Periapical periodontitis of some form is a very common condition. The prevalence of periapical periodontitis is generally reported to vary according to age group, e.g. 33% in those aged 20–30, 40% in 30- to 40-year-olds, 48% in 40- to 50-year-olds, 57% in 50- to 60-year-olds and 62% in those over the age of 60. Most epidemiologic data has been generated in European countries, especially Scandinavia. Millions of root canal treatments are carried out in the United States each year, although the total number of root canal treatments is an imperfect indicator of the prevalence of periapical periodontitis, since not always is it performed due to the presence of periapacial periodontitis, and not all cases of asymptomatic periodontitis will be treated in this manner, either due to lack of patient attendance or watchful waiting.

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.

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.

Periapical periodontitis (also termed apical periodontitis, AP, or periradicular periodontitis) is an acute or chronic inflammatory lesion around the apex of a tooth root which is usually caused by bacterial invasion of the pulp of the tooth. The term is derived from "peri-" meaning "around", "apical" referring to the apex of the root (the tip of the root), and "-itis" meaning a disease characterized by inflammation. Periapical periodontitis can be considered a sequela in the natural history of dental caries (tooth decay), irreversible pulpitis and pulpal necrosis, since it is the likely outcome of untreated dental caries, although not always. In some cases, periapical periodontitis can occur due to occlusal high spots post-restoration, endodontic root filling material extrusion or bacterial invasion and infection from a gingival communication (rather than a pulpal source). Periapical periodontitis may develop into a periapical abscess, where a collection of pus forms at the end of the root, the consequence of spread of infection from the tooth pulp (odontogenic infection), or into a periapical cyst, where an epithelial lined, fluid filled structure forms.

Aetiology of CTS is multifactorial, the causative factors include:

- previous restorative procedures.

- occlusal factors

- developmental conditions/anatomical considerations.

- trauma

- others, e.g, aging dentition or presence of lingual tongue studs.

Most commonly involved teeth are mandibular molars followed by maxillary premolars, maxillary molars and maxillary premolars. in a recent audit, mandibular first molar thought to be most affected by CTS possibly due to the wedging effect of opposing pointy, protruding maxillary mesio-palatal cusp onto the mandibular molar central fissure.

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.

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 (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.

If left untreated, a severe tooth abscess may become large enough to perforate bone and extend into the soft tissue eventually becoming osteomyelitis and cellulitis respectively. From there it follows the path of least resistance and may spread either internally or externally. The path of the infection is influenced by such things as the location of the infected tooth and the thickness of the bone, muscle and fascia attachments.

External drainage may begin as a boil which bursts allowing pus drainage from the abscess, intraorally (usually through the gum) or extraorally. Chronic drainage will allow an epithelial lining to form in this communication to form a pus draining canal (fistula). Sometimes this type of drainage will immediately relieve some of the painful symptoms associated with the pressure.

Internal drainage is of more concern as growing infection makes space within the tissues surrounding the infection. Severe complications requiring immediate hospitalization include Ludwig's angina, which is a combination of growing infection and cellulitis which closes the airway space causing suffocation in extreme cases. Also infection can spread down the tissue spaces to the mediastinum which has significant consequences on the vital organs such as the heart. Another complication, usually from upper teeth, is a risk of septicaemia (infection of the blood) from connecting into blood vessels, brain abscess (extremely rare), or meningitis (also rare).

Depending on the severity of the infection, the sufferer may feel only mildly ill, or may in extreme cases require hospital care.

Successful treatment of a dental abscess centers on the reduction and elimination of the offending organisms.

This can include treatment with antibiotics and drainage. If the tooth can be restored, root canal therapy can be performed. Non-restorable teeth must be extracted, followed by curettage of all apical soft tissue.

Unless they are symptomatic, teeth treated with root canal therapy should be evaluated at 1- and 2-year intervals after the root canal therapy to rule out possible lesional enlargement and to ensure appropriate healing.

Abscesses may fail to heal for several reasons:

- Cyst formation

- Inadequate root canal therapy

- Vertical root fractures

- Foreign material in the lesion

- Associated periodontal disease

- Penetration of the maxillary sinus

Following conventional, adequate root canal therapy, abscesses that do not heal or enlarge are often treated with surgery and filling the root tips; and will require a biopsy to evaluate the diagnosis.

The prognosis is excellent, as no treatment is usually required.

If the offending tooth is extracted, the area of condensing osteitis may remain in the jaws indefinitely, which is termed osteosclerosis or bone scar.

Repair with cementum or dentin occurs after partial root resorption, fusing the tooth with the bone. It may occur following dental trauma, especially occlusal trauma, or after periapical periodontitis caused by pulp necrosis. Ankylosis itself is not a reason to remove a permanent tooth, however teeth which must be removed for other reasons are made significantly more difficult to remove if they are ankylosed.

There is no universally accepted treatment strategy, but, generally, treatments aim to prevent movement of the segments of the involved tooth so they do not move or flex independently during biting and grinding and so the crack is not propagated.

- Stabilization (core buildup) (a composite bonded restoration placed in the tooth or a band is placed around the tooth to minimize flexing)

- Crown restoration (to do the same as above but more permanently and predictably)

- Root Canal therapy (if pain persists after above)

- Extraction

Such deposits form bulbous enlargements on the roots and may interfere with extractions, especially if adjacent teeth become fused (concrescence). It may also result in pulpal necrosis by blocking blood supply via the apical foramen.

Infection of periapical tissues of a high immunity host by organisms of low virulence which leads to a localized bony reaction to a low grade inflammatory stimulus.

It can be caused by any of the following:

- Nutritional factors.

- Some diseases (such as undiagnosed and untreated celiac disease, chicken pox, congenital syphilis).

- Hypocalcemia.

- Fluoride ingestion (dental fluorosis).

- Birth injury.

- Preterm birth.

- Infection.

- Trauma from a deciduous tooth.

Can be caused by many things. A way to remember the causes is "PIG ON TAP"

Local factors-

- Occlusal Trauma

- Trauma

- Non-functional tooth

- Unopposed tooth (and impacted teeth, embedded teeth, teeth without antagonists)

Systemic factors-

- Idiopathic

- Pituitary Gigantism

- Paget's Disease

- Acromegaly

- Periapical granuloma

- Arthritis

- Calcinosis

- Rheumatic fever

It may be one of the complications of Paget's disease of bone in the form of generalized hypercementosis.

It may also be a compensatory mechanism in response to attrition to increase occlusal tooth height.

Ankylosis of deciduous teeth ("submerged teeth") may rarely occur. The most commonly affected tooth is the mandibular (lower) second deciduous molar. Partial root resorption first occurs and then the tooth fuses to the bone. This prevents normal exfoliation of the deciduous tooth and typically causes impaction of the permanent successor tooth. As growth of the alveolar bone continues and the adjacent permanent teeth erupt, the ankylosed deciduous tooth appears to submerge into the bone, although in reality it has not changed position. Treatment is by extraction of the involved tooth, to prevent malocclusion, periodontal disturbance or dental caries.

Turner's hypoplasia is an abnormality found in teeth. Its appearance is variable, though usually is manifested as a portion of missing or diminished enamel on permanent teeth. Unlike other abnormalities which affect a vast number of teeth, Turner's hypoplasia usually affects only one tooth in the mouth and, it is referred to as a Turner's tooth.

Treatment and prognosis are usually based upon keeping these teeth and preserving the alveolus. For erupted teeth, endodontics is an option if the tooth is devitalized and restorable. For unerupted teeth, function can be restored with a removable partial denture until all major growth has been completed and a final restoration can be placed.

Extra teeth, lost teeth, impacted teeth, or abnormally shaped teeth have been cited as causes of malocclusion. A small underdeveloped jaw, caused by lack of masticatory stress during childhood, can cause tooth overcrowding. Ill-fitting dental fillings, crowns, appliances, retainers, or braces as well as misalignment of jaw fractures after a severe injury are other causes. Tumors of the mouth and jaw, thumb sucking, tongue thrusting, pacifier use beyond age 3, and prolonged use of a bottle have also been identified as causes.

In an experiment on two groups of rock hyraxes fed hardened or softened versions of the same foods, the animals fed softer food had significantly narrower and shorter faces and thinner and shorter mandibles than animals fed hard food. Experiments have shown similar results in other animals, including primates, supporting the theory that masticatory stress during childhood affects jaw development. Several studies have shown this effect in humans. Children chewed a hard resinous gum for two hours a day and showed increased facial growth.

During the transition to agriculture, the shape of the human mandible went through a series of changes. The mandible underwent a complex series of shape changes not matched by the teeth, leading to incongruity between dental and mandibular form. These changes in human skulls may have been "driven by the decreasing bite forces required to chew the processed foods eaten once humans switched to growing different types of cereals, milking and herding animals about 10,000 years ago."

To establish appropriate alignment and occlusion, the sizes of upper and lower front teeth, or upper and lower teeth in general, need to be proportional. Inter-arch tooth size discrepancy (TSD) is defined as a disproportion in the mesio-distal dimensions of teeth of opposing dental arches, which can be seen in 17% to 30% of orthodontic patients.

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.

The best method of maintaining the health of teeth is to practice exemplary oral hygiene. More tooth loss is likely to occur if intervention takes place. However, factors such as present complaint, patient age, severity of the problem, can affect the treatment plan or options.