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

Our plain-English summary of 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, by H. Ohno, O. Miyakawa, N. Shiokawa (Dental Materials Journal, 1982).

The study

• Authors: H. Ohno, O. Miyakawa, N. Shiokawa
• Journal: Dental Materials Journal
• Published: 1982;1(1):47-54
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

In plain English

This laboratory study came from dental materials researchers in Japan. It did not study people or health. Asbestos appeared only as a lining material inside the metal ring used to make dental castings, and the article does not name the type of asbestos fiber. The authors set an epoxy resin model of an MOD tooth-filling pattern in casting material inside the ring. They used a light-based stress method called two-dimensional photoelasticity to see how the model bent as the material set and expanded. They varied the water-to-powder ratio, the number of asbestos lining layers (none, or one to five), whether the asbestos was dry, wet, or treated with silicone oil or vaseline, and where the model sat in the ring. Without a lining, the model was squeezed, more at the top (occlusal) part than at the sides. Distortion grew with more asbestos layers up to three. It was greater with less water in the mix, with dry rather than wet asbestos, and when the model's cervical margins were near the lining. The authors concluded that the overall pattern of distortion stayed the same except when there was no asbestos lining.

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 experiment (dental materials testing) using an epoxy resin model and two-dimensional photoelasticity; no human or animal subjects
• Who was studied: A simple idealized epoxy resin MOD pattern (a model of a dental filling pattern) set in casting material in a casting ring, following the methods of Part I of the series; Niigata University, Japan. The number of specimens is not stated.
• Exposure: Asbestos used as a casting-ring lining (fiber type not named): no lining, or one to five layers of asbestos dampened with 1.5 ml water per layer. Three-layer linings were also tested dry, wet, sprayed with silicone oil, or treated with vaseline. Water-to-powder ratios were 0.41, 0.36 and 0.31, and three pattern positions in the ring were tested.
• Main results:
  • With no asbestos lining, the model was under compressive stress that was not uniform: it was larger in the occlusal portion than in the mesiodistal portions.
  • With wet asbestos linings, deformation increased as the number of layers rose up to three layers, then reached a plateau.
  • Deformation was greater with smaller water-to-powder ratios.
  • With three-layer linings, deformation was greater with dry asbestos than with wet asbestos.
  • Deformation was similar with the occlusal portion near the lining and with the pattern in the center of the ring, and larger with the cervical margin close to the asbestos lining.
  • The overall form (behavior) of the distortion did not change across conditions, except with no asbestos lining.
• The authors' conclusion: The authors concluded that deformation of the pattern increases when the casting material both inside and outside the pattern expands a lot. They also concluded that placing the cervical margins near the asbestos lining increases deformation through greater water-driven (hygroscopic) setting expansion, and that the form of the distortion stays the same except with no lining.

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• Potential health hazards of ceramic ring lining material — D.R. Davis (1987)
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