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

Our plain-English summary of The fit of gold-alloy full-crown castings made with pre-wetted casting ring liners, by E.F. Morey, R. Earnshaw (Journal of Dental Research, 1992).

The study

• Authors: E.F. Morey, R. Earnshaw
• Journal: Journal of Dental Research
• Published: 1992;71(12):1858-64
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

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.

In plain English

This University of Sydney laboratory study measured how well gold-alloy full-crown dental castings fitted when casting rings were lined with one of six pre-wetted liners. Three were asbestos products (coded GA, KA and SH) and three were cellulose products (AU, BE and WM), all used with one gypsum-bonded investment. It did not study human health or asbestos exposure. At least 10 castings were measured per liner. Castings made without a liner were undersized by a mean of 0.61%. With liners, mean inaccuracy ranged from +0.01% (KA, asbestos) to -0.37% (WM, cellulose). Taking plus or minus 0.2% as clinically acceptable, all KA and BE castings fell within that range; one of 11 GA castings did not. Castings outside the range numbered 12/12 with SH, 7/10 with AU and 11/11 with WM. Inaccuracy showed a probable correlation with the investment's laboratory-measured potential expansion, but no significant correlation with the liner properties measured. The authors concluded that liner choice significantly affects casting accuracy, and stressed that their results apply only to the batches and conditions tested.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (dental materials) experiment measuring the fit of gold-alloy full-crown castings made with different pre-wetted casting ring liners, plus laboratory measurements of liner properties and investment expansion
• Who was studied: No people were studied. The study tested six ring-lining materials: three asbestos (GA, KA, SH) and three cellulose (AU, BE, WM). Each liner was used to make 10 to 12 castings, compared with control castings made in unlined rings. The work was done at the University of Sydney, Australia.
• Exposure: Pre-wetted asbestos and cellulose casting ring liners used with Cristobalite Inlay gypsum-bonded investment (W/P = 0.40) and a high-noble-metal gold alloy. This was not a human exposure.
• Main results:
  • Control castings made in unlined rings were undersized, with a mean diametral discrepancy of 0.61% (11 castings)
  • With lined rings, mean casting inaccuracy ranged from +0.01% with KA (asbestos) to -0.37% with WM (cellulose)
  • Against a tolerance of plus or minus 0.2%, one of 11 GA castings fell outside the range (-0.27%)
  • Castings outside the plus or minus 0.2% range numbered 12/12 with SH, 7/10 with AU and 11/11 with WM. All castings with KA and BE were within it.
  • Compared with the control, all wet liners increased total investment expansion, by 30% (SH and BE) to 49% (KA)
  • The GA and KA liners did not change the effective W/P ratio of the mix. The other four liners raised it to between 0.44 and 0.47.
  • Casting inaccuracy showed a probable correlation with potential investment expansion (p less than 0.05), but no significant correlation with the measured liner properties, alone or in combination
• The authors' conclusion: The authors concluded that, in casting techniques using a pre-wetted ring liner, the choice of lining material is an important factor with a significant effect on casting inaccuracy. They added that a liner's influence can otherwise be determined only by directly measuring the fit of castings made under practical conditions.
• Limitations the authors state:
  • The authors stated that the specific results apply only to the batches tested and to the experimental conditions used
  • Compressibility was measured at an arbitrary stress of 0.8 MPa, so the values serve only to compare liners

Related studies

• Dimensional accuracy of small gold alloy castings. Part 4. The casting ring and ring liners — E.F. Morey (1992)
• Full-crown castings made with water-saturated and dry casting ring liners — F. Keyf, G. Erman (2000)
• Dimensional accuracy of small gold alloy castings. Part 1. A brief history and the behaviour of inlay waxes — E.F. Morey (1991)
• The effect of casting ring liners on the potential expansion of a gypsum-bonded investment — R. Earnshaw (1988)
• The accuracy of occlusal cusp height in cast crowns — J. Takahashi, M. Okazaki, et al. (1983)
• A procedure for restoring proximal contact surfaces of cast gold restorations with solder — P.M. Kimondollo (1991)

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