Third molar extraction is one of the most frequent procedures undertaken in the National Health Service in the UK¹. In the US, it has been reported that 10 million impacted third molars were extracted from approximately 5 million people each year at an annual cost of over US$ 3 billion². Prophylactic extraction of asymptomatic impacted teeth is one of the most common reasons for the extraction^3-5. It has been reported that prophylactic extraction can prevent possible pathologies such as caries and root resorption of adjacent teeth, pericoronitis, gingivitis, periodontal disease, and the development of cysts or tumors⁶, and can also remove a cause of crowding of the dentition⁷. In some Western countries, the prophylactic extraction of asymptomatic third molars has long been considered “appropriate care”^4,8. It has been shown that about 85% of third molar extractions in Australia⁵ and 44% in the UK⁸ are likely to be prophylactic. However, a Dutch clinical guideline for third molars recommends more conservative strategies than preventive surgeries for asymptomatic molars that are fully bone impacted, fully erupted, and functional with good cleaning, or that have a close anatomical relationship with the mandibular nerve canal⁹. Another reason for the extraction of third molars is when they are symptomatic or have already caused diseases, such as pain associated with infection, dental caries, or altered periodontal health of the adjacent teeth^3,10. The extraction of third molars is also considered to be indicated when the molars may interfere with planned prosthodontic, orthodontic, or surgical treatments¹⁰.

Several previous studies have reported common complications associated with third molar extractions^11-15. The prevalence of the complications ranged from 4.6% to 30.9% in one previous study¹¹. Approximately 10% of patients of third molar extractions, have sought post-surgical emergency appointments^12,13. The complications may occur intraoperatively or postoperatively. The most common intraoperative complications included bleeding, damage to adjacent teeth, injury to surrounding tissues, displacement of teeth into adjacent spaces, and fracture of the root¹⁴, while the most common postoperative complications included dry socket, pain, swelling, trismus, infection, and hemorrhage¹⁵. These complications have been well-known and well-documented in both research and clinical practice.

In clinical practice, weighing the risks and benefits associated with the extraction of third molars is an important task for both patients and clinicians when they make decisions. Before any surgical procedures, the patient should be provided with full information on the pros and cons of surgery, as well as perioperative risks and postoperative complications, including the potential for any uncommon complications¹¹. Additionally, while most clinicians already have an in-depth understanding of common complications, there is an urgent need to increase the clinicians’ awareness of possible uncommon complications because such knowledge may help clinicians recognize complications early to ensure adequate therapy¹⁶ and to optimize the clinical management of third molar extraction.

To date, multiple case reports or case series reported different uncommon complications. Brauer¹⁶ conducted a systematic review to summarize possible uncommon complications, which included abscess formation, displacement of teeth and instruments, asphyxia death, life-threatening hemorrhage, brain abscess, epidural abscess, benign paroxysmal positional vertigo, subcutaneous and tissue space emphysema, subdural empyema, and herpes zoster syndrome. Even if those complications were very rare, they could be clinically important and could have devastating outcomes. To the best of our knowledge however, the review from Brauer¹⁶ was the only one that focused on uncommon complications of third molar extractions to date. Their review only summarized uncommon complications based on 22 studies through 2008. However, there were more cases with uncommon complications reported since then, and some of the complications were newly identified^17-19. Therefore, an up-to-date summary of uncommon complications is needed.

The aim of the present study is to explore the types and frequencies of uncommon complications associated with third molar extractions based on a scoping review of case reports and case series.

The scoping review was carried out based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) checklist²⁰.

The initial search identified a total of 473 records from PubMed and Embase. During the screening of titles and abstracts, 203 of them met the eligibility criteria and were included for the subsequent full-text review. Another 73 records were identified for full-text review from the hand searching. During the screening of full-texts, 90 studies did not meet the eligibility criteria and were eventually excluded. Therefore, a total of 186 studies were included for the subsequent analysis in the present study.(Fig. 1) The 186 studies were from 30 countries, most of which were from the US (n=28), Turkey (n=23), the UK (n=15), Brazil (n=14), and Japan (n=14). In the 186 studies, five had no available full text option and were included as abstracts only.

A total of 248 patients were included in the study. Of the patients, 124 patients (50.0%) were female and 121 patients (48.8%) were male. The sex of the other three patients was not reported. The mean age±standard deviation (SD) of the patients was 34±14 years. The history of disease was reported in 31 patients, such as diabetes, hypertension, ischemic stroke, depression, B-type hepatitis, polycystic ovarian syndrome, grand-mal epilepsy, rheumatoid arthritis, leflunomide-induced pancytopenia, lung transplant, and extensive arteriovenous malformation. Two patients were pregnant when their third molars were extracted. Postoperative complications were identified in most of the included patients (55.6%), while intraoperative and preoperative complications were identified in 37.9% and 6.5% of the patients, respectively. The postoperative complications were identified from 0 to 3 years after the third molar extractions. Most of the identified complications were not life-threatening and only had a transient impact on patients. The characteristics of the included patients, their extracted third molars, and associated complications are presented in Table 1.

In the present study, we identified a total of 51 types of uncommon complications associated with third molar extractions in 248 patients. Most uncommon complications were identified in the craniofacial and cervical regions after the extraction procedures. Iatrogenic displacement of the molars or root fragments into the craniofacial area, late mandibular fracture, and subcutaneous emphysema in the orofacial and cervical regions were the most frequently identified uncommon complications. Among all the identified complications, most of them were transient and non-life-threatening, which indicated that most of the complications only had a short-term and mild impact on the patients. However, a small number of patients suffered persistent and life-threatening complications, including death. In total, 37 patients were identified to have life-threatening complications and 20 patients had long-term or irreversible complications associated with third molar extraction.

The present study summarizes uncommon complications, and their primary symptoms, associated with third molar extractions. For clinicians, the findings of the present study help increase the awareness of possible uncommon complications that they may encounter when they perform a third molar extraction. This awareness can also help clinicians balance the benefits and harm of a third molar extraction more comprehensively and make optimal decisions on treatment strategies for their patients. Furthermore, considering that many uncommon complications seem to be iatrogenic, including displacement of the tooth or root fragments into the craniofacial area, subcutaneous emphysema, mandibular nerve injury, breakage and/or migration of a dental tool in the craniofacial area, and mandibular fracture, the results indicate that clinicians should take more efforts to avoid such complications. For example, clinicians should improve their surgical expertise and take adequate preoperative clinical and radiographic examination of the patients. Regarding the patients, the findings of the study can help them understand the potential risks of third molar extractions and help them make decisions more cautiously together with their clinicians so that legal disputes caused by potential complications can be avoided. The findings of the present study also provide useful information to policymakers when they make clinical policies on management strategies for third molars and indications of third molar extractions. Eventually, the findings of the present study can improve patient health outcomes.

However, it should be noted that the mechanisms that link some identified uncommon complications with third molar extractions are still unknown. Whether some uncommon complications, such as Guillain-Barré syndrome²⁴ and sensorineural hearing loss²⁵, are caused directly by the extraction procedures or the uncommon complications occur due to some other reason is not clear. Additionally, the risk of uncommon complications may not be the same for all patients. A patient’s health may be an important factor of serious uncommon complications. Among the patients included in the study, patients with a history of disease or who were pregnant were 8.7 and 4.2 times more likely to have life-threatening complications and long-term/irreversible complications, respectively, than patients with no history of disease or who were not pregnant. Patients with mandibular third molar extractions had 2.5 times higher odds to have a life-threatening complication than those with maxillary third molar extractions. Therefore, in terms of complications that are serious but extremely rare, it may not be necessary to impact the regular treatment plans, clinical guidelines, and policies for normal patients. However, the clinicians need to be more cautious about the treatment of high-risk patients.

In interpreting the findings of the present study, some limitations should be taken into consideration. First, we could not use uniform criteria for the judgment of uncommon complications in the present review, because a standardized classification of uncommon complications does not exist, and various definitions may have been used in the included reports. Furthermore, to the best of our knowledge, no previous report provided the exact prevalence of the reported complications in third molar extractions. Hence, all the complications that were reported in the form of case reports or case series were assumed to be uncommon²⁶ and were included in the present review. Also, no authors in the included case reports reported any standardized definitions they used to judge if the reported complications were uncommon. Whether a complication was worth reporting in a case report due to its rarity was completely determined by the authors based on their own subjective judgment. Additionally, whether the uncommon complications were life-threatening or long-term/irreversible was determined based on our own subjective judgment, rather than standardized criteria because no commonly used standardized classification systems are currently available for the fatality and permanence of the complications. This, however, could bias the results of the review.

Second, only case reports and case series were included in the study. There were several methodological limitations in these types of studies. One of the important limitations was the publication bias²⁷. For example, the identified uncommon complications in the present study may be only the tip of the iceberg, and there could be more uncommon complications that were not reported in publications because the public reporting of such negative events may not be encouraged in some national cultures²⁸ and some researchers or clinicians may not be enthusiastic to publish the case reports or case series²⁷. Therefore, the included case reports and case series may not be representative of the entire spectrum of uncommon complications associated with third molar extractions. Another methodological limitation is that the case reports or case series were always retrospective. Therefore, the medical records may not contain all relevant important data and documentation of the clinical data was not performed according to a standardized protocol in many of the included case reports and case series²⁷. Thus, many included patients had missing values in some important variables, such as the impaction status and symptoms of the molars in the study. However, case reports and case series are often the major or even the only source for detecting uncommon adverse events²⁶. For uncommon complications associated with third molar extractions, other types of studies designed with a higher ranking on the evidence hierarchy, such as randomized controlled trials or cohort studies, are impossible to run due to a lack of patients to be enrolled.

Many uncommon complications associated with third molar extractions were identified in the present scoping review. Most complications associated with the extraction of mandibular third molars were postoperative in the craniofacial and cervical regions. Most complications were mild and transient, while a small number of complications were potentially life-threatening and long-term or irreversible.

Supplementary data is available at https://www.jkaoms.org/