Introduction

Removal of third molars is a common surgical procedure carried out by a dental surgeon and can result in a variety complications, which include dry socket, bleeding, infection, trismus and nerve damage.1,2,3 Mandibular fracture is rare, but a very serious complication following third molar removal with a reported incidence of 0.0033% to 0.0049%.4,5,6 These fractures could occur in the intra-operative or postoperative period and can cause significant distress to the patient and the practitioner (Figs 1,2). Most publications in the literature are in the form of isolated case reports and small case series,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22 which makes the evaluation of potential risk factors difficult. In this study, we analysed 130 cases of mandibular fractures following third molar removal reported in the literature, including 4 cases managed in the local maxillofacial unit, and seek to identify potential risk factors and preventive measures.

Figure 1
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Pre-extraction bilateral impacted third molars

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Figure 2
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Post-extraction bilateral mandibular fractures

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Materials and methods

We undertook a Medline search covering the period 1970–2011 and identified English articles in the literature, which reported the occurrence of mandibular fractures following removal of third molars. The search terms and strategy is documented in Table 1. We selected articles which documented original patient data and included four patients treated in the maxillofacial unit, which together form the basis of this analysis.

Table 1 Search terms and strategy. Bracketed figures indicate number of publications
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Titles and abstracts of all relevant articles published in the literature were screened. Full text analysis of potentially relevant publications was performed and included a hand search of their bibliography. Articles providing original patient information were selected for analysis.

The factors analysed were the demographic details of the patients, side of fracture, extent of impaction (Pell and Gregory),23 angulation (vertical, horizontal, mesioangular, distoangular), degree of impaction (partial/full),23 associated pathologies, type of anaesthesia employed for tooth removal, presentation of fracture, time to fracture and management of fracture.

Results

The search strategy identified 113 potential articles, which were analysed further to see if they conformed to the inclusion criteria (Table 1). A total of 18 articles, which reported original patient data on 126 cases were identified and listed in Table 2.5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22 The details of the four patients treated in our unit are presented in Table 3. A summary of all post- and intra-operative mandibular fractures following wisdom tooth removal is presented in Table 4.

Table 2 Articles documenting mandibular fractures associated with impacted third molar removal
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Table 3 Details of patients managed in the local maxillofacial unit
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Table 4 Summary of mandibular fractures following third molar removal
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Demographic details

The age and sex of the patient were documented in 123 and 129 cases respectively.

There was an overall male predominance, with a male:female ratio of 2.4:1. Intra-operative fractures were more common among females (M:F – 1:1.3) and postoperative fractures were more common among males (M:F – 3.9:1). The age range of subjects was from 19 to 79 years of age, with a peak incidence in the 36 to 60-year age group. Intra-operative fractures occurred over the age range of 26 to 79 years, with a peak incidence in the 36 to 45-year age group. Postoperative fractures occurred between 20 and 78 years of age, with a peak incidence in the 36 to 60-year age group.

Side of fracture

Details of the side of fracture were documented in 53 cases. Postoperative fractures occurred more frequently on the right side (right:left – 1.9:1) and intra-operative fractures were more common on the left side (right:left – 1:1.6). Three fractures were bilateral.

Angulation (vertical, horizontal, mesioangular and distoangular)

The angulation of the tooth was documented in 101 cases. Fractures occurred most frequently in the mesioangular (32.6%) and least frequently in the distoangular (12.8%) group.

Degree of impaction (partial/full)

The degree of impaction was noted in 92 cases. Mandibular fractures occurred most frequently following removal of fully impacted teeth (72%).

Extent of impaction (Pell and Gregory classification)23

The extent of impaction was documented in 41 cases. Mandibular fractures were more common in the Class II/III and Type B/C compared to Class I and Type A impactions. Intra-operative and postoperative fractures were more common following the removal of Class II and Type C impactions.

Associated pathologies

Pre-operation infective episodes associated with the wisdom tooth were documented in 63 cases. The others pathologies included cysts (10 cases), enlarged follicle (14 cases) and postoperative infection (4 cases).

Type of anaesthesia employed for tooth removal

The type of anaesthesia employed to remove the wisdom teeth was documented in 37 cases and was distributed between general (17) and local (20) anaesthesia.

Presentation of fracture

The mode of presentation of the fracture was documented in 88 cases. Sixty-eight patients (77%) noted a 'cracking' noise at the time of fracture. Ten patients presented with a history of pain/swelling (11%), five patients with a history of trauma (5%), four with malocclusion (4.5%) and two with numbness (2%).

Time of fracture

The time of fracture was documented in 118 cases and occurred postoperatively in 86 cases and intra-operatively in 32 cases (postoperative:intra-operative – 2.7:1). Postoperative fractures occurred between the following 1 and 70 days and were most frequent in the second and third weeks (57%).

Treatment of fracture

The management of the fractured mandible was noted in 92 cases and included a range of modalities. Thirty-nine cases (42%) were treated by closed reduction/intermaxillary fixation (IMF), 28 (30%) by open reduction and internal fixation (ORIF), 9 (10%) by ORIF + IMF and 16 (17%) by soft diet.

Discussion

Fracture of the mandible is a rare but recognised complication following lower third molar removal. Accurate estimates are difficult to ascertain, though questionnaire reports suggest an incidence of between 0.0033% and 0.0049%.4,5,6 Various factors have been implicated in the increased frequency of mandibular fractures.5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,24

Our case series and those reported in the literature confirm increasing age as a predictor of mandibular fractures, with a peak incidence in the 36–60 year age group.5,6,9,10,21 Wisdom teeth were most frequently removed in patients below 25 years of age,1,2,25 whereas mandibular fractures in this age group were not the most common. The decreased elasticity, risk of osteoporosis, bone atrophy, greater potential of tooth ankylosis, higher incidence of pathologies, postoperative complications and the prolonged healing phase, have all been considered to contribute to the increased risk of mandibular fractures in the older age group.9,10,11,19,26,27 Though the total number of fractures in the above 60 year age group was small (15 patients, 12%), the relative frequency of fracture is likely to be much higher, as only a small proportion of patients have their wisdom teeth removed in this age group (5–10%).28,29 There was a higher frequency of fractures among males which is thought to be secondary to the increased masticatory forces generated5,6,30 and the increased risk of trauma.

Mandibular fractures were more common following removal of mesioangular, vertical, horizontal and distoangular teeth respectively and were similar to the relative frequency of these impactions in the general population (mesioangular (45%), vertical (40%), horizontal (10%) and distoangular (5%)).31 The angulation of the wisdom tooth has been reported as a factor determining the difficulty of removal, with mesioangular, horizontal/vertical and distoangular impactions considered to be progressively more difficult.31 This review does not support a direct relationship between the presumed difficulty of removal based on angulation and the risk of mandibular fracture. The relatively increased risk of fractures associated with horizontal impactions could be related to the need for additional bone removal and deeper point of application often required.32

Mandibular fractures were in general, more common following removal of right sided wisdom teeth (right:left – 1.8:1), though interestingly intra-operative fractures were more common following removal of left sided teeth (right:left – 1:1.6). It is difficult to explain the association between laterality and the risk of mandibular fractures.

The degree (partial/complete) and the extent (Pell and Gregory)23 of impaction were found to be predictors of mandibular fractures.5,6,9,10,13,21 Fully impacted and Class B/C and Type II/III impactions were more frequently associated with mandibular fractures. These teeth proportionally occupy a greater volume of the mandibular bone and their extraction is likely to necessitate more bone removal, resulting in a reduction in the remaining bone stock and weakening of the mandible, predisposing it to fractures.5,6,9,10,13 Buccal bone, especially along the external oblique ridge, provides significant strength to the mandibular angle and its removal to facilitate extraction further weakens the mandible. Awareness of these factors and attempts to minimise the amount and location of bone removed by judicious tooth/root division can potentially reduce the risk of fractures. Garcia et al.33 did not find Pell and Gregory classification to be useful in predicting the difficulty of wisdom teeth removal and Renton et al.32 found patient factors also played an important role in determining the difficulty of removal.

Pre-operative infections associated with the impacted tooth have been suggested to predispose to postoperative fractures.5,9,12,21 All patients in our series had episodes of infection before tooth removal. In the United Kingdom, where only symptomatic wisdom teeth are currently considered for removal in line with the NICE guidelines,34 it is interesting that only two previous reports of fractures have been recorded in the last 29 years.7,8 Large cysts can cause 'significant' reduction in the bone volume and predispose to fractures, though this should be obvious pre-operatively. Severe postoperative infections and osteomyelitis can similarly cause bone resorption and result in a pathological fracture.5,15 The use of pre- or postoperative antibiotics and their relationship to mandibular fractures was not always available in the reported articles.

Postoperative fractures were much more frequent than intra-operative fractures (postoperative:intra-operative – 2.7:1) and the magnitude of this discrepancy has not always been highlighted in the previous reports. Postoperative fractures occurred most frequently (57%) in the second and third week following tooth removal.5,6,20 Most patients reported a crack (77%), history of trauma or pain/swelling before the fracture. This period would be consistent with the predominantly osteoclastic phase of bone healing.26 In these circumstances, excessive masticatory forces and relatively minor trauma could precipitate a fracture and account for the increased frequency in this postoperative period.5,6,20 Al-Belasy et al., however, did not find any relationship between masticatory forces and mandibular fractures following removal of wisdom teeth.35

Intra-operative fractures were more common in the 26-45 year age group and differed from postoperative fractures, which were more common in the 36–60 year age group. Intra-operative fractures were more common in females (M:F – 1:1.3), and markedly differed to the male predominance of postoperative fractures (M:F – 3.9:1). This has not been reported in the previous studies and highlights the merit of analysing a large group of patients. Some authors have suggested that intra-operative fractures are subsequent to improper instrumentation, excessive use of force and poor technique.9,20 Though it has been suggested that poor technique is a potential cause of iatrogenic mandibular fracture, there is little information about the specific techniques used in these reports. In current practice, the bone removal and tooth division is performed by high speed surgical handpieces and the tooth/root fragments extirpated with fine elevators. Grau–Monclas et al. reported that the use of the Winter's elevator was associated with intra-operative fractures.21 These large, thick elevators allow the application of significant force and their use should be avoided whenever possible and if necessary, should be restricted to experienced clinicians. Intra-operative fractures were more frequent following removal of complete, Class II/III and Type C impactions, which often require more bone removal and do not afford the margin for poor technique before a fracture. Poor technique along with the thinner mandible in females might contribute to the increased frequency of fractures in this group. Minimal bone removal with greater reliance on appropriate tooth division and gentle elevation, using 'finger' pressure, should be the norm for the removal of all wisdom teeth and 'difficult' wisdom teeth in particular.

Diagnosis of postoperative fractures can be difficult, with only a small minority presenting with obvious malocclusion. Initial radiographs can fail to reveal a fracture and a high index of suspicion and repeat imaging a few days later may be necessary to visualise the fracture line.13,20 This could account for some of the delayed 'presentation' in the postoperative group.

Mandibular fractures following wisdom teeth removal were treated by differing modalities. Interestingly, the majority of fractures (58%) were managed 'conservatively' with soft diet, IMF/closed reduction. Open reduction internal fixation (30%) and additional intermaxillary fixation (10%) were utilised in the remaining cases. The reasons for this discrepancy is not obvious in the reported cases, but could include the obvious diagnosis and configuration of the fracture, easier access to instrumentation, personnel and theatre time in the case of intra-operative fractures and the relative lack of symptoms, malocclusion and delayed presentation in the case of postoperative fractures.

The risk of fractures can be minimised by accurate diagnosis, thorough assessment of the difficulty of extraction, identifying high risk patients and formulating a comprehensive treatment plan, which includes the most appropriate surgical approach, extent and location of bone removal, sectioning of the tooth and the necessity for prophylactic plating. A sensitive surgical technique is mandatory and in the case of deeply impacted/displaced teeth, consideration should be given to prophylactic plating or an extra-oral approach.36,37 Coronectomy, which has principally been evaluated in relation to minimising the risk of damage to the inferior dental nerve,38 might have a role in decreasing the risk of mandibular fracture associated with deeply impacted teeth. Postoperative care should include a soft diet and avoidance of trauma/contact sports for at least four weeks.

Mandibular fractures following third molar removal should be in large part predictable, even if not preventable. Informed consent for patients with a risk of fracture is mandatory. Patient education as regards to its likely timing (2–3 weeks), presenting characteristics ('cracking noise', pain/swelling, altered bite) and the necessity to seek immediate help is essential and in keeping with good clinical practice.

Finally, the maintenance of accurate and contemporaneous notes cannot be overstressed. The patient should be fully informed of the events and arrangements made for immediate transfer to the maxillofacial unit, in case of the fracture occurring/presenting to a dental practitioner. In the case of the event occurring/presenting in the hospital, arrangements must be made for the patient to be evaluated by a senior practitioner and decisions made of the most appropriate management. In both circumstances, it is also prudent to inform and seek advice from the dental/medical insurance provider (Table 5).

Table 5 Roll of the clinician
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