An investigation of the potential biohazards associated with asbestos-substitute casting ring liners

Our plain-English summary of An investigation of the potential biohazards associated with asbestos-substitute casting ring liners, by G.J. Tulachka, W.A. Brantley, G.P. McGivney, et al (The Journal of Prosthetic Dentistry, 1987).

The study

• Authors: G.J. Tulachka, W.A. Brantley, G.P. McGivney, G.J. Ziebert
• Journal: The Journal of Prosthetic Dentistry
• Published: 1987;57(1):108-12
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Summary of the article

This laboratory study, from Marquette University School of Dentistry in Milwaukee, examined whether ceramic casting ring liners used as asbestos substitutes in dentistry release airborne fibers of a size considered hazardous. It also compared them with asbestos liners. Three brands of ceramic liner were tested: Kaoliner, used dry, and R-Liner and Ney-Liner, used wet. Asbestos liners, used wet, served as the control. To simulate daily dental laboratory use, strips of liner were adapted by finger pressure to five casting rings. The rings were filled with investment, burned out, water-quenched and broken apart. No metal was cast. Air was sampled during baseline, liner placement and break-out with two area pumps (8 hours each) and one personal pump (1 hour), giving eight samples per liner. Fibers were counted by optical microscopy using OSHA asbestos counting rules. Fiber-containing samples were examined by scanning electron microscopy (SEM) with elemental analysis. All four liners produced fibers, but every sample was below the detection level, at less than 0.01 fibers/cc. This compared with the OSHA permissible exposure limit of 2 F/cc and a proposed limit of 0.5 F/cc. The dry Kaoliner produced the most fibers, and most fibers were collected during liner placement. Ceramic fibers seen by SEM measured about 50 to 80 µm long and 1 to 1.5 µm in diameter, within the size range of greatest health concern. The authors concluded that ceramic ring liners should be considered potential biohazards, along with asbestos 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

In a laboratory experiment, the authors measured airborne fibers released when dental casting ring liners were handled under simulated dental laboratory conditions. They tested three brands of ceramic liners (Kaoliner, R-Liner and Ney-Liner) and used an asbestos liner as a comparison. The article does not name the asbestos fiber type. Eight air samples were collected for each liner, including baseline samples taken before the procedures and samples taken during liner placement and later break-out. All four liners released some fibers, but in every sample, including asbestos, concentrations were below 0.01 fibers per cc of air. The OSHA permissible exposure limit was then 2 fibers per cc, with 0.5 proposed. Kaoliner, the only liner used dry, released the most fibers. The wet ceramic and asbestos liners released similar, smaller numbers. In general, the most fibers were collected during placement. Electron microscope images showed ceramic fibers about 50 to 80 micrometers long and 1 to 1.5 micrometers wide, within the size range the authors described as of greatest health concern. No metal was cast into the rings. The authors concluded that ceramic ring liners should be considered potential biohazards, along with 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: Laboratory experiment simulating dental laboratory casting procedures, with air sampling and fiber counting
• Who was studied: No people were studied. Four casting ring liner materials (three ceramic brands and an asbestos control) were handled in a room at Marquette University School of Dentistry, Milwaukee, Wisconsin. Eight air samples were taken per liner. These included baseline samples taken with the high-volume pump before the placement and break-out procedures. During each procedure, one 1-hour personal sample and two 8-hour area samples were taken.
• Exposure: Airborne fibers from three ceramic (alumino-silicate) casting ring liners: Kaoliner, used dry, and R-Liner and Ney-Liner, used wet. An asbestos liner, used wet, served as the control; the asbestos fiber type is not stated. Fibers were measured during liner placement and during break-out after burnout at 1400 degrees C.
• Main results:
  • All four liners (the three ceramic liners and the asbestos liner) produced fibers under some circumstances.
  • In all samples, including asbestos, fiber concentrations were less than 0.01 fibers per cc of air. These counts were below the detection levels of the methods used. The OSHA permissible exposure levels were 2 F/cc (present) and 0.5 F/cc (proposed).
  • The most fibers were collected during placement of Kaoliner, the only liner used dry.
  • The R-Liner, Ney-Liner and asbestos liners, all used wet, produced similar and smaller numbers of fibers.
  • The number and concentration of asbestos fibers were similar to those from the three ceramic liners for the same sampling phases.
  • In general, for each liner, the most fibers were collected while the liner was being fitted into the casting ring.
  • Representative ceramic fibers seen by electron microscope measured about 50 micrometers long by 1.5 micrometers wide (Kaoliner), 67 by 1 (R-Liner) and 80 by 1 (Ney-Liner). These are within the size range the authors described as of greatest health concern: longer than 20 micrometers and thinner than 3 micrometers.
• The authors' conclusion: The authors concluded that, until conclusive evidence to the contrary is accumulated, ceramic ring liners should be considered potential biohazards, along with asbestos liners.
• Limitations the authors state:
  • No metal was cast into the rings. Casting might have produced additional fibers.
  • Water quenching left the investment and liner moist, which the authors thought presumably lowered fiber production at break-out.
  • Fibers were found in baseline samples taken before break-out, suggesting residual fibers from the previous day. So the authors could not conclude that break-out itself produced fibers.
  • The study did not assess health effects. The authors stated more research is needed on long-term health effects of ceramic liner materials.

Topics

Medical terms in this study, explained in our Lexicon: OSHA, Scanning Electron Microscopy (SEM), Elemental Analysis, Permissible Exposure Limit (PEL).

Related studies

• The effect of casting ring liners on the potential expansion of a gypsum-bonded investment — R. Earnshaw (1988)
• 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)
• Release of asbestos fibers during casting ring liner manipulation — D.R. Davis (1995)
• Full-crown castings made with water-saturated and dry casting ring liners — F. Keyf, G. Erman (2000)
• Potential health hazards of ceramic ring lining material — D.R. Davis (1987)

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