Calculus (dental)

thumb|right|Heavy staining and calculus deposits exhibited on the [[Commonly used terms of relationship and comparison in dentistry|lingual surface of the mandibular anterior teeth, along the gumline]]

thumb|Calculus deposit (indicated with a red arrow) on x-ray image

In dentistry, dental calculus or tartar is a form of hardened dental plaque. It is caused by precipitation of minerals from saliva and gingival crevicular fluid (GCF) in plaque on the teeth. This process of precipitation kills the bacterial cells within dental plaque, but the rough and hardened surface that is formed provides an ideal surface for further plaque formation. This leads to calculus buildup, which compromises the health of the gingiva (gums). Calculus can form both along the gumline, where it is referred to as supragingival (), and within the narrow sulcus that exists between the teeth and the gingiva, where it is referred to as subgingival ().

Calculus formation is associated with a number of clinical manifestations, including bad breath, receding gums and chronically inflamed gingiva. Brushing and flossing can remove plaque from which calculus forms; however, once formed, calculus is too hard (firmly attached) to be removed with a toothbrush. Calculus buildup can be removed with ultrasonic tools or dental hand instruments (such as a periodontal scaler).

Etymology

The word comes from Latin , from , probably related to Greek , which many trace to a Proto-Indo-European root for . Calculus was a term used for various kinds of stones. This spun off many modern words, including calculate (), and calculus, which came to be used, in the 18th century, for accidental or incidental mineral buildups in human and animal bodies, like kidney stones and minerals on teeth.

Chemical composition

Calculus is composed of both inorganic (mineral) and organic (cellular and extracellular matrix) components.

In supra-gingival calculus

The mineral proportion of supragingival calculus ranges from approximately 40–60%, depending on its location in the dentition, and consists primarily of calcium phosphate crystals organized into four principal mineral phases, listed here in order of increasing ratio of phosphate to calcium:

hydroxyapatite,
whitlockite,
octacalcium phosphate,
and brushite,

The organic component is approximately 85% cellular and 15% extracellular matrix. The cells within calculus are primarily bacterial, but also include at least one species of archaea (Methanobrevibacter oralis) and several species of yeast (e.g., Candida albicans). The organic extracellular matrix in calculus consists primarily of proteins and lipids (fatty acids, triglycerides, glycolipids, and phospholipids), 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.

In sub-gingival calculus

Sub-gingival calculus is composed almost entirely of two components: fossilized anaerobic bacteria whose biological composition has been replaced by calcium phosphate salts, and calcium phosphate salts that have joined the fossilized bacteria in calculus formations.

The following minerals are detectable in calculus by X-ray diffraction:

brushite ()
octacalcium phosphate ()
magnesium-containing whitlockite ()
carbonate-containing hydroxyapatite (approximately but containing some carbonate).

Calculus formation

Dental calculus typically forms in incremental layers that are easily visible using both electron microscopy and light microscopy. 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, The reason fossilized bacteria are initially attracted to one part of the subgingival tooth surface over another is not fully understood. However, once the first layer is attached, more calculus components are naturally attracted to the same places due to electrical charge. This is because the calcium phosphate salts contained in them exist as electrically unstable ions (unlike calcium phosphate, the primary component of teeth). The fossilized bacteria pile up rather haphazardly, while free-floating ionic components (calcium phosphate salts) fill in the gaps. 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. and mothers giving birth to pre-term low weight infants, but there is no conclusive evidence yet that periodontitis is a significant risk factor for either of these two conditions.

Prevention

Toothpaste with pyrophosphates or zinc citrate has been shown to produce a statistically significant reduction in plaque accumulation, but the effect of zinc citrate is so modest that its clinical importance is questionable. Some calculus may form even without plaque deposits, by direct mineralisation of the pellicle.

Calculus in other animals

Calculus formation in other animals is less well studied than in humans, but it is known to form in a wide range of species. Domestic pets, such as dogs and cats, frequently accumulate large calculus deposits. Animals with highly abrasive diets, such as ruminants and equids, rarely form thick deposits and instead tend to form thin calculus deposits that often have a metallic or opalescent sheen. In animals, calculus should not be confused with crown cementum, a layer of calcified dental tissue that encases the tooth root underneath the gingival margin and is gradually lost through periodontal disease.

Archaeological significance

Dental calculus has been shown to contain well preserved microparticles, DNA and protein in archaeological samples. The information these molecules contain can reveal information about the oral microbiome of the host and the presence of pathogens. It is also possible to identify dietary sources as well as study dietary shifts and occasionally evidence of craft activities.

Removal of calculus after formation

Plaque and calculus deposits are a major etiological factor in the development and progression of oral disease. An important part of the scope of practice of a dental hygienist is the removal of plaque and calculus deposits. This is achieved through the use of specifically designed instruments for debridement of tooth surfaces. Treatment with these types of instruments is necessary as calculus deposits cannot be removed by brushing or flossing alone. To effectively manage disease or maintain oral health, thorough removal of calculus deposits should be completed at frequent intervals. The recommended frequency of dental hygiene treatment can be made by a registered professional, and is dependent on individual patient needs. Factors that are taken into consideration include an individual's overall health status, tobacco use, amount of calculus present, and adherence to a professionally recommended home care routine.

Hand instruments are specially designed tools used by dental professionals to remove plaque and calculus deposits that have formed on the teeth. Curettes can be divided into two subgroups: universals and area specific instruments. Universal curettes can be used in multiple areas, while area specific instruments are designed for select tooth surfaces. The use of lasers in periodontal therapy offers a unique clinical advantage over conventional hand instrumentation, as the thin and flexible fibers can deliver laser energy into periodontal pockets that are otherwise difficult to access.