The type and availability of nutrients is important in
establishing microbial growth. Nutrients may be
derived from the oral cavity, degenerating connective
tissue, dentinal tubule contents, or a serum-like fluid
from periapical tissue. Exogenous nutrients, such as
fermentable carbohydrates, affect the microbial ecology
of the coronal part of an exposed root canal by
promoting growth of species that primarily obtain
energy by carbohydrate fermentation. Endogenous
proteins and glycoproteins are the principal nutrients in
the main body of the root canal system and this
substrate encourages the growth of anaerobic bacteria
capable of fermenting amino acids and peptides.
The succession of strict over facultative anaerobes
with time is most likely due to changes in available
nutrition, as well as a decrease in oxygen availability.
Facultatively anaerobic bacteria dominated by
streptococci grow well in anaerobiosis, however their
prime energy source is carbohydrates. A decrease in
availability of carbohydrates in the root canal occurs
when there is no direct communication with the oral
cavity, which severely limits growth opportunities for
facultative anaerobes.
Growth of mixed bacterial populations may depend
on a food chain in which the metabolism of one species
supplies essential nutrients for the growth of other
members of the population.
Black-pigmented
anaerobic rods ( Prevotellaand Porphyromonas species)
are examples of bacteria that have very specific
nutritional requirements. They are dependent on
vitamin K and hemin for growth. Vitamin K can be
produced by other bacteria.
Hemin becomes available
when haemoglobin is broken down, but some bacteria
may also produce hemin. A wide range of nutritional
interactions is recognized among oral bacteria and
these may also influence the associations between
bacteria in the root canal.
After degradation of pulp tissue, a sustainable source
of proteins develops because bacteria induce periapical
inflammation that leads to an influx of a serum-like
exudate into the canal. This fluid contains proteins and
glycoproteins, and the bacteria that dominate this stage
of the infection are likely to be those that either have a
proteolytic capacity, or maintain a cooperative synergy
with those that can utilize this substrate for bacterial
metabolism.