Untreated, the infection may lead to rapid destruction of the periodontium and can spread, as necrotizing stomatitis or noma, into neighbouring tissues in the cheeks, lips or the bones of the jaw. As stated, the condition can occur and be especially dangerous in people with weakened immune systems. This progression to noma is possible in malnourished susceptible individuals, with severe disfigurement possible.

In developed countries, this disease occurs mostly in young adults. In developing countries, NUG may occur in children of low socioeconomic status, usually occurring with malnutrition (especially inadequate protein intake) and shortly after the onset of viral infections (e.g. measles).

Predisposing factors include smoking, viral respiratory infections and immune defects, such as in HIV/AIDS. Uncommon, except in lower socioeconomic classes, this typically affects adolescents and young adults, especially in institutions, armed forces, etc., or people with HIV/AIDS. The disease has occurred in epidemic-like patterns, but it is not contagious.

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 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

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.

Malnutrition, whether by malabsorption, or poor diet, especially hematinic deficiencies (iron, vitamin B12, folic acid) can predispose to oral candidiasis, by causing diminished host defense and epithelial integrity. For example, iron deficiency anemia is thought to cause depressed cell-mediated immunity. Some sources state that deficiencies of vitamin A or pyridoxine are also linked.

There is limited evidence that a diet high in carbohydrates predisposes to oral candidiasis. "In vitro" and studies show that Candidal growth, adhesion and biofilm formation is enhanced by the presence of carbohydrates such as glucose, galactose and sucrose.

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.

Smoking, especially heavy smoking, is an important predisposing factor but the reasons for this relationship are unknown. One hypothesis is that cigarette smoke contains nutritional factors for "C. albicans", or that local epithelial alterations occur that facilitate colonization of candida species.

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.

Overall, the incidence of dry socket is about 0.5–5% for routine dental extractions, and about 25–30% for impacted mandibular third molars (wisdom teeth which are buried in the bone).

Females are more frequently affected than males, but this appears to be related to oral contraceptive use rather than any underlying gender predilection. The majority of dry sockets occur in individuals aged between 20 and 40 which is when most dental extractions occur, although for any given individual it is more likely to occur in with increasing age.

Other possible risk factors include periodontal disease, acute necrotizing ulcerative gingivitis, local bone disease, Paget's disease of bone, osteopetrosis, cemento-osseous dysplasia, a history of previously developing a dry socket with past extractions and inadequate oral hygiene. Other factors in the postoperative period that may lead to loss of the blood clot include forceful spitting, sucking through a straw, and coughing or sneezing.

Smoking and tobacco use of any kind are associated with increased risk of dry socket. This may be partially due to the vasoconstrictive action of nicotine on small blood vessels. Abstaining from smoking in the days immediately following a dental extraction reduces the risk of a dry socket occurring.

Periodontitis is an inflammation of the periodontium, i.e., the tissues that support the teeth. The periodontium consists of four tissues:

- gingiva, or gum tissue,

- cementum, or outer layer of the roots of teeth,

- alveolar bone, or the bony sockets into which the teeth are anchored, and

- periodontal ligaments (PDLs), which are the connective tissue fibers that run between the cementum and the alveolar bone.

The primary cause of gingivitis is poor or ineffective oral hygiene, which leads to the accumulation of a mycotic and bacterial matrix at the gum line, called dental plaque. Other contributors are poor nutrition and underlying medical issues such as diabetes. Diabetics must be meticulous with their homecare to control periodontal disease. New finger prick tests have been approved by the Food and Drug Administration in the US, and are being used in dental offices to identify and screen patients for possible contributory causes of gum disease, such as diabetes.

In some people, gingivitis progresses to periodontitis – with the destruction of the gingival fibers, the gum tissues separate from the tooth and deepened sulcus, called a periodontal pocket. Subgingival microorganisms (those that exist under the gum line) colonize the periodontal pockets and cause further inflammation in the gum tissues and progressive bone loss. Examples of secondary causes are those things that, by definition, cause microbic plaque accumulation, such as restoration overhangs and root proximity.

Smoking is another factor that increases the occurrence of periodontitis, directly or indirectly, and may interfere with or adversely affect its treatment.

Ehlers–Danlos syndrome is a periodontitis risk factor and so is the Papillon–Lefèvre syndrome also known as palmoplantar keratoderma.

If left undisturbed, microbial plaque calcifies to form calculus, which is commonly called tartar. Calculus above and below the gum line must be removed completely by the dental hygienist or dentist to treat gingivitis and periodontitis. Although the primary cause of both gingivitis and periodontitis is the microbial plaque that adheres to the tooth surfaces, there are many other modifying factors. A very strong risk factor is one's genetic susceptibility. Several conditions and diseases, including Down syndrome, diabetes, and other diseases that affect one's resistance to infection, also increase susceptibility to periodontitis.

Another factor that makes periodontitis a difficult disease to study is that human host response can also affect the alveolar bone resorption. Host response to the bacterial-mycotic insult is mainly determined by genetics; however, immune development may play some role in susceptibility.

According to some researchers periodontitis may be associated with higher stress. Periodontitis occurs more often in people from the lower end of the socioeconomic scale than people from the upper end of the socioeconomic scale.

Bacterial

- (Plaque-induced) gingivitis—A common periodontal (gum) disease is Gingivitis. Periodontal refers to the area the infection affects, which include the teeth, gums, and tissues surrounding the teeth. Bacteria cause inflammation of the gums which become red, swollen and can bleed easily. The bacteria along with mucus form a sticky colorless substance called plaque which harbours the bacteria. Plaque that is not removed by brushing and flossing hardens to form tartar that brushing doesn't clean. Smoking is a major risk factor. Treatment of gingivitis is dependent on how severe and how far the disease has progressed. If the disease is not too severe it is possible to treat it with chlorhexidine rinse and brushing with fluoride toothpaste to kill the bacteria and remove the plaque, but once the infection has progressed antibiotics may be needed to kill the bacteria.

- Periodontitis—When gingivitis is not treated it can advance to periodontitis, when the gums pull away from the teeth and form pockets that harbor the bacteria. Bacterial toxins and the body's natural defenses start to break down the bone and connective tissues. The tooth may eventually become loose and have to be removed.

- Scarlet fever is caused by streptococci species, and starts as tonsilitis and pharyngitis before involving the soft palate and the tongue. It usually occurs in children where a fever occurs and a rash develops on the skin. It is treated with penicillin and the prognosis is generally excellent.

Viral

- Herpes simplex (infection with herpes simplex virus, or HSV) is very common in the mouth and lips. This virus can cause blisters and sores around the mouth (herpetic gingivostomatitis) and lips (herpes labialis). HSV infections tend to recur periodically. Although many people get infected with the virus, only 10% actually develop the sores. The sores may last anywhere from 3–10 days and are very infectious. Some people have recurrences either in the same location or at a nearby site. Unless the individual has an impaired immune system, e.g., owing to HIV or cancer-related immune suppression, recurrent infections tend to be mild in nature and may be brought on by stress, sun, menstrual periods, trauma or physical stress.

- Mumps of the salivary glands is a viral infection of the parotid glands. This results in painful swelling at the sides of the mouth in both adults and children. The infection is quite contagious. Today mumps is prevented by getting vaccinated in infancy. There is no specific treatment for mumps except for hydration and painkillers. Sometimes mumps can cause inflammation of the brain, testicular swelling or hearing loss.

Fungal

- Oral candidiasis is by far the most common fungal infection that occurs in the mouth. It usually occurs in immunocompromised individuals. Individuals who have undergone a transplant, HIV, cancer or use corticosteroids commonly develop candida of the mouth and oral cavity. Other risk factors are dentures and tongue piercing. The typical signs are a white patch that may be associated with burning, soreness, irritation or a white cheesy like appearance. Once the diagnosis is made, candida can be treated with a variety of anti fungal drugs.

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.

OFG is uncommon, but the incidence is increasing. The disease usually presents in adolescence or young adulthood. It may occur in either sex, but males are slightly more commonly affected.

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

An example is gingivitis.

This type of gingival enlargement is sometimes termed "drug induced gingival enlargement" or "drug influenced gingival enlargement", abbreviated to "DIGO". Gingival enlargement may also be associated with the administration of three different classes of drugs, all producing a similar response: Gingival overgrowth is a common side effect of phenytoin, termed "Phenytoin-induced gingival overgrowth" (PIGO).

- anticonvulsants (such as phenytoin, phenobarbital, lamotrigine, vigabatrin, ethosuximide, topiramate and primidone NOT common for valproate)

- calcium channel blockers (antihypertensives such as nifedipine, amlodipine, and verapamil). The dihydropyridine derivative isradipidine can replace nifedipine and does not induce gingival overgrowth.

- cyclosporine, an immunosuppresant.

Of all cases of DIGO, about 50% are attributed to phenytoin, 30% to cyclosporins and the remaining 10-20% to calcium channel blockers.

Drug-induced enlargement has been associated with a patient's genetic predisposition, and its association with inflammation is debated. Some investigators assert that underlying inflammation is necessary for the development of drug-induced enlargement, while others purport that the existing enlargement induced by the drug effect compounds plaque retention, thus furthering the tissue response. Careful attention to oral hygiene may reduce the severity of gingival hyperplasia. In most cases, discontinuing the culprit drug resolves the hyperplasia.

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.

This is a common condition present in denture wearers. It appears as reddened but painless mucosa beneath the denture. 90% of cases are associated with Candidia species, and it is the most common form of oral candidiasis. Treatment is by antifungal medication and improved dental hygiene, such as not wearing the denture during sleep.

Caused by various autoimmune diseases as well as allergies. Erosive lichen planus, mucous membrane pemphigoid, pemphigus vulgaris, and lupus erythematosus.

Allergic contact stomatitis (also termed "allergic gingivostomatitis" or "allergic contact gingivostomatitis") is a type IV (delayed) hypersensitivity reaction that occurs in susceptible atopic individuals when allergens penetrate the skin or mucosa.

Allergens, which may be different for different individuals, combine with epithelial-derived proteins, forming haptens which bind with Langerhans cells in the mucosa, which in turn present the antigen on their surface to T lymphocytes, sensitizing them to that antigen and causing them to produce many specific clones. The second time that specific antigen is encountered, an inflammatory reaction is triggered at the site of exposure. Allergic contact stomatitis is less common than allergic contact dermatitis because the mouth is coated in saliva, which washes away antigens and acts as a barrier. The oral mucosa is also more vascular (has a better blood supply) than skin, meaning that any antigens are more quickly removed from the area by the circulation. Finally, there is substantially less keratin in oral mucosa, meaning that there is less likelihood that haptens will form.

Allergic contact stomatitis appears as non-specific inflammation, so it may be mistaken for chronic physical irritation. There may be burning or soreness of the mouth and ulceration. Chronic exposure to the allergen may result in a lichenoid lesion. Plasma cell gingivitis may also occur, which may be accompanied by glossitis and cheilitis.

Allergens that may cause allergic contact stomatitis in some individuals include cinnamaldehyde, Balsam of Peru, peppermint, mercury, gold, pyrophosphates, zinc citrate, free acrylic monomer, nickel, fluoride, and sodium lauryl sulfate. These allergens may originate from many sources, including various foods and drink, chewing gum, toothpaste, mouthwash, dental floss, dental fillings, dentures, orthodontic bands or wires, and many other sources. If the substance containing the allergen comes into contact with the lips, allergic contact cheilitis can occur, together with allergic contact stomatitis.

The diagnosis is confirmed by patch test, and management is by avoidance of exposure to the allergen.

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.

It is commonly seen in Boxer dogs and other brachycephalic breeds, and in the English Springer Spaniel. It usually starts around middle age and progresses. Some areas of the gingiva can become quite large but have only a small attachment to the rest of the gingiva, and it may completely cover the teeth. Infection and inflammation of the gingiva is common with this condition. Under anesthesia, the enlarged areas of gingiva can be cut back with a scalpel blade or CO laser, but it often recurs. Gingival enlargement is also a potential sequela of gingivitis. As in humans, it may be seen as a side effect to the use of ciclosporin.

Desquamative gingivitis is a descriptive clinical term, not a diagnosis. Dermatologic conditions cause about 75% of cases of desquamative gingivitis, and over 95% of the dermatologic cases are accounted for by either oral lichen planus or cicatricial pemphigoid. The exact cause of desquamative gingivitis cannot be determined about a third of cases.

- Oral lichen planus

- Cicatricial pemphigoid or less commonly bullous pemphigoid

- Pemphigus vulgaris

- Linear immunoglobulin A disease

- Dermatitis herpetiformis

- Lupus erythematosus

- Chronic ulcerative stomatitis

- Chronic bacterial, fungal, and viral infections

- Reactions to medications, mouthwashes, and chewing gum

Rare causes include:

- Crohn’s disease

- Sarcoidosis

- Leukemia

- factitious (self inflicted) lesions

- Squamous cell carcinoma (can be mistaken for desquamative gingivitis)

Plasma cell gingivits is rare, and plasma cell cheilitis is very rare. Most people with plasma cell cheilitis have been elderly.