Grossman, E. S.

Matejka, J. M.

English

Wits Institutional Repository on DSPACE

EFFECT OF AMALGAM TYPE ON ARTIFICIAL CARIES
E.S. Grossman and J.M. Matejka 
MRC/WITS Dental Research Institute, Johannesburg
Cut cavity surfaces of freshly amalgam- 
restored teeth are particularly 
vulnerable to bacterial attack. A gap 
is always present at the tooth-amalgam 
interface following restoration 
allowing the passage of oral fluids and 
bacteria. There bacteria rapidly 
ferment ingested carbohydrates, causing 
the surrounding pH to drop, carious 
lesions to form and consequent re­
restoration of the tooth. Should 
bacteria gain access to the dentine, 
pulpal inflammation can be sufficiently 
severe to result in tooth loss. 
Amalgams have short term anti-bacterial 
properties1 which could prevent prompt 
bacterial penetration at this 
interface. The impact of aged amalgams 
on lesion development is not known. 
This study was undertaken to examine 
the influence of amalgam type on 
artificial, secondary carious lesion 
formation adjacent to amalgam-restored 
teeth aged for 3 months and 1 year.
Cavities were cut in 64 extracted 
intact human premolars and restored 
with a high (tCu) or a low (ACu) copper 
amalgam. After ageing in 1% NaCl with 
thymol for 3 months and 1 year, the 
teeth were subjected to a bacterial 
artificial caries challenge2. Each 
tooth was coated with nail varnish 
leaving the restoration margin and a 
1mm peripheral area exposed. After 
sterilisation with gamma irradiation 
specimens were individually placed in 
sterile McCartney bottles filled with 
sufficient sterile brain heart infusion 
broth containing 3% sucrose to cover 
the tooth and were incubated for 3 days 
at 37°C to check sterilisation. Teeth 
were transfered under sterile 
conditions to a fresh broth inoculated 
with Streptococcus mutans ATCC 25175, 
a strain isolated from carious dentine, 
and incubated for 36 days changing the 
medium twice weekly. Thereafter the 
teeth were rinsed and resin embedded. 
One ground section 100-120pm thick, 
midway through the restoration, was 
prepared from each specimen and viewed 
using polarised light (Fig. 3). A 
Kontron Image Analysing System was used 
to measure lesion dimensions. The data
were subjected to one way ANOVA and 
Tukey's test to establish statistical 
significance.
No statistically significant difference 
was apparent between lesions formed 
after 3 months and 1 year of ageing. 
The % wall lesion depth was 
significantly greater in TCu (21%) than 
ACu (12%). The outer lesion was 
significantly further from the cavity 
wall in ACu (38pm) than TCu (2pm).
The results of the study indicate that 
amalgam type has a significant effect 
on the formation of artificial carious 
lesions in the tooth adjacent to a 
restoration. Previous studies have 
shown that more marginal seal material 
is formed by ACu3 which can result in 
less marginal leakage4 than TCu. This 
implies that bacteria cannot easily 
gain access into the marginal gap of 
ACu. Once within the gap, elements 
which migrate from the amalgam whether 
into the tooth structure or to form the 
marginal seal, could prevent bacterial 
multiplication and increase tooth 
resistance to demineralisation. 
Judicious choice of amalgam type could 
decrease the likelihood of caries 
development at the amalgam-tooth 
margin.
References
1. Tobias, R.S. et al., (1988) Int.
Endodont. J. 21. 381.
2. Dummer, P.M.H., Edmunds, D.H. & 
Green, R.M. (1982) Caries Res. 16, 193.
3. Grossman, E.S., Witcomb, M.J. & 
Matejka, J.M. (1994) J. Prosthet. Dent. 
In press.
4. Grossman, E.S. & Matejka, J.M. 
(1993) J. Prosthet. Dent. 69, 469.
Fig. 1. A carious lesion (c) formed 
next to the amalgam restoration (a).
61


Effect of amalgam type on artificial caries

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Effect of amalgam type on artificial caries

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