Biomedical Engineering Reference
In-Depth Information
(azoles, nystatin) should be reserved for patient treatment and are less active against
biofilms on dentures (see
infra
); moreover, they may cause the emergence of resistant
strains. Use of antiphlogistic solutions has been highly successful; as many of them are
fungicidal. However, there are no comparative studies that examine all aspects of the
problem.
Rarely, if ever, do study authors take into account the views of all professionals involved in
denture care, not only the opinions of the dentist who treats the patient, but also those of the
prosthetist who sees the potential deleterious effects of some decontaminating procedures
and the microbiologist who isolates and studies yeast
in vitro
. Microbiologists are able to
determine the minimum inhibitory concentrations of antifungals on
Candida
growth in
suspensions, or better (but less often), on
Candida
biofilms produced in the laboratory.
Dental technicians are involved in the relationship with the materials they provide, biofilms,
and the decontamination procedures. Clinicians' decisions cannot rely on evidence-based
studies alone since they lack data from large-scale clinical trials (i.e.,
in vivo
studies).
4.1 Anti-biofilm agents
Many molecules that are embedded in antiseptic mouthwash or in effervescent tablets are
candidacidal. Sodium hypochlorite, a major component of bleach that is also produced
in
vivo
by myeloperoxidase from the neutrophils, has an anti-
Candida
effect. Ozonated water
with or without ultrasound reduces yeasts' adherence to the resin. The use of ultrasound
reduces the concentration required for effectiveness of most antiseptics or fungicide
antimycotics. The use of a microwave oven is not recommended because the conditions that
suppress the yeasts are too close to those that damage some prosthesis materials. When
misused, some products can damage the materials: the repeated use of chlorhexidine colors
resins brown; hypochlorite at a high dose bleaches them. Hydrogen peroxide is active only
at a very high concentration that is close to the mucosal toxicity level; moreover, in the
presence of hydrogen peroxide,
Candida
over-expresses catalase and glutathione oxidase,
which in turn reduces the concentration of hydrogen peroxide and protects the yeast cells
against oxidation.
An alternative to prevent biofilm formation could involve a reduction of microorganism
adherence to materials by anti-adhesive/anti-microbial coatings, with or without drug
release. Indeed, the anchoring of microorganisms to surfaces such as mucosa, teeth, or
biomaterial is a pivotal step in initiating biofilms into the oral cavity. Adhesion can be
quantified by measurement of the microorganisms' retention after fixed incubation periods
and washings or by the microorganisms' retention against a continuous flow of medium
(Cannon et al., 2010). Many protocols have been proposed to limit biofilm formation on
various materials used in dentistry (recently reviewed by Busscher et al., 2010): antibiotic
and peptide coatings, silver and polymer-brush coatings, and quaternary ammonium
couplings.
In vitro
, titanium dioxide coating inhibits
Candida
adhesion to the denture's base
in acrylic resin (Arai et al., 2009). Surface protection from bacteria and yeast by chitosan
coating is also worthy of further pharmacologic and clinical studies (Carlson et al., 2008).
Surface treatment must solve numerous challenges before clinical implementation: the
amount of bioavailable drug on the material's surface, kinetic and safety of the released
compounds, interferences with the oral environment, and the quest for multifunctional
effects such as biofilm control, tissue integration, and/or tissue regeneration.
