed by traditional moist heat-polymerization and those processed by use of a new tension system. MATERIAL AND METHODS: A metal master die was fabricated to simulate an edentulous maxillary arch without irregularities in the alveolar ridge walls. A silicone mold of this metallic die was prepared, and 40 stone casts were formed from the mold with type III dental stone. The casts were randomly assigned to 4 test groups (A-D) of 10 specimens each. A uniform denture base pattern was made on each stone cast with a 1.5-mm thickness of base-plate wax, measured with a caliper. The patterns were invested for traditional hot water processing. A polymethyl methacrylate dough was prepared and packed for processing. The flasks in groups A and B were closed with the traditional pressure technique and placed in spring clamps after final closure. The flasks in groups C and D were pressed between the metallic plates of the new tension system after the final closure. The group A and C flasks were immediately immersed in the water processing unit at room temperature (25 degrees +/- 2 degrees C). The unit was programmed to raise the temperature to 74 degrees C over 1 hour, and then maintained the temperature at 74 degrees C for 8 hours. The group B and D flasks were bench stored at room temperature (25 degrees +/- 2 degrees C) for 6 hours and were then subjected to the same moist heat polymerization conditions as groups A and C. All processed dentures were bench cooled for 3 hours. After recovery from the flasks, the base-cast sets were transversally sectioned into 3 parts (corresponding to 3 zones): (1) distal of the canines, (2) mesial of the first molars, and (3) mesial of the posterior palate). These areas had been previously established and standardized by use of a pattern denture in the sawing device to determine the sections in each base-cast set. Base-cast gaps were measured at 5 predetermined points on each section with an optical micrometer that had a tolerance of 0.001 mm. Collected data were analyzed with analysis of variance and Tukey's test. RESULTS: Denture bases processed with the new tension system exhibited significantly better base adaptation than those processed with traditional acrylic resin packing. Immediately after polymerization (Groups A and C), mean dimensional change values were 0.213 +/- 0.055 mm for the traditional packing technique and 0.173 +/- 0.050 mm for new tension system. After delayed polymerization (Groups B and D), the values were 0.216 +/- 0.074 mm for the traditional packing technique and 0.164 +/- 0.032 mm for new tension system. With both techniques, dimensional changes in the posterior palatal zone were greater (conventional = 0.286 +/- 0.038 mm; new system = 0.214 +/- 0.024 mm) than those elsewhere on the base-cast set. CONCLUSION: Within the limitations of this study, the new tension packing system was associated with decreased dimensional changes in the simulated maxillary denture bases processed with heat-polymerization.

Acrylic Resins↗
PubMedDate not supplied

The effect of five investing techniques on air bubble entrapment and casting nodules.

Five different investing techniques were used to invest lost-wax casting patterns. The use of an investing technique that subjects the invested casting ring to air pressure (40 lb per square inch) during setting was found to produce less air bubble/cast nodule incidence than did the other four techniques investigated. Not all cast nodules can be seen by the unaided eye; magnification is needed. More cast nodules than air bubbles were seen at the interface of pattern and investment, showing that there may be many air bubbles below the investment surface that are entered by the incoming alloy during casting. The effect of a surface-tension reducing (STR) agent on the air bubble incidence between pattern and investment depends on the investing technique used, although all techniques used showed a reduction in cast nodule incidence when an STR agent was used. Sprue direction was also found to influence the incidence of casting nodules.

Air↗
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↗
PubMedDate not supplied

The evaluation of factors affecting the castability of metal ceramic alloy--investment combinations.

An evaluation of the castability of metal ceramic alloy-investment combinations using a mesh test and utilizing a factorial design concept has shown that different metal ceramic alloys (gold-based, palladium-based, and nickel-chromium-based alloys) react differently, as far as castability is concerned, to various factors involved in the casting process. These factors were divided into two groups: procedural factors, that included sprue diameter, investing technique, and melting and casting method; and operator factors, which included alloy casting temperature, mould temperature, and heat-soak times. Each of these factors had two or three levels.

Chromium Alloys↗