Potential health hazards of ceramic ring lining material

Our plain-English summary of Potential health hazards of ceramic ring lining material, by D.R. Davis (The Journal of Prosthetic Dentistry, 1987).

The study

• Author: D.R. Davis
• Journal: The Journal of Prosthetic Dentistry
• Published: 1987;57(3):362-9
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

This pilot study asked whether ceramic ring lining materials, introduced in dentistry and industry as asbestos substitutes, contain fibers in the size ranges reported to cause mesothelioma in rats. Two ceramic liners, Kaoliner (Dentsply) and Kerr flask liner (Sybron Kerr), were examined. For comparison, the author used reference samples of South African blue asbestos (crocidolite) and brown asbestos (amosite) from the California Academy of Sciences, and two dental asbestos samples identified by morphology as white asbestos (chrysotile). Fibers were obtained from the liners either by cutting and scraping them over distilled water or by extracting the binder with chloroform. The fibers were then filtered, gold-coated, and viewed and measured by scanning electron microscopy at about x5000. A control sample was also run. Fibers in the dimensional ranges most toxic to rats were found in both ceramic liners. Extracting the binder yielded many more small-diameter fibers than scraping. Measured ceramic fibers included one of 11.8 µm length and 0.20 µm diameter (aspect ratio 59). The control showed no fibers. The ceramic fibers resembled the straight fibers of blue and brown asbestos rather than the curly white asbestos fibers, which could not be measured reliably. The author concluded that, until inhalation studies and human epidemiologic data are available, ceramic ring lining material should be considered potentially hazardous. Present evidence does not support the claim that it is safer than white asbestos ring liners.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This 1987 pilot laboratory study asked whether two ceramic ring liners used in dentistry as asbestos substitutes, Kaoliner and Kerr flask liner, contained fibers of the sizes that earlier studies had linked to mesothelioma in rats. Fibers were freed from the liners by cutting and scraping or by dissolving the binder with chloroform, then measured under a scanning electron microscope, alongside reference samples of blue asbestos (crocidolite), brown asbestos (amosite) and two dental asbestos products resembling white asbestos (chrysotile). Fibers in the size ranges most toxic to rats were found in both liners. Removing the binder yielded many more thin fibers than scraping; a control sample with no fibrous material showed none. The author reported that the liner fibers resembled blue and brown asbestos fibers rather than curly white asbestos fibers. No people or animals were studied. The author concluded that the human toxicity of these fibers remains unclear, that ceramic liners should be considered potentially hazardous until inhalation studies and human data are available, and that present evidence did not support the claim that they are safer than white asbestos liners.

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: Pilot laboratory study: fibers recovered from dental materials and examined and measured by scanning electron microscope (SEM); no human or animal subjects
• Who was studied: Two ceramic ring lining materials used in dental casting, Kaoliner (Dentsply International) and Kerr flask liner (Sybron Kerr). For comparison: reference samples of South African blue asbestos (Cape fields) and brown asbestos (Transvaal fields) from the California Academy of Sciences, and two dental asbestos samples (Buffalo Dental Manufacturing Co. and Whip Mix Corp.) identified by SEM as morphologically consistent with white asbestos (chrysotile). The work was done at the University of California School of Dentistry, San Francisco.
• Exposure: Ceramic fibers from the two liners, compared with crocidolite, amosite and chrysotile dental asbestos. Fibers were obtained from the liners by two methods: cutting and scraping the liner ends, or extracting the binder with chloroform. Samples were then filtered, gold-coated and photographed by SEM at approximately x5000.
• Main results:
  • Both ceramic liners, Kaoliner and Kerr flask liner, contained fibers in the size ranges most toxic to rats. In the article's table, these are fibers longer than 4 micrometers with diameters of 1.5 micrometers or less.
  • Cutting and scraping the liners yielded fewer fibers than extracting the organic binder.
  • In scraped Kaoliner material, most free fibers had diameters larger than 1.5 micrometers.
  • Scraped Kerr flask liner produced free fibers and clumps of fibers of varying diameters. Many were coated with what appeared to be binder.
  • Both liners yielded many more small-diameter fibers when the binder was extracted.
  • The control sample, which went through all steps without any fibrous material, showed no fibers.
  • Under the microscope, fibers from both liners resembled the prismatic fibers of blue and brown asbestos rather than white asbestos.
  • White asbestos fibers could not be measured reliably because they are curly.
• The authors' conclusion: The author concluded that the two ceramic ring lining materials contained fibers of the dimensions most likely to induce mesotheliomas in rats. The author considered the human toxicity of these fibers unclear and stated that ceramic ring lining material should be considered potentially hazardous until inhalation studies and human epidemiologic data are available. The author also stated that present evidence does not support the contention that ceramic ring liners are safer than white asbestos ring liners.
• Limitations the authors state:
  • The two collection methods gave different results, and the author gave two possible reasons: room air currents may have swept away smaller fibers during scraping, or binder may have held smaller fibers more tightly. The author said air sampling would be needed to resolve this and to show how many fibers are released into the air.
  • The rat studies used to define the hazardous fiber sizes injected fibers into the chest cavity (intrapleural inoculation). The author noted that such studies do not address the body's defense mechanisms or how fibers behave in the airways.
  • The author cautioned that applying rat findings to humans is uncertain: doses in many animal studies were excessive, species reacted differently, and rat lungs appear extremely sensitive.
  • The author stated that the toxicity of these ceramic (simple aluminosilicate) fibers to humans remains unclear.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Crocidolite, Amosite, Chrysotile, Scanning Electron Microscopy (SEM), Aspect Ratio (Length-to-diameter ratio).

Related studies

• An investigation of the potential biohazards associated with asbestos-substitute casting ring liners — G.J. Tulachka, W.A. Brantley, et al. (1987)
• Fibrous ceramic aluminum silicate as an alternative to asbestos liners — G. Priest, J.A. Horner (1980)
• The effect of casting ring liners on the potential expansion of a gypsum-bonded investment — R. Earnshaw (1988)
• Refractory ceramic fibers: Fiber characteristics, potential health effects and clinical observations — M.J. Utell, L.D. Maxim (2018)
• The fit of gold-alloy full-crown castings made with pre-wetted casting ring liners — E.F. Morey, R. Earnshaw (1992)
• Dimensional accuracy of small gold alloy castings. Part 4. The casting ring and ring liners — E.F. Morey (1992)

Browse more research in The Journal of Prosthetic Dentistry, or return to medical research.