Causes
Normally pericoronitis occurs in the tissues around the crown of a partially erupted mandibular third molar tooth (lower wisdom tooth). Several factors may act in combination to trigger an acute episode of pericoronitis.
The lower mandibular third molar is a commonly impacted tooth, as it is one of the last teeth to erupt into the dental arch. If the jaw is too small the wisdom tooth may erupt at an abnormal angle, e.g. mesioangularly, when it is tilted forwards. This is sometimes known colloquially as wisdom teeth "coming in sideways". Instead of erupting fully into the mouth, the tooth contacts the distal side (the side at the back) of the second molar and may be impacted in this position, i.e. it is stuck against another tooth and will not erupt any further. The partially erupted and possibly also tilted tooth remains half covered by gingival tissue (gum). The soft tissue that directly overlies the tooth is termed the operculum, or gingival flap. The operculum creates an ideal environment for the accumulation of food debris and micro-organisms (especially bacterial plaque) between it and the partially erupted tooth. This is also termed a plaque stagnation area. There is an inflammatory response in the adjacent soft tissues.
The inflammatory response causes edema (swelling) in the soft tissues directly above and around the tooth. The inflamed soft tissue, now increased in size may now be impinging on the space occupied by the upper molars during the bite. Hence, the upper molars may bite into and further traumatize the soft tissues surrounding the lower third molar. The Upper third molar will often be "over-erupted" because it has not met another tooth to bite into and keeps growing down. Teeth which have never been in a position to grind with another tooth are frequently sharp, as they have suffered no attrition (tooth wear caused by tooth to tooth contact). Trauma from the opposing tooth and swelling from the presence of bacteria beneath the operculum may become a spiraling cycle.
If bacteria begin to invade the soft tissues from the stagnation areas beneath the operculum, at this stage it is termed an active infection. Pericoronal infection is normally caused by a mixture of bacterial species that normally are present in the mouth, such as Streptococci and particularly various anaerobic species. Infection of the soft tissues may cause pus to form within an abscess, which is the body's attempt to isolate the infection. The abscess often spontaneously drains into the mouth via the area underneath the operculum, although sometimes there may be a discharging sinus tract that is in other locations in the mouth, e.g. further forward next to the other molar teeth. This may cause confusion as it appears that a different tooth is infected rather than the wisdom tooth.
The chronically inflamed soft tissues around the tooth may give few if any symptoms. A sudden, acute exacerbation of the inflammation may occur, e.g. if a piece of food gets stuck under the operculum, trapping bacteria beneath it, or if the host immune system becomes temporarily compromised (e.g. during influenza or upper respiratory tract infections, or a period of stress). In this respect, acute pericoronitis can be considered an opportunistic infection, or rather, an opportunistic exacerbation of a chronic process which is normally largely kept in check by a competent immune system.
Trismus indicates that the inflammation/infection involves the muscles of mastication (the muscles that move the jaw). Pain when biting may be caused by an upper tooth pressing into a swollen operculum over a lower tooth.
The halitosis that often accompanies pericoronitis is due to the stagnantion of food debris and bacteria underneath the operculum. The bacteria putrefy proteins in this environment and release malodorous volatile sulfur compounds. The bad taste is related the exudation of pus from beneath the flap.
Pericoronal infection may remain localized in the tissues around the crown or spread into adjacent potential spaces. Acute pericoronitis is often responsible for the spread of infection to areas of the neck or face. As such, the infection may result in an obvious facial swelling, or even compromise the airway depending upon the direction of spread. Pus in the region of the lower third molar may spread in any one of several directions and involve potential spaces. This is unpredictable and mostly related to local anatomic factors such as muscle attachments. Possible potential spaces which may become involved with a spreading pericoronal infection include the sublingual space, submandibular space, parapharyngeal space, pterygomandibular space, infratemporal space, submasseteric space and buccal space. Ludwig's angina is bilateral infection involving the submandibular and sublingual spaces. This is a serious condition because the airway can become compressed by the swelling. It is a rare complication of pericoronitis.
Chronic pericoronitis may be the etiology for the development of paradental cyst, an inflammatory odontogenic cyst. Areas of chronic pericoronitis may cause the radiographic appearance of the local bone to become more radiopaque than surrounding bone. An area of ulceration may develop on the operculum in the long term, which resembles necrotizing ulcerative gingivitis. The presence of supernumerary teeth (extra teeth) makes pericoronitis more likely.
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