Biomedical Engineering Reference
In-Depth Information
“Listerine” is the commercial name of a commonly used mouth rinse that
contains “essential oils” as active antimicrobial compounds. In its formulation we
found thymol (0.06 %), eucalyptol (0.09 %), methyl salicylate (0.06 %) and
menthol (0.04 %). Listerine acts on the biofilm by destabilizing the bacterial cell
wall (Leszczy
´
ska et al.
2011
).
Hexetidine is also a common antiplaque agent added to mouthwashes.
Hexetidine is a very safe oral antiseptic with broad antibacterial and antifungal
activity in vivo and in vitro. Hexetidine has lower antiplaque activity than chlor-
hexidine but without the negative staining effect (Afennich et al.
2011
). Given
hexetidine is a pyrimidine derivative, the most likely mechanism of action is by
exerting a competitive action with thiamine.
Cetylpyridinium chloride (CPC) is a quaternary ammonium compound with
broad spectrum antibacterial activity that adsorbs readily to oral surfaces. This
molecule has both hydrophilic and hydrophobic groups, providing the possibility
for hydrophilic and hydrophobic interactions. The positively charged hydrophilic
region of the CPC molecule has high binding affinity for bacterial cells whose
surface has net negative charge. The strong positive charge and hydrophobic region
of CPC enables the compound to interact with the microbial cell surface and
integrate into the cytoplasmic membrane. As a result of this interaction, there is
disruption of membrane integrity resulting in cell death (Leszczy
´
ska et al.
2011
;
Tattawasart et al.
2000
).
Finally, both amine fluoride (Kay and Wilson
1988
) and stannous fluoride
(Mayhew and Brown
1981
) possess bactericidal activity against oral bacteria. In
addition, amine fluoride has been shown to inhibit the growth of mixed bacterial
populations found in subgingival plaque (Bansal et al.
1990
; Bullock et al.
1989
).
Additionally, stannous and amine fluorides can also inhibit the adhesion of
Strep-
tococcus sanguis
to glass conditioned with either saliva or bovine serum albumin.
6.3 Antibiotics and the Oral Biofilm
The use of antibiotics in oral medicine has a long history, especially as prophylactic
agents for preventive management. In addition, antibiotics are used for therapeutic
reasons in cases where infections of oral hard and soft tissues, such as teeth and
gingiva, cannot be controlled by local debridement and can spread to distant organs
and therefore require supplemental therapy. Nonetheless, the use of antibiotics in
dental practice has been restricted by clinicians to limit spreading antibiotic resis-
tance among oral isolates. Moreover, bacteria growing in biofilms are more resis-
tant to antibiotics than their planktonic counterparts. Antibiotic concentrations
necessary to inhibit biofilms can be 10-1,000 times higher than those needed to
inhibit bacteria growing planktonically (Sim˜es
2011
). The mechanism by which
bacteria become more resistant in the biofilm is not completely understood and is
likely multifactorial. Lewis has proposed that a fraction of the biofilm are persister
or dormant variants of regular cells that have a reduced metabolism by a
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