Biomedical Engineering Reference
In-Depth Information
11.7 ANTIMICROBIAL PROPERTIES OF BIOACTIVE
GLASSES
The oral microflora consists of several hundred microbial species.
Colonisation of certain microorganisms causes caries and periodon-
titis. Microorganism-associated infection around a dental implant might
lead to bone resorption and implant failure. The first antibacterial effects
of bioactive glasses against microbes were reported by Stoor
et al
. [15].
Fine-grained S53P4 glass with an average particle size around 20
m
was found to exhibit antibacterial properties when used as a paste with
a high particle concentration, 1.7 g of glass per millilitre of bacterial
culture solution. The antibacterial effect was attributed to the high pH
of the interfacial solution caused by the dissolution of sodium and cal-
cium ions from the glass. The rapid increase of the osmotic pressure
in the paste due to ion dissolution was assumed to affect the viability
of the bacteria as well. Bioactive S53P4 glass has been proven effec-
tive in killing pathogens connected with enamel caries (
Streptococcus
mutans
), root caries (
Actinomyces naeslundii
,
S. mutans
) and periodon-
titis (
Actinobacillus actinomycetemcomitas
,
Porphyromonas gingivalis
,
Prevotella intermedia
).
Silver ions are known to be antimicrobial and they can be intro-
duced into a glass easily (e.g. by substituting Na for Ag). The Ag
ions are then released during dissolution, giving the possibility of man-
ufacturing bioactive glasses with bacteria-killing capability. The first
silver-containing antibacterial glass was a sol-gel derived composition
(wt%): 76SiO
2
-19CaO-2P
2
O
5
-3Ag
2
O [16]. The minimum concentra-
tions of glass required to kill
Escherichia coli
,
Pseudomonas aeruginosa
and
Staphylococcus aureus
were 1, 0.5 and 0.5mg/ml, respectively.
These three bacteria are associated with biomaterial-related infection
sites. Too rapid and high silver dissolution might be cytotoxic to the
tissues but, importantly, at these levels, other cells such as human bone
cells were not affected. In the same studies, the 45S5 glass did not show
any antimicrobial effects. In later studies, however, nanosized 45S5 has
been shown to kill
Enterococcus faecalis
, a microorganism associated
with failed root canal treatments [17]. Doping surfaces of bioactive glass
particles with silver ions by molten ion exchange can be used to tailor
the release of the silver ions [18].
Bioactive glasses have been found to inhibit the growth of 29 aer-
obic and 17 anaerobic clinically important bacteria
in vitro
[19]. The
aerobic bacteria were cultured with six melt-quenched and two sol-gel
derived glasses, while the anaerobic bacteria were cultured with two
μ
