By Yasmin Aziz
An impacted tooth can be defined as a tooth that is prevented from erupting into its normal functional position due to malposition, lack of space, or obstruction (1). Mandibular third molars (3Ms) are the most commonly impacted teeth, with 152,000 patients in England having their 3Ms removed annually (2). Due to the prevalence of impacted 3Ms, the decision-making process of whether to remove or retain them is frequently undertaken. There is a general agreement that pathological, symptomatic 3Ms should be removed to alleviate the patient’s symptoms. The main indications for 3M removal include pericoronitis, dental caries, periodontal disease, and cyst formation (3). However, when it comes to the preventative removal of asymptomatic or disease free 3Ms, this decision is more complex.
Current Guidance
In 1997, the Faculty of Dental Surgery (FDS) published their recommendations for the management of 3Ms (4). These were adopted, with amendments, by NICE in 2000 and have formed the foundation of guidance for 3M management in the UK for the past two decades. NICE guidance on the extraction of 3Ms, also known as TA1, outlines that the surgical removal of impacted 3Ms should be limited to patients with evidence of 3M pathology (5).
Age
A recent systematic review found that asymptomatic 3Ms frequently become pathological with increasing age. Dental caries and periodontal disease were the most common pathologies associated with impacted 3Ms (Fig 1) (6). A significant correlation was found between the presence of disto- cervical caries in mandibular second molars (2Ms) and patients with mesio- angular and horizontally impacted 3Ms (7). External root resorption of the mandibular 2Ms can also result in the presence of mesioangular or horizontally impacted 3Ms (Fig 2). The prevalence of external root resorption was found to be 5.31% when diagnosed using panoramic radiographs, and 22.88% when using cone beam computed tomography (CBCT). CBCT is associated with high radiation doses, therefore, is not routinely indicated unless localisation of the 3M roots in relation to the inferior alveolar nerve (IAN) is required (8). This suggests that conditions such as external root resorption may be underdiagnosed, leading to delayed presentation and additional complications in older age. As the UK has an ageing population, it is vital to ensure adequate oral function is maintained by preserving the adjacent posterior molars, which may also be essential for denture retention in elderly patients (9). This is important to prevent potential co-morbidities such as malnutrition and immunodeficiency in an elderly population, which would significantly affect people’s quality of life (QOL) and place additional strain on the NHS (10).
Since the implementation of TA1, the mean age for 3M removal has increased from 25 years in 2000 to 32 years in 2010 (11). There is growing concern that extractions in older age may cause delayed recovery. Older patients were found to experience significantly more intraoperative and postoperative complications when undergoing 3M removal. However, these findings were from retrospective studies where selection bias was evident (12). Higher quality experimental evidence is required to accurately assess the relationship between surgical extraction of mandibular 3Ms and age.
Cost
Treatment of pathologies relating to the 2M due to an impacted 3M, may involve extraction of the 3M to prevent the reoccurrence of disease, as well as, extraction or restoration of the 2M with a direct/ indirect restoration. Endodontic treatment of the 2M may also be required due to the proximity of distal cervical caries and external root resorption to the pulp. One study estimated that the cost to NHS England for treating disto-cervical caries in mandibular 2Ms could amount to £55 million per annum (2). This is substantially more than the estimated £12 million per annum that theTA1 guidance predicted to save by discouraging prophylactic extraction of 3Ms (5). In 2009-2010, 77,000 patients per annum underwent 3M removal, the highest level for 20 years (11). This suggests that TA1 guidance has not been as cost-effective as predicted, with rates of prophylactic extractions increasing year on year (Fig 3). Therefore, the financial savings from retaining 3Ms have been short lived. This may reflect the delayed additional cost of treating complications associated with retained 3Ms. Calculated costs should be interpreted with caution as they are formulated using estimated averages, ranging incidence values, and NHS treatment costs which are based on courses of treatment rather than fee per item of treatment provided (13). Indirect costs such as loss of patient earnings and loss of access for other patients can also vary extensively (2). Ultimately, the decision to retain or remove disease- free 3Ms should be based on the risks and benefits to each individual patient. Information regarding further expenses should be relayed to the patient to help them make informed decisions regarding their treatment.
Complications of 3M Surgery
Common complications following M3 surgery include postoperative pain, infection, dry socket, delayed healing, swelling, trismus and haematoma. Iatrogenic injury such as bone fracture and nerve damage can also result from M3 extraction. Whilst the prevalence of these injuries is low, their effect on QOL and healing time is substantial (14). A prospective clinical study found the incidence of permanent IAN and lingual nerve (LN) deficit was 0.35% and 0.69%, respectively (15). Dentists and oral surgeons can take precautions to reduce the complications associated with 3M removal. A coronectomy can reduce the incidence of IAN and LN injury, however, is associated with its own risks such as possible mobilization of the retained roots and the need for further surgery (16).
Multifactorial Decision Making
The decision to undertake prophylactic removal of partially erupted, impacted 3Ms is multifactorial, and is influenced by the patient’s medical, social, and dental history. For instance, lifestyle choices such as smoking is associated with post-operative alveolitis following dental extraction (17). For deployed military personal who have limited access to dental care, 3M related pathology was found to be a significant cause of non-battle injury, where travelling for dental treatment can be life- threatening (18). 3M’s can also be retained and utilised in orthodontics where there has been loss of first molars or 2Ms (19). Therefore, prophylactic removal of 3Ms is extremely complex and may involve multidisciplinary communication to ensure a holistic patient centred approach is taken (Fig 4). Furthermore, the resources available need to be considered, with the COVID-19 pandemic, most oral surgery departments face a back log of extractions that need to be performed for patients in pain due to a shortage of resources and increased pressure on secondary dental services(20).
Figure 4: Multifactorial decision- making pathway for 3M management.
Conclusion
Currently, the evidence base for retention of asymptomatic third molars is stronger than the evidence in support of prophylactic removal due to the well-reported complications associated with 3M surgery. However, the TA1 guidance discouraging prophylactic removal has failed to reduce rates of 3M extraction. Therefore, until stronger evidence supporting prophylactic removal of 3Ms becomes available and the waiting times for oral surgery referral have reduced, a preventative approach for all 3M should not be employed. Nevertheless, dentists should be able to identify significant risk factors associated with pathology such as mesioangular and horizontal impaction of 3Ms and explain to patients the implications of retention and removal. Clinicians should employ a multifactorial decision-making process whilst considering the patient’s lifestyle and the associated costs and benefits of different management strategies.
References
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This is an academic review, I hope it is an interesting topic for dental students and dentists. This is not intended as clinical recommendations, if you are having wisdom tooth problems, please see a dentist.
Dissecting Dentistry 