Oral microbiota. The oral microbiota includes a vast range of bacteria with most of the organisms that colonize the mouth benefiting human health by adding to the defence against exogenous harmful species, however some of the microbiota are pathogenic and can, if not controlled, lead to oral health problems (Xxxxx et al., 2009). Bacteria are present in saliva, but due to desquamation, accumulation on the soft tissue in the mouth is limited. This is exemplified by the fact that a robust biofilm is not formed in the oral cavity of infants until tooth eruption (Xxxxx., 2000). Bacteria can accumulate on tooth surfaces because they are hard non-shedding surfaces; some areas of the tooth are more prone to greater plaque depth due to physical protection e.g. fissures on occlusal surfaces, and the gingival margin (Xxxxx & Xxxxxxxx., 1995). Teeth and the gingival margin create a subgingival environment that contains gingival curricular fluid (GCF), which is rich in nutrients and allows migrating bacteria from supragingival biofilms to form subgingival biofilms. However, it has been hypothesised that it is a shift in the subgingival microbiological composition from predominantly gram-positive bacteria to gram-negative bacteria that is the cause of gum disease (Berezow & Xxxxxxx., 2011). This is a different process than observed with the formation of dental caries, which often occurs when there is a shift in microbiological composition within the gram-positive species to more cariogenic species, i.e. an increased in the population of Streptococcus mutans species (Xxxxx., 2000). The difference between gram-positive and gram-negative bacteria is the number of cell walls an organism has which is determined through staining techniques; gram-positive species have one cell wall and gram-negative have 2 cell walls. Therefore antimicrobial agents will have varying efficacy on these categories depending on the mechanism of action (Neu & Xxxxx., 1996; Xxxxxxx et al., 2010). The compositions of these two categories and indeed species within these categories of bacteria vary in the mouth depending on a person’s health, diet and oral hygiene, but if they are not controlled they aggregate and form oral plaque.
