Stages of Development

Traditionally, plaque biofilm development was described in six stages:

• Stage 1: Formation of an acellular layer called the acquired pellicle, composed of glycoproteins, phosphoproteins, and lipids.

• Stage 2: Initial attachment, when free-floating early colonizers of the teeth, such as Streptococcus sanguinis form an initial attachment to the pellicle by weak and reversible van der Waals forces.

• Stage 3: Irreversible attachment, where organisms that were unable to attach to the pellicle begin to adhere to the first layer of colonizers with irreversible attachments via specific adhesion-receptor interactions and form microcolonies embedded in an extracellular matrix.

• Stage 4: Early Maturation (also called Maturation I), with early colonizers becoming established.

• Stage 5: Late Maturation (also called Maturation II), a thick, three-dimensional layer of dental plaque biofilm formed.

• Stage 6: Dispersion, when wnzymes that degrade the biofilm (such as dispersin B) allow some bacteria to detach themselves from the biofilm and travel to new sites, to start the cicle again.²⁰

However, latest technology has allowed the observation that 90% of the microbes in saliva can be found as multicellular structures, instead of free living bacterial cells (planktonic; fluid phase). Bacteria are also found coadhered with human epithelial cells, forming a highly complex and structurally diverse community. Notably, it is now understood that (Figure 6):

• Stage 1 - Pellicle formation: is characterized by the formation of an acellular layer called enamel pellicle formation.

• Stage 2 - Attachment: this stage is marked by both aggregates and single cells can bind to the tooth surface (solid phase), and these microbial aggregates in saliva harbor different bacterial taxa, including those traditionally considered early and late colonizers. Thus, the polymicrobial community can adhere to the surface collectively as structured colonizing units without an orderly attachment in a sequential fashion.

• Stage 3 - Biofilm initiation and development: Actively growing aggregates expand tridimensionally, often engulfing the single cells and merging with other active growers to build the oral biofilm, forming spatially and compositionally heterogeneous superstructures but with reduced microbial diversity.

• Stage 4 – Dispersion: when microbial aggregates detach from the biofilm and a new cycle starts.²¹

Figure 6. A) Saliva is dominated by polymicrobial aggregates harboring different species together in addition to free-living bacterial cells. Bacteria are also found coadhered with human epithelial cells. B) Bacteria that traditionally have been considered early and late colonizers are found together in the adhering aggregates and in early formed human plaque samples, indicating that they bind concomitantly to the surface as a colonizing unit. C) Microbial aggregates attached to the enamel pellicle act as growth nuclei that grow more actively and faster than the attached single cells, which stay mostly static. Actively growing aggregates expand tridimensionally, often engulfing the static cells and merging with active growers, forming superstructures.

Figure 6. A) Saliva is dominated by polymicrobial aggregates harboring different species together in addition to free-living bacterial cells. Bacteria are also found coadhered with human epithelial cells. B) Bacteria that traditionally have been considered early and late colonizers are found together in the adhering aggregates and in early formed human plaque samples, indicating that they bind concomitantly to the surface as a colonizing unit. C) Microbial aggregates attached to the enamel pellicle act as growth nuclei that grow more actively and faster than the attached single cells, which stay mostly static. Actively growing aggregates expand tridimensionally, often engulfing the static cells and merging with active growers, forming superstructures.