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Results for “DENTAL CASTING INVESTMENT”

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At least 19 recordsLinked to original sources
PubMed1985

Internal setting expansion of a dental casting investment measured with strain gauges.

A study was undertaken to investigate the feasibility of using strain gauges to evaluate the internal setting expansion of dental casting investments. A strain gauge was invested in the center of a casting ring to determine the linear setting expansion at the site of the wax pattern. The findings suggest that strain gauges can be used to measure setting expansion internally more accurately than volumetric or external surface measurement techniques. It was also found that winged strain gauges were more stable in the investment than wingless strain gauges.

Chemical Phenomena↗
PubMed2006

(31)P solid-state MAS-NMR spectroscopy of the compounds that form in phosphate-bonded dental casting investment materials during setting.

OBJECTIVES: To use (31)P solid-state MAS-NMR to determine which compounds form in phosphate-bonded dental casting investment material during setting, when the ambient temperature is altered. To determine whether they differ in material originating at the center of the mix from material that adheres to the mixing bowl wall. METHODS: (1)H high powered decoupled (HPDC) and (1)H cross polarized (CP) (31)P solid-state MAS-NMR spectroscopy were used at a resonance frequency of 121.4MHz to determine molecular structure. Four commercial products were examined. Manufacturer's instructions were followed and special liquid used without dilution. Ambient temperature was between 18 and 37 degrees C. RESULTS: Molecular structures change with ambient temperature and product. Amorphous Mg(3)(PO(4))(2) or struvite dominate with newberyite, cattiite, amorphous Mg(2)P(2)O(7) and amorphous MgHPO(4) present as minor phases. Exceptionally, amorphous MgHPO(4) dominates. Differences in structure were found in material taken from the center of the mix compared with that scraped from the bowl wall, but the incidence may be specific to the product/mixer combination and not a general effect. SIGNIFICANCE: The formation of compounds in phosphate-bonded investment can be affected by ambient temperature. This effect and the use of material adhering to the bowl wall (instead of that from the center of the mix) are possible causes for the unpredictability of setting expansion measurements between laboratories. There is variation between products. When phosphate-bonded investment is required for casting, a consistent ambient temperature must be used and it would be wise to mix sufficient material to avoid scraping the bowl.

Dental Casting Investment↗
PubMed2006

The determination of phosphorus containing compounds in dental casting investment products by 31P solid-state MAS-NMR spectroscopy.

OBJECTIVES: To use (31)P solid-state MAS-NMR to determine the phosphorus compounds that occur in dental casting investment material: (a) as-received, (b) after setting and (c) after burn-out and discover whether such compounds are the same in each material across a product range. METHODS: [(1)H] High powered decoupling (HPDC) and [(1)H] cross-polarization (CP) (31)P solid-state MAS-NMR spectroscopy at a resonance frequency of 121.4 MHz were used. Six commercial products were examined. Manufacturer's instructions were followed and a special liquid was used without dilution. RESULTS: All products contain ammonium dihydrogen phosphate as the acid phosphate required for the setting reaction. All set by the formation of struvite and significant amounts of amorphous magnesium orthophosphate. In three products, lesser amounts of newberyite were present and in another the equivalent amorphous compound was formed. When burnt-out, magnesium metaphosphate or pyrophosphate was the dominant matrix compound. A higher burn-out temperature favoured pyrophosphate formation. Farringtonite was present to a lesser extent with the metaphosphate. SIGNIFICANCE: Compounds that were not detected in earlier X-ray powder diffraction spectroscopy studies were detected by NMR, notably amorphous and glassy compounds (magnesium orthophosphate in set investment and magnesium metaphosphate in burnt-out material). The variation between products was significant and far greater than expected from the published scientific literature. Since the formation of compounds is affected by technical procedure and ambient conditions, these findings could offer some insight into the cause of the unpredictability of expansion measurements between laboratories. Further research is being undertaken.

Dental Casting Investment↗
PubMed1980

An improved dental casting investment.

In the present investigation a gypsum-bonded investment is presented with negligible setting expansion and a thermal expansion of 1.7%. This investment can and should be used without a steel casting ring. In combination with an earlier described die-spacing technique the new investment facilitates the production of gold inlays and crowns which, independent of type, will show a suitable degree of loose-fit in or on the preparations in the patient's mouth.

Calcium Sulfate↗