This study will examine the composition of dental plaque-a naturally occurring substance
that sticks to the teeth and can cause tooth decay and gum disease. A better understanding
of how plaque builds up in the mouth may help in developing improved ways of controlling it.
Healthy normal volunteers between the ages of 18 and 65 who work at the National Institutes
of Health main campus in Bethesda, Maryland, may participate in this study. Candidates will
be screened for eligibility with a medical and dental history.
This study involves a maximum of five visits to the dental clinic. At the first visit,
participants will have a dental examination, and a mold will be made of the mouth. To make
the mold, a small plastic tray containing impression material will be placed in the
volunteer's mouth and held in place for about 2 minutes to set. The tray will then be
removed and a mold will be made from the impression. The mold will be used to make the
mouthpiece used in study 1, described below, and the tooth fittings used in study 2, also
described below. Volunteers will participate in one of these two studies.
Study 1. Volunteers in study 1 will have their mouthpiece checked at the second visit, have
a teeth cleaning, and have the mold put in place. The mouthpiece will be worn for up to 8
hours, during which time soft foods can be eaten. Mouthwash should not be used while the
device is in place. At the volunteer's third (last) visit, the mouthpiece will be removed
and the volunteer will spit into a tube to collect saliva for examination for bacteria.
Study 2. Volunteers in study 2 will have their teeth cleaned at the second visit and the
tooth fittings placed onto the back teeth with a dental adhesive. The fittings will be worn
for up to 72 hours, during which time volunteers can eat a regular diet and brush their
teeth. Mouthwash should not be used while the fittings are in place. At the third, fourth
and fifth visits, some of the fittings will be removed and, if necessary, the tooth surface
will be polished. The last of the fittings will be removed at the fifth visit and the
volunteer will spit into a tube to collect saliva for examination for bacteria.
Dental caries and periodontal disease are closely associated with dental plaque, the biofilm
that results from microbial colonization of the tooth surface. Various experimental models
have been described for the initial phase of colonization, including one that utilizes
enamel chips positioned within the oral cavity for periods of time up to 24 hours. Scanning
electron microscopy of chips removed after 4 hrs in vivo revealed individual bacteria
attached to the pellicle-coated surface. Growth of these pioneer organisms resulted in
microcolonies that merged to form a spreading monolayer of cocci and rods. Over 80% of the
bacteria present in early biofilms were identified as members of four closely related
viridans streptococcal species, Streptococcus sanguis, S. oralis, S. mitis and S. gordonii.
Veillonella spp, and Actinomyces naeslundii each composed about 5%. Interestingly,
veillonellae, actinomyces and streptococci all increased during the first 24 hrs of
colonization thereby suggesting important roles for these bacteria in normal daily plaque
accumulation [early biofilm development].
One of the major uncertainties raised by the wide-spread ability of cells of oral bacteria
to interact physically in vitro is whether these coaggregations function in vivo. Using
direct immunofluorescence, we have demonstrated the coincident juxtaposition in dental
plaque of streptococci and actinomyces, suggesting that these known coaggregating partners
may use coaggregation as a means to colonize enamel. Our overall goal is to determine
spatial organization of different viridans streptococci in biofilms that form during initial
colonization of the tooth surface. These bacteria include two groups with distinctive
properties. One group contains strains of S. sanguis and S. gordonii with GalNAc-sensitive
adhesions and the other contains strains of S. oralis and other species with complementary
receptors for intrageneric coaggregation. The models for biofilm formation will include an
in vitro flow-cell model in which streptococci with known adhesive properties attach and
grow on a saliva-coated surface and an in vivo model in which enamel chips are colonized
within the oral cavity for periods of time up to 72 hours. The results of these studies
should provide significant insights into the involvement of interbacterial adhesion in
biofilm development. Our goal from these studies is to investigate the spatial organization
of streptococci and their coaggregation partner actinomyces and veillonellae in biofilms
formed in vivo compared to in vitro. We hope to make significant advances in understanding
the distribution of these species in initial dental plaque formation. Since the streptococci
are the predominant organism in early dental plaque, we propose that understanding their
contribution to microbial communities will lead to important advances in designing effective
oral health regimens.
- INCLUSION CRITERIA:
Aged 18 to 65 years
History of medical conditions affecting salivary flow.
History of immunosuppressant therapy.
Use of tobacco.
Use of antibiotics within the preceding four months.
Use of medications thought to affect salivary flow.
Missing any maxillary premolar, first, or second molar.
Unwilling or unable to give informed consent.