June 1, 2009
by Robert Eng, BSc., DMD, FRCD(C)
Removal of third molars (wisdom teeth) remains one of the most common procedures and indications for referral to Oral and Maxillofacial surgeons. While surgery is generally considered to be routine and may even be classified as a typical “rite of passage while growing up” in the broadest sense of common culture, it does remain at heart a surgical procedure, and the concept of prophylactic removal is not without a degree of controversy. In the ever-growing trend of conservative thinking regarding need for medical and surgical procedures, it is prudent to re-evaluate the current state of knowledge regarding third molars and the potential indications for removal and consequences of either late removal or development of pathology associated with impacted wisdom teeth.
Recently, a clinical abstract published in “Ontario Dentist” suggested that there was “…no reliable evidence to support the removal of asymptomatic wisdom teeth in adults” (emphasis as originally published) and appeared under a broad headline: Wisdom Teeth — Second Thoughts.1 Unfortunately, while well-meaning and “evidence-based,” the data from the articles reviewed represents older (1982 and 1998 studies) information which actually was intended to review the cost-effectiveness with respect to removal of wisdom teeth in arch length changes after orthodontic treatment. While the clinical abstract suggested that the two randomized clinical trials assessed issues such as pericoronitis, caries, cysts and root resorption, no mention of these variables were actually addressed in the original articles.2
In fact, the clinical abstract conveniently edited the original statement from the article reviewed, which actually states: “This review concludes that there is no reliable evidence to support or refute routine prophylactic removal of asymptomatic wisdom teeth in adults.” Sensationalist titles aside, the truth of the issue is that the purpose of the original study was actually a measure of cost-effectiveness in assessing post-orthodontic arch-length changes, not a review of the scientific literature with respect to the implications of properly assessing the indications for, and sequelae of removal or watching impacted wisdom teeth.
This is not a new issue. For several years back, there have been two dissenting published guidelines with respect to management of impacted third molars. The UKbased National Health Service and the “National Institute for Clinical Excellence” (NICE) published guidelines in 2000 citing a “lack of evidence for prophylactic removal of asymptomatic wisdom teeth”.3 The difficulty in applying these guidelines universally is that they are based around the premise of a nationally funded programme in which removal of impacted third molars is typically hospital-based, with the attendant increased costs associated with hospital and operating room use.
In contrast, the American Association of Oral and Maxillofacial Surgeons (AAOMS) has been conducting a series of longitudinal studies for almost 30 years, since the 1979 National Institutes for Health (NIH) conference for the removal of third molars. The NIH study failed to demonstrate a definitive consensus with respect to definitive indications for prophylactic removal of wisdom teeth.
Where the NIH guidelines did reach agreement was three well-defined criteria for the removal of third molars (Box 1). It also pointed out the need to longitudinal studies to assess the indications and limitations for recommending prophylactic removal of asymptomatic teeth.4 The culmination of almost 30 years of research has been a series of papers published in an ongoing fashion and capped by the 2007 AAOMS White Paper on Third Molar Data, which is a systematic review of over 200 scientific publications regarding a series of issues regarding third molars and the potential indications for and against their removal.5
The intent of this article is to review the data from the 2007 AAOMS White Paper, and general clinical indications regarding third molar surgery. The ability to objectively assess the indications for surgery on a case-by-case basis and to apply sound and rational clinical principles to planning the surgery will hopefully result in a minimizing of the morbidity associated with impacted wisdom teeth.
The AAOMS White Paper evaluated distinct areas such as periodontal health, and effects of wisdom tooth surgery on periodontal structures, the genesis and development of wisdom teeth, and predictive models with respect to eruption patterns, age-related issues and orthodontic and prosthodontic considerations associated with wisdom teeth. Finally, specific surgical considerations with respect to pre-operative evaluation and technical aspects of surgery were explored. Here are some of the major points from the White Paper.
Defining The Problem: What Is An Asymptomatic Wisdom Tooth?
At what point, and by what criteria, do we determine a wisdom tooth, impacted or otherwise, to be considered asymptomatic? There will likely be a significant difference between the perception of a wisdom tooth as asymptomatic, and the clinical findings that can be objectively measured.
Historically, the NIH consensus guidelines have served as a benchmark for determining whether a tooth was asymptomatic from a clinical perspective. Patient perception tends to be more subjective and tends to revolve more around issues such as pain, swelling, bleeding and the perception of issues such as perceived future tooth movement. For these reasons, the origin of the referral for removal of wisdom teeth can often be patient-initiated. Is this a justified approach?
The challenge is to move beyond a subjective assessment, and to look at what objective signs of current or impending pathology can be assessed, and the implications that these signs might point towards. The paradigm shift in looking towards preventive management — the idea that it is better to intercept and prevent potential issues than to simply react and deal with the consequences — certainly plays into the role of prophylactic removal of the impacted wisdom teeth.6
Genesis of Wisdom Teeth
Eruption of the third molars typically occurs in the later teenage years through the early 20s, although it is has been shown that late movement can occur beyond the third decade of life.7 Timing of the eruption varies widely. Eruption can be seen as early as 13-14 years of age, and typically follows root development. Conversely, it is also possible for delayed root formation to occur, and result in incomplete development of impacted wisdom teeth or late eruption.
The third molar is typically the last to develop in the dental arch. Typical development of the third molar tooth germ begins around the age of 8-9 years with radiographic appearance distal to the second molars. The crown is typically visible by 14 years of age and root formation is generally considered to be nearly complete by the age of 20-21.8
The ability to predict with a degree of accuracy the potential for eruption of the third molar would allow for much more controlled template for determining the need for removal. A number of radiographic techniques to assess the potential for impaction of the third molars exist, all measuring variables relating to the existing and likely future space for eruption.9-11 In spite of these varied techniques, there remains a degree of uncertainty with regards to the definitive ability to predict complete eruption of the third molars.
The most widely accepted concepts that are likely to determine eruption include angulation of the tooth, relative degree of root formation at the time of assessment, relative depth of impaction, available space for eruption (typically regarded as the space from the anterior aspect of the ascending ramus to the distal of the second molar) and the size of the impacted third molar (Fig. 1).
The ability to erupt does not necessar
ily ensure the health of the wisdom teeth. In addition to the space for eruption, there needs to be sufficient space and access for the patient to ensure adequate hygiene. Failure on this point may result in pathology not only around the wisdom teeth, but also the adjacent structures.12-13 One of the critical points to emerge from long-term studies is the fact that wisdom teeth do continue to erupt and move past the middle of the third decade of life.7
Conventional thought is that wisdom teeth “grow until you are 25 or so” which has the potential to influence the management of impacted teeth in older adults. In addition to the potential for continued movement of the teeth, it has been suggested that pathologic changes associated with the wisdom teeth tends to increase with age, and the surgery is more difficult and recovery tends to be prolonged in older patients.14-17
Periodontal Concerns in Third Molar removal
The impact of the presence, removal and pathologic changes associated with wisdom teeth on the periodontal health of patients is a long-standing issue, and emerging evidence of the possible association of periodontal disease and systemic health makes this a potentially more urgent issue to understand. A 1988 NIH conference “Removal of Third Molars” focused on the potential for pathologic sequelae associated with impacted third molars. Earlier studies assessed the incidence of root resorption of adjacent second molars from impacted third molars, and a relatively high prevalence (24.2%) was noted with a positive correlation to older age. 18 In more recent developments, a series of long-term trials focusing on systemic health risks has found that greater periodontal probing depths (>5mm) are typically associated with the presence of visible third molars.19-20
In fact, one of the more telling findings in recent literature is from a 2007 study in which an association with progressive periodontal disease on non-third molar teeth was found around patients with asymptomatic third molars21 (Fig. 2). Measurements such as pocket depth and bleeding were found to increase around first and second molars over a 4-year period,22 leading to the suggestion that “asymptomatic” wisdom teeth can, in certain circumstances be potentially classified as a chronic health risk, given the association of periodontal disease with systemic health issues.23-26 There is also the question as to whether the mere presence of third molars, asymptomatic or otherwise will definitively result in periodontitis, or influences the risk of adjacent teeth developing periodontitis. The difficulty is that historically, many studies have excluded third molars from findings, on the basis that reproducibility of measurements within studies is limited by the ongoing development of the third molars. These assumptions have been shown to lack true validity, and there are ongoing studies to assess the prevalence and severity of periodontitis as a result of the presence of wisdom teeth. 5,27-28
In addition to the presence of periodontal pathology, a number of studies also have looked into the impact of removal of third molars on the periodontal status of the adjacent second molars. The vast majority of these studies focus on the mandibular third molars, and are typically assessed on the basis of attachment levels, pocket depths and bone levels on the second molars.22
While most studies tend to agree that there is a potential for negative long-term outcomes in terms of increased pocketing and attachment loss following surgery, it was clearly noted that early removal (</25 years of age), post-operative hygiene and plaque control, and the lack of pre-existing periodontal pathology prior to surgery were the most critical elements in mini- mizing the likelihood of adverse post-surgical outcomes.21,29-30
Surgical technique can be a predictor of post-surgical discomfort and swelling, but there did not appear to be a significant difference in the surgical approach (i. e. flap design) in determining the potential for post-operative periodontal issues. 31-32 In a related matter, the use of guided-tissue regenerative techniques (GTR) and placement of demineralized bone powder (DBP) has not been shown to generally result in improved outcomes in routine cases, although it may benefit certain high-risk cases (significant preexisting periodontal pathology/ pocketing, poor plaque control and advanced age).33-35 This should not be taken as an indication to apply these techniques on a routine basis. There are currently ongoing trials to determine under what conditions there could be a demonstrated benefit from adjunctive regenerative techniques to minimize long-term periodontal risk from third molar surgery.
Microflora around Second and Third Molars
Inflammation around third molars (pericoronitis) (Fig. 3) has been long implicated with multiple anaerobic and facultative anaerobic bacteria. The flora associated with pericoronitis is very broad with over 440 organisms implicated in various papers. 36-37 The most important of these are the anaerobic and facultative anaerobes, which have the potential to progress into life-threatening situations with the progression into deep space infections. Aggressive treatment, including eventual removal of the tooth is curative for most infections, but the sequelae associated with severe infections can be great (Figs. 4 & 5).
In addition, the microbiological flora associated with pericoronitis has also been implicated in refractory periodontitis, 38 and the development of increased pocketing over time in older individuals with “asymptomatic” wisdom teeth has been correlated with the presence of inflammatory mediators. This may herald the onset of progressive periodontal disease beyond the third molar region. Indeed, several studies have demonstrated the presence of inflammatory markers (Prostaglandin E2, Interlukin ) in the pockets of asymptomatic wisdom teeth,39-40 and there has been early correlation of systemic effects presenting in the form of adverse obstetric outcomes in patients with otherwise asymptomatic retained third molars. 26
Along with the research towards the effects of periodontal disease and systemic health, emerging data may serve to point towards a rationale for early intervention in removal of asymptomatic wisdom teeth prior to disease markers appearing.
Caries experience around third molars is also progressive. As previously noted, even though teeth may erupt into occlusion, there is still often insufficient space to allow adequate mechanical hygiene, and the result is an increased risk of caries development around third molars.12
In a recent study involving patients with erupted third molars followed over a three year period, those patients older than 25 years of age showed a higher incidence of caries than younger patients.60,61 In fact, one study correlated caries experience in third molars with non-third molar teeth, and suggested that up to 40% of third molars will develop caries by the end of the third decade.61 The potential risk for caries combined with decreased access for hygiene poses a long-term risk for spread to adjacent teeth, and likely contributes to the periodontal disease progression.60
Effects of Age related to Third Molars
General findings that symptoms such as pain, swelling and food impactions were the most commonly cited findings reported by patients41. Frequency and severity of symptoms increased with age. As expected, pain and swelling represents the most common indication for seeking treatment. Additional parameters such as progression in periodontal disease, caries and post-operative risks such as the aforementioned periodontal defects, surgical risks such as nerve damage,42 oro-antral communication, 43 fractures44 and prolonged recovery
were all associated with advancing age at the time of wisdom tooth removal.14,15
One issue that bears repeating is that of pathologic developments around retained impacted teeth. Late development of cysts, odontogenic tumours and other lesions can develop over time, and may, in the case of cystic transformation occur without significant radiographic changes or signs. 55-57 One recent study suggested up to 34% of asymptomatic follicles display metaplastic changes consistent with cystic transformation,57 and the percentage may prove to be even higher as studies are ongoing.55
Does this suggest the need for early wisdom tooth removal? There have been numerous studies assessing the efficacy of early removal, or germectomy, which is defined as removal of the wisdom tooth with less than one-third root formation, and a distinct periodontal ligament still present45-47. While results do seem to suggest lower complication rates, and a less-prolonged post-operative recovery, there is still insufficient long-term data from randomized clinical trials to justify this as a general philosophy. Certainly from a technical standpoint, very early intervention can be somewhat clinically difficult and may pose risks to adjacent teeth still in development. The final decision to recommend germectomy remains a case-by-case decision by the health care team.
Orthodontic and Prosthodontic considerations related to third molars
The referral for removal of wisdom teeth to “prevent my teeth from shifting after my braces” is still commonly seen. Does the literature support this statement? There are studies both for and against the case regarding third molars and crowding, but the degree of impact and significance of the findings may be limited.
Despite multiple studies and evaluation of various parameters, it is still not possible to isolate the presence of wisdom teeth alone as a sole cause in the development of late incisor crowding. Dental crowding is generally accepted to be multi-factorial, and there remains no definitive way to predict, prevent and fully explain dental crowding. The most prudent course at present is to explain to patients (and parents!) that while wisdom teeth (impacted or otherwise) may play a role in dental crowding -possibly significant -it is not possible to accurately predict which patients are more at risk for late crowding48-51.
The need for removal of impacted teeth in line of proposed orthognathic surgery is well-documented, and typically occurs at least 6 months prior to the planned orthognathic movement. The rationale is that available space is required for placement of fixation screws, and the presence of wisdom teeth (or removal at the time of the orthognathic surgery) may result in less available bone for adequate rigid fixation. In addition to the need for adequate space for the fixation screws, presence of impacted teeth may adversely affect the osteotomy, resulting in the potential for a less-than-ideal result from the orthognathic movement. On occasion, deeply impacted maxillary third molars may be left in place, and removed during the LeFort I osteotomy.
The case for removal of impacted third molars that are interfering with the proper development or eruption of second molars is also well-documented, and may lead to early removal before root formation begins.6 Much more controversial is the role of removing second molars and allowing third molars to erupt in place as a means of facilitating early crowding issues. The inability to accurately predict the eruption of the wisdom teeth means there is a degree of risk that the patient may still require eventual removal of the third molars, and be left without the posterior molar teeth at an early age.
Prophylactic removal of asymptomatic wisdom teeth under fixed or removable prostheses has been a common recommendation. The difficulty is that there is limited randomized data to support or refute this position.6 Many case studies demonstrate the possibility of pathology associated with “teeth under the denture,” but what is the true incidence?
What is known is that wisdom teeth can continue to move and change position after the third decade of life,10 and that deferral of surgery to later in life leads to an increased risk for complications associated with the removal of the teeth.41,52 The potential for pathology associated with wisdom teeth is well-documented, but not all impacted teeth will develop pathology,53 and it is difficult to predict which ones will. 54 A percentage of impacted wisdom teeth will undergo cystic transformation over time (Figs. 6 & 7), and in fact has been demonstrated to occur in the absence of radiographic evidence of pathology (i. e. widened radiographic space around the impacted molar).55-57 However, in light of the demonstrated potential for increased morbidity associated with removal at an advanced age, it does bear prudence to consider watching and periodic reevaluation of teeth when not clinically symptomatic in most cases of deeply impacted third molars that are free of periodontal disease, caries and which do not adversely affect adjacent teeth in older individuals.
Additional developments in radiographic imaging modalities such as the availability of cone-beam CT (CBCT) has not demonstrated a significant impact on morbidity associated with removal of third molars, especially with respect to inferior alveolar nerve (IAN) damage. On one hand, it has been suggested that for asymptomatic wisdom teeth in older individuals, risk of IAN trauma is zero if surgery is not attempted.5 On the other hand, clear demonstration of nerve entrapment and/or significant proximity might encourage the use of alternative surgical techniques such as partial removal of the wisdom tooth (coronectomy). In addition, knowledge of the relationship of the IAN canal relative to the position of the tooth may help to plan the surgical approach to minimize the risk of damage to adjacent structures.58 More studies are needed to demonstrate the efficacy of CBCT as an effective modality for management of impacted wisdom teeth (Fig. 8).
Systemic health risks associated with management of impacted teeth also bear close evaluation. It has long been accepted that interceptive management of third molars and additional teeth are indicated when certain medical cases are present. Pre-operative cardiac and organ transplant patients are often referred for removal of questionable teeth. In light of reemerging evidence around the “focal infection” theories, and the impact of teeth on systemic health, the impact of dentoalveolar inflammatory disease on remote organs and systems might prove to be a clear-cut indication for early or intercepting management of third molars. Certainly the findings of progressive disease around subjectively asymptomatic teeth may give pause for thought. The overall impact of teeth on systemic health is one of the emerging lines of inquiry, and further evidence is forthcoming into the role of prophylactic removal of third molars in this regard.5,6
Risks associated with removal of Third Molars
Pain and swelling, dry socket, paresthesia, post-operative infection remain the most common post-surgical sequelae from wisdom tooth surgery. Absence of pre-existing inflammation and symptoms has been correlated with a lower incidence of post-operative complications. In that setting, early removal of the impacted third molars seems to make sense. Certainly an economic argument has been made that removal of wisdom teeth at an early age results in faster recovery, less pain and morbidity, as well as long-term periodontal risk. In addition, the economic impact of a school-aged child missing one or two days of school is less than that of an adult who may miss a prolonged period of work while recovering from surgery. In addition, if impacted third molars are remov
ed before pathologic changes have taken place, there is less of an impact in terms of need for adjunctive procedures to manage the pathologic conditions.59
Fractures have been associated with the removal of wisdom teeth. One study suggests that median age of iatrogenic fracture during wisdom tooth removal is about 45 years of age,44 suggesting a potential decrease in morbidity with early removal. It should be noted that the incidence of fracture during removal of third molars is low, and can be avoided by judicious use of force during luxation of the teeth, especially in older individuals (Fig. 9).
The referral of patients for third molar surgery remains a common practice. The current state of knowledge attempts to correlate the historical cultural acceptance of prophylactic removal with hard scientific evidence demonstrating a justified need for removal. There is emerging evidence that the state of health of the oral cavity generally influences systemic health, to a greater or lesser degree, and these influences may change as we age.
No one doubts the need for removal when clear-cut pathology exists around impacted wisdom teeth. What is beginning to emerge is new evidence justifying the historical practice of prophylactically removing wisdom teeth at an early age to minimize the risk of developing problems associated with the impacted teeth, and the morbidity associated with managing these cases at an advanced age (Box 2).
Although there will still be cases in which removal of wisdom teeth is not undertaken, it is also clear that patients need to be counselled on an ongoing basis about the potential for pathologic changes associated with the teeth, and periodic examination and re-evaluation is warranted. oh
Dr. Eng is in private practice in Toronto, ON. He is a part-time clinical instructor at the University of Toronto and visiting clinical instructor at Tufts University in Boston, MA, and the current president of the Ontario Society of Oral and Maxillofacial Surgeons.
Oral Health welcomes this original article. References available upon request.
It is prudent to re-evaluate the current state of knowledge regarding third molars
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