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At least 55 records · Page 3Linked to original sources
PubMed2006

Experimental binder-free investments reused to cast dental precious alloys.

This study aimed to develop reusable dental investments. SiO2 and MgO were selected as refractory materials to prepare three types of investment (coded as 60S-40M, 80S-20M, 100S) with 40, 20, and 0 wt% of MgO. Each type of investment was reused twice. Thermal expansion and compressive strength were examined and statistically evaluated by ANOVA. To evaluate fit of castings, full crowns were cast by using a commercial Au-Ag-Pd alloy with all investment types. Marginal fit was statistically analyzed by cement thickness. It was found that although MgO strengthened the mold, it had little influence on expansion. The strength of 60S-40M was the highest, and 100S had the greatest advantage with regard to thermal expansion. In the evaluation for clinical applicability, all investments were able to cast successfully, but their castings might be undersized. Among the experimental binder-free investments reused for dental casting in this study, 100S in particular showed to be a good candidate for repeated fabrication of precision fit castings.

Compressive Strength↗
PubMed2003

Gypsum-bonded investment and dental precision casting (II) investment for the quick casting technique.

Part I of this study presented a hypothesis that the thermal expansion of gypsum-bonded investment should become higher under heating conditions favorable for the formation of ahemihydrate. The present study aimed at proving this hypothesis by simulating the rapid heating condition employed in the quick casting technique. The expansion values obtained were 1.72-1.93% after 30 min in three investments, two rapid heating and one conventional types. Under a comparable measuring pressure a common laboratory measurement (5 degrees C/min) gave significantly lower expansions of 1.32-1.36% at 700 degrees C for the same investments (p<0.01). The shrinkage observed at 350-400 degrees C in this measurement was not observed in the rapid heating. Realistically large molds prepared from the conventional gypsum-bonded investment need to be investigated for their potentially high thermal expansion.

Calcium Sulfate↗
PubMed1989

Microscopy analysis of dental titanium casting investment materials.

Scanning electron microscopy (SEM) analysis and qualitative energy dispersive x-ray microanalysis (EDS) of investment materials for dental titanium casting were performed. Two commercial investment materials, Ohara and Castmatic, and an experimental zirconia material were analyzed. The microstructural constituents and the unfired and fired structures were included. Larger refractory particles and matrix embedding smaller particles were observed with each material. Detection of aluminum, silicon, magnesium, zirconium and oxygen provided a basis to reason the presence of alumina (Al2O3), silica (SiO2), magnesia (MgO), and zirconia (ZrO2). Hence, Ohara contained quartz and an alumino-silicate, Castmatic contained magnesia and quartz and experimental zirconia contained zirconia and an alumino-silicate, taken to be kyanite, as components providing refractoriness and expansion. Even though unequivocal detection of phosphorous in the spectra for Ohara was not obtained (P K alpha = 2.013 keV; Zr L alpha = 2.042 keV), an emission peak at 2.0 keV was taken to be due to P and related, along with MgO, to bonding by magnesium phosphate. For Castmatic, unfired strength was thought to be due to calcium chloride and calcium silicate and fired strength to forsterite, (2MgO.SiO2). Detection of calcium and chlorine also suggested bonding of experimental zirconia via calcium chloride. Extensive microcracking occurred around refractory particles and through matrix in experimental zirconia which is likely to have resulted from the firing of kyanite to 1400 degrees C, to the monoclinic to tetragonal transformation of any unstabilized ZrO2, or to the thermal expansion mismatch between kyanite and matrix.

Dental Casting Investment↗
PubMed2003

[Effects of investment materials on cast shrinkage of base metal alloys].

OBJECTIVE: To compare the influence of different investment materials, methods and crown height on the cast shrinkage of full crowns made of dental base metal alloy. METHODS: All of the 288 wax patterns were made and divided into three groups according to their crown height. In every group, wax patterns were invested in metal rings and paper rings with three types investment material and cast with base metal alloys. Then the inside diameters of castings were measured and analyzed by statistical package SPSS. RESULTS: Differences between groups invested with the three types of material were significant(P < 0.01). There were significant difference between the groups investing with metal rings and paper rings(P < 0.01). CONCLUSION: The component of investment material and invested ring can affect the cast shrinkage of dental base metal alloy apparently.

Crowns↗
PubMed1993

Titanium. A review of investments for high temperature casting.

Conventional silica (SiO2) based dental casting investments are used for the casting of pure titanium using casting machines specifically developed for this metal. Highly reactive molten titanium reduces SiO2 and titanium is in turn oxidised. For this reason possible alternatives to SiO2 have been studied in the past decade and MgO and Al2O3 are the most common in current commercial investments released for titanium casting. The surface of titanium castings presents a layered structure and its evaluation in relation to clinical performance requires further study. It is also urgently required to know setting and thermal behaviour of the newly developed investments for successful compensation of metal shrinkage.

Aluminum Oxide↗