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Does the Presence or Position of Lower Third Molars Alter the Risk of Mandibular Angle or Condylar Fractures?
Accepted Manuscript Does the Presence and/or Position of Lower Third Molars Alter the Risk of Mandibular Angle or Condylar Fractures? Saba Naghipur, BSc Adnan Shah, BDS, MDS Reda Fouad Elgazzar, BDS, MSc, PhD PII:
S0278-2391(14)00376-0
DOI:
10.1016/j.joms.2014.04.004
Reference:
YJOMS 56286
To appear in:
Journal of Oral and Maxillofacial Surgery
Received Date: 26 December 2013 Revised Date:
2 April 2014
Accepted Date: 6 April 2014
Please cite this article as: Naghipur S, Shah A, Elgazzar RF, Does the Presence and/or Position of Lower Third Molars Alter the Risk of Mandibular Angle or Condylar Fractures?, Journal of Oral and Maxillofacial Surgery (2014), doi: 10.1016/j.joms.2014.04.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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TITLE: Does the Presence and/or Position of Lower Third Molars Alter the Risk of Mandibular
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Angle or Condylar Fractures?
AUTHORS: Saba Naghipur, BSc1
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Adnan Shah, BDS, MDS1
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Reda Fouad Elgazzar, BDS, MSc, PhD1
Department of Dental Diagnostics and Surgical Sciences, Faculty of Dentistry,
University of Manitoba, Winnipeg, MB, Canada.
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CORRESPONDING AUTHOR: Saba Naghipur
University of Manitoba, Faculty of Dentistry
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780 Bannatyne Ave, Winnipeg, MB, Canada R3T 0W2 Phone: 204-789-3631
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Fax: 204-789-3912
Email: [email protected]
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ABSTRACT Purpose: The purpose of this study was to determine whether a relationship exists between the presence of mandibular third molars (M3s) and mandibular angle and
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condylar fractures, and whether the risk of these fractures varies with M3 position.
Methods: A retrospective cohort study was conducted in patients presenting to the Oral
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and Maxillofacial Surgery service from April 2007 to March 2012 with mandibular
fractures. Data sources were the patients’ hospital charts and panoramic radiographs. The
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predictor variables were the presence and position of M3s. M3 position was based on the Pell and Gregory classification and angulation was determined by measuring the angle between the long axis of M3s and the mandibular occlusal plane. The outcome variables were the presence of angle and condylar fracture. Other study variables included age, sex
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and fracture etiology. Data was analyzed using chi square and Student’s t-test.
Results: The study sample consisted of 446 patients with 731 mandibular fractures. Our
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results showed that the risk of mandibular angle fracture was significantly higher in both patients and mandible sides with impacted M3s (P<0.001), whereas the risk of condylar
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fracture was significantly higher in both patients and mandible sides lacking impacted M3s (P<0.001). A relationship between the position of M3s to either angle or condylar fractures could not be demonstrated (P>0.05).
Conclusion: The presence of impacted M3s increased the risk of angle fracture while simultaneously decreasing the risk of condylar fracture. However, no relationship appeared to exist between M3 position and fracture pattern.
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INTRODUCTION Many clinical factors influence the pattern of mandibular fractures, including the severity and nature of the impacting force, as well as biomechanical properties of the
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mandible, including bone density, mass and normal or pathologic anatomic structures that create weak areas within the bone.1=3 The influence of mandibular third molars (M3s) on mandibular fractures has received much attention in the literature and is one of the only
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factors clinicians can potentially influence when determining whether extraction is advisable. However, whether impacted M3s without clinical symptoms should be
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surgically removed remains controversial.
Previous retrospective studies have consistently reported that patients with impacted M3s are at a higher risk of suffering mandibular angle fractures than those without impacted M3s.4-6 This has been attributed to decreased bony volume at the
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mandibular angle region caused by the presence of an impacted M3. Based on these findings, some investigators have advocated for the removal of impacted M3s, particularly in young athletes involved in contact sports, as a prophylactic measure to
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prevent future mandibular angle fractures.4,7 However, more recent studies have found that patients without M3s are more likely to develop another type of mandibular fracture,
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mandibular condylar fracture, compared to those with impacted M3s.8-9 Given the challenges associated with repair of the mandibular condylar and the higher risk of postoperative complications,10 it may not be beneficial to remove impacted M3s as a means of preventing angle fractures. While many studies have examined the effect of M3s on mandibular angle or condylar fractures separately, relatively few have examined its effect on both types of
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fractures in the same population. The purpose of this study was twofold; 1) to determine whether the presence of M3s increases or decreases of risk of mandibular angle and condylar fracture and 2) to determine if this relationship is dependent on the position of
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M3s in the mandible. Given the theory that the M3s decrease the bony volume in the
angle region, we hypothesized that the presence of M3s would increase the risk of angle fracture while simultaneously decreasing the risk of condylar fracture and that the degree
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of tooth impaction would be directly related to the risk of fracture.
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METHODS Study Design and Sample
To address the research goals, a retrospective cohort study design was used. The sample cohort was composed of all individuals aged 15 years and older who presented for
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evaluation and management of mandibular fracture to the Oral and Maxillofacial Surgery service at Health Sciences Center in Winnipeg, Manitoba from April 1st 2007 to March
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31st 2012.
Variables and Data Collection
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The primary study variables were the presence and position of M3s (predictor
variables) and the presence or absence of angle and condylar fracture (outcome variables). Patient hospital charts and panoramic radiographs were reviewed to determine the presence and position of M3s and the presence of angle and condylar fracture. The horizontal and vertical position of M3s was classified according to the Pell and Gregory system.11 The horizontal position of M3s was grouped based on the amount
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of space available between the anterior border of the vertical ramus and the second molar and the vertical position was classified based on the relative position of M3s to the crown of the second molar (Table 1). Using this classification, M3 position could be grouped
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into 1 of 9 categories (IA, IB, IC…IIIC). Group IA was considered a normal pattern of eruption and not impacted; all other groups were considered impacted M3s. Patients designated as Class IA and/or no M3 in both mandibular sides were placed into the
side were placed into the impacted M3 present group.
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impacted M3 absent group. Patients with at least one impacted M3 in either mandibular
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Angulation of M3s was defined by the angle of intersection between the long axis of the M3 and the mandibular occlusal plane. A horizontal impaction parallel to the occlusal plane and having the occlusal portion of the crown adjacent to the root surface of the mandibular second molar was defined as 0o. The angulation increased as the occlusal
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surface of M3 rotated upright and then distally toward the occlusal plane. Horizontal angulation was then defined as 0-10o or 350 to 359o, mesioangular from 11-80o, vertical angulation from 81-110o and distoangular from 111-170o.12
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Mandibular angle fractures were defined according to Kelly and Harrigan13 as fractures located posterior to the second molar tooth, extending from any point on the
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curve formed by the junction of the body and the ramus in the retromolar area to any point on the curve formed by the inferior border of the body and posterior border of the ramus of the mandible. Condylar fracture was defined as a fracture with the fracture line occurring above the sigmoid notch. For the purposes of description and to identify confounding variables, data was also collected for the following variables: age (years), sex (male or female), fracture
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etiology (assault, fall, sport, road traffic accident (RTA), other) and presence of concomitant mandibular fractures (angle, condylar, body, symphysis, ramus and
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coronoid). All data were abstracted from patient records.
Data Analysis
A database was constructed using Excel (Microsoft ®, Redmond, WA, USA) and
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statistical analysis performed using SPSS software version 15.0 (SPSS Inc, Chicago, IL, USA). Data was analyzed by calculating the means and standard deviations and cohort
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comparisons were made using chi square test, Student’s t-test and analysis of variance. Statistical significance was inferred if P<0.05. The study was approved by the Health Research Ethics Board at the University of Manitoba.
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RESULTS
The study cohort consisted of 446 patients with 731 total mandibular fractures. The average age of the cohort was 29.3 + 11.3 years and consisted of 377 (84.5%) males
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and 69 (15.5%) females. The most common etiology of fracture was assault (362; 81.1%), followed by falls (31; 7.0%), sports-related injuries (20; 4.5%), other causes (20;
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4.5%) and RTAs (13; 2.9%). The most common fracture pattern was bi-fracture (243; 54.5%), followed by mono-fracture (182; 40.8%) and multi-fracture (21; 4.7%). Fractures of the mandibular body were observed most frequently (292; 39.9%), followed by angle (251; 34.3%), condylar (148; 20.2%), symphysis (26; 3.6%), ramus (10; 1.4%), and coronoid fracture (4; 0.6%).
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Mandibular angle fracture was observed in 247 patients, with 4 patients having bilateral angle fractures. Mandibular condylar fractures were observed in 130 patients, with 18 patients having bilateral condylar fractures. Ten patients had an angle and
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condylar fracture simultaneously, including four patients with both fractures on the same mandibular side. A detailed analysis of the demographic variables is shown in Table 2. The risk of mandibular angle fracture was statistically higher in younger patients
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(P<0.001), but no statistical difference in age or sex was found among patients with
condylar fracture (P>0.05). The risk of angle fractures was significantly higher in patients
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with impacted M3s (one or both mandibular sides) compared to those without impacted M3s (70.0 vs. 39.4%; P<0.001). Conversely, the risk of condylar fracture was lower in patients with impacted M3s compared to those without impacted M3s (21.9 vs. 37.1%; P<0.001). When assessed for fracture etiology, the most common cause of both angle and
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condylar fractures was assault, with both results reaching statistical significance. However, the highest risk of angle fractures occurred in assaults (58.8%), while the highest risk of condylar fractures occurred in RTAs (61.5%).
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The cohort of 446 patients had 892 mandibular sides, of which 394 sides (44.2%) had an impacted M3. After grouping each M3 into either the impacted M3 present group
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(Groups IB-IIIC) or impacted M3 absent group (Group IA or no M3), an analysis of fracture type revealed that sides with impacted M3s were significantly more likely to experience mandibular angle fracture than sides without impacted M3s (P<0.001; relative risk (RR) = 1.877; 95% CI: 1.514–2.327). We also observed that mandibular sides with impacted M3s were significantly less likely to incur condylar fracture compared to sides with impacted M3s (P<0.001; RR = 0.570; 95% CI: 0.413-0.787) (Table 3).
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A total of 539 M3s from 300 patients were analyzed by panoramic radiographs and classified according to the Pell and Gregory system into horizontal position, vertical position and angulation. The relationship between M3 position and mandibular angle
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fracture on the ipsilateral side of the M3 is shown in Table 4. The most common
horizontal position among mandibular sides with angle fracture was Class II (90), and this also conveyed the greatest relative risk for fracture (RR = 1.133; 95% CI: 0.887-
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1.447). The most common vertical position was Class A teeth (93), whereas the relative risk was highest among Class B (RR = 1.173; 95% CI: 0.922-1.492). When grouped
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according to M3 angulation, mesioangular impactions were the most common in mandibular sides with angle fracture (140) and distoangular impactions presented with the greatest relative risk (RR = 1.453; 95% CI: 0.595-3.549). However, statistical significance was not reached for any of the three positioning groups (horizontal position,
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vertical position and angulation) in relation to angle fracture (P>0.05). Using the same analysis, the relationship between mandibular condylar fracture and M3 position was assessed (Table 5). The most common horizontal position of M3s
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on the same side of condylar fractures was Class I (32) and this also presented the greatest relative risk of fracture (RR = 1). The most common vertical position was Class
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A (38); this also carried the greatest relative risk for fracture (RR = 1). When grouped by M3 angulation, mesioangular impactions were found to be most common (42), but horizontal impactions presented the greatest relative risk (RR = 1.042; 95% CI: 0.4492.419). Again, statistical significance was not attained for any of the three positioning groups in relation to condylar fracture (P>0.05).
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In our final analysis, mandibular sides in the impacted M3 absent group (n = 498) were further subdivided into sides with normally erupted M3s (ie: Class IA) and sides lacking M3s. The rate and relative risk of mandibular angle and condylar fractures was
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then compared between the two groups (Tables 6 and 7). Our results showed that the rate and relative risk of angle fracture were both significantly higher in mandibular sides with normally erupted M3s compared to sides lacking M3s, with these results reaching
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statistical significance (P<0.001). Conversely, the rate and relative risk of condylar
fracture was greater in sides lacking M3s, although these results did not reach statistical
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significance (P = 0.102).
DISCUSSION
The purpose of this study was to determine if the presence and/or position of M3s
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alters the risk of mandibular angle or condylar fracture. We hypothesized that M3s would increase the risk of angle fracture while simultaneously decreasing the risk of condylar fracture, and that this relationship would depend on the position of M3s within the
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mandible. The results of this study confirmed an increased risk of angle fractures in the presence of M3s and a decreased risk of condylar fractures in their absence. However, no
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statistically significant relationship could be found between M3 position and fracture pattern.
Among the many factors that influence the pattern of mandibular fractures, the
effect of M3s has been the best studied. In particular, the relationship between mandibular angle fracture and M3s has been closely examined. The reason for the higher risk of angle fractures in the presence of impacted M3s is thought to be because the
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mandibular angle is weakened as the tooth occupies more osseous space in the jaw, thereby decreasing the quantity of bone in this region. This hypothesis was supported by Reitzik et al.14 who’s work with vervet monkey mandibles showed that mandible sides
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with impacted M3s fractured with 60% of the force required to fracture mandible sides containing normally erupted M3s. In the current study, we found that the risk of angle
fracture increased by 1.8 times in patients with an impacted M3 (one or both mandibular
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sides) and 1.9 times in mandibular sides with an impacted M3. This is in agreement with most studies which have shown a 2-to-4 fold increased risk of angle fracture in the
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presence of M3s.4-6 We also investigated and compared the risk of angle fracture in patients lacking an M3 and in patients with normally erupted M3s. We found that the latter group experienced approximately double the risk, compared patients lacking M3s, with the results reaching statistical significance.
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After measuring the degree of M3 impaction by horizontal and vertical position according to the Pell and Gregory system, we found that the risk of angle fracture was highest among Class II and Class B molars. This finding is consistent with studies from
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Choi et al12 and Duan and Zhang15 who also observed higher risk in these two groups. This finding has been explained by pointing out that mandibular angle fractures have an
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area of tension at the superior border and an area of compression at the inferior border, according to muscle insertion, muscle force and bite force positioned on the proximal and distal segments of the fracture. M3s that disrupt the continuity of the cortical bridge of the superior border may cause an inherent weakness in the angle, thereby requiring less force and muscle tension to cause an angle fracture. This may explain why the highest risk of fracture has been seen in Class II and Class B positions of M3s, in which the
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superior border is interrupted, rather than Class III and Class C, where the superior border is intact.15 However, evidence from other studies including from Ma’aita and Alwrikat16 suggests mandibular angle fracture rates are highest in the presence of M3s with Class III
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and Class C positions. Therefore, the relationship between the position of M3s and angle fractures remains controversial. Furthermore, our study found no statistical significance in the risk of angle fracture based on M3 position. This is in agreement with some studies
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that have found similar findings4,6 but contrary to others that have shown a statistically significant relationship between M3 position and angle fracture.5,15,17
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The condylar process is another common fracture site in the mandible. It is not often exposed to direct external force because of its protection by the temporomandibular joint and associated structures but external force applied to other sites in the mandible can cause indirect trauma and result in condylar fracture. In the current study, we found that
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the risk of condylar fracture increased by 1.7 times in patients lacking an impacted M3 and 1.8 times in mandibular sides lacking an impacted M3, with these findings consistent with most other published studies.8,9,17 We also found that mandibular sides lacking an
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M3 had an increased risk of fracture when compared to sides with normally erupted M3s, although not statistically significant. Similar to the hypothesis regarding decreased bone
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quantity in the angle region, previous studies have contended that the reason for this finding is that mandibles lacking M3s have increased bone quantity in areas where an M3 would typically reside, allowing the mandible to better resist fractures and concentrating any externally applied force to the relatively weaker condylar process. The resultant fracture of the condylar neck is also considered a protective mechanism to prevent traumatic dislocation of the condyle into the middle cranial fossa.
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Less is known about the relationship between M3 position and risk of condylar factures. Our results showed that among mandibular sides with M3s, the highest relative risk of fracture occurred in sides with Class I and Class A molars. This is consistent with
significant relationship, which our study could not substantiate.
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the findings from previous studies,12,15,17although these investigators found a statistically
The interpretation of our findings should be considered in light of several
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limitations. First, many clinical and biomechanical factors influence the risk of angle and condylar fractures. Therefore, we acknowledge it would be incorrect to assume a cause-
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and-effect relationship between the presence or absence of M3s and these fractures. Second, our study utilized the Pell and Gregory classification, which may not be the most accurate method to determine the quantity of bone in the angle region. A study by Iida et al18 proposed an alternate way to radiographically approximate the bony space at the
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angle by defining the angle region using anatomical landmarks and subtracting the bony space occupied by the impacted M3. Using this method, the authors found that the highest rate of angle fractures occurred in angles with the smallest area of remaining bone
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while the lowest rate of fractures occurred in angles with the largest area. Such investigations may provide more consistent results and be more valuable in determining
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the risk of mandible fracture in relation to M3 position. The treatment of mandibular condylar fracture is generally considered to be more
technically difficult than treatment of angle fractures because of difficulties in surgical access and visibility. Reduction and fixation of the condylar process also carries a greater risk of operative complications including facial nerve damage and post-operative complications such as malocclusion.10 Several authors4,7 have recommended prophylactic
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extraction of M3s in young athletes involved in contact sports because it may decrease the risk of mandibular angle fracture due to external force. We agree that earlier extraction of M3s may decrease the risk of angle fractures. However, because mandibles
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lacking M3s may be predisposed to condylar fracture, which potentially carries more
serious complications, the decision to extract M3s to reduce the risk of angle fracture
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requires careful consideration by the clinician.
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REFERENCES 1. Halazonetis JA. The weak regions of the mandible. Br J Oral Surg 6:37, 1968
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2. Weiss L. Static loading of the mandible: Oral Surg Oral Med Oral Pathol 19:253, 1965
3. Amaratunga NA. A comparative study of the clinical aspects of edentulous and
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dentulous mandibular fractures. J Oral Maxillofac Surg 46:3, 1998
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4. Tevepaugh DB, Dodson TB. Are mandibular third molars a risk factor for angle fractures? J Oral Maxillofac Surg 53:646, 1995
5. Lee JT, Dodson TB. The effect of mandibular third molar presence and position on the
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risk of angle fracture. J Oral Maxillofac Surg 58:394, 2000
6. Meisami T, Sojat A, Sandor GK, Lawrence HP, Clokie CM. Impacted third molars and
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risk of angle fracture. Int J Oral Maxillofac Surg 31:140, 2002
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7. Schwimmer A, Stern R, Kritchman D. Impacted third molars: a contributing factor in mandibular fractures in contact sports. Am J Sports Med 11:262, 1983
8. Zhu SJ, Choi BH, Kim HJ, Park WS, Huh JY, Jung JH, Kim BY, Lee SH. Relationship between the presence of unerupted mandibular third molars and fractures of the mandibular condyle. Int J Oral Maxillofac Surg 34:382, 2005
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9. Iida S, Nomura K, Okura M, Kogo M. Influence of the incompletely erupted lower
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third molar on mandibular angle and condylar fractures. J Trauma 57:613, 2004
10. Ellis E. Complications of mandibular condyle fracture. Int J Oral Maxillofac Surg
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27:255, 1998
11. Pell G, Gregory G. Impacted mandibular third molars, classification and modified
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technique for removal. Dental Digest 39:330, 1933
12. Choi BJ, Park S, Lee DW, Ohe JY, Kwon YD. Effect of lower third molars on the
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incidence of mandibular angle and condylar fractures. J Craniofac Surg 22:1521, 2011
13. Kelly D, Harrigan W. A survey of facial fractures related to teeth and edentulous
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regions. J Oral Surg 33:146, 1975
14. Reitzik M, Lownie JF. Cleaton JP, Austin J. Experimental fractures of the monkey
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mandibles. Int J Oral Surg 7:100, 1978
15. Duan DH, Zhang Y. Does the presence of mandibular third molars increase the risk of angle fracture and simultaneously decrease the risk of condylar fracture? Int J Oral Maxillofac Surg 37:25, 2010
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16. Ma’aita J, Alwrikat A. Is the mandibular third molar a risk factor for mandibular angle fracture? Oral Surg Oral Med Oral Pathol Oral Radiol Endod 89:143, 2000
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17. Thangavelu A, Yoganandha R, Vaidhyanathan A. Impact of impacted mandibular third molars in mandibular angle and condylar fractures. Int J Oral Maxillofac Surg
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39:136, 2010
18. Iida S, Hassfeld S, Reuther R, Nomura K, Muhling J. Relationship between the risk
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of mandibular angle fractures and the status of incompletely erupted mandibular third
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molar. J Craniomaxillofac Surg 33:158, 2005
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TABLES Table 1: Pell and Gregory classification.
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Amount of space available between mandibular ramus and second molar Adequate space for eruption Inadequate space for eruption Third molar located all or mostly within ramus Relationship of third molar crown to second molar crown Level at occlusal plane Between cemento-enamel junction of the second molar and occlusal plane Below the cemento-enamel junction of the second molar
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Horizontal Class I Class II Class III Vertical Class A Class B Class C
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Table 2: Demographic variables according to angle and condylar fracture status in 446 patients. Angle Fracture Present (%) Absent (%) 27.2 + 9.7 32.0 + 12.6
P <0.001 0.102
106 (28.1) 24 (34.8)
271 (71.9) 45 (65.2)
0.263
70 (30.0) 129 (60.6)
<0.001
51 (21.9) 79 (37.1)
182 (78.1) 134 (62.9)
<0.001
149 (41.2) 21 (67.7) 10 (50.0) 8 (61.5) 11 (55.0) 199
0.026
99 (27.3) 13 (41.9) 1 (5.0) 8 (61.5) 9 (45.0) 130
263 (72.7) 18 (58.0) 19 (95.0) 5 (38.5) 11 (55.0) 316
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162 (43.0) 37 (53.6)
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Variable Age, mean (years) Sex Male (n = 377) 215 (57.0) Female (n = 69) 32 (46.4) Impacted M3 Present (n = 233) 163 (70.0) Absent (n = 213) 84 (39.4) Fracture Etiology Assault (n = 362) 213 (58.8) Fall (n = 31) 10 (32.3) Sport (n = 20) 10 (50.0) RTA* (n = 13) 5 (38.5) Other (n = 20) 9 (45.0) Total 247 *RTA = Road Traffic Accident
Condylar Fracture Present (%) Absent (%) P 30.1 + 10.6 29.0 + 11.6 0.335
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Table 3: Influence of impacted M3 on mandibular angle and condylar fracture in 892 mandibular sides.
P <0.001
46 (11.7) 102 (20.5)
348 (88.3) 396 (79.5)
P <0.001
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Mandibular sides with impacted M3 Present (n = 394) 150 (38.1) 244 (61.9) Absent (n = 498) 101 (20.3) 397 (79.7) a Relative risk: 1.877; 95% CI: 1.514–2.327 b Relative risk: 0.570; 95% CI: 0.413-0.787
Condylar Fractureb Present (%) Absent (%)
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Angle Fracturea Present (%) Absent (%)
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Table 4: Risk of angle fracture in mandibular sides with relation to M3 position. Angle Fracture Present Absent Total
Risk
Relative Risk
95% CI
145 143 54
220 233 86
0.600
0.341 0.386 0.372
1 1.133 1.091
0.887–1.447 0.784–1.519
93 75 29
179 112 51
272 187 80
0.433
0.342 0.401 0.363
1 1.173 1.060
0.922–1.492 0.759–1.480
41 140 13 3
98 213 27 4
139 353 40 7
0.183
0.295 0.397 0.325 0.429
1 1.345 1.102 1.453
1.009–1.792 0.658–1.845 0.595–3.549
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75 90 32
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Horizontal Position Class I Class II Class III Vertical Position Class A Class B Class C Angulation Vertical Mesioangular Horizontal Distoangular
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Table 5: Risk of condylar fraction in mandibular sides with relation to M3 position. Condylar Fracture Present Absent Total
Risk
Relative Risk
95% CI
188 206 76
220 233 86
0.603
0.145 0.116 0.116
1 0.797 0.799
0.494–1.284 0.411–1.554
38 25 6
234 162 74
272 187 80
0.301
0.140 0.134 0.075
1 0.957 0.537
0.599–1.530 0.235–1.224
20 42 6 1
119 311 34 6
139 353 40 7
0.859
0.144 0.119 0.150 0.143
1 0.827 1.042 0.993
0.504–1.357 0.449–2.419 0.155–6.374
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32 27 10
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Horizontal Position Class I Class II Class III Vertical Position Class A Class B Class C Angulation Vertical Mesioangular Horizontal Distoangular
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Table 6: Risk of angle fracture in relation to mandibular sides with normally erupted M3 and no M3.
98 299
145 353
Risk
<0.001
0.324 0.153
Relative Risk 1 0.472
95% CI 0.336–0.663
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Normally erupted M3* 47 No M3 54 *Normally erupted M3 = Class IA
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Angle Fracture Present Absent Total
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Table 7: Risk of condylar fracture in relation to mandibular sides with normally erupted M3 and no M3..
122 274
145 353
Risk
0.102
0.159 0.224
Relative Risk 1 1.411
95% CI 0.925–2.152
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Normally erupted M3* 23 No M3 79 *Normally erupted M3 = Class IA
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Condylar Fracture Present Absent Total
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S0278-2391(14)00376-0
DOI:
10.1016/j.joms.2014.04.004
Reference:
YJOMS 56286
To appear in:
Journal of Oral and Maxillofacial Surgery
Received Date: 26 December 2013 Revised Date:
2 April 2014
Accepted Date: 6 April 2014
Please cite this article as: Naghipur S, Shah A, Elgazzar RF, Does the Presence and/or Position of Lower Third Molars Alter the Risk of Mandibular Angle or Condylar Fractures?, Journal of Oral and Maxillofacial Surgery (2014), doi: 10.1016/j.joms.2014.04.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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TITLE: Does the Presence and/or Position of Lower Third Molars Alter the Risk of Mandibular
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Angle or Condylar Fractures?
AUTHORS: Saba Naghipur, BSc1
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Adnan Shah, BDS, MDS1
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Reda Fouad Elgazzar, BDS, MSc, PhD1
Department of Dental Diagnostics and Surgical Sciences, Faculty of Dentistry,
University of Manitoba, Winnipeg, MB, Canada.
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CORRESPONDING AUTHOR: Saba Naghipur
University of Manitoba, Faculty of Dentistry
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780 Bannatyne Ave, Winnipeg, MB, Canada R3T 0W2 Phone: 204-789-3631
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Fax: 204-789-3912
Email: [email protected]
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ABSTRACT Purpose: The purpose of this study was to determine whether a relationship exists between the presence of mandibular third molars (M3s) and mandibular angle and
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condylar fractures, and whether the risk of these fractures varies with M3 position.
Methods: A retrospective cohort study was conducted in patients presenting to the Oral
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and Maxillofacial Surgery service from April 2007 to March 2012 with mandibular
fractures. Data sources were the patients’ hospital charts and panoramic radiographs. The
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predictor variables were the presence and position of M3s. M3 position was based on the Pell and Gregory classification and angulation was determined by measuring the angle between the long axis of M3s and the mandibular occlusal plane. The outcome variables were the presence of angle and condylar fracture. Other study variables included age, sex
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and fracture etiology. Data was analyzed using chi square and Student’s t-test.
Results: The study sample consisted of 446 patients with 731 mandibular fractures. Our
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results showed that the risk of mandibular angle fracture was significantly higher in both patients and mandible sides with impacted M3s (P<0.001), whereas the risk of condylar
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fracture was significantly higher in both patients and mandible sides lacking impacted M3s (P<0.001). A relationship between the position of M3s to either angle or condylar fractures could not be demonstrated (P>0.05).
Conclusion: The presence of impacted M3s increased the risk of angle fracture while simultaneously decreasing the risk of condylar fracture. However, no relationship appeared to exist between M3 position and fracture pattern.
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INTRODUCTION Many clinical factors influence the pattern of mandibular fractures, including the severity and nature of the impacting force, as well as biomechanical properties of the
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mandible, including bone density, mass and normal or pathologic anatomic structures that create weak areas within the bone.1=3 The influence of mandibular third molars (M3s) on mandibular fractures has received much attention in the literature and is one of the only
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factors clinicians can potentially influence when determining whether extraction is advisable. However, whether impacted M3s without clinical symptoms should be
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surgically removed remains controversial.
Previous retrospective studies have consistently reported that patients with impacted M3s are at a higher risk of suffering mandibular angle fractures than those without impacted M3s.4-6 This has been attributed to decreased bony volume at the
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mandibular angle region caused by the presence of an impacted M3. Based on these findings, some investigators have advocated for the removal of impacted M3s, particularly in young athletes involved in contact sports, as a prophylactic measure to
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prevent future mandibular angle fractures.4,7 However, more recent studies have found that patients without M3s are more likely to develop another type of mandibular fracture,
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mandibular condylar fracture, compared to those with impacted M3s.8-9 Given the challenges associated with repair of the mandibular condylar and the higher risk of postoperative complications,10 it may not be beneficial to remove impacted M3s as a means of preventing angle fractures. While many studies have examined the effect of M3s on mandibular angle or condylar fractures separately, relatively few have examined its effect on both types of
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fractures in the same population. The purpose of this study was twofold; 1) to determine whether the presence of M3s increases or decreases of risk of mandibular angle and condylar fracture and 2) to determine if this relationship is dependent on the position of
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M3s in the mandible. Given the theory that the M3s decrease the bony volume in the
angle region, we hypothesized that the presence of M3s would increase the risk of angle fracture while simultaneously decreasing the risk of condylar fracture and that the degree
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of tooth impaction would be directly related to the risk of fracture.
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METHODS Study Design and Sample
To address the research goals, a retrospective cohort study design was used. The sample cohort was composed of all individuals aged 15 years and older who presented for
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evaluation and management of mandibular fracture to the Oral and Maxillofacial Surgery service at Health Sciences Center in Winnipeg, Manitoba from April 1st 2007 to March
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31st 2012.
Variables and Data Collection
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The primary study variables were the presence and position of M3s (predictor
variables) and the presence or absence of angle and condylar fracture (outcome variables). Patient hospital charts and panoramic radiographs were reviewed to determine the presence and position of M3s and the presence of angle and condylar fracture. The horizontal and vertical position of M3s was classified according to the Pell and Gregory system.11 The horizontal position of M3s was grouped based on the amount
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of space available between the anterior border of the vertical ramus and the second molar and the vertical position was classified based on the relative position of M3s to the crown of the second molar (Table 1). Using this classification, M3 position could be grouped
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into 1 of 9 categories (IA, IB, IC…IIIC). Group IA was considered a normal pattern of eruption and not impacted; all other groups were considered impacted M3s. Patients designated as Class IA and/or no M3 in both mandibular sides were placed into the
side were placed into the impacted M3 present group.
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impacted M3 absent group. Patients with at least one impacted M3 in either mandibular
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Angulation of M3s was defined by the angle of intersection between the long axis of the M3 and the mandibular occlusal plane. A horizontal impaction parallel to the occlusal plane and having the occlusal portion of the crown adjacent to the root surface of the mandibular second molar was defined as 0o. The angulation increased as the occlusal
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surface of M3 rotated upright and then distally toward the occlusal plane. Horizontal angulation was then defined as 0-10o or 350 to 359o, mesioangular from 11-80o, vertical angulation from 81-110o and distoangular from 111-170o.12
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Mandibular angle fractures were defined according to Kelly and Harrigan13 as fractures located posterior to the second molar tooth, extending from any point on the
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curve formed by the junction of the body and the ramus in the retromolar area to any point on the curve formed by the inferior border of the body and posterior border of the ramus of the mandible. Condylar fracture was defined as a fracture with the fracture line occurring above the sigmoid notch. For the purposes of description and to identify confounding variables, data was also collected for the following variables: age (years), sex (male or female), fracture
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etiology (assault, fall, sport, road traffic accident (RTA), other) and presence of concomitant mandibular fractures (angle, condylar, body, symphysis, ramus and
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coronoid). All data were abstracted from patient records.
Data Analysis
A database was constructed using Excel (Microsoft ®, Redmond, WA, USA) and
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statistical analysis performed using SPSS software version 15.0 (SPSS Inc, Chicago, IL, USA). Data was analyzed by calculating the means and standard deviations and cohort
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comparisons were made using chi square test, Student’s t-test and analysis of variance. Statistical significance was inferred if P<0.05. The study was approved by the Health Research Ethics Board at the University of Manitoba.
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RESULTS
The study cohort consisted of 446 patients with 731 total mandibular fractures. The average age of the cohort was 29.3 + 11.3 years and consisted of 377 (84.5%) males
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and 69 (15.5%) females. The most common etiology of fracture was assault (362; 81.1%), followed by falls (31; 7.0%), sports-related injuries (20; 4.5%), other causes (20;
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4.5%) and RTAs (13; 2.9%). The most common fracture pattern was bi-fracture (243; 54.5%), followed by mono-fracture (182; 40.8%) and multi-fracture (21; 4.7%). Fractures of the mandibular body were observed most frequently (292; 39.9%), followed by angle (251; 34.3%), condylar (148; 20.2%), symphysis (26; 3.6%), ramus (10; 1.4%), and coronoid fracture (4; 0.6%).
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Mandibular angle fracture was observed in 247 patients, with 4 patients having bilateral angle fractures. Mandibular condylar fractures were observed in 130 patients, with 18 patients having bilateral condylar fractures. Ten patients had an angle and
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condylar fracture simultaneously, including four patients with both fractures on the same mandibular side. A detailed analysis of the demographic variables is shown in Table 2. The risk of mandibular angle fracture was statistically higher in younger patients
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(P<0.001), but no statistical difference in age or sex was found among patients with
condylar fracture (P>0.05). The risk of angle fractures was significantly higher in patients
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with impacted M3s (one or both mandibular sides) compared to those without impacted M3s (70.0 vs. 39.4%; P<0.001). Conversely, the risk of condylar fracture was lower in patients with impacted M3s compared to those without impacted M3s (21.9 vs. 37.1%; P<0.001). When assessed for fracture etiology, the most common cause of both angle and
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condylar fractures was assault, with both results reaching statistical significance. However, the highest risk of angle fractures occurred in assaults (58.8%), while the highest risk of condylar fractures occurred in RTAs (61.5%).
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The cohort of 446 patients had 892 mandibular sides, of which 394 sides (44.2%) had an impacted M3. After grouping each M3 into either the impacted M3 present group
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(Groups IB-IIIC) or impacted M3 absent group (Group IA or no M3), an analysis of fracture type revealed that sides with impacted M3s were significantly more likely to experience mandibular angle fracture than sides without impacted M3s (P<0.001; relative risk (RR) = 1.877; 95% CI: 1.514–2.327). We also observed that mandibular sides with impacted M3s were significantly less likely to incur condylar fracture compared to sides with impacted M3s (P<0.001; RR = 0.570; 95% CI: 0.413-0.787) (Table 3).
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A total of 539 M3s from 300 patients were analyzed by panoramic radiographs and classified according to the Pell and Gregory system into horizontal position, vertical position and angulation. The relationship between M3 position and mandibular angle
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fracture on the ipsilateral side of the M3 is shown in Table 4. The most common
horizontal position among mandibular sides with angle fracture was Class II (90), and this also conveyed the greatest relative risk for fracture (RR = 1.133; 95% CI: 0.887-
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1.447). The most common vertical position was Class A teeth (93), whereas the relative risk was highest among Class B (RR = 1.173; 95% CI: 0.922-1.492). When grouped
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according to M3 angulation, mesioangular impactions were the most common in mandibular sides with angle fracture (140) and distoangular impactions presented with the greatest relative risk (RR = 1.453; 95% CI: 0.595-3.549). However, statistical significance was not reached for any of the three positioning groups (horizontal position,
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vertical position and angulation) in relation to angle fracture (P>0.05). Using the same analysis, the relationship between mandibular condylar fracture and M3 position was assessed (Table 5). The most common horizontal position of M3s
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on the same side of condylar fractures was Class I (32) and this also presented the greatest relative risk of fracture (RR = 1). The most common vertical position was Class
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A (38); this also carried the greatest relative risk for fracture (RR = 1). When grouped by M3 angulation, mesioangular impactions were found to be most common (42), but horizontal impactions presented the greatest relative risk (RR = 1.042; 95% CI: 0.4492.419). Again, statistical significance was not attained for any of the three positioning groups in relation to condylar fracture (P>0.05).
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In our final analysis, mandibular sides in the impacted M3 absent group (n = 498) were further subdivided into sides with normally erupted M3s (ie: Class IA) and sides lacking M3s. The rate and relative risk of mandibular angle and condylar fractures was
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then compared between the two groups (Tables 6 and 7). Our results showed that the rate and relative risk of angle fracture were both significantly higher in mandibular sides with normally erupted M3s compared to sides lacking M3s, with these results reaching
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statistical significance (P<0.001). Conversely, the rate and relative risk of condylar
fracture was greater in sides lacking M3s, although these results did not reach statistical
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significance (P = 0.102).
DISCUSSION
The purpose of this study was to determine if the presence and/or position of M3s
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alters the risk of mandibular angle or condylar fracture. We hypothesized that M3s would increase the risk of angle fracture while simultaneously decreasing the risk of condylar fracture, and that this relationship would depend on the position of M3s within the
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mandible. The results of this study confirmed an increased risk of angle fractures in the presence of M3s and a decreased risk of condylar fractures in their absence. However, no
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statistically significant relationship could be found between M3 position and fracture pattern.
Among the many factors that influence the pattern of mandibular fractures, the
effect of M3s has been the best studied. In particular, the relationship between mandibular angle fracture and M3s has been closely examined. The reason for the higher risk of angle fractures in the presence of impacted M3s is thought to be because the
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mandibular angle is weakened as the tooth occupies more osseous space in the jaw, thereby decreasing the quantity of bone in this region. This hypothesis was supported by Reitzik et al.14 who’s work with vervet monkey mandibles showed that mandible sides
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with impacted M3s fractured with 60% of the force required to fracture mandible sides containing normally erupted M3s. In the current study, we found that the risk of angle
fracture increased by 1.8 times in patients with an impacted M3 (one or both mandibular
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sides) and 1.9 times in mandibular sides with an impacted M3. This is in agreement with most studies which have shown a 2-to-4 fold increased risk of angle fracture in the
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presence of M3s.4-6 We also investigated and compared the risk of angle fracture in patients lacking an M3 and in patients with normally erupted M3s. We found that the latter group experienced approximately double the risk, compared patients lacking M3s, with the results reaching statistical significance.
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After measuring the degree of M3 impaction by horizontal and vertical position according to the Pell and Gregory system, we found that the risk of angle fracture was highest among Class II and Class B molars. This finding is consistent with studies from
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Choi et al12 and Duan and Zhang15 who also observed higher risk in these two groups. This finding has been explained by pointing out that mandibular angle fractures have an
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area of tension at the superior border and an area of compression at the inferior border, according to muscle insertion, muscle force and bite force positioned on the proximal and distal segments of the fracture. M3s that disrupt the continuity of the cortical bridge of the superior border may cause an inherent weakness in the angle, thereby requiring less force and muscle tension to cause an angle fracture. This may explain why the highest risk of fracture has been seen in Class II and Class B positions of M3s, in which the
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superior border is interrupted, rather than Class III and Class C, where the superior border is intact.15 However, evidence from other studies including from Ma’aita and Alwrikat16 suggests mandibular angle fracture rates are highest in the presence of M3s with Class III
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and Class C positions. Therefore, the relationship between the position of M3s and angle fractures remains controversial. Furthermore, our study found no statistical significance in the risk of angle fracture based on M3 position. This is in agreement with some studies
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that have found similar findings4,6 but contrary to others that have shown a statistically significant relationship between M3 position and angle fracture.5,15,17
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The condylar process is another common fracture site in the mandible. It is not often exposed to direct external force because of its protection by the temporomandibular joint and associated structures but external force applied to other sites in the mandible can cause indirect trauma and result in condylar fracture. In the current study, we found that
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the risk of condylar fracture increased by 1.7 times in patients lacking an impacted M3 and 1.8 times in mandibular sides lacking an impacted M3, with these findings consistent with most other published studies.8,9,17 We also found that mandibular sides lacking an
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M3 had an increased risk of fracture when compared to sides with normally erupted M3s, although not statistically significant. Similar to the hypothesis regarding decreased bone
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quantity in the angle region, previous studies have contended that the reason for this finding is that mandibles lacking M3s have increased bone quantity in areas where an M3 would typically reside, allowing the mandible to better resist fractures and concentrating any externally applied force to the relatively weaker condylar process. The resultant fracture of the condylar neck is also considered a protective mechanism to prevent traumatic dislocation of the condyle into the middle cranial fossa.
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Less is known about the relationship between M3 position and risk of condylar factures. Our results showed that among mandibular sides with M3s, the highest relative risk of fracture occurred in sides with Class I and Class A molars. This is consistent with
significant relationship, which our study could not substantiate.
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the findings from previous studies,12,15,17although these investigators found a statistically
The interpretation of our findings should be considered in light of several
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limitations. First, many clinical and biomechanical factors influence the risk of angle and condylar fractures. Therefore, we acknowledge it would be incorrect to assume a cause-
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and-effect relationship between the presence or absence of M3s and these fractures. Second, our study utilized the Pell and Gregory classification, which may not be the most accurate method to determine the quantity of bone in the angle region. A study by Iida et al18 proposed an alternate way to radiographically approximate the bony space at the
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angle by defining the angle region using anatomical landmarks and subtracting the bony space occupied by the impacted M3. Using this method, the authors found that the highest rate of angle fractures occurred in angles with the smallest area of remaining bone
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while the lowest rate of fractures occurred in angles with the largest area. Such investigations may provide more consistent results and be more valuable in determining
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the risk of mandible fracture in relation to M3 position. The treatment of mandibular condylar fracture is generally considered to be more
technically difficult than treatment of angle fractures because of difficulties in surgical access and visibility. Reduction and fixation of the condylar process also carries a greater risk of operative complications including facial nerve damage and post-operative complications such as malocclusion.10 Several authors4,7 have recommended prophylactic
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extraction of M3s in young athletes involved in contact sports because it may decrease the risk of mandibular angle fracture due to external force. We agree that earlier extraction of M3s may decrease the risk of angle fractures. However, because mandibles
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lacking M3s may be predisposed to condylar fracture, which potentially carries more
serious complications, the decision to extract M3s to reduce the risk of angle fracture
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requires careful consideration by the clinician.
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REFERENCES 1. Halazonetis JA. The weak regions of the mandible. Br J Oral Surg 6:37, 1968
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2. Weiss L. Static loading of the mandible: Oral Surg Oral Med Oral Pathol 19:253, 1965
3. Amaratunga NA. A comparative study of the clinical aspects of edentulous and
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dentulous mandibular fractures. J Oral Maxillofac Surg 46:3, 1998
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4. Tevepaugh DB, Dodson TB. Are mandibular third molars a risk factor for angle fractures? J Oral Maxillofac Surg 53:646, 1995
5. Lee JT, Dodson TB. The effect of mandibular third molar presence and position on the
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risk of angle fracture. J Oral Maxillofac Surg 58:394, 2000
6. Meisami T, Sojat A, Sandor GK, Lawrence HP, Clokie CM. Impacted third molars and
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risk of angle fracture. Int J Oral Maxillofac Surg 31:140, 2002
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7. Schwimmer A, Stern R, Kritchman D. Impacted third molars: a contributing factor in mandibular fractures in contact sports. Am J Sports Med 11:262, 1983
8. Zhu SJ, Choi BH, Kim HJ, Park WS, Huh JY, Jung JH, Kim BY, Lee SH. Relationship between the presence of unerupted mandibular third molars and fractures of the mandibular condyle. Int J Oral Maxillofac Surg 34:382, 2005
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9. Iida S, Nomura K, Okura M, Kogo M. Influence of the incompletely erupted lower
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third molar on mandibular angle and condylar fractures. J Trauma 57:613, 2004
10. Ellis E. Complications of mandibular condyle fracture. Int J Oral Maxillofac Surg
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27:255, 1998
11. Pell G, Gregory G. Impacted mandibular third molars, classification and modified
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technique for removal. Dental Digest 39:330, 1933
12. Choi BJ, Park S, Lee DW, Ohe JY, Kwon YD. Effect of lower third molars on the
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incidence of mandibular angle and condylar fractures. J Craniofac Surg 22:1521, 2011
13. Kelly D, Harrigan W. A survey of facial fractures related to teeth and edentulous
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regions. J Oral Surg 33:146, 1975
14. Reitzik M, Lownie JF. Cleaton JP, Austin J. Experimental fractures of the monkey
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mandibles. Int J Oral Surg 7:100, 1978
15. Duan DH, Zhang Y. Does the presence of mandibular third molars increase the risk of angle fracture and simultaneously decrease the risk of condylar fracture? Int J Oral Maxillofac Surg 37:25, 2010
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16. Ma’aita J, Alwrikat A. Is the mandibular third molar a risk factor for mandibular angle fracture? Oral Surg Oral Med Oral Pathol Oral Radiol Endod 89:143, 2000
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17. Thangavelu A, Yoganandha R, Vaidhyanathan A. Impact of impacted mandibular third molars in mandibular angle and condylar fractures. Int J Oral Maxillofac Surg
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39:136, 2010
18. Iida S, Hassfeld S, Reuther R, Nomura K, Muhling J. Relationship between the risk
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of mandibular angle fractures and the status of incompletely erupted mandibular third
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molar. J Craniomaxillofac Surg 33:158, 2005
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TABLES Table 1: Pell and Gregory classification.
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Amount of space available between mandibular ramus and second molar Adequate space for eruption Inadequate space for eruption Third molar located all or mostly within ramus Relationship of third molar crown to second molar crown Level at occlusal plane Between cemento-enamel junction of the second molar and occlusal plane Below the cemento-enamel junction of the second molar
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Horizontal Class I Class II Class III Vertical Class A Class B Class C
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Table 2: Demographic variables according to angle and condylar fracture status in 446 patients. Angle Fracture Present (%) Absent (%) 27.2 + 9.7 32.0 + 12.6
P <0.001 0.102
106 (28.1) 24 (34.8)
271 (71.9) 45 (65.2)
0.263
70 (30.0) 129 (60.6)
<0.001
51 (21.9) 79 (37.1)
182 (78.1) 134 (62.9)
<0.001
149 (41.2) 21 (67.7) 10 (50.0) 8 (61.5) 11 (55.0) 199
0.026
99 (27.3) 13 (41.9) 1 (5.0) 8 (61.5) 9 (45.0) 130
263 (72.7) 18 (58.0) 19 (95.0) 5 (38.5) 11 (55.0) 316
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162 (43.0) 37 (53.6)
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Variable Age, mean (years) Sex Male (n = 377) 215 (57.0) Female (n = 69) 32 (46.4) Impacted M3 Present (n = 233) 163 (70.0) Absent (n = 213) 84 (39.4) Fracture Etiology Assault (n = 362) 213 (58.8) Fall (n = 31) 10 (32.3) Sport (n = 20) 10 (50.0) RTA* (n = 13) 5 (38.5) Other (n = 20) 9 (45.0) Total 247 *RTA = Road Traffic Accident
Condylar Fracture Present (%) Absent (%) P 30.1 + 10.6 29.0 + 11.6 0.335
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Table 3: Influence of impacted M3 on mandibular angle and condylar fracture in 892 mandibular sides.
P <0.001
46 (11.7) 102 (20.5)
348 (88.3) 396 (79.5)
P <0.001
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Mandibular sides with impacted M3 Present (n = 394) 150 (38.1) 244 (61.9) Absent (n = 498) 101 (20.3) 397 (79.7) a Relative risk: 1.877; 95% CI: 1.514–2.327 b Relative risk: 0.570; 95% CI: 0.413-0.787
Condylar Fractureb Present (%) Absent (%)
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Angle Fracturea Present (%) Absent (%)
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Table 4: Risk of angle fracture in mandibular sides with relation to M3 position. Angle Fracture Present Absent Total
Risk
Relative Risk
95% CI
145 143 54
220 233 86
0.600
0.341 0.386 0.372
1 1.133 1.091
0.887–1.447 0.784–1.519
93 75 29
179 112 51
272 187 80
0.433
0.342 0.401 0.363
1 1.173 1.060
0.922–1.492 0.759–1.480
41 140 13 3
98 213 27 4
139 353 40 7
0.183
0.295 0.397 0.325 0.429
1 1.345 1.102 1.453
1.009–1.792 0.658–1.845 0.595–3.549
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75 90 32
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Horizontal Position Class I Class II Class III Vertical Position Class A Class B Class C Angulation Vertical Mesioangular Horizontal Distoangular
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Table 5: Risk of condylar fraction in mandibular sides with relation to M3 position. Condylar Fracture Present Absent Total
Risk
Relative Risk
95% CI
188 206 76
220 233 86
0.603
0.145 0.116 0.116
1 0.797 0.799
0.494–1.284 0.411–1.554
38 25 6
234 162 74
272 187 80
0.301
0.140 0.134 0.075
1 0.957 0.537
0.599–1.530 0.235–1.224
20 42 6 1
119 311 34 6
139 353 40 7
0.859
0.144 0.119 0.150 0.143
1 0.827 1.042 0.993
0.504–1.357 0.449–2.419 0.155–6.374
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32 27 10
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Horizontal Position Class I Class II Class III Vertical Position Class A Class B Class C Angulation Vertical Mesioangular Horizontal Distoangular
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Table 6: Risk of angle fracture in relation to mandibular sides with normally erupted M3 and no M3.
98 299
145 353
Risk
<0.001
0.324 0.153
Relative Risk 1 0.472
95% CI 0.336–0.663
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Normally erupted M3* 47 No M3 54 *Normally erupted M3 = Class IA
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Angle Fracture Present Absent Total
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Table 7: Risk of condylar fracture in relation to mandibular sides with normally erupted M3 and no M3..
122 274
145 353
Risk
0.102
0.159 0.224
Relative Risk 1 1.411
95% CI 0.925–2.152
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Normally erupted M3* 23 No M3 79 *Normally erupted M3 = Class IA
P
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Condylar Fracture Present Absent Total
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