Detection & characterisation of microoganisms in denture plaque
Oral health status declines with age and as a result the need for removable prostheses
increases.T he microbiology of denture plaque has received little attention in comparison
with dental plaque, yet it differs in location, and composition. Denture plaque and poor
denture hygienea re suggestedto be causeso f denturer elateds tomatitis, may contribute to
oral malodour,a nd can also facilitate colonisationo f the prosthesisb y potentially infectious
The aims of this study were to evaluate current and novel methods for detection and
characterisationo f denturep laquea nd to contributet o the knowledgei n this neglecteda rea.
In a clinical study the fluorescence of in vivo denture plaque was assessed using
Quantitative Light-induced Fluorescence (QLF), which was developed for early dental
cariesd etectionu sing a blue excitation light (405 nm) and capturing fluorescencee mission.
Areas were seen to fluoresce red, orange and green and the causative microorganisms were
recovered and identified. Red fluorescence was due to the anaerobes Prevotella
melaninogenica and Actinomyces israelii and orange to Candida albicans. These species
are generally acknowledged to be secondary colonisers, present in more mature plaque.
Green fluorescence was observed in streptococcal species (early colonisers) and
Fusobacterium nucleatum (important bridging organism in plaque development).
Low recovery of red fluorescing species indicated a lack of cultivability, viability or an
inter-species dependence. Denture plaque populations were therefore investigated using
culture- independent PCR and denaturing gradient gel electrophoresis (DGGE). PCRDGGE
profiling indicated a highly diverse personalised microbiota for each denture plaque
sample, and the red fluorescent plaque harboured an increased bacterial diversity compared to green fluorescent plaque. However, problems with 16S rRNA gene sequence
heterogeneityh ighlight the needf or resultst o be supplementedb y culture studies.
Identification of the fluorophore responsiblef or fluorescencew as necessaryto validate
the origin of fluorescence using QLF. The spectral characteristics of red fluorescing
microorganismsw ere typical of fluorescentp orphyrins,p articularly protoporphyrini x.
Most studies looking at plaque removal and antimicrobial efficacy use simple staining
and visualisation for plaque removal in vivo, and batch culture for antimicrobial efficacy in
vitro. Both methodsr equire improvementsa nd standardisationC. urrent and novel methods
(including the QLF) for in vivo assessment of denture hygiene based on plaque
quantification were investigated. Image analysis methods offer permanent images,
improved accuracy and increased sensitivity over subjective visual ranking yet increase
assessmenttim e considerably.F indings suggestt hat QLF may be suitablef or screeningf or
the presence of mature plaque development with indications of the presence of specific
obligate anaerobic bacteria, but not for plaque quantification.
A constant depth film fermenter (CDFF) was used to investigate the stability and
composition of oral salivary and denture plaque microcosms with and without C. albicans.
Further characterisation of denture plaque enabled development of a more realistic 'model'
denture plaque biofilm for in vitro antimicrobial efficacy testing methods using denture
This study has contributed to knowledge concerning the microbiology of denture
plaque, and, by evaluating a range of in vivo and in vitro methods, has enabled the
recommendation of objective tests for the evaluation of denture hygiene products for full