Biomedical Engineering Reference
In-Depth Information
the case not only when peroxidase and substrates system were dissolved in the liquid phase
into which the material was immersed, but also when peroxidase precoated on material was
activated by simple addition of the substrates to the liquid surrounding this material. Those
data also demonstrated the efficiency of peroxidase systems against a
Candida
strain during
a three-week incubation period and concomitantly suggested a possible interest in coating
the material with peroxidase.
Other investigations demonstrated 1) that lactoperoxidase activity was not modified by
coating onto titanium, 2) that lactoperoxidase incorporated in oral gel maintained its activity
for at least one year, and 3) that the substrate exhaust (namely hydrogen peroxide and
iodide) was the true limiting factor (Bosch et al., 2000; Ahariz et al., 2000). Previous
investigations indicated an antibacterial effect on Gram-positive and Gram-negative
bacteria, which suggests a non-specific inhibitory effect of hypoiodite on microbial
metabolism and growth (Courtois et al., 1995). The ability to transfer this knowledge from
bench to clinic is questionable. Indeed, the immunogenicity of a material surface coated with
lactoperoxidase should restrict the applications of this system to
ex vivo
conditions. Besides
the toxicity of oxidant products on host cells, the competition between iodide and
thiocyanate is another limiting factor for
in vivo
use. Thiocyanate is not only present in
several exocrine secretions (e.g., human saliva) but is also the preferential substrate of
lactoperoxidase. Simultaneous incorporation of iodide and thiocyanate in the same gel
decreased the beneficial effect of 2 mM iodide in the presence of increasing concentrations of
thiocyanate ranging from 0.25 to 4 mM, which correspond to the normal range of this ion in
saliva.
5. Precautions for testing new devices
in vivo
Finally, the investigators must be aware of the biases frequently encountered in clinical trials
that evaluate microbial contamination and colonization of oral devices and prosthesis.
Recommendations and guidelines to evaluate the benefits of prophylactic anti-
Candida
procedures are similar to these advocated for any oral care product. Two important biases
that must be taken into account are the influence of investigators on patients' hygiene
behavior (Grimoud et al., 2005) and the galenic formulation of products lacking the active
molecule. Evaluation of dentifrice efficiency for denture hygiene also needs other controls:
one testing the product without brushing and one testing the mechanical brushing alone.
The abrasive effect of the product must be evaluated, and the abrasiveness of saliva itself is
another concern to be considered.
Quantification of the
Candida
biomass that is adherent to the device is difficult in practice.
Yeast samples from the oral environment can be collected by rinsing, imprinting, or
swabbing. Swabs and imprints are more suitable for gathering yeasts attached to surfaces,
and swabbing is easier for clinical studies on a larger scale. Procedures to quantify yeast
biomass
in vitro
are not applicable
in vivo
for epidemiological studies and hygiene purposes,
particularly since denture-wearers are not always compliant. Dentures can be rinsed in
saline and brushed in standard condition to harvest microbial cells. The suspension is
thereafter serially diluted for counting (Panzeri et al., 2009).
Another study (Vanden Abbeele et al., 2008) documented the reliability of oral swabbing to
investigate yeast carriage on denture. Sampling dentures for
Candida
is more than just a
diagnostic tool: it could present an opportunity to verify the patient's compliance with
hygiene advice as well as the efficiency of new topical antifungals. Yeast counts after swab
