Dental caries is an infectious disease caused primarily by "Streptococcus mutans", characterized by acid demineralization of the enamel, which can progress to further breakdown of the more organic, inner dental tissue (dentin). Everybody is susceptible to caries but the probability of development depends on the patient’s individual disease indicators, risk factors and preventive factors. Factors that are considered high-risk for developing carious lesions on the teeth include:

- Low fluoride exposure

- Time, length, and frequency of sugar consumption

- Quality of tooth cleaning

- Fluctuations in salivary flow rates and composition

- Behavior of the individual

- Socioeconomic status of the individual

- Quality and composition of biofilms

Organic acids released from dental plaque lead to demineralization of the adjacent tooth surface, and consequently to dental caries. Saliva is also unable to penetrate the build-up of plaque and thus cannot act to neutralize the acid produced by the bacteria and remineralize the tooth surface.

Periodontitis is an infection of the gums which leads to bone destruction around the teeth in the jaw. Periodontitis occurs after gingivitis has been established, but not all individuals who have gingivitis will get periodontitis. Plaque accumulation is vital in the progression of periodontitis as the bacteria in plaque release enzymes which attack the bone and cause it to break down, and at the same time osteoclasts in the bone break down the bone as a way to prevent further infection. This can be treated with strict oral hygiene such as tooth brushing and cleaning in between the teeth as well as surgical debridement completed by a dental professional.

Risk factors associated with gingivitis include the following:

- age

- osteoporosis

- low dental care utilization (fear, financial stresses, etc.)

- poor oral hygiene

- overly aggressive oral hygiene such as brushing with stiff bristles

- mouth-breathing during sleep

- medications that dry the mouth

- cigarette smoking

- genetic factors

- pre-existing conditions

There is only very weak evidence linking to coronary heart disease.

There is little evidence linking progression of periodontal disease to low birth weight or preterm birth:

"In these women with periodontitis and within this study's limitations, disease progression was not associated with an increased risk for delivering a pre-term or a low birthweight infant."

There is recently emerged evidence linking chronic periodontitis with head and neck squamous cell carcinoma: "Patients with periodontitis were more likely to have poorly differentiated oral cavity SCC than those without periodontitis (32.8% versus 11.5%; P = 0.038)".

There is evidence to suggest that periodontal disease may play a role in the pathogenesis of Alzheimer's Disease.

Daily oral hygiene measures to prevent periodontal disease include:

- Brushing properly on a regular basis (at least twice daily), with the patient attempting to direct the toothbrush bristles underneath the gumline, helps disrupt the bacterial-mycotic growth and formation of subgingival plaque.

- Flossing daily and using interdental brushes (if the space between teeth is large enough), as well as cleaning behind the last tooth, the third molar, in each quarter

- Using an antiseptic mouthwash: Chlorhexidine gluconate-based mouthwash in combination with careful oral hygiene may cure gingivitis, although they cannot reverse any attachment loss due to periodontitis.

- Using periodontal trays to maintain dentist-prescribed medications at the source of the disease: The use of trays allows the medication to stay in place long enough to penetrate the biofilms where the microorganism are found.

- Regular dental check-ups and professional teeth cleaning as required: Dental check-ups serve to monitor the person's oral hygiene methods and levels of attachment around teeth, identify any early signs of periodontitis, and monitor response to treatment.

- Microscopic evaluation of biofilm may serve as a guide to regaining commensal health flora.

Typically, dental hygienists (or dentists) use special instruments to clean (debride) teeth below the gumline and disrupt any plaque growing below the gumline. This is a standard treatment to prevent any further progress of established periodontitis. Studies show that after such a professional cleaning (periodontal debridement), microbial plaque tends to grow back to precleaning levels after about three to four months. Nonetheless, the continued stabilization of a patient's periodontal state depends largely, if not primarily, on the patient's oral hygiene at home, as well as on the go. Without daily oral hygiene, periodontal disease will not be overcome, especially if the patient has a history of extensive periodontal disease.

Periodontal disease and tooth loss are associated with an increased risk, in male patients, of cancer.

Contributing causes may be high alcohol consumption or a diet low in antioxidants.

Pericoronitis usually occurs in young adults, around the time when wisdom teeth are erupting into the mouth. If the individual has reached their twenties without any attack of pericoronitis, it becomes substantially less likely one will occur thereafter.

Dentists and dental hygienists measure periodontal disease using a device called a periodontal probe. This thin "measuring stick" is gently placed into the space between the gums and the teeth, and slipped below the gumline. If the probe can slip more than below the gumline, the patient is said to have a gingival pocket if no migration of the epithelial attachment has occurred or a periodontal pocket if apical migration has occurred. This is somewhat of a misnomer, as any depth is, in essence, a pocket, which in turn is defined by its depth, i.e., a 2-mm pocket or a 6-mm pocket. However, pockets are generally accepted as self-cleansable (at home, by the patient, with a toothbrush) if they are 3 mm or less in depth. This is important because if a pocket is deeper than 3 mm around the tooth, at-home care will not be sufficient to cleanse the pocket, and professional care should be sought. When the pocket depths reach in depth, the hand instruments and cavitrons used by the dental professionals may not reach deeply enough into the pocket to clean out the microbial plaque that causes gingival inflammation. In such a situation, the bone or the gums around that tooth should be surgically altered or it will always have inflammation which will likely result in more bone loss around that tooth. An additional way to stop the inflammation would be for the patient to receive subgingival antibiotics (such as minocycline) or undergo some form of gingival surgery to access the depths of the pockets and perhaps even change the pocket depths so they become 3 mm or less in depth and can once again be properly cleaned by the patient at home with his or her toothbrush.

If patients have 7-mm or deeper pockets around their teeth, then they would likely risk eventual tooth loss over the years. If this periodontal condition is not identified and the patients remain unaware of the progressive nature of the disease, then years later, they may be surprised that some teeth will gradually become loose and may need to be extracted, sometimes due to a severe infection or even pain.

According to the Sri Lankan tea laborer study, in the absence of any oral hygiene activity, approximately 10% will suffer from severe periodontal disease with rapid loss of attachment (>2 mm/year). About 80% will suffer from moderate loss (1–2 mm/year) and the remaining 10% will not suffer any loss.

Extrinsic discolorations are common and have many different causes. The same range of factors are capable of staining the surface of restorations (e.g., composite fillings, porcelain crowns). Some extrinsic discolorations that are allowed to remain for a long time may become intrinsic.

- Dental plaque: Although usually virtually invisible on the tooth surface, plaque may become stained by chromogenic bacteria such as "Actinomyces" species.

- Calculus: Neglected plaque eventually calcifies, and leads to formation of a hard deposit on the teeth, especially around the gumline. The color of calculus varies, and may be grey, yellow, black or brown.

- Tobacco: Tar in smoke from tobacco products (and also smokeless tobacco products) tends to form a yellow-brown-black stain around the necks of the teeth above the gumline.

- Betel chewing.

- Certain foods and drinks. Foods, such as vegetables, that are rich with carotenoids or xanthonoids can stain teeth. Ingesting colored liquids like sports drinks, cola, coffee, tea and red wine can discolor teeth.

- Certain topical medications.

- Chlorhexidine (antiseptic mouthwash) binds to tannins, meaning that prolonged use in persons who consume coffee, tea or red wine is associated with extrinsic staining (i.e., removable staining) of teeth.

- Cetylpyridinium chloride, which is found in many antimicrobial mouthwashes, can result in staining due to dead bacterial residue.

- Metallic compounds. Exposure to such metallic compounds may be in the form of medication or other environmental exposure. Examples include iron (black stain), iodine (black), copper (green), nickel (green) and cadmium (yellow-brown).

- Antibiotics. Tetracycline and its derivatives are capable of intrinsic discoloration (discussed below). However other antibiotics may form insoluble complexes with calcium, iron and other elements that cause extrinsic staining.

Once the plaque stagnation area is removed either through further complete tooth eruption or tooth removal then pericoronitis will likely never return. A non-impacted tooth may continue to erupt, reaching a position which eliminates the operculum. A transient and mild pericoronal inflammation often continues while this tooth eruption completes. With adequate space for sustained improved oral hygiene methods, pericoronitis may never return. However, when relying on just oral hygiene for impacted and partially erupted teeth, chronic pericoronitis with occasional acute exacerbation can be expected.

Dental infections such as a pericoronal abscess can develop into septicemia and be life-threatening in persons who have neutropenia. Even in people with normal immune function, pericoronitis may cause a spreading infection into the potential spaces of the head and neck. Rarely, the spread of infection from pericoronitis may compress the airway and require hospital treatment (e.g. Ludwig's angina), although the majority of cases of pericoronitis are localized to the tooth. Other potential complications of a spreading pericoronal abscess include peritonsillar abscess formation or cellulitis.

Chronic pericoronitis may be the etiology for the development of paradental cyst, an inflammatory odontogenic cyst.

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).

Causes of intrinsic discoloration generally fall into those that occur during tooth development and those acquired later in life. The known causes of intrinsic staining are listed below, however some causes are unknown.

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

The cause of plaque-induced gingivitis is bacterial plaque, which acts to initiate the body's host response. This, in turn, can lead to destruction of the gingival tissues, which may progress to destruction of the periodontal attachment apparatus. The plaque accumulates in the small gaps between teeth, in the gingival grooves and in areas known as "plaque traps": locations that serve to accumulate and maintain plaque. Examples of plaque traps include bulky and overhanging restorative margins, claps of removable partial dentures and calculus (tartar) that forms on teeth. Although these accumulations may be tiny, the bacteria in them produce chemicals, such as degradative enzymes, and toxins, such as lipopolysaccharide (LPS, otherwise known as endotoxin) or lipoteichoic acid (LTA), that promote an inflammatory response in the gum tissue. This inflammation can cause an enlargement of the gingiva and subsequent formation. Early plaque in health consists of a relatively simple bacterial community dominated by Gram-positive cocci and rods. As plaque matures and gingivitis develops, the communities become increasingly complex with higher proportions of Gram-negative rods, fusiforms, filaments, spirilla and spirochetes. Later experimental gingivitis studies, using culture, provided more information regarding the specific bacterial species present in plaque. Taxa associated with gingivitis included "Fusobacterium nucleatum" subspecies "polymorphum", "Lachnospiraceae" [G-2] species HOT100, "Lautropia" species HOTA94, and "Prevotella oulorum" (a species of "Prevotella" bacterium), whilst "Rothia dentocariosa" was associated with periodontal health. Further study of these taxa is warranted and may lead to new therapeutic approaches to prevent periodontal disease.

Most dental pain can be treated with routine dentistry. In rare cases, toothache can be a symptom representing a life-threatening condition, such as a deep neck infection (compression of the airway by a spreading odontogenic infection) or something more remote like a heart attack.

Dental caries, if left untreated, follows a predictable natural history as it nears the pulp of the tooth. First it causes reversible pulpitis, which transitions to irreversible pulpitis, then to necrosis, then to necrosis with periapical periodontitis and, finally, to necrosis with periapical abscess. Reversible pulpitis can be stopped by removal of the cavity and the placement of a sedative dressing of any part of the cavity that is near the pulp chamber. Irreversible pulpitis and pulp necrosis are treated with either root canal therapy or extraction. Infection of the periapical tissue will generally resolve with the treatment of the pulp, unless it has expanded to cellulitis or a radicular cyst. The success rate of restorative treatment and sedative dressings in reversible pulpitis, depends on the extent of the disease, as well as several technical factors, such as the sedative agent used and whether a rubber dam was used. The success rate of root canal treatment also depends on the degree of disease (root canal therapy for irreversible pulpitis has a generally higher success rate than necrosis with periapical abscess) and many other technical factors.

Toothache may occur at any age, in any gender and in any geographic region. Diagnosing and relieving toothache is considered one of the main responsibilities of dentists. Irreversible pulpitis is thought to be the most common reason that people seek emergency dental treatment. Since dental caries associated with pulpitis is the most common cause, toothache is more common in populations that are at higher risk of dental caries. The prevalence of caries in a population is dependent upon factors such as diet (refined sugars), socioeconomic status, and exposure to fluoride (such as areas without water fluoridation). In the United States, an estimated 12% of the general population reported that they suffered from toothache at some point in the six months before questioning. Individuals aged 18–34 reported much higher experience of toothache than those aged 75 or over. In a survey of Australian schoolchildren, 12% had experienced toothache before the age of five, and 32% by the age of 12. Dental trauma is extremely common and tends to occur more often in children than adults.

A periodontal abscess most commonly occurs as a complication of advanced periodontal disease (which is normally painless). A periodontal pocket contains dental plaque, bacteria and subgingival calculus. Periodontal pathogens continually find their way into the soft tissues, but normally they are held in check by the immune system. A periodontal abscess represents a change in this balance, related to decreased local or systemic resistance of the host. An inflammatory response occurs when bacteria invade and multiply within the soft tissue of the gingival crevice/periodontal pocket. A pus-filled abscess forms when the immune system responds and attempts to isolate the infection from spreading.

Communication with the oral environment is maintained via the opening of the periodontal pocket. However, if the opening of a periodontal pocket becomes obstructed, as may occur if the pocket has become very deep (e.g. with furcation involvement), then plaque and calculus are trapped inside. Food packing may also obstruct a periodontal pocket. Food packing is usually caused by failure to accurately reproduce the contact points when dental restorations are placed on the interproximal surfaces of teeth. Another potential cause occurs when a periodontal pocket is scaled incompletely. Following this procedure, the gingival cuff tightens around the tooth, which may be enough to trap the bacteria left in the pocket. A gingival retraction cord which is accidentally left "in situ" is an occasional cause of a periodontal abscess.

Penetrating injury to the gingiva e.g. with a toothbrush bristle, fishbone, toothpick or periodontal instrument may inoculate bacteria into the tissues. Trauma to the tissues, e.g. caused by an impact on a tooth, or excessive pressure exerted on teeth during orthodontic treatment. Occlusal overload may also be involved in the development of a periodontal abscess, but this is rare and usually in combination with other factors. Bruxism is a common cause of excessive occlusal forces.

Systemic immune factors such as diabetes can predispose to the formation of periodontal abscesses.

Perforation of a root canal during endodontic therapy can also lead to a periodontal abscess.

In the early stages, chronic periodontitis has few symptoms and in many individuals the disease has progressed significantly before they seek treatment.

Symptoms may include the following:

- Redness or bleeding of gums while brushing teeth, using dental floss or biting into hard food (e.g. apples) (though this may occur even in gingivitis, where there is no attachment loss)

- Gum swelling that recurs

- Halitosis, or bad breath, and a persistent metallic taste in the mouth

- Gingival recession, resulting in apparent lengthening of teeth. (This may also be caused by heavy-handed brushing or with a stiff tooth brush.)

- Deep pockets between the teeth and the gums (pockets are sites where the attachment has been gradually destroyed by collagen-destroying enzymes, known as "collagenases")

- Loose teeth, in the later stages (though this may occur for other reasons as well)

Gingival inflammation and bone destruction are often painless. Patients sometimes assume that painless bleeding after teeth cleaning is insignificant, although this may be a symptom of progressing chronic periodontitis in that patient.

Subgingival calculus is a frequent finding.

There is a slow to moderate rate of disease progression but the patient may have periods of rapid progression ("bursts of destruction"). Chronic periodontitis can be associated with local predisposing factors(e.g. tooth-related or iatrogenic factors). The disease may be modified by and be associated with systemic diseases (e.g. diabetes mellitus, HIV infection) It can also be modified by factors other than systemic disease such as smoking and emotional stress.

Major risk factors: Smoking, lack of oral hygiene with inadequate plaque biofilm control.

Measuring disease progression is carried out by measuring probing pocket depth (PPD) and bleeding indices using a periodontal probe. Pockets greater than 3mm in depth are considered to be unhealthy. Bleeding on probing is considered to be a sign of active disease. Discharge of pus, involvement of the root furcation area and deeper pocketing may all indicate reduced prognosis for an individual tooth.

Age is related to the incidence of periodontal destruction: "...in a well-maintained population who practises oral home care and has regular check-ups, the incidence of incipient periodontal destruction increases with age, the highest rate occurs between 50 and 60 years, and gingival recession is the predominant lesion before 40 years, while periodontal pocketing is the principal mode of destruction between 50 and 60 years of age."

Dental plaque accumulates at the surfaces when proper cleaning and maintaining is not done. There is inflammation due to the bacteria released from the toxins. calculus forms and if not removed, causes this disease.

A periodontal abscess (also termed lateral abscess, or parietal abscess), is a localized collection of pus (i.e. an abscess) within the tissues of the periodontium. It is a type of dental abscess. A periodontal abscess occurs alongside a tooth, and is different from the more common periapical abscess, which represents the spread of infection from a dead tooth (i.e. which has undergone pulpal necrosis). To reflect this, sometimes the term "lateral (periodontal) abscess" is used. In contrast to a periapical abscess, periodontal abscesses are usually associated with a vital (living) tooth. Abscesses of the periodontium are acute bacterial infections classified primarily by location.

There are many possible causes of gingival bleeding. The main cause of gingival bleeding is the formation and accumulation of plaque at the gum line due to improper brushing and flossing of teeth. The hardened form of plaque is calculus. An advanced form of gingivitis as a result of formation of plaque is periodontitis. Other causes that can exacerbate gingival bleeding include:

- placement of new dentures

- tooth or gum infection

- diabetes mellitus

- idiopathic thrombocytopenic purpura

- leukemia

- malnutrition

- use of aspirin and anticoagulants(blood thinners) such as warfarin and heparin

- hormonal imbalances during puberty and pregnancy

- iron overload

Other less common causes are:

- vitamin C deficiency (scurvy) and vitamin K deficiency

- dengue fever

True dental caries is uncommon among companion animals. Although it has not been accurately documented in cats, the incidence of caries in dogs has been estimated at approximately 5%. The term "feline cavities" is commonly used to refer to TRs; however, sacchrolytic acid-producing bacteria are not involved in this condition.

Treatment for TRs is limited to tooth extraction because the lesion is progressive. Amputation of the tooth crown without root removal has also been advocated in cases demonstrated on a radiograph to be type 2 resorption without associated periodontal or endodontic disease because the roots are being replaced by bone. However, X-rays are recommended prior to this treatment to document root resorption and lack of the periodontal ligament.

Tooth restoration is not recommended because resorption of the tooth will continue underneath the restoration. Use of alendronate has been studied to prevent TRs and decrease progression of existing lesions.

If there is persistent continuation of inflammation and bleeding, a prescription of antiplaque rinse would be useful.

Xerostomia is a very common symptom. A conservative estimate of prevalence is about 20% in the general population, with increased prevalences in females (up to 30%) and the elderly (up to 50%).

A gingival disease is the term given to any disorder primarily affecting the gingiva.

An example is gingivitis.