When the gingiva become so irritated that there is a loss of the connective tissue fibers that attach the gums to the teeth and bone that surrounds the tooth, this is known as periodontitis. Dental plaque is not the sole cause of periodontitis; however it is many times referred to as a primary aetiology. Plaque that remains in the oral cavity long enough will eventually calcify and become calculus. Calculus is detrimental to gingival health because it serves as a trap for increased plaque formation and retention; thus, calculus, along with other factors that cause a localized build-up of plaque, is referred to as a secondary aetiology of periodontitis. When plaque is supragingival, the bacterial content contains a great proportion of aerobic bacteria and yeast, or those bacteria which utilize and can survive in an environment containing oxygen. Subgingival plaque contains a higher proportion of anaerobic bacteria, or those bacteria which cannot exist in an environment containing oxygen. Several anaerobic plaque bacteria, such as Porphyromonas gingivalis, secrete antigenic proteins that trigger a strong inflammatory response in the periodontium, the specialized tissues that surround and support the teeth. Prolonged inflammation of the periodontium leads to bone loss and weakening of the gingival fibers that attach the teeth to the gums, two major hallmarks of periodontitis. Supragingival calculus formation is nearly ubiquitous in humans, but to differing degrees. Almost all individuals with periodontitis exhibit considerable subgingival calculus deposits.
Trace amounts of host, dietary, and environmental microdebris are also found within calculus, including salivary proteins, plant DNA, milk proteins, starch granules, textile fibers, and smoke particles. Calculus formation
The processes of calculus formation from dental plaque are not well understood. Supragingival calculus formation is most abundant on the buccal (cheek) surfaces of the maxillary (upper jaw) molars and on the lingual (tongue) surfaces of the mandibular (lower jaw) incisors. These areas experience high salivary flow because of their proximity to the parotid and sublingual salivary glands. Subgingival calculus forms below the gumline and is typically darkened in color by the presence of black-pigmented bacteria, whose cells are coated in a layer of iron obtained from heme during gingival bleeding. Dental calculus typically forms in incremental layers that are easily visible using both electron microscopy and light microscopy. These layers form during periodic calcification events of the dental plaque, but the timing and triggers of these events are poorly understood. The formation of calculus varies widely among individuals and at different locations within the mouth. Many variables have been identified that influence the formation of dental calculus, including age, gender, ethnic background, diet, location in the oral cavity, oral hygiene, bacterial plaque composition, host genetics, access to professional dental care, physical disabilities, systemic diseases, tobacco use, and drugs and medications. Clinical significance
Plaque accumulation causes the gingiva to become irritated and inflamed, and this is referred to as gingivitis.