Many oral pathologies, such as dental caries, periodontal disease and 
peri-implantitis are plaque-related. Dental plaque is a microbial biofilm formed 
by organisms tightly bound to a solid substrate and each other by means of an 
exopolymer matrix. Bacteria exhibit different properties when contained within a 
biofilm. Knowing the mechanisms controlling the formation and development of 
biofilms can help to understand the emergence and progression of such 
pathologies and to plan effective treatment. Most periodontal pathogens are 
common saprophytes of the oral cavity, expressing their virulence only in a 
susceptible host or when some changes come about in the oral environment. 
Physical, metabolic and physiological interactions may cause positive or 
negative effects among the various microbiota present. Such mechanisms of 
antagonism/synergy select the bacterial population and alterations of its 
composition affect the balance with the host and may lead to pathology. The 
effectiveness of antimicrobial agents, as measured through in vitro tests, is 
dramatically reduced in vivo due to the properties of the microbial community: 
mature, intact biofilms are less sensitive to such agents, as the exopolymer 
matrix, bacterial enzymes and slow growth rate hinder the action of 
chemotherapeutic agents. The present literature review aims to examine the most 
representative studies, focusing on the characteristics of bacterial communities 
and the crucial shift from oral health to plaque-related diseases.