An odontogenic infection is an infection that originates within a tooth or in the closely surrounding tissues. The term is derived from "" (from ancient Greek "odous" - "tooth") and "" (from Greek "genos" - "birth"). Odontogenic infections may remain localized to the region where they started, or spread into adjacent or distant areas.

It is estimated that 90-95% of all orofacial infections originate from the teeth or their supporting structures. Furthermore, about 70% of odontogenic infections occur as periapical inflammation, i.e. acute periapical periodontitis or a periapical abscess. The next most common form of odontogenic infection is the periodontal abscess.

Sinusitis is inflammation of the paranasal air sinuses. Infections associated with teeth may be responsible for approximately 20% of cases of maxillary sinusitis. The cause of this situation is usually a periapical or periodontal infection of a maxillary posterior tooth, where the inflammatory exudate has eroded through the bone superiorly to drain into the maxillary sinus. Once an odontogenic infection involves the maxillary sinus, it is possible that it may then spread to the orbit or to the ethmoid sinus.

Acute pericoronitis (i.e. sudden onset and short lived, but significant, symptoms) is defined as "varying degrees of inflammatory involvement of the pericoronal flap and adjacent structures, as well as by systemic complications." Systemic complications refers to signs and symptoms occurring outside of the mouth, such as fever, malaise or swollen lymph nodes in the neck.

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.

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).

Pericoronitis may also be chronic or recurrent, with repeated episodes of acute pericoronitis occurring periodically. Chronic pericoronitis may cause few if any symptoms, but some signs are usually visible when the mouth is examined.

There are four types of abscesses that can involve the periodontal tissues:

1. Gingival abscess—a localized, purulent infection involves only the soft gum tissue near the marginal gingiva or the interdental papilla.

2. Periodontal abscess—a localized, purulent infection involving a greater dimension of the gum tissue, extending apically and adjacent to a periodontal pocket.

3. Pericoronal abscess—a localized, purulent infection within the gum tissue surrounding the crown of a partially or fully erupted tooth. Usually associated with an acute episode of pericoronitis around a partially erupted and impacted mandibular third molar (lower wisdom tooth).

4. combined periodontal/endodontic abscess

The main symptom is pain, which often suddenly appears, is made worse by biting on the involved tooth, which may feel raised and prominent in the bite. The tooth may be mobile, and the lesion may contribute to destruction of the periodontal ligament and alveolar bone. The pain is deep and throbbing. The oral mucosa covering an early periodontal abscess appears erythematous (red), swollen and painful to touch. The surface may be shiny due to stretching of the mucosa over the abscess. Before pus has formed, the lesion will not be fluctuant, and there will be no purulent discharge. There may be regional lymphadenitis.

When pus forms, the pressure increases, with increasing pain, until it spontaneously drains relieving the pain. When pus drains into the mouth, a bad taste is perceived. Usually drainage occurs via the periodontal pocket, or else the infection may spread as a cellulitis or a purulent odontogenic infection. Local anatomic factors determine the direction of spread (see fascial spaces of the head and neck). There may be systemic upset, with malaise and pyrexia.

Acute periapical periodontitis, also termed acute apical periodontitis, acute periradicular periodontitis, or symptomatic periapical periodontitis.

The radiographic features of periapical inflammatory lesions vary depending on the time course of the lesion. Because very early lesions

may not show any radiographic changes, diagnosis of these lesions relies solely on the clinical symptoms . More chronic lesions may show lytic (radiolucent) or sclerotic (radiopaque) changes, or both.

The signs and symptoms depend upon the type of OM, and may include:

- Pain, which is severe, throbbing and deep seated.

- Initially fistula are not present.

- No dental pain, but headache or other facial pain, as in the descriptive former term "neuralgia-inducing" (cavitational osteonecrosis).

- Fibromyalgia.

- Chronic fatigue syndrome.

- Swelling. External swelling is initially due to inflammatory edema with accompanying erythema (redness), heat and tenderness, and then later may be due to sub-periosteal pus accumulation. Eventually, subperiosteal bone formation may give a firm swelling.

- Trismus (difficulty opening the mouth), which may be present in some cases and is caused by edema in the muscles.

- Dysphagia (difficulty swallowing), which may be present in some cases and is caused by edema in the muscles.

- Cervical lymphadenitis (swelling of the lymph nodes in the neck).

- Aesthesia or paresthesia (altered sensation such as numbness or pins and needles) in the distribution of the mental nerve.

- Fever which may be present in the acute phase and is high and intermittent

- Malaise (general feeling of being unwell) which may be present in the acute phase

- Anorexia (loss of appetite).

- Leukocytosis (elevated numbers of white blood cells) which may be present in the acute phase

- Elevated erythrocyte sedimentation rate and C reactive protein are sometimes present.

- An obvious cause in the mouth (usually) such as a decayed tooth.

- Teeth that are tender to percussion, which may develop as the condition progresses

- Loosening of teeth, which may develop as the condition progresses.

- Pus may later be visible, which exudes from around the necks of teeth, from an open socket, or from other sites within the mouth or on the skin over the involved bone.

- Fetid odor.

Unlike acute OM in the long bones, acute OM in the jaws gives only a moderate systemic reaction and the person remains surprisingly well. Acute OM of the jaws may give a similar appearance to a typical odontogenic infection, but cellulitis does not tend to spread from the periosteal envelope of the involved bone. If the infection is not controlled, the process becomes chronic and systemic symptoms are usually present, including draining fistulas, loosening of teeth and sequestra formation. Untreated chronic osteomyelitis tends to feature occasional acute exacerbations.

The classification is similar to the classification of OM generally, according to the length of time the inflammation has been present and whether there is suppuration (the formation of pus). "Acute osteomyelitis" is loosely defined as OM which has been present for less than one month and "chronic osteomyelitis" is the term used for when the condition lasts for more than one month. Suppurative osteomyelitis of the jaws is uncommon in developed regions, and more common in developing countries. In Europe and the United States, most cases follow dental infections or mandibular fractures. There have been many reported cases occurring in Africa which are coexistent with acute necrotizing ulcerative gingivitis or cancrum oris.

In the pre-antibiotic era, acute OM of the jaws was more extensive. Massive, diffuse infections commonly involved the whole side of the mandible, or the whole of one side and the opposite side as far as the mental foramen. Localized osteomyelitis tended to be described as either "vertical", where a short segment of the body of the mandible from the alveolar crest to the lower border was involved, and "alveolar", where a segment of alveolar bone down to the level of the inferior alveolar canal would sequestrate, including the sockets of several teeth. Treatment with antibiotics has significantly altered the natural history of OM of the jaws. Today, however, the condition is often a hidden infection, due in part to not being visible on most dental X-rays. In addition, some schools of dentistry do not recognize "silent" OM of the jaws—occurrence of the condition without visually obvious manifestations—in their curriculum. In addition, as circulation is intrinsically diminished in jawbones, antibiotics are frequently ineffective.

There are two main types: compound and complex.

- A "compound" odontoma still has the three separate dental tissues (enamel, dentin and cementum), but may present a lobulated appearance where there is no definitive demarcation of separate tissues between the individual "toothlets" (or denticles). It usually appears in the anterior maxilla.

- The "complex" type is unrecognizable as dental tissues, usually presenting as a radioopaque area with varying densities. It usually appears in the posterior maxilla or in the mandible.

In addition to the above forms, the dilated odontoma is an infrequent developmental alteration that appears in any area of the dental arches and can affect deciduous, permanent and supernumerary teeth. Dens invaginatus is a developmental anomaly resulting from invagination of a portion of crown forming within the enamel organ during odontogenesis. The most extreme form of dens invaginatus is known as dilated odontoma.

Common marginal gingivitis in response to subgingival plaque is usually a painless condition. However, an acute form of gingivitis/periodontitis, termed acute necrotizing ulcerative gingivitis (ANUG), can develop, often suddenly. It is associated with severe periodontal pain, bleeding gums, "punched out" ulceration, loss of the interdental papillae, and possibly also halitosis (bad breath) and a bad taste. Predisposing factors include poor oral hygiene, smoking, malnutrition, psychological stress, and immunosuppression. This condition is not contagious, but multiple cases may simultaneously occur in populations who share the same risk factors (such as students in a dormitory during a period of examination). ANUG is treated over several visits, first with debridement of the necrotic gingiva, homecare with hydrogen peroxide mouthwash, analgesics and, when the pain has subsided sufficiently, cleaning below the gumline, both professionally and at home. Antibiotics are not indicated in ANUG management unless there is underlying systemic disease.

Apical abscesses can spread to involve periodontal pockets around a tooth, and periodontal pockets cause eventual pulp necrosis via accessory canals or the apical foramen at the bottom of the tooth. Such lesions are termed periodontic-endodontic lesions, and they may be acutely painful, sharing similar signs and symptoms with a periodontal abscess, or they may cause mild pain or no pain at all if they are chronic and free-draining. Successful root canal therapy is required before periodonal treatment is attempted. Generally, the long-term prognosis of perio-endo lesions is poor.

Periapical cysts begin as asymptomatic and progress slowly. Subsequent infection of the cyst causes swelling and pain. Initially, the cyst swells to a round hard protrusion, but later on the body resorbs some of the cyst wall, leaving a softer accumulation of fluid underneath the mucous membrane.

Larger cysts may cause bone expansion or displace roots. Discoloration of the affected tooth may also occur. Patient will present negative results to electric and ice test of the affected tooth but will be sensitive to percussion. Surrounding gingival tissue may experience lymphadenopathy. The alveolar plate may exhibit crepitus when palpated.

Periapical cysts exist in two structurally distinct classes:

Periapical true cysts - cysts containing cavities entirely surrounded in epithelial lining. Resolution of this type of cyst requires surgical treatment such as a cystectomy.

Periapical pocket cysts - epithelium lined cavities that have an opening to the root canal of the affected tooth. Resolution may occur after traditional root canal therapy.

Secondary symptoms of periapical cysts include inflammation and infection of the pulp causing dental caries. This infection is what causes necrosis of the pulp.

Expansion of the cyst causes erosion of the floor of the maxillary sinus. As soon as it enters the maxillary antrum, the expansion rate increases due to available space for expansion. Performing a percussion test by tapping the affected teeth will cause shooting pain. This is often clinically diagnostic of pulpal infection.

Radiographically, it is virtually impossible to differentiate granuloma from a cyst. If the lesion is large it is more likely to be a cyst. Radiographically, both granulomas and cysts appear radiolucent. Many lesions of the mandible in particular appear cystlike in appearance. It is often necessary to obtain a biopsy and evaluate the tissue under a microscope to accurately identify the lesion.

In most cases AIT is characterized by onset of pain, firmness, tenderness, redness or swelling in the anterior aspect of the neck. Patients will also present with a sudden fever, dysphagia and dysphonia. Symptoms may be present from 1 to 180 days, with most symptoms lasting an average of about 18 days. The main issue associated with the diagnosis of AIT is differentiating it from other more commonly seen forms of thyroid conditions. Pain, fever and swelling are often much more severe and continue to get worse in patients who have AIT compared to those with other thyroid conditions. Patients who are suspected of having AIT often undergo tests to detect for elevated levels of white blood cells as well as an ultrasound to reveal unilobular swelling. Depending on the age and immune status of the patient more invasive procedures may be performed such as fine needle aspiration of the neck mass to facilitate a diagnosis.

In cases where the infection is thought to be associated with a sinus fistula it is often necessary to confirm the presence of the fistula through surgery or laryngoscopic examination. While invasive procedures can often tell definitively whether or not a fistula is present, new studies are working on the use of computed tomography as a useful method to visualize and detect the presence of a sinus fistula.

There are several paired paranasal sinuses, including the frontal, ethmoidal, maxillary and sphenoidal sinuses. The ethmoidal sinuses are further subdivided into anterior and posterior ethmoid sinuses, the division of which is defined as the basal of the middle turbinate. In addition to the severity of disease, discussed below, sinusitis can be classified by the sinus cavity which it affects:

- Maxillary – can cause pain or pressure in the maxillary (cheek) area ("e.g.," toothache, or headache) (J01.0/J32.0)

- Frontal – can cause pain or pressure in the frontal sinus cavity (located above eyes), headache, particularly in the forehead (J01.1/J32.1)

- Ethmoidal – can cause pain or pressure pain between/behind the eyes, the sides of the upper part of the nose (the medial canthi), and headaches (J01.2/J32.2)

- Sphenoidal – can cause pain or pressure behind the eyes, but often refers to the skull vertex (top of the head), over the mastoid processes, or the back of the head.

The proximity of the brain to the sinuses makes the most dangerous complication of sinusitis, particularly involving the frontal and sphenoid sinuses, infection of the brain by the invasion of anaerobic bacteria through the bones or blood vessels. Abscesses, meningitis and other life-threatening conditions may result. In extreme cases the patient may experience mild personality changes, headache, altered consciousness, visual problems, seizures, coma and possibly death.

Sinus infection can spread through anastomosing veins or by direct extension to close structures. Orbital complications were categorized by Chandler et al. into five stages according to their severity (see table). Contiguous spread to the orbit may result in periorbital cellulitis, subperiosteal abscess, orbital cellulitis, and abscess. Orbital cellulitis can complicate acute ethmoiditis if anterior and posterior ethmoidal veins thrombophlebitis enables the spread of the infection to the lateral or orbital side of the ethmoid labyrinth. Sinusitis may extend to the central nervous system, where it may cause cavernous sinus thrombosis, retrograde meningitis, and epidural, subdural, and brain abscesses. Orbital symptoms frequently precede intracranial spread of the infection . Other complications include sinobronchitis, maxillary osteomyelitis, and frontal bone osteomyelitis. Osteomyelitis of the frontal bone often originates from a spreading thrombo-phlebitis. A periostitis of the frontal sinus causes an osteitis and a periostitis of the outer membrane, which produces a tender, puffy swelling of the forehead.

The diagnosis of these complications can be assisted by noting local tenderness and dull pain, and can be confirmed by CT and nuclear isotope scanning. The most common microbial causes are anaerobic bacteria and "S. aureus". Treatment includes performing surgical drainage and administration of antimicrobial therapy. Surgical debridement is rarely required after an extended course of parenteral antimicrobial therapy. Antibiotics should be administered for at least 6 weeks. Continuous monitoring of patients for possible intracranial complication is advised.

Anaerobes can be isolated from most types of upper respiratory tract and head and neck and infection and are especially common in chronic ones. These include tonsillar, peritonsillar and retropharyngeal abscesses, chronic otitis media, sinusitis and mastoiditis, eye ocular) infections, all deep neck space infections, parotitis, sialadenitis, thyroiditis, odontogenic infections, and postsurgical and nonsurgical head and neck wounds and abscesses., The predominant organisms are of oropharyngeal flora origin and include AGNB, "Fusobacterium" and Peptostreptococcus spp.

Anaerobes involve almost all dental infections. These include dental abscesses, endodontal pulpitis and periodontal (gingivitis and periodontitis) infections, and perimandibular space infection. Pulpitis can lead to abscess formation and eventually spread to the mandible and other neck spaces. In addition to strict anaerobic bacteria, microaerophilic streptococci and "Streptococcus salivarius" can also be present.

"Fusobacterium" spp. and anaerobic spirochetes are often the cause of acute necrotizing ulcerative gingivitis (or Vincent's angina) which is a distinct form of ulcerative gingivitis.

Deep neck infections that develop as a consequence of oral, dental and pharyngeal infections are generally polymicrobial in nature. These include extension of retropharyngeal cellulitis or abscess, mediastinitis following esophagus perforation, and dental or periodontal abscess.

An odontoma (also termed odontome) is a benign tumour of odontogenic origin (i.e. linked to tooth development). Specifically, it is a dental hamartoma, meaning that it is composed of normal dental tissue that has grown in an irregular way.

The average age of people found with an odontoma is 14. The condition is frequently associated with one or more unerupted teeth. Though most cases are found impacted within the jaw there are instances where odontomas have erupted into the oral cavity.

Acute infectious thyroiditis (AIT) also known as suppurative thyroiditis, microbial inflammatory thyroiditis, pyrogenic thyroiditis and bacterial thyroiditis.

The thyroid is normally very resistant to infection. Due to a relatively high amount of iodine in the tissue, as well as high vascularity and lymphatic drainage to the region, it is difficult for pathogens to infect the thyroid tissue. Despite all this, a persistent fistula from the piriform sinus may make the left lobe of the thyroid susceptible to infection and abscess formation. AIT is most often caused by a bacterial infection but can also be caused by a fungal or parasitic infection, most commonly in an immunocompromised host.

An eruption cyst, or eruption hematoma, is a bluish swelling that occurs on the soft tissue over an erupting tooth. It is usually found in children. The fluid in the cyst is sometimes clear creating a pale-coloured cyst although often they are blue. An eruption cyst (eruption hematoma) is a developmental soft-tissue cyst of odontogenic origin that forms over an erupting tooth.

In adults the most common source of aspiration pneumonia is aspiration of oropharyngeal secretions or gastric contents. In children the most common cause is aspiration of infected amniotic fluid, or vaginal secretions. Severe periodontal or gingival diseases are important risk factors for establishment of an anaerobic pleuropulmonary infection. Progression of the infection from pneumonitis into necrotizing pneumonia and pulmonary abscess can occur, with or without the development of empyema., The infection is often polymicrobial in nature and isolates of community-acquired infection (in 60–80% of cases) are aerobic and anaerobic belonging to the individual's oropharyngeal flora. The anaerobic bacteria commonly recovered are "Prevotella, Porphyromonas, Fusobacterium" and "Peptostreptococcus" spp., and the aerobic bacteria are beta-hemolytic and microaerophilic streptococci. Anaerobic bacteria can also be isolated in about 35% of individuals who suffer from nosocomial-acquired aspiration pneumonia and pneumonia associated with tracheostomy with and without mechanical ventilation, where they are often isolated along with Enterobacteriaceae, "Pseudomonas" spp. and "Staphylococcus aureus". It is important that specimens are obtained in a method that avoids their contamination by the oral micro flora.