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At least 73 records · Page 4Linked to original sources
PubMed1990

[Development of dental quick casting with zircon-phosphoric acid investments].

The application of zircon (ZrSiO4) that has high refractoriness, high thermal conductivity and a low coefficient of thermal expansion, to quick casting investment was studied. Various zircon powders and phosphoric acid solutions were tested with respect to the higher thermal shock resistance. The formulation and properties of zircon-phosphoric acid investment materials such as water/powder ratio, fluidity of slurry, setting time, setting expansion, thermal expansion, thermal analysis, green and fired compressive strength were measured. Formulation of zircon slurry for coating was zircon flower #600 30%, zircon flower #350 10%, and zircon sand CP 60%, and that for sanding was zircon flower #200. The mixing liquid was 15% phosphoric acid and liquid/powder ratio was 0.1. The slurry using phosphoric acid had good fluidity and good workability. The 24-hour green strength was 1 MPa, fired strength was 10 MPa, 24-hour setting expansion was -0.04% and the thermal expansion at 1000 degrees C was 0.31%. Immediately after coating with zircon slurry, the coating layer was dried, sintered and dewaxed by thermal shock. The thermal shock consisted of the following four-step manipulations. The first is hot air drying (50 degrees C, 5 minutes), the second is heat shock (900 degrees C, 3 seconds), the third is redrying (220 degrees C, 3 minutes) and the fourth is dewaxing (550 degrees C, 3 minutes). Small casting of pure titanium and K-metal could be done successfully by the quick casting method using the zircon-phosphoric acid investments. It was found that the total expansion of the secondary investments influenced the casting adapatability.

Dental Casting Investment↗
PubMed2001

Application of laser measuring, numerical simulation and rapid prototyping to titanium dental castings.

OBJECTIVES: This paper describes a method of making titanium dental crowns by means of integrating laser measuring, numerical simulation and rapid prototype (RP) manufacture of wax patterns for the investment casting process. METHODS: Four real tooth crowns (FDI No. 24, 25, 26, 27) were measured by means of 3D laser scanning. The laser digitized geometry of the crowns was processed and converted into standard CAD models in STL format, which is used by RP systems and numerical simulation software. Commercial software (MAGMASOFT) was used to simulate the casting process and optimize the runner and gating system (sprue) design. RP crowns were 'printed' directly on a ModelMaker II 3D Plotting System. A silicone negative mold (soft tool) was made from the RP crowns, then more than hundreds wax crowns were duplicated. The duplicated crowns were joined to the optimized runner and gating system. By using the investment casting process 20-25 replicas of each crown were made on a centrifugal casting machine. All castings were examined for porosity by X-ray radiographs. RESULTS: By using the integrated scanning, simulation, RP pattern and casting procedure, cast crowns, free of porosity, with excellent functional contour and a smooth surface finish, were obtained from the first casting trial. SIGNIFICANCE: The coupling of laser digitizing and RP indicates a potential to replace the traditional 'impression taking and waxing' procedure in dental laboratory, with the quality of the cast titanium prostheses also being improved by using the numerically optimized runner and gating system design.

Calcium Sulfate↗
PubMed2001

Measurement of the setting and thermal expansion of dental investments used for the superplastic forming of dental implant superstructures.

OBJECTIVES: The study examined the setting and thermal expansions of seven dental casting investments intended for use in the superplastic forming (SPF) of Ti6A14V for dental implant superstructures. The total expansion is compared with the coefficient of thermal expansion of the alloy. METHODS: The unrestricted setting expansion of the investment was measured at room temperature using a lined brass trough and dial gauge. The thermal expansion was measured at a heating rate of 5 degrees C/min up to 900 degrees C. The thermal expansion of Ti6A14V was measured at a heating rate of 15 degrees C/min. RESULTS: The Selevest investment had a small shrinkage on setting. The largest setting expansions were observed with Rema Exakt and Fujivest. Selevest DM and Fujivest had the greatest thermal expansions. Rema Exakt had the greatest overall expansion. The total expansion of Rematitan most closely matched the thermal expansion of Ti6A14V when the manufacturer's recommended special liquid to water ratio for crowns and bridges was used. SIGNIFICANCE: SPF is a novel technique which is being applied to the manufacture of dental prostheses. As dental casting investments are used to make the dies used for SPF the dimensional changes associated with these materials should be matched to the dimensional changes of the Ti6A14V alloy used in order to achieve a passive fit. This study has identified Rematitan as an investment whose total expansion may enable an accurately fitting SPF implant superstructure to be made.

Algorithms↗
PubMed1990

Influence of heating rate in thermal expansion of dental phosphate-bonded investment material.

The thermal expansion of a phosphate-bonded investment material was tested when three heating rates were used during the heating procedure. One of them was too low, one too high, and the third, in the middle. The examination was done through the fit of 12 MOD inlays and 12 full crowns in steel master dies. From the results it can be concluded that rates that are too fast must be avoided in the heating procedure, because they reduce the thermal expansion of the phosphate-bonded investment material and thus produce castings with limited fit.

Crowns↗