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Department of Oral and Maxillofacial Surgery, School of Dental Medicine, University at Buffalo, 3435 Main Street, #112 Squire Hall, Buffalo, NY 14214, USA
Erupted, disease-free third molar teeth may be retained indefinitely.
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Periodontal abnormality is common at third molar sites, and may be difficult to control or eradicate with conventional periodontal therapy techniques because of abnormal eruption patterns or proximity of teeth to the mandibular ramus.
•
Third molar sites commonly harbor microbial flora known to be associated with periodontal disease, and evidence suggests that third molar sites may first be affected by periodontitis that moves to more anterior locations over time.
•
The periodontal status of second molars tends to improve after extraction of third molars that exhibit periodontal abnormality.
•
Pericoronal tissue that is histologically indistinguishable from a dentigerous cyst may affect greater than one-third of impacted third molars without abnormal pericoronal radiolucency, and this is more common in patients after age 20 years.
•
At present, the relationship of retained third molars to systemic disease is tenuous.
Introduction
There has been much discussion in the literature regarding the prevalence of third molar pathology and extraction.
The cost to the individual and to society (in the form of lost productivity), and the morbidity associated with surgery for third molar extraction, seems to form the basis for many investigators to discourage extraction of asymptomatic teeth. So-called prophylactic extraction of third molar teeth has, in fact, been deemed a “public health hazard.”
Influence of angular position and degree of impaction of third molars on development of symptoms: long-term follow-up under good oral hygiene conditions.
Few published articles, however, have taken into account the possibility of early or occult disease that could be eliminated by intervention before symptom development, and it has been rightly recognized that lack of symptoms does not necessarily equate to lack of disease.
Just as no dentist would fail to treat a carious lesion because it is asymptomatic, the surgeon should recognize that the presence (and sometimes likelihood) of asymptomatic disease may necessitate extraction of retained third molars at an age when morbidity is likely to be less and recovery faster.
As it has been recognized that third molars that are not fully erupted commonly change position over time (even past the “normal” eruption age), it is prudent to monitor retained teeth for development of pathosis for a lifetime.
For example, in one 5-year study where retained third molar teeth were monitored, it was necessary to extract about one-third of them during the time frame of the investigation,
patients will frequently present with nebulous complaints of headache, “pressure,” or pain that is not readily attributable to the teeth. In many of these scenarios, clinical examination will not be able to definitively attribute the symptoms to the third molars. The surgeon is then faced with the dilemma of recommending retention or extraction for a given individual. It is hoped that the following discussion will aid in both the diagnosis and management of these patients.
For the purposes of this article, pathologic manifestations will be divided into soft-tissue conditions (primarily pericoronitis and periodontal disease), conditions affecting hard tissues of teeth, and lytic lesions of bone. Each is discussed in turn.
Soft-tissue conditions
Pericoronitis and Infection
Pericoronitis, an inflammatory condition associated with the soft tissue around a partially erupted third molar, commonly occurs when a lower third molar tooth cannot erupt fully and remains partially covered by a soft-tissue operculum because of its position in the jaw (Fig. 1). It has been suggested that the teeth most likely to develop pericoronitis are vertically positioned lower third molars at or near the level of the occlusal plane,
with only intermittent symptoms, but is often acutely recurrent in a specific individual. The gingival tissues may be exquisitely tender and purulent, causing significant discomfort for the patient, and limiting jaw opening and chewing function. In certain circumstances, as with deployed service personnel, the condition can be particularly problematic.
There is also evidence that mandibular third molar pericoronitis may be associated with more underlying periodontal inflammatory disease in young adults when compared with a similar population without pericoronitis,
Older published literature may not provide a complete picture of the bacterial flora associated with this condition because it is based on culture techniques that are not capable of growing all microbial species present. Newer molecular methodologies have discovered several uncultivable organisms not previously identified at third molar sites, and it has been suggested by some investigators that the soft tissues around third molars with acute or chronic pericoronitis may provide a niche for the establishment of periodontal abnormality at other oral sites.
Pericoronitis may be managed with a variety of interventions, including subgingival curettage to remove plaque and foreign bodies, irrigation with antimicrobials such as chlorhexidine, or antibiotic therapy. Operculectomy, although sometimes effective in reducing symptoms in the short term, does not appear to provide long-term benefit for most patients.
In cases where the erupted or partially erupted upper third molar impinges on a lower operculum, extraction of the upper third molar may aid pain control and speed the healing process. Extraction of the lower third molar tooth is generally indicated for patients once any infection and swelling have resolved, especially if recurrent.
Although most cases of pericoronitis will resolve with local intervention, a small percentage will progress to major infection. The frequency of this outcome is reported to be low, however: on the order of 0.016 cases per year per 1000 patients at risk.
Such individuals are seriously ill, often demonstrating multispace infections compromising the airway, and requiring intubation, extensive drainage procedures in the operating room, and critical-care management for several days. It appears that most hospitalizations result from diseased third molars or nonelective removal of diseased third molars.
Acute or chronic symptoms thought to be related to third molars have also been reported to delay the diagnosis and treatment of cancer in a small number of cases.
Clinicians should, of course, be aware that pain or other symptoms at third molar sites may reflect more serious conditions than localized pericoronitis.
Periodontal Disease
There is mounting evidence that asymptomatic third molar teeth, especially lower third molar teeth, are frequently associated with pathologic periodontal probing depths.
In addition, the gingivae around these teeth have been repeatedly shown to harbor bacteria known to be associated with the development of periodontitis. Some investigators have demonstrated that these pathogenic bacteria are found first at third molar sites, which may thus serve as a reservoir for the development of more generalized periodontal disease.
These findings suggest that early removal of lower third molars unlikely to erupt into a healthy periodontal state may prevent or delay the onset of adult periodontitis. In addition, they suggest that periodontal probing should be an integral part of clinical assessment to adequately advise the patient about retention or extraction of third molars.
As already indicated, periodontal pathogens are commonly found in pericoronal tissues of third molar teeth, and have been reported even in otherwise periodontally healthy individuals.
In this same population, periodontal abnormality worsens over time in non–third molar sites, but this is more likely to happen in patients with at least one probing depth of at least 4 mm in the third molar region.
and the presence of a visible third molar was significantly associated with more severe periodontal disease at sites more anterior, particularly on second and first molars.
Improvement in the periodontal status of the second molar over time has been demonstrated after removal of both the lower and upper third molar, at least in younger adults,
Improvement in alveolar bone height has been demonstrated at the distal of the second molar after extraction of impacted mandibular third molars in comparison with their retention.
In general, second molar periodontal health improves or remains constant after extraction of the third molar. A possible exception to this outcome, however, is the patient with normal periodontal health preoperatively, as these individuals may see the periodontal status of the second molar worsen after third molar extraction
report a 30% rate of caries or filled surfaces for erupting third molars within 6 years; the prevalence of third molar caries also appears to increase over time.
Because many of these teeth are malposed and/or never achieve complete eruption, they may be difficult candidates for dental restoration (Fig. 2). In such cases, extraction may be the most efficacious treatment.
Fig. 2Impacted, symptomatic third molar in a 70-year-old man demonstrating dental caries, lack of bone on the second molar, and pericoronal radiolucency.
In addition to dental caries in the third molar, third molar angulation may predispose to caries on the distal surface of the second molar tooth, with prevalence of second molar caries up to 12.6% in one studied population.
Early carious lesions on the second molar can be difficult to distinguish from so-called cervical burnout, and treatment may thus not occur in the early stages of disease. Second molar lesions often begin in the area of the cementoenamel junction because of a mesioangularly or horizontally impacted third molar, and may involve significant portions of the distal second molar root. Resorption of the second molar root may occur even in the absence of dental caries (Fig. 3). In advanced lesions, restoration of the second molar is not possible, and both the second and third molar teeth must be extracted.
Fig. 3(A) Severe second molar root resorption caused by maxillary third molar. (B) Severe second molar root resorption caused by mandibular third molar (same patient as in A). This individual had similar findings on all second molars.
Every oral and maxillofacial surgeon is familiar with displaced third molar teeth associated with large radiolucencies (Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8). Sometimes associated with pain, swelling, or functional disturbances, these lesions most often have no signs or symptoms, and the condition is discovered incidentally during a radiographic survey. Lesions may occur in any age group, with extremes of age posing the greatest challenge in management. Because these patients are generally referred to the oral surgeon for diagnosis and management, the population seen by surgeons is skewed toward individuals with disease; what seems common in specialty practice could, in fact, be relatively rare in the general population. The frequency of these lytic lesions thus cannot be determined solely from practice populations because of selection bias in specialty practice. How, then, can the likelihood of cyst or tumor development associated with retained third molar teeth be determined?
Fig. 4Arrows illustrate typical small dentigerous cyst surrounding a maxillary third molar tooth in a female patient.
Fig. 5(A) Dentigerous cyst associated with a displaced, impacted third molar tooth in a 94-year-old woman (white arrows). Red arrow indicates impacted maxillary third molar with discontinuity in overlying bone but no overt disease. (B) Similar dentigerous cyst in an 83-year-old male patient.
The preponderance of literature regarding the development of odontogenic cysts and tumors associated with third molar teeth is radiographic, retrospective, and/or cross-sectional in nature.
Commonly an author will retrieve existing panoramic radiographs from a series of patients and assess them for the presence of radiolucencies around third molar teeth. Although this provides some information, there are several factors that preclude the ability to assess prevalence of cystic (or tumorous) change. First, many of the radiographs will demonstrate that the third molars are absent because they have previously been removed. Of course, it is not clear if such teeth had been removed to treat disease or if they were extracted prophylactically. Second, a radiographic study of this type cannot rule out early hard-tissue or soft-tissue disease. Panoramic radiography may not demonstrate early dental caries, and developing cysts or tumors may not yet have caused discernible bone destruction. Nevertheless, at least one retrospective study has reported an alarming frequency of radiographically detectable pathosis in 46.4% in 2432 impacted lower third molars,
Histologic assessment of tissues remains the gold standard for disease diagnosis, and several peer-reviewed publications have reported findings when soft tissues associated with third molars were analyzed histologically.
demonstrated similar findings, with a dentigerous cyst reported in nearly 46% of pericoronal radiolucencies (0.1–3.0 mm) around impacted third molar teeth. Several recent studies have evaluated soft tissues retrieved from third molar sites without radiographic evidence of disease (follicular spaces 3 mm or less), and have reported pathologic change in high percentages, greater than 50% in some reports.
designed a prospective evaluation of soft tissues from third molars without radiographic evidence of disease (less than 2.5 mm pericoronal radiolucency). Tissues were evaluated independently by 3 different oral pathologists, and only when all 3 agreed that a specimen represented disease was the tissue deemed to be pathologic. In this study, 31 of 96 specimens were diagnosed as dentigerous cyst; no other pathologic lesions were identified.
A similar trend was reported by Adelsperger and colleagues,
in whose study 99 specimens were evaluated independently by 2 oral pathologists. In the event of a disagreement in diagnosis, a consensus diagnosis was achieved. Surprisingly, 34% of the specimens were found to represent dentigerous cysts, concurring nearly exactly with the findings reported by Glosser. In this study, however, a subset of follicular and cystic tissues was further assessed for the presence of proliferating cell nuclear antigen (PCNA), a marker of active cellular division. A high percentage of positivity was found in the cystic tissues (62.5%), whereas none of the examined follicular tissues showed mitotic activity. Although there were no gender differences in the percentage of cystic tissues, the actively growing cysts were associated with increasing age, suggesting that these may have become radiographically evident at some future time. Others have also associated a higher frequency of cystic change in patients older than 20 years,
Patients presenting to a private oral surgeon completed a questionnaire regarding their perceptions of symptoms associated with their third molar teeth. Again, pericoronal tissues were submitted for histologic diagnosis, and again nearly one-third of sites were found to have dentigerous cysts. On analysis, however, symptoms of infection, swelling, pain, or “pressure” showed no correlation with the location of the cysts. Nearly equal percentages of cysts and follicles had some symptom, and symptoms could thus not predict which teeth harbored odontogenic cysts.
Some controversy exists among pathologists regarding the diagnosis of dentigerous cysts. Whereas many consider squamous metaplasia of pericoronal tissues to indicate the diagnosis, others argue that histology alone cannot confirm the presence of cystic change.
The findings of increased cellular activity demonstrated by some of the previously referenced investigators support the conclusion that the histologic findings represent pathosis. Whether these actively growing tissues continue to grow, become quiescent, or involute over time has yet to be determined. It is likely, however, that because pericoronal tissues are not routinely submitted for histologic diagnosis, associated disease is underdiagnosed.
Summary
Controversy continues to cloud the issue of third molar retention, although enough information is available for the surgeon to make informed decisions in recommending retention or extraction for his or her patients. The following points should be considered when advising patients:
•
Erupted, disease-free third molar teeth may be retained indefinitely
•
“Asymptomatic” does not mean “disease-free”
•
Periodontal abnormality is common at third molar sites, and may be difficult to control or eradicate with conventional periodontal therapy techniques because of abnormal eruption patterns or proximity of teeth to the mandibular ramus
•
Third molar sites commonly harbor a microbial flora known to be associated with periodontal disease, and evidence suggests that third molar sites may first be affected by periodontitis that moves to more anterior locations over time
•
Acute or chronic pericoronitis sites may also harbor periodontal pathogens
•
The periodontal status of second molars tends to improve after extraction of third molars that exhibit periodontal abnormality
•
Pericoronal tissue that is histologically indistinguishable from dentigerous cyst may affect greater than one-third of impacted third molars without abnormal pericoronal radiolucency, and this is more common in patients after age 20 years
•
Symptoms do not correlate with the location of most dentigerous cysts
•
Third molar position may change long after the “normal” eruption time
•
At present, the relationship of retained third molars to systemic disease is tenuous
The surgeon would do well to incorporate periodontal probing into the examination of the third molar for documentation of periodontal abnormality associated with erupted, partially erupted, and impacted third molar teeth. Patients who elect to retain third molars should undergo clinical and radiographic examination regularly (perhaps as frequently as every 2 years) for early diagnosis of disease, because the prevalence of third molar abnormality (especially asymptomatic) appears to be much higher than previously thought. Younger patients unable or unwilling to have regular surveillance may wish to consider removal of teeth at high risk of present or future disease at an age when surgical morbidity is likely to be less.
References
Obiechina A.E.
Arotiba J.T.
Fasola A.O.
Third molar impaction: evaluation of the symptoms and pattern of impaction of mandibular third molar teeth in Nigerians.
Influence of angular position and degree of impaction of third molars on development of symptoms: long-term follow-up under good oral hygiene conditions.
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