Dimensional accuracy of small gold alloy castings. Part 1. A brief history and the behaviour of inlay waxes

Our plain-English summary of Dimensional accuracy of small gold alloy castings. Part 1. A brief history and the behaviour of inlay waxes, by E.F. Morey (Australian Dental Journal, 1991).

The study

• Author: E.F. Morey
• Journal: Australian Dental Journal
• Published: 1991;36(4):302-9
• Type of article: Review
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Part 1 reviews published studies which relate to materials and techniques contributing to the dimensional accuracy of small dental castings. A brief history of the cire perdue or lost-wax method of casting alloys and the development of modern dental casting materials and techniques are presented. Data on the behaviour of inlay wax, in particular its contraction and distortion, are reviewed as is the extensive literature about the casting shrinkage of gold alloys (Part 2) and the setting and thermal expansion of investments under both laboratory and practical conditions (Part 3). Part 4 discusses the role of the casting ring and its asbestos liner. Asbestos as a liner has now largely been replaced by two alternative materials, one based on cellulose and the other on ceramic fibres. The limited literature on the effect of these newer materials on casting accuracy is also reviewed, as their introduction may require significant changes in the traditional technology of dental casting.

In plain English

This article is a review, Part 1 of a series, of published studies on what affects how accurately small gold dental castings fit. It did not study people or health effects. The author traced the history of lost-wax casting and reviewed earlier reports on how inlay wax shrinks and distorts. Asbestos appears only as a casting-ring liner. The article recounts that soft asbestos liners were introduced as a heat-resisting cushion and were later found to cause water-related expansion of the investment, by an undetermined amount. Reviewed studies reported wax shrinkage from mouth to room temperature of 0.3 per cent to 2.3 per cent, though the author noted much of this research did not simulate dental conditions. Summing up the many figures quoted for the thermal expansion of inlay waxes, the author called them a large and confusing range of values. In one reviewed study of over 400 wax patterns, most distortion occurred within two to three hours of storage. According to the abstract, a later part discusses the asbestos liner and the cellulose and ceramic-fibre materials that largely replaced it.

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: Review of published studies (Part 1 of a series)
• Who was studied: No people were studied. The article reviewed published research and historical accounts on materials and techniques for small dental gold castings, mainly inlay waxes.
• Exposure: No health exposure was studied. Asbestos is mentioned only as a soft liner for the metal casting ring in dental casting. Later parts of the series deal with the liner and its cellulose and ceramic-fibre replacements.
• Main results:
  • The review reported that earlier work established that the asbestos liner, whether used wet or dry, produces hygroscopic expansion of the investment, but by an undetermined amount.
  • Figures quoted by other authors for wax shrinkage from mouth temperature to room temperature varied from 0.3 per cent to 2.3 per cent. The author noted that much of this research was not carried out using simulated dental conditions.
  • Summing up the reported figures for the thermal expansion of inlay waxes, the author stated that a large and confusing range of values has been quoted.
  • The American Dental Association Specification for Inlay Wax allows Type B inlay wax a maximum of 0.2 per cent linear expansion from 25 to 30 degrees C, and a maximum of 0.6 per cent from 25 to 37 degrees C.
  • In a reviewed study by Phillips and Biggs of over 400 wax patterns, most distortion occurred during the first two to three hours of storage.
• The authors' conclusion: The author concluded that great advances have been made in dental casting since 1907. The author also concluded that distortion of wax patterns by stress relief depends on storage time, storage temperature and temperature changes after the pattern is formed.
• Limitations the authors state:
  • The author noted that much of the research reporting wax shrinkage figures was not carried out under simulated dental conditions.

Related studies

• Dimensional accuracy of small gold alloy castings. Part 4. The casting ring and ring liners — E.F. Morey (1992)
• The fit of gold-alloy full-crown castings made with pre-wetted casting ring liners — E.F. Morey, R. Earnshaw (1992)
• The effect of casting ring liners on the potential expansion of a gypsum-bonded investment — R. Earnshaw (1988)
• A procedure for restoring proximal contact surfaces of cast gold restorations with solder — P.M. Kimondollo (1991)
• Distortion of a MOD pattern caused by the setting and hygroscopic expansion of the investment in the casting ring. II. Influence of W/P ratio, pattern position in the ring, and the condition of the asbestos lining — H. Ohno, O. Miyakawa, et al. (1982)
• The accuracy of occlusal cusp height in cast crowns — J. Takahashi, M. Okazaki, et al. (1983)

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