Marginal Accuracy of Castings Produced with Different Investment Systems

Our plain-English summary of Marginal Accuracy of Castings Produced with Different Investment Systems, by R.K. Yadav (Medical Journal, Armed Forces India, 2009).

The study

• Author: R.K. Yadav
• Journal: Medical Journal, Armed Forces India
• Published: 2009;65(2):146-9
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: The use of casting ring to produce accurate castings has been challenged with the introduction of a ringless casting technique. This study compared the marginal accuracy of all - metal complete coverage crowns fabricated with ringless, split plastic ring and metal ring investment systems.

Methods: A total of 40 all- metal complete coverage crowns were fabricated on a metal die. The crowns were divided in 4 groups (Group A, B, C and D) of 10 patterns each. A ringless system of investing and casting was used for group A whereas a split plastic ring system was used for group B. Groups C and D utilized metal ring with single and double layers of asbestos free cellulose acetate liner respectively for investing and casting procedures. The restorations were seated on the metal die and the vertical marginal discrepancy was evaluated by measuring the gap between the finish line on the die and the margins of the crown on four specific sites with an optical microscope. Statistical analysis was carried out using ANOVA and multiple comparison "t" test.

Result: The mean vertical marginal discrepancy for groups A, B, C and D was 95μm, 136μm, 128μm and 104μm respectively. Vertical marginal discrepancy on each surface was compared among the four groups. Difference of vertical marginal discrepancy on buccal surface (p<0.0001) as well as distal surface (p<0.005) was highly significant whereas it was non-significant on lingual and mesial surfaces (p>0.05).

Conclusion: Accurate castings with better marginal fit can be produced with ringless casting technique.

In plain English

This laboratory study of dental crowns did not examine asbestos or its health effects. Asbestos appears only because the metal casting rings were lined with an asbestos-free cellulose acetate liner. Forty all-metal crowns were made with four investing and casting methods, ten per group: ringless (Group A), split plastic ring (Group B), metal ring with one liner layer (Group C) and metal ring with two liner layers (Group D). Each crown was seated on a metal model of a prepared lower molar, and the gap at its margin was measured with an optical microscope. The mean gaps were 95μm, 136μm, 128μm and 104μm for Groups A to D. Differences among the groups were statistically significant on the buccal and distal surfaces, not on the lingual and mesial surfaces. Group A's gap was significantly smaller than Groups B and C but not significantly different from Group D. The author concluded that the ringless technique produced clinically acceptable, accurate castings with better marginal fit. The author added that the conventional metal ring technique should not be abandoned and that further studies were needed.

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 (in vitro) experiment comparing four investing and casting techniques for dental crowns; marginal gaps measured by optical microscope
• Who was studied: Not people: 40 all-metal complete coverage crowns, in four groups of 10, fitted to a metal die made from a left mandibular second molar prepared on a typodont
• Exposure: No asbestos exposure was studied. The variable was the investing and casting technique: ringless, split plastic ring, metal ring with a single layer of asbestos-free cellulose acetate liner, and metal ring with a double layer of that liner
• Main results:
  • Mean vertical marginal discrepancy was 95μm for Group A (ringless), 136μm for Group B (split plastic ring), 128μm for Group C (metal ring, single liner) and 104μm for Group D (metal ring, double liner)
  • Differences among the four groups were highly significant on the buccal surface (p less than 0.0001) and the distal surface (p less than 0.005)
  • There was no significant difference among the groups on the lingual and mesial surfaces (p greater than 0.05)
  • Group A's average discrepancy was significantly lower than Groups B and C, with no significant difference between Groups A and D; Group D was significantly lower than Group B, with no significant difference between Groups B and C
  • Ranked from best to worst marginal fit: Group A, Group D, Group C, Group B
  • Group A castings had the smallest standard deviation, which the author read as more consistent results
• The authors' conclusion: The author concluded that the ringless technique produced clinically acceptable, accurate castings with better marginal fit. The author also stated that the conventional metal ring technique is well documented and should not be abandoned.
• Limitations the authors state:
  • None of the castings in any group showed ideal marginal fit
  • No adjustments were made on the internal surface of the castings, which the author offered as one explanation for the discrepancies
  • The author stated that further studies are needed to substantiate the results

Related studies

• The effect of casting ring liners on the potential expansion of a gypsum-bonded investment — R. Earnshaw (1988)
• 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)
• Dimensional accuracy of small gold alloy castings. Part 4. The casting ring and ring liners — E.F. Morey (1992)
• Dimensional accuracy of small gold alloy castings. Part 1. A brief history and the behaviour of inlay waxes — E.F. Morey (1991)
• Producing samples for the organization of proficiency tests. Study of the homogeneity of replicas produced from two atmosphere generation systems — L. Freville, J.C. Moulut, et al. (2010)
• Behaviour of the new asbestos amphibole fluor-edenite in different lung cell systems — V. Cardile, M. Renis, et al. (2004)

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