Dental plaque is a complex microbial community. It is made up primarily of bacteria, but also contains inorganic compounds. It is estimated that dental plaque has approximately four-hundred types of bacteria, including, but not limited to rods, filaments, cocci and eukaryotic cells (a more complex cell, encased within a cytoskeleton). Plaque is considered to be a soft-deposit. It settles on teeth and gums. In its soft, initial stage, plaque is easy to brush off the teeth.
The inorganic compounds in plaque, mainly calcium and phosphorus, are what create the larger problem. These inorganic compounds are derived largely from saliva. When left on the teeth, the inorganic compounds harden. Once the plaque has calcified it cannot be brushed away. The process of the hardening of the plaque is referred to calcification, and the resulting hard layer is called calculus. The calculus leaves a rough surface on the tooth, which in turn provides an even more welcome surface for yet more plaque to gather and multiply.
It is important that teeth are brushed regularly in order to remove the plaque so that it will not harden into calculus. The consequence of not doing so is two-fold. As just stated, the calculus provides a welcome home to new plaque, allowing the bacterial components to multiply faster and easier, in relative comfort. The more plaque that is allowed to be deposited, the greater the area of calcification on the tooth's surface, creating an even greater area of a welcome environment for yet more plaque. It becomes a self-feeding cycle.
The secondary issue is that the same welcome environment that the rough calcified surface provides for plaque is equally attractive to other types of bacterial species. In addition to the prime environment, these species are also attracted to the natural bacteria in plaque. These secondary species of bacteria begin to accumulate after about three days of undisturbed plaque being left on the teeth. After about a week of being undisturbed, the microbial community living on the surface of the teeth attracts a third set of bacteria, even more troublesome than the original bacteria, or it's hangers-on of secondary bacteria.
The upshot is that un-brushed teeth become a welcome environment for all manner of bacteria. Not only does unattended plaque threaten the health of the teeth and gums, but other health issues are now being connected to poor oral care. Heart disease, asthma, stroke and even cancers are now being discovered to contain the same cells that are found in plaque, leading scientists to make a link between poor dental care and larger health issues. The best way to combat future problems is to brush regularly and see a dentist twice a year for a dental check-up and a cleaning.