Dental biofilm consists of acquired pellicle, attached bacteria and EPS (extracellular polymeric substances). Bacteria attach to the pellicle and to each other to form several layers of attached bacteria. After attachment to the acquired pellicle bacteria produce EPS. EPS surrounds the bacterial layers making the biofilm harder to remove from the tooth surface.
Dental plaque is a dental biofilm that has had the time to grow on the surface of a tooth and is now visible on inspection. If dental plaque is allowed to remain on a tooth and mineralize it will become calculus or tartar. The longer the biofilm has to grow the thicker and harder it gets. Plaque and tartar are highly adherent to the teeth and are rarely removed by tooth brushing alone. Plaque and tartar usually require a professional cleaning to remove.
Plaque is a mature biofilm that can be seen by visual inspection.