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Sun Apr 10 18:09:43 EST 2005


***************
The cells in contact with [...] all the non-extracted BIS-GMA samples
were rounded or floating which is characteristic of dead or dying cells.
The differences between the toxicity of the unextracted samples and
toxic plasticised PVC were not significant (p < 0.05).
***************

So how does toxic PVC compare with amalgam if BIS-GMA toxicity levels 
have not been independently measured, the comparison would tell us.

 That doesn't prove amalgam is worse than composites, but it
: does mean that the substance loss would have to be a much greater
: proportion of a composite filling to get the same toxic exposure. But
: this is theoretical; the fact is the chronic substance release from
: composites is much LESS than from amalgam.
: ---------------------------------------------------------------------
: Dagfinn Reiersol    reiersol at online.no
: Oslo, Norway
: ---------------------------------------------------------------------

I would say it is greater:
****************
Results
The average amounts (and standard deviations) of material extracted from
the polymerized samples with methanol, chloroform and toluene were 4.60
(0.04), 7.50 (0.05), 11.10 (0.05) weight by weight per cent
respectively. The amount of material unaccounted for ranged from 0.03 to
0.07 wt %.

[BIS-GMA was virtually the only extracted material with trace amounts of
a light stabiliser (2-hydroxy-4-methoxy-benzophenone) as well as a
phenyl ester of benzoic acid which was probably degraded from BIS-GMA.]
**************

According to my taste sense I very roughly estimate half of the emission
rate of it to be gone in 2 years. That means something like 5% of a
filling in 2 years, if the emission rate is governed by the amount remaining.

Other interesting work including attempt at clarification of confusion
over toxic and allergic on thread, `Abstracts & questions metacrylate...'
on sci.med.dentistry,alt.health.dental-amalgam

Dodo Dodphin.

Ref:

Cytotoxicity of a BIS-GMA dental composite before and after leaching in
organic solvents.

Journal of Biomedical Materials Research, Vol 25,443-457(1991).

M.Anne Rathbun (W.R.Grace & Co)
Robert G  Craig (Univ of Michigan)
Carl T Hanks (Univ of Michigan)
Frank E Filisko (Univ of Michigan)

Introduction

Chronic pulpitis results from the use of dental composites that have not
been properly lined. Thus investigators such as Stanley et al, and
Suarez et al haver recommended that composites be classified as toxic.
Baume and Fiore-Donna stated that this pulp reaction to composite was
mild if more than 1 mm or more of remaining dentin. However decayed
teeth displayed more severe reactions. Chemicals and bacteria have been
proposed as explanations for pulpal irritation from dental composites.

[...]

The objectives of this study were to investigate the cytotoxicity of
polymerized BIS-GMA composite in cell cultures before and after leaching
out potential irritants with various solvents, and to identify the
extractants in order to determine which components were responsible for
cellular reactions.

Materials and Methods.

The composite selected was Silar because its composition is similar to
many composites; it contains BIS-GMA, TEGMA (triethyleneglycol
dimethacrylate, and colloidal silica filler.

[...]

Leachable material from the samples was obtained by extraction with high
purity ethanol, chloroform or toluene.

[...]

Composite samples to be subjected to solvent extraction were placed in
100 ml of solvent immediately after setting for 4 days at room
temperature.

[...]

The relative toxicity of the samples was assessed using an in vitro cell
monolayer system for visual inspection and protein synthesis rates.

[...]

Results
The average amounts (and standard deviations) of material extracted from
the polymerized samples with methanol, chloroform and toluene were 4.60
(0.04), 7.50 (0.05), 11.10 (0.05) weight by weight per cent
respectively. The amount of material unaccounted for ranged from 0.03 to
0.07 wt %.

[BIS-GMA was virtually the only extracted material with trace amounts of
a light stabiliser (2-hydroxy-4-methoxy-benzophenone) as well as a
phenyl ester of benzoic acid which was probably degraded from BIS-GMA.]

[...]

Cells in contact with non-toxic teflon and with all of the extracted
BIS-GMA samples showed healthy morphology, good cell-to-material
contact, and many appeared to be undergoing cellular division.

[...]

The cells in contact with [...] all the non-extracted BIS-GMA samples
were rounded or floating which is characteristic of dead or dying cells.
The differences between the toxicity of the unextracted samples and
toxic plasticised PVC were not significant (p < 0.05). Extraction of the
composite samples resulted in approximately 90% decrease in the toxicity
of all samples tested when compared to the nonextracted composite
samples.

[...]

Discussion

[...]

The rate of leaching of low-molecular-weight fragments from the polymer
matrix should be even slower in water or saliva than in the organic
solvents as a result of decreased solubility. It would be expected that
pulpal tissues would be exposed to lower concentrations of low-
molecular-weight organic compounds at longer periods of time as they are
leached into the saliva, which might result in a low-level chronic
response until all the fragments are extracted.[...]

Whether low-molecular-weight BIS-GMA chemical components or bacteria are
more important in producing a pulpal response is not known presently.
However, it appears that the chemical components should produce a
response that would subside after the low-molecular-weight fragments are
leached out, while the pulpal response to bacteria would continue as
long as marginal leakage around the composite occurred. However, with
the continued improvement in dentin and enamel bonding agents, chemical
effects could become more important than bacterial.

[...]



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