In dentistry, 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 ("above the gum"), and within the narrow sulcus that exists between the teeth and the gingiva, where it is referred to as subgingival ("below the gum").

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, it is too hard and 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).

A person experiencing caries may not be aware of the disease. The earliest sign of a new carious lesion is the appearance of a chalky white spot on the surface of the tooth, indicating an area of demineralization of enamel. This is referred to as a white spot lesion, an incipient carious lesion or a "microcavity". As the lesion continues to demineralize, it can turn brown but will eventually turn into a cavitation ("cavity"). Before the cavity forms, the process is reversible, but once a cavity forms, the lost tooth structure cannot be regenerated.

A lesion that appears dark brown and shiny suggests dental caries were once present but the demineralization process has stopped, leaving a stain. Active decay is lighter in color and dull in appearance.

As the enamel and dentin are destroyed, the cavity becomes more noticeable. The affected areas of the tooth change color and become soft to the touch. Once the decay passes through enamel, the dentinal tubules, which have passages to the nerve of the tooth, become exposed, resulting in pain that can be transient, temporarily worsening with exposure to heat, cold, or sweet foods and drinks. A tooth weakened by extensive internal decay can sometimes suddenly fracture under normal chewing forces. When the decay has progressed enough to allow the bacteria to overwhelm the pulp tissue in the center of the tooth, a toothache can result and the pain will become more constant. Death of the pulp tissue and infection are common consequences. The tooth will no longer be sensitive to hot or cold, but can be very tender to pressure.

Dental caries can also cause bad breath and foul tastes. In highly progressed cases, an infection can spread from the tooth to the surrounding soft tissues. Complications such as cavernous sinus thrombosis and Ludwig angina can be life-threatening.

Attrition occurs as a result of opposing tooth surfaces contacting. The contact can affect cuspal, incisal and proximal surface areas.

Indications of attrition can include:

- Loss of tooth anatomy: This results in loss of tooth characteristics including rounding or sharpening of incisal edges, loss of cusps and fracturing of teeth. Enamel of molar teeth may appear thin and flat. When in occlusion the teeth may appear the same height which is particularly apparent for anterior teeth.

- Sensitivity or pain: Attrition may be entirely asymptomatic, or there may be dentin hypersensitivity secondary to loss of the enamel layer, or tenderness of the periodontal ligament caused by occlusal trauma.

- Tooth discolouration: A yellow appearance of the tooth surface may be due to the enamel being worn away, exposing the darker yellower dentin layer underneath.

- Altered occlusion due to decreasing vertical height, or occlusal vertical dimension.

- Compromised periodontal support can result in tooth mobility and drifting of teeth

- Loss in posterior occlusal stability

- Mechanical failure of restorations

Acid erosion often coexists with abrasion and attrition. Abrasion is most often caused by brushing teeth too hard.

Any frothing or swishing acidic drinks around the mouth increases the risk of acid erosion.

The symptoms of gingivitis are somewhat non-specific and manifest in the gum tissue as the classic signs of inflammation:

- Swollen gums

- Bright red or purple gums

- Gums that are tender or painful to the touch

- Bleeding gums or bleeding after brushing and/or flossing

- Bad breath (halitosis)

Additionally, the stippling that normally exists in the gum tissue of some individuals will often disappear and the gums may appear shiny when the gum tissue becomes swollen and stretched over the inflamed underlying connective tissue. The accumulation may also emit an unpleasant odor. When the gingiva are swollen, the epithelial lining of the gingival crevice becomes ulcerated and the gums will bleed more easily with even gentle brushing, and especially when flossing.

Dental plaque is a biofilm or mass of bacteria that grows on surfaces within the mouth. It is a sticky colorless deposit at first, but when it forms tartar, it is often brown or pale yellow. It is commonly found between the teeth, on the front of teeth, behind teeth, on chewing surfaces, along the gumline, or below the gumline cervical margins. Dental plaque is also known as microbial plaque, oral biofilm, dental biofilm, dental plaque biofilm or bacterial plaque biofilm.

Progression and build-up of dental plaque can give rise to tooth decay – the localised destruction of the tissues of the tooth by acid produced from the bacterial degradation of fermentable sugar – and periodontal problems such as gingivitis and periodontitis; hence it is important to disrupt the mass of bacteria and remove it. Plaque control and removal can be achieved with correct daily or twice-daily tooth brushing and use of interdental aids such as dental floss and interdental brushes.

Oral hygiene is important as dental biofilms may become acidic causing demineralization of the teeth (also known as dental caries) or harden into dental calculus (also known as tartar). Calculus cannot be removed through tooth brushing or with interdental aids, but only through professional cleaning.

Tooth decay, also known as dental caries or cavities, is a breakdown of teeth due to acids made by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complications may include inflammation of the tissue around the tooth, tooth loss, and infection or abscess formation.

The cause of caries is acid from bacteria dissolving the hard tissues of the teeth (enamel, dentin and cementum). The acid is produced from food debris or sugar on the tooth surface. Simple sugars in food are these bacteria's primary energy source and thus a diet high in simple sugar is a risk factor. If mineral breakdown is greater than build up from sources such as saliva, caries results. Risk factors include conditions that result in less saliva such as: diabetes mellitus, Sjogren's syndrome and some medications. Medications that decrease saliva production include antihistamines and antidepressants. Caries is also associated with poverty, poor cleaning of the mouth, and receding gums resulting in exposure of the roots of the teeth.

Prevention of dental caries includes regular cleaning of the teeth, a diet low in sugar, and small amounts of fluoride. Brushing the teeth twice per day and flossing between the teeth once a day is recommended by many. Fluoride may be from water, salt or toothpaste among other sources. Treating a mother's dental caries may decrease the risk in her children by decreasing the numbers of certain bacteria. Screening can result in earlier detection. Depending on the extent of destruction, various treatments can be used to restore the tooth to proper function or the tooth may be removed. There is no known method to grow back large amounts of tooth. The availability of treatment is often poor in the developing world. Paracetamol (acetaminophen) or ibuprofen may be taken for pain.

Worldwide, approximately 2.3 billion people (32% of the population) have dental caries in their permanent teeth. The World Health Organization estimates that nearly all adults have dental caries at some point in time. In baby teeth it affects about 620 million people or 9% of the population. They have become more common in both children and adults in recent years. The disease is most common in the developed world due to greater simple sugar consumption and less common in the developing world. Caries is Latin for "rottenness".

Dental fluorosis (also termed mottled enamel) is an extremely common disorder, characterized by hypomineralization of tooth enamel caused by ingestion of excessive fluoride during enamel formation.

It appears as a range of visual changes in enamel causing degrees of intrinsic tooth discoloration, and, in some cases, physical damage to the teeth. The severity of the condition is dependent on the dose, duration, and age of the individual during the exposure. The "very mild" (and most common) form of fluorosis, is characterized by small, opaque, "paper" white areas scattered irregularly over the tooth, covering less than 25% of the tooth surface. In the "mild" form of the disease, these mottled patches can involve up to half of the surface area of the teeth. When fluorosis is moderate, all of the surfaces of the teeth are mottled and teeth may be ground down and brown stains frequently "disfigure" the teeth. Severe fluorosis is characterized by brown discoloration and discrete or confluent pitting; brown stains are widespread and teeth often present a corroded-looking appearance.

People with fluorosis are relatively resistant to dental caries (tooth decay caused by bacteria), although they may be of cosmetic concern. In moderate to severe fluorosis, teeth are physically damaged.

There are many signs of dental erosion, including changes in appearance and sensitivity. One of the physical changes can be the color of teeth. There are two different colors teeth may turn if dental erosion is occurring, the first being a change of color that usually happens on the cutting edge of the central incisors. This causes the cutting edge of the tooth to become transparent. A second sign is if the tooth has a yellowish tint. This occurs because the white enamel has eroded away to reveal the yellowish dentin. A change in shape of the teeth is also a sign of dental erosion. Teeth will begin to appear with a broad rounded concavity, and the gaps between teeth will become larger. There can be evidence of wear on surfaces of teeth not expected to be in contact with one another. If dental erosion occurs in children, a loss of enamel surface characteristics can occur. Amalgam restorations in the mouth may be clean and non-tarnished. Fillings may also appear to be rising out of the tooth, the appearance being caused when the tooth is eroded away leaving only the filling. The teeth may form divots on the chewing surfaces when dental erosion is occurring. This mainly happens on the first, second, and third molars. One of the most severe signs of dental erosion is cracking, where teeth begin to crack off and become coarse. Other signs include pain when eating hot, cold, or sweet foods. This pain is due to the enamel having been eroded away, exposing the sensitive dentin.

The main types of dental abscess are:

- Periapical abscess: The result of a chronic, localized infection located at the tip, or apex, of the root of a tooth.

- Periodontal abscess: begins in a periodontal pocket (see: periodontal abscess)

- Gingival abscess: involving only the gum tissue, without affecting either the tooth or the periodontal ligament (see: periodontal abscess)

- Pericoronal abscess: involving the soft tissues surrounding the crown of a tooth (see: Pericoronitis)

- Combined periodontic-endodontic abscess: a situation in which a periapical abscess and a periodontal abscess have combined (see: Combined periodontic-endodontic lesions).

The two main classification systems are described below. Others include the tooth surface fluorosis index (Horowitz et al. 1984), which combines Deans index and the TF index; and the fluorosis risk index (Pendrys 1990), which is intended to define the time at which fluoride exposure occurs, and relates fluorosis risk with tooth development stage.

Enamel infractions are microcracks seen within the dental enamel of a tooth. They are commonly the result of dental trauma to the brittle enamel, which remains adherent to the underlying dentine. They can be seen more clearly when transillumination is used.

Enamel infractions are found more often in older teeth, as the accumulated trauma is greatest.

Enamel infractions can also be found as a result of iatrogenic damage inadvertently caused by instrumentation during dental treatments.

Gingivitis is a non-destructive disease that occurs around the teeth. The most common form of gingivitis, and the most common form of periodontal disease overall, is in response to bacterial biofilms (also called plaque) that is attached to tooth surfaces, termed "plaque-induced gingivitis".

While some cases of gingivitis never progress to periodontitis, data indicates that periodontitis is always preceded by gingivitis.

Gingivitis is reversible with good oral hygiene; however, without treatment, gingivitis can progress to periodontitis, in which the inflammation of the gums results in tissue destruction and bone resorption around the teeth. Periodontitis can ultimately lead to tooth loss. The term means "inflammation of the gum tissue".

Abrasion is a pathological, non-carious tooth loss that most commonly affects the premolars and canines. Abrasion frequently presents at the cemento-enamel junction and can be caused by many contributing factors, all with the ability to affect the tooth surface in varying degrees.

Sources of abrasion may arise from oral hygiene habits such as toothbrushes, toothpicks, floss, and dental appliance or may arise from other habits such as nail biting, chewing tobacco or another object. Abrasion can also occur from the type of dentifrice being utilized as some have more abrasive qualities such as whitening toothpastes.

The appearance may vary depending on the aetiology of abrasion, however most commonly presents in a V-shaped caused by excessive lateral pressure whilst tooth-brushing. The surface is shiny rather than carious, and sometimes the ridge is deep enough to see the pulp chamber within the tooth itself.

In order for successful treatment of abrasion to occur, the aetiology first needs to be identified and ceased, e.g. overzealous brushing. Once this has occurred subsequent treatment may involve the changes in oral hygiene or toothpaste, application of fluoride to reduce sensitivity or the placement of a restoration to aid in reducing the progression of further tooth loss.

The word comes from Latin "calculus" "small stone", from "calx" "limestone, lime", probably related to Greek "chalix" "small stone, pebble, rubble" which many trace to a Proto-Indo-European root for "split, break up". "Calculus" was a term used for various kinds of stones. This spun off many modern words, including "calculate" (use stones for mathematical purposes), 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.

Tartar, on the other hand, originates in Greek as well ("tartaron"), but as the term for the white encrustation inside casks, aka potassium bitartrate commonly known as cream of tartar. This came to be a term used for calcium phosphate on teeth in the early 19th century.

Necrotic pulp is a finding in dentistry to describe dental pulp within a tooth which has become necrotic. Directly meaning, death of the pulp. It is a finding of interest to dentists as the process of pulp death may be painful causing a toothache.

Sequelae of a necrotic pulp include acute apical periodontitis, dental abscess or radicular cyst and discolouration of the tooth.

Tests for a necrotic pulp include: vitality testing using a thermal test or an electric pulp tester. Discolouration may be visually obvious, or more subtle.

Treatment usually involves endodontics or extraction.

The pain is continuous and may be described as extreme, growing, sharp, shooting, or throbbing. Putting pressure or warmth on the tooth may induce extreme pain. The area may be sensitive to touch and possibly swollen as well. This swelling may be present at either the base of the tooth, the gum, and/or the cheek, and sometimes can be reduced by applying ice packs.

An acute abscess may be painless but still have a swelling present on the gum. It is important to get anything that presents like this checked by a dental professional as it may become chronic later.

In some cases, a tooth abscess may perforate bone and start draining into the surrounding tissues creating local facial swelling. In some cases, the lymph glands in the neck will become swollen and tender in response to the infection. It may even feel like a migraine as the pain can transfer from the infected area. The pain does not normally transfer across the face, only upwards or downwards as the nerves that serve each side of the face are separate.

Severe aching and discomfort on the side of the face where the tooth is infected is also fairly common, with the tooth itself becoming unbearable to touch due to extreme amounts of pain.

Early Childhood Caries (ECC), formerly known as nursing bottle caries, baby bottle tooth decay, night bottle mouth and night bottle caries, is a disease that affects teeth in children aged between birth and 71 months. ECC is characterized by the presence of 1 or more decayed (noncavitated or cavitated lesions), missing (due to caries), or filled tooth surfaces in any primary tooth. ECC has been shown to be a very common, transmissible bacterial infection, usually passed from the primary caregiver to the child. The main bacteria responsible for dental caries is Streptococcus mutans (S. Mutans) and Lactobacillus. There is also evidence that supports that those who are in lower socioeconomic populations are at greater risk of developing ECC.

Dental attrition is a type of tooth wear caused by tooth-to-tooth contact, resulting in loss of tooth tissue, usually starting at the incisal or occlusal surfaces. Tooth wear is a physiological process and is commonly seen as a normal part of aging. Advanced and excessive wear and tooth surface loss can be defined as pathological in nature, requiring intervention by a dental practitioner. The pathological wear of the tooth surface can be caused by bruxism, which is clenching and grinding of the teeth. If the attrition is severe, the enamel can be completely worn away leaving underlying dentin exposed, resulting in an increased risk of dental caries and dentin hypersensitivity. It is best to identify pathological attrition at an early stage to prevent unnecessary loss of tooth structure as enamel does not regenerate.

Early childhood caries (ECC) is a multi-factorial disease, referring to various risk factors that inter-relate to increase risk of developing the disease. These risk factors include but not limited to, cariogenic bacteria, diet practices and socioeconomic factors. Normally after 6 months, deciduous teeth begin to erupt means, they are susceptible to tooth decay or dental caries. In some unfortunate cases, infants and young children have experienced severe tooth decay called ECC. This can result in the child experiencing severe pain, extensive dental restorations or extractions. The good news is that ECC is preventable, however, still remains a large burden particularly towards health care expenditure.

Supernumerary teeth can be classified by shape and by position. The shapes include the following:

- Supplemental (where the tooth has a normal shape for the teeth in that series);

- Tuberculate (also called "barrel shaped");

- Conical (also called "peg shaped");

- Compound odontoma (multiple small tooth-like forms);

- Complex odontoma (a disorganized mass of dental tissue)

When classified by position, a supernumerary tooth may be referred to as a "mesiodens", a "paramolar", or a "distomolar".

The most common supernumerary tooth is a mesiodens, which is a malformed, peg-like tooth that occurs between the maxillary central incisors.

Fourth and fifth molars that form behind the third molars are another kind of supernumerary teeth.

Increased sensitivity to stimuli, specifically hot and cold, is a common symptom of pulpitis. A prolonged throbbing pain may be associated with the disease. However, pulpitis can also occur without any pain.

Pulpitis is inflammation of dental pulp tissue. The pulp contains the blood vessels the nerves and connective tissue inside a tooth and provides the tooth’s blood and nutrients. Pulpitis is mainly caused by bacteria infection which itself is a secondary development of caries (tooth decay). It manifests itself in the form of a toothache.

Dental trauma refers to trauma (injury) to the teeth and/or periodontium (gums, periodontal ligament, alveolar bone), and nearby soft tissues such as the lips, tongue, etc. The study of dental trauma is called dental traumatology.

Loss of attachment:

- By far the most common cause is periodontal disease (gum disease). This is painless, slowly progressing loss of bony support around teeth. It is made worse by smoking and the treatment is by improving the oral hygiene above and below the gumline.

- Dental abscesses can cause resorption of bone and consequent loss of attachment. Depending on the type of abscess, this loss of attachment may be restored once the abscess is treated, or it may be permanent.

- Many other conditions can cause permanent or temporary loss of attachment and increased tooth mobility. Examples include: Langerhans cell histiocytosis.

Increased forces on the tooth:

- Bruxism (abnormal clenching and grinding of teeth) can aggravate attachment loss and tooth mobility if periodontal disease is already present. The tooth mobility is typically reversible and the tooth returns to normal level of mobility once the bruxism is controlled.

- Dental trauma. Luxations, and root fractures of teeth can cause sudden mobility after a blow. Dental trauma may be isolated or associated with other facial trauma.

- Increased biting force on one tooth can cause temporary increased mobility until corrected. A common scenario is a new filling or crown which is a fraction of a millimeter too prominent in the bite, which after a few days causes periodontal pain in that tooth and/or the opposing tooth.