出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/05/21 22:25:26」(JST)
A wisdom tooth, in humans, is any of the usual four third molars. Wisdom teeth usually appear between the ages of 16 and 25.[1] Most adults have four wisdom teeth, but it is possible to have fewer or more, in which case the extras are called supernumerary teeth. Wisdom teeth commonly affect other teeth as they develop, becoming impacted or "coming in sideways." They are often extracted when this occurs.
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Impacted wisdom teeth (i.e., those that have failed to erupt through the gum line) fall into one of several categories:
Typically mesioangular impactions are the most difficult to extract in the maxilla (upper jaw) and easiest to extract in the mandible (lower jaw), while distoangular impactions are the easiest to extract in the maxilla and most difficult to extract in the mandible. Frequently, a fully erupted upper wisdom tooth requires bone removal if the tooth does not yield easily to forceps or elevators. Failure to remove distal or buccal bone while removing one of these teeth can cause the entire maxillary tuberosity to be fractured off, thereby tearing out the floor of the maxillary sinus.[citation needed]
Impacted wisdom teeth may also be categorized on whether they are still completely encased in the jawbone. If it is completely encased in the jawbone, it is a bony impaction. If the wisdom tooth has erupted out of the jawbone but not through the gumline, it is called a soft tissue impaction.
In a small portion of patients, cysts and tumors occur around impacted wisdom teeth, requiring surgical extraction. Estimates of the incidence of cysts around impacted teeth vary from 0.001% to 11%, with a higher incidence in older patients, suggesting that the chance of a cyst or tumor increases the longer an impaction exists. A retrospective review of approximately 10,000 impacted teeth, suggested that the incidence of malignant tumours was 0.02% (2 cases in 9,994 teeth).[2]
The oldest known impacted wisdom tooth belonged to a European woman of the Magdalenian period (18,000–10,000 BC).[3]
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Sometimes the wisdom tooth fails to erupt completely through the gum bed and the gum at the back of the wisdom tooth extends over the biting surface, forming a soft tissue flap or lid around the tooth called an operculum. Teeth covered by an operculum can be difficult to clean with a toothbrush. Additional cleaning techniques can include using a needle-less plastic syringe to vigorously wash the tooth with moderately pressured water or to softly wash it with hydrogen peroxide.
However, debris and bacteria can easily accumulate under an operculum, which may cause pericoronitis, a common infection problem in young adults with partial impactions that is often exacerbated by occlusion with opposing third or second molars. Common symptoms include a swelling and redness of the gum around the eruption site, difficulty in opening the mouth, a bad odor or taste in the mouth, and pain in the general area which may also run down the entire lower jaw or possibly the neck. Untreated pericoronitis can progress to a much more severe infection.
If the operculum does not disappear, recommended treatment is extraction of the wisdom tooth. An alternative treatment involving removal of the operculum, called operculectomy, has been advocated. There is a high risk of permanent or temporary numbness of the tongue due to damage of the nerve with this treatment and it is no longer recommended as a standard treatment in oral surgery.
Chronic inflammation in the gingival tissue of the partially erupted third-molar, i.e. chronic pericoronitis, may be the etiology for the development of paradental cyst, an inflammatory odentogenic cyst.
Wisdom teeth are extracted for two general reasons: either the wisdom teeth have already become impacted, or the wisdom teeth could potentially become problematic if not extracted. Potential problems caused by the presence of properly grown-in wisdom teeth include infections caused by food particles easily trapped in the jaw area behind the wisdom teeth where regular brushing and flossing is difficult and ineffective. Such infections may be frequent, and cause considerable pain and medical danger. Other reasons wisdom teeth are removed include misalignment which rubs up against the tongue or cheek causing pain, potential crowding or malocclusion of the remaining teeth (a result of there being not enough room on the jaw or in the mouth), as well as orthodontics.[4]
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There are several problems that might occur after the extraction(s) have been completed. Some of these problems are unavoidable and natural, while others are under the control of the patient. The suggestions contained in the sections below are general guidelines by which a patient will be expected to abide, but the patient should follow all directions that are given by the surgeon in addition to the following guidelines. Above all, the patient must not disregard the given instructions; doing so is extremely dangerous and could result in any number of problems ranging in severity from being merely inconvenient (dry socket) to potentially life-threatening (serious infection of the extraction sites).
Bleeding and oozing are inevitable and should be expected to last up to three days (although by day three it should be less noticeable). Rinsing the mouth during this period is counter-productive, as the bleeding stops when the blood forms clots at the extraction sites, and rinsing out the mouth will most likely dislodge the clots. The end result will be a delay in healing time and a prolonged period of bleeding. Gauze pads should be placed at the extraction sites, and then should be bitten down on with firm and even pressure. This will help to stop the bleeding, but should not be overdone as it is possible to irritate the extraction sites and prolong the bleeding or remove the clot. The bleeding should decrease gradually and noticeably upon changing the gauze. If the bleeding lasts for more than a day without decreasing despite having followed the surgeon's directions, the surgeon should be contacted as soon as possible. This is not supposed to happen under normal circumstances and signals that a serious problem is present. A wet tea bag can replace the gauze pads. Tannin contained in tea can help reduce the bleeding.[5]
Due to the blood clots that form in the exposed sockets as well as the abundant bacterial flora in the mouth, an offensive smell may be noticeable a short time after surgery. The persistent odor often is accompanied by an equally rancid-tasting fluid seeping from the wounds. The smell and taste are described by some individuals as unbearable at times, yet regular rinsing of the mouth with salt water or mouthwash can help to temporarily reduce the smell and/or taste. These symptoms will diminish over an indeterminate amount of time, although one to two weeks is normal. While not a cause for great concern, a post-operative appointment with one's surgeon seven to ten days after surgery is highly recommended to make sure that the healing process has no complications and that the wounds are relatively clean. If infection does enter the socket, a qualified dental professional can gently plunge a plastic syringe (without the hypodermic needle) full of a mixture of equal parts hydrogen peroxide and water or chlorhexidine gluconate, which also comes in the form of a mouth wash, into the sockets to remove any food or bacteria that may collect in the back of the mouth. This is less likely if the person has his/her wisdom teeth removed at an early age.
A dry socket, also known as alveolar osteitis, is a painful inflammation of the alveolar bone (not an infection); it occurs when the blood clots at an extraction site are dislodged, fall out prematurely, or fail to form. In some cases, this is beyond the control of the patient. However, in other cases this happens because the patient has disregarded the instructions given by the surgeon. Smoking, blowing one's nose, spitting, or drinking with a straw in disregard to the surgeon's instructions can cause this, along with other activities that change the pressure inside of the mouth, such as sneezing or playing a musical instrument. The risk of developing a dry socket is greater in smokers, in diabetics, if the patient has had a previous dry socket, in the lower jaw, and following complicated extractions. The extraction site will become irritated and painful, due to inflammation of the bone lining the tooth socket (osteitis). The symptoms are made worse when food debris is trapped in the tooth socket. The patient should contact their surgeon if they suspect that they have a case of dry socket. The surgeon may elect to clean the socket under local anesthetic to cause another blood clot to form or prescribe medication in topical form (e.g. Alvogel) to apply to the affected site. A non-steroidal anti-inflammatory drug (NSAID) such as ibuprofen may be prescribed by the surgeon for pain relief. Generally dry sockets are self-limiting and heal in a couple of weeks without treatment.
Swelling should not be confused with dry socket, although painful swelling should be expected and is a sign that the healing process is progressing normally. There is no general duration for this problem; the severity and duration of the swelling vary from case to case. The surgeon will tell the patient how long they should expect swelling to last, including when to expect the swelling to peak and when the swelling will start to subside. If the swelling does not begin to subside when it is supposed to, the patient should contact his or her surgeon immediately. Swelling usually lasts one week. While the swelling will generally not disappear completely for several days after it peaks, swelling that does not begin to subside or gets worse may be an indication of infection. Swelling that re-appears after a few weeks is an indication of infection caused by a bone or tooth fragment still in the wound and should be treated immediately.
Nerve injury is primarily an issue with extraction of third molars but can occur with the extraction of any tooth should the nerve be near the surgical site. Two nerves are typically of concern and are found in duplicate (on the left and right side):
Such injuries can occur while lifting teeth (typically the inferior alveolar) but are most commonly caused by inadvertent damage with a surgical drill. Such injuries are rare and are usually temporary.[6] Depending on the type of injury (i.e. Seddon classification: neuropraxia, axonotmesis, and neurotmesis) they can be prolonged or permanent. In rare cases it is also possible for bleeding into the nerve canal to also cause an injury to the nerve due to the increased pressure of the blood build up. The risk of nerve damage can be reduced by performing a coronectomy instead of a complete extraction.
Preventive removal of the third molars is a common practice in developed countries and is usually recommended by dentists. According to Pediatric Dentistry: Infancy Through Adolescence, 4th Edition:
"Evaluation of third molars is usually completed during mid- to late adolescence. Parents commonly ask about treating these teeth. The reasons for extraction of third molars include impaction or failure to erupt; potential or existing pathosis such as cysts or ameloblastoma; decay; posteruption malposition; nonfunction as a result of an absent opposing tooth; difficulty with hygiene; and recurrent pericoronitis. If any of these are considerations, third molars should be removed during adolescence.... The evaluation of developing third molars in adolescent athletes is of particular importance. Not only can an athletic season suddenly be interrupted by the annoying and often painful eruption of third molars with associated acute pericoronitis, but mandibular fractures in the gonial angle region of developing third molars can also occur in adolescent athletes."[4]
Several dental textbooks encourage the removal of third molars. From Contemporary Oral and Maxillofacial Surgery, 5th Edition:
"As a general rule, all impacted teeth should be removed unless removal is contraindicated. Extraction should be performed as soon as the dentist determines that the tooth is impacted. Removal of impacted teeth becomes more difficult with advancing age. The dentist should typically not recommend that impacted teeth be left in place until they cause difficulty. If the tooth is left in place until problems arise, the patient may experience an increased incidence of local tissue morbidity, loss of or damage to adjacent teeth and bone, and potential injury to adjacent vital structures. Additionally, if removal of impacted teeth is deferred until they cause problems later in life, surgery is more likely to be complicated and hazardous because the patient may have compromising systemic diseases and the surrounding bone becomes more dense. A fundamental precept of the philosophy of dentistry is that problems should be prevented. Preventive dentistry dictates that impacted teeth are to be removed before complications arise unless removal will cause more serious problems."[7]
The rationale of prophylactically removing third molars prior to their complete root formation is that the likelihood of nerve damage or other complications is extremely low. This is not the case however with symptomatic removal of a third molar after root formation is complete and more intimate with the inferior alveolar nerve and as the mandible becomes more dense with age.[8]
However, studies have shown that dentists graduated from different countries—or even from different dental schools in the same country[9]—may have different clinical decisions regarding third molar removal for the same clinical condition. For example, dentists graduated from Israeli dental schools may recommend more often for the removal of asymptomatic impacted third molar than dentists graduated from Latin-American or Eastern European dental schools.[10]
In 2006, the Cochrane Collaboration published a systematic review of randomized controlled trials in order to evaluate the effect of preventive removal of asymptomatic wisdom teeth.[11] The authors found no evidence to either support or refute this practice. There was reliable evidence showing that preventative removal did not reduce or prevent late incisor crowding. The authors of the review suggested that the number of surgical procedures could be reduced by 60% or more. Likewise, ClinicalEvidence published a summary largely based on the Cochrane review that concluded prophylactic extraction is "likely to be ineffective or harmful."[12] It advised against extracting asymptomatic, disease-free wisdom teeth because of the risk of damage to the inferior alveolar nerve.
Some evidence suggests that the extraction of the asymptomatic tooth may be beneficial if caries are present on the adjacent second molar, or if periodontal pockets are present distal to the second molar.[13]
The American Association of Oral and Maxillofacial Surgeons has published an extensive White Paper on Third Molar Data summarizing the most current research into the subject of third molar extraction.[14] It states that, "The presence of visible third molars is associated with elevated levels of periodontitis... which involves adjacent teeth and is progressive and only partially responsive to therapy."[14] In developed countries, the presence of wisdom teeth is associated with substandard dental care,[15] leading to an increased likelihood of periodontitis, which may be caused by a lack of dental care rather than the presence of wisdom teeth. Periodontal bacteria causes gum disease, and may travel through the blood stream, resulting in systemic infections associated with the heart, kidneys and other organs. Further, studies have found such bacteria in amniotic fluid and is considered a factor in low birth weight infants.[16]
In the U.K., the National Institute for Health and Clinical Excellence, which advises on best practise and appraises the cost-effectiveness of treatments for the National Health Service, has argued that there is no evidence that removing disease-free impacted wisdom teeth is beneficial, and recommends against removal to avoid the various risks and discomforts of the procedure.[17]
The American Association of Oral and Maxillofacial Surgeons recommends that third molars be removed in patients who, in the opinion of their family dentists, suffer from periodontal infections where the probing depth exceeds 3 mm. It argues that it is advisable to have the third molars of such patients removed in young adulthood to avoid the complications that may occur when third molars have grown to maturity. In these cases, there is a greater likelihood of nerve damage and other potential concerns.[14]
The American Public Health Association recommends against prophylactic removal of asymptomatic, non-pathological wisdom teeth, including wisdom teeth that are impacted,[18] on the basis that the removal of third molars (wisdom teeth), like the removal of any teeth, should be based on evidence of diagnosed pathology or demonstrable need, rather than anticipated future pathology. The APHA's position is based on scientific research that documents the risks of injury to the nerves of the jaw that can cause permanent numbness of the lip and tongue, damage to the temporomandibular (jaw) joint and adjacent teeth.
Wisdom teeth are vestigial third molars that used to help human ancestors in grinding down plant tissue. The common postulation is that the skulls of human ancestors had larger jaws with more teeth, which were possibly used to help chew down foliage to compensate for a lack of ability to efficiently digest the cellulose that makes up a plant cell wall. As human diets changed, smaller jaws gradually evolved, yet the third molars, or "wisdom teeth", still commonly develop in human mouths.[19]
Agenesis of wisdom teeth in human populations ranges from practically zero in Tasmanian Aborigines to nearly 100% in indigenous Mexicans.[20] The difference is related to the PAX9 gene (and perhaps other genes).[21]
Scientists in Japan have been able to successfully harvest stem cells from wisdom teeth.[22] This discovery is of great clinical importance, as wisdom tooth extractions are a relatively common type of oral surgery. Patients who have their wisdom teeth removed are currently able to opt to have stem cells from those teeth isolated and saved, in case they should ever need the cells.
Wisdom teeth can be transplanted to replace lost molars. Rejection applies to teeth just like it does to other body tissue, and donor trials so far have been unsuccessful. The transplantation will cause some damage to the tooth during the transplant process, most notably the nerve, but moving the tooth to another position for the same person is now considered successful and beneficial.[23]
They are generally thought to be called wisdom teeth because they appear so late – much later than the other teeth, at an age where people are presumably "wiser" than as a child, when the other teeth erupt.[24] The term probably came as a translation of the Latin dens sapientiae.
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| リンク元 | 「third molar」「wisdom tooth」 |
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