Biomedical Engineering Reference
In-Depth Information
10.3.2.3
Titanium dioxide (TiO
2
)
Titanium dioxide (TiO
2
) is the commonest titanium compound, and its ability to act as a
photocatalytic antimicrobial compound is well established
[70]
.TiO
2
is widely used in a num-
ber of applications, as a powder and increasingly in a nanoparticulate form, and is generally
considered to be nontoxic at the concentrations normally employed. However, there are recent
concerns that nano-titanium oxide may present a hazard to health through inflammation as
generated by release of interleukin 1
[71]
. The anatase form of nano-TiO
2
and UV light exci-
tation are required to ensure maximum antimicrobial activity. TiO
2
photocatalysis is able to
promote the peroxidation of the polyunsaturated phospholipid component of the microbial lipid
membrane, induce loss of respiratory activity, and elicit cell death
[72]
.ThestudyofTsuang
et al.
[73]
demonstrated TiO
2
-mediated photocatalytic and bactericidal activities against obli-
gate aerobes (P. aeruginosa), facultative anaerobes (S. aureus, E. coli and Enterococcus hirae),
and obligate anaerobes (Bacteroides fragilis). Concentrations of titanium oxide (predominantly
anatase phase; in the absence of UV light; particle size: approximately 18 nm; surface area:
87 m
2
/g) required to have a growth inhibitory and killing effect against a range of pathogens
including E. coli and MRSA have been shown to be 1.0
α
2.5 mg/mL, respectively
(K. Memarzadeh and R.P. Allaker, unpublished observations). While with those organisms
implicated in oral infections, including A. actinomycetemcomitans, P. gingivalis, Prev. interme-
dia, and F. nucleatum, growth inhibitory and killing concentrations under anaerobic conditions
are in the same order at 0.25
2.5 and
.
2.5 and
2.5 mg/mL, respectively
[41]
.
.
10.3.3
Oral applications of nanoparticulate metals and metal oxides
Silver nanoparticles are being investigated to reduce bacterial and fungal adhesion to oral biomater-
ials and devices, e.g., incorporation into denture materials (
Figure 10.2
)
[4]
and orthodontic adhe-
sives
[74]
. The optimum amount of silver nanoparticles used within such polymer materials will be
of critical importance to avoid an adverse effect upon their physical properties. The study of Ahn
et al.
[74]
clearly demonstrated that experimental composite adhesives (ECAs) had rougher surfaces
than conventional adhesives due to the addition of silver nanoparticles, although bacterial adhesion
to ECAs was shown to be less than that to conventional adhesives and was not influenced by saliva
coating. No significant difference between ECAs and conventional adhesives was shown as regards
bond shear strength.
Biofilm growth is known to contribute to secondary caries and the failure of resin-based dental
composites. Within this context, zinc oxide nanoparticles have undergone in vitro testing using bio-
film culture test systems
[75]
. ZnO nanoparticles blended into a variety of composites were shown
to significantly inhibit S. sobrinus biofilm growth at concentrations not less than 10% w/w over a
3-day test period. The structural characteristics of composites would need to be carefully assessed
with a 10% ZnO loading.
With reference to dental implants, numerous companies market novel synthetic hydroxyapatite
(HA) materials as the “optimal” osteoconductive implant coating available, and some companies
have developed nanoscaled varieties. Some have employed coatings and application methods differ-
ent from the conventional coating techniques, including a HA material available in nanophase and
a nanocrystalline silver-based antimicrobial coating that should reduce the potential for bacterial
