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 Table of Contents  
Year : 2020  |  Volume : 32  |  Issue : 1  |  Page : 17-21

Correlation of mandibular gonial angle and mandibular angle fracture: A radiographic study

Department of Oral Medicine & Radiology, Government Dental College & Hospital, Nagpur, Maharashtra, India

Date of Submission21-Nov-2019
Date of Decision05-Mar-2020
Date of Acceptance11-Mar-2020
Date of Web Publication17-Apr-2020

Correspondence Address:
Dr. Nikhila B Shroff
Government Dental College and Hospital, Nagpur- 440003, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jiaomr.jiaomr_190_19

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Objectives: The purpose of the study was to evaluate the correlation between mandibular gonial angle and mandibular third molar with the risk of mandibular angle fracture. Materials and Methods: The study sample consisted of 294 orthopantomograms (OPG) of mandibular fracture. The sample was broadly divided into two groups, i.e. angle fracture group and non-angle fracture group. Gonial angle was measured digitally using software IWCR ROCKEY version 3.2 and status of third molar was assessed in the angle fracture group. Results: The mean age of the patients is 30.29 ± 8 years. Out of 294 OPGs, 226 were non-angle fracture and 68 were angle fracture. The mean gonial angle of patients in angle fracture group was 117.91 ± 7.74°, which was 0.9° larger than the non-angle fracture group (mean 117.03 ± 8.43; P = 0.4427). The third molar was present in 88% of angle fractures and 57% were impacted molars. Conclusion: There was no correlation between high gonial angle and mandibular angle fracture. Impacted third molar can be one of the risk factors for mandibular angle fracture.

Keywords: Mandibular angle fracture, mandibular gonial angle, mandibular third molar

How to cite this article:
Shroff NB, Motghare PC, Kumbhare SP, Kalaskar AR. Correlation of mandibular gonial angle and mandibular angle fracture: A radiographic study. J Indian Acad Oral Med Radiol 2020;32:17-21

How to cite this URL:
Shroff NB, Motghare PC, Kumbhare SP, Kalaskar AR. Correlation of mandibular gonial angle and mandibular angle fracture: A radiographic study. J Indian Acad Oral Med Radiol [serial online] 2020 [cited 2020 Jun 4];32:17-21. Available from: http://www.jiaomr.in/text.asp?2020/32/1/17/282611

   Introduction Top

Mandible is the largest, strongest, and lowest bone in the human face having a complex role in the esthetics of the face and functional occlusion. Because of the prominent position of the mandible, it is more vulnerable to fracture.[1] Fracture of mandible accounts for 36-59% of all maxillofacial fractures,[2] out of which mandibular angle fracture comprises of 25-30%.[3] The frequency of mandibular fracture is increasing with the increase in trauma such as traffic accidents, industrial accidents, falling, sports, and interpersonal violence.[4]

Mandibular angle fracture is defined as the fracture line begins where the anterior border of the mandible ramus meets the body of the mandible and extends inferiorly through the inferior border or posteriorly extends towards the gonial angle.[5] There are several factors associated with mandibular angle fractures such as the severity of the impact forces, biomechanical properties consisting of bone density, mass, and irregular anatomic structure, which may exhibit lower resistance,[6],[7],[8] presence of impacted third molar[9], and high gonial angle.[10],[11],[12]

The gonial angle is an important parameter for determining the growth pattern of an individual.[13] Gonial angle (mandibular angle) is an imaginary tangential line along the inferior border of the mandible along the posterior border of the ramus.[14] The gonial angle can be assessed using different methods like direct facial measurement, photographs, or radiographically.[15] Lateral cephalograms are used for long time to measure the gonial angle. But because lateral cephalograms are superimposed,[16] other modalities such as orthopantomograms (OPG),[17] computed tomography (CT), cone-beam CT (CBCT)[18] have shown an accuracy in measuring the gonial angle and right and left side can be assessed separately. OPGs are now widely used owing to its easy availability, low cost, and less radiation dose.[19]

Some studies have established a positive correlation between the gonial angle and the bony architecture of an individual.[20] High gonial angle has less muscle activity and bite forces compared with a low gonial angle.[21] So the purpose of the present study was to evaluate the correlation between mandibular gonial angle and mandibular third molar with the risk of mandibular angle fracture in the Indian population.

   Materials and Methods Top

Study design and sample

A retrospective cross-sectional study was designed for patients who underwent treatment for mandibular fractures from 2016 to 2018. Retrospectively 294 OPGs with mandibular fractures, which were taken for investigation purpose between 2016 and 2018 at the Department of Oral Medicine and Radiology, Government Dental College and Hospital Nagpur were selected for the study after the approval of the institutional ethics committee.

Inclusion and exclusion criteria

Preoperative digital OPGs (Planmeca OPG Machine, IWCR ROCKEY 3.2 version) of patients in the age range of 20 to 50 years depicting mandibular fractures were selected for the study. OPGs with poor contrast, blurred images, any lesions such as cyst, tumours, developmental disturbances, osteoporosis, pathologic fractures, dentoalveolar fractures or edentulous mandibular fractures, bilateral mandibular angle fracture, any facial asymmetry, etc., completely edentulous state, panfacial trauma were excluded from the study.

Variables and data collection

The predictor variable was the presence or absence of a high gonial angle and the primary outcome was the presence or absence of mandibular angle fracture. In mandibular angle fracture, the presence or absence of the third molar was also determined. The angle fracture was considered when the radiolucent line appeared posterior to the second molar and was located at any point on the curve formed by the junction of the horizontal and the posterior border of the ascending ramus of the mandible (Kelly and Harrigan, 1975).

The data were collected from medical records included age, gender of the patients, and anatomic site of mandibular fracture. The study sample was divided based on the anatomic site of fracture as symphysis, parasymphysis, condyle, body, angle, ramus and combination of two mandibular fractures. For data analysis, the sample was broadly classified into two groups –angle fracture and non-angle fracture (symphysis, parasymphysis, condyle, body, ramus and combination of two mandibular fractures).

  • Gonial Angle (Degrees)-The gonial angle was measured digitally by drawing the tangent to the posterior border of the ramus and tangent to the lower border of the mandible using IWCR ROCKEY software 3.2 version [Figure 1]. Measurements were done by two observers. The normal range for the gonial angle was fixed as 121.8 degrees +/- 6.2, based on norms specific to the present study population.[22] Any value above 128° was considered high gonial angle and below 115.6° was marked low gonial angle.

Data analysis

Data obtained from the study were analyzed using Statistical Package for the Social Sciences (SPSS) software (Version 16, IBM Corp). Qualitative variables in the study were compared using the Chi-square test and quantitative variables with one-way analysis of variance (ANOVA) test. Statistical significance was set at P value of <0.05 for the study. Interobserver and intraobserver analyses were done by kappa statistics. There was strong agreement between two observers and agreement of the same observer at different intervals which was 89.5% and 86%, respectively, which indicates no interobserver and intraobserver variability.
Figure 1: Orthopantomogram demonstrating (1) measurement of gonial angle (RED) and (2) Mandibular third molar angulation (BLACK)

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   Results Top

In this study, we observed 294 mandibular fracture (90% men and 10% women) in the age group ranging from 20 to 50 years and the mean age of the patients was 30.29 ± 8.0 years. The distribution of fractures based on the anatomic site was 68 angle fractures and 226 non-angle fractures [Figure 2]. The presence of mandibular third molar in angle fractures was also determined.
Figure 2: Graph showing distribution of mandibular fractures according to anatomic site

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The fracture site-wise distribution of the gonial angle is shown in [Figure 3]. The mean gonial angle of patients in angle fracture group was 117.91 ± 7.74°, which is 0.9° larger than non-angle fracture group (mean 117.03 ± 8.43; P = 0.4427) [Table 1].
Figure 3: Graph showing fracture site-wise distribution of patients with high, normal, and low gonial angles

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Table 1: Summary of outcome variables

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Relation between gonial angle and mandibular angle fracture

In angle fracture group, 59% of patients had normal gonial angle (mean, 122.51 ± 3.32, P < 0.001.), 37% had low gonial angle (mean 109.46 ± 3.85) and 4% had high gonial angle (mean131.33 ± 2.08) [Figure 4]. It was observed that mandibular third molars were involved in 60 (88%) of angle fractures and were absent in 8 (12%) [Figure 5]. We observed 34 (57%) cases of angle fractures associated with an impacted mandibular third molar and were erupted in 26 (43%) cases [Figure 6].
Figure 4: Pie chart showing distribution of gonial angles in the angle fracture group

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Figure 5: Pie chart showing the presence/absence of mandibular third molar in angle fracture

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Figure 6: Pie chart showing relationship of the angle fracture to the status of the third molar

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Subjects with high gonial angles had an unadjusted 0.52-fold increase in risk for angle fracture over subjects with normal or low gonial angles (Relative risk –0.52 (95% confidence interval, 0.16 to 1.71), P value 0.2723). Subjects with high gonial angles were also statistically associated with only 0.502 times increased chance for angle fracture (Adj. odds ratio: 0.502, 95% confidence limit: 0.09-1.79, P value 0.273) when compared with subjects without high gonial angles [Table 2]. This indicates that there is a non-significant association between high gonial angle and incidence of angle fracture. The odds ratio was adjusted for the confounding variable in the presence of impacted teeth by using a logistic regression model.
Table 2: Risk assessment

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Relation between impacted third molar and angle fracture

Distribution of sample was done according to the type of inclination of mandibular third molar (Winter's classification). In this study, mesioangular impactions were more with 21 (62%) cases, which was statistically significant (p < 0.05), followed by vertical impaction in 7 (20%) cases, horizontal impaction in 5 (15%) cases, and distoangular impaction in 1 (3%) case [Figure 7].
Figure 7: Pie chart showing distribution of impacted teeth in angle fracture group according to Winter's classification

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   Discussion Top

The gonial angle is a valuable indicator for evaluating the growth pattern of an individual and also determines the rotation of the mandible. The downward and backward rotations of mandible is called a high gonial angle. These patients indicate an increased gonial angle. Whereas upward and forward rotation of mandible is called a low gonial and such patients indicate decrease in gonial angle.[23]

Bhullar compared the gonial angles in lateral cephalogram and OPG and showed that OPG can be used to determine the gonial angle as accurately as lateral cephalogram.[16] More accurate measurement of the right and left side can be done without superimposition. Mattila et al. measured the gonial angle using panoramic radiographs and lateral cephalograms, compared the values with those found using dry skulls, and concluded that the measurements made using the panoramic radiographs were more accurate.[24] Shahabi et al. compared the external gonial angle determined using lateral cephalograms and panoramic radiographs of class I patients and concluded that panoramic radiography could be used for determining the gonial angle as accurately as a lateral cephalogram.[25] In this study, accurate measurement of the gonial angle was done digitally and compared with the standard norms for the Indian population. Several studies have shown that OPG can measure gonial angle accurately without any superimpositions.[26],[27]

Panneerselvam et al. revealed a positive relation between high gonial angle and mandibular angle fractures by observing that the mean gonial angle in angle fracture group was 126 ± 7.9° which is 4.5° larger than the other mandibular fracture showing that the patients with high gonial angle were 11.7 times more likely to sustain angle fracture than the subjects with normal or low gonial angle.[10] In a study by Dhara et al., the mean gonial angle in cases of angle fractures was 128.5 ± 5.4° which is 10.2° greater than that of non-angle fractures, suggesting the association of high gonial angle with mandibular angle fracture. This study also showed that patients with high gonial angles are 8.7 times likely to have an angle fracture, thus increasing the risk.[11] Another study by Elias et al. on CT also observed a mean gonial angle in the angle fracture group to be 131.3° as compared to 118.1° in the rest of mandibular fracture suggesting that an increase in gonial angle increases the risk of angle fracture.[12] In our study, we found that in the angle fracture group, 37% had low gonial angle (mean 109.46 ± 3.85) and 4% had high gonial angle (mean131.33 ± 2.08) suggesting a correlation between low mandibular gonial angle and mandibular fracture, which is contradictory to the aforementioned studies. Theoretically, the displacement of fracture fragments is dependent on the fracture line, the extent of muscle pull. As per the literature, increasing the gonial angle from 90 to 150 ° causes a 48% decrease in the mechanical advantage of temporalis and 35% decrease in masseter muscle[28] suggesting that there are less chances of angle fracture in high gonial angle. Thus, the gonial angle is not only the factor leading to angle fracture but other factors like intensity of trauma, muscle pull, impacted third molar should be taken into consideration.

This study also showed the presence of third molar in 88% of angle fracture. Among them, 57% were impacted. The increase incidence of mandibular angle fracture was observed in a mesioangular impacted third molar. These findings were similar to that of Fuselier et al. and Thangavelu et al. who also proved that mesioangular impactions were the most commonly associated with angle fractures.[9],[29] As the root of mesioangular impacted third molar is directed toward the angle of mandible, stress is concentrated around the root apex, which may act as a wedge splitting the mandibular angle, by which the injury forces are redirected toward the mandibular angle, and decreases the amount of bone by more than 20%, which increases the risk of angle fracture.

   Conclusion Top

This study concludes that there was no correlation between high mandibular gonial and mandibular angle fracture. There was also a statistical correlation between mandibular impacted third molar and mandibular angle fracture, more in mesioangular cases. We suggest studies with a more homogeneous sample, and with recently advanced imaging modalities. The study including a greater number of samples with equal distribution of angle and non-angle fracture can be done to achieve more reliable results.

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Conflicts of interest

There are no conflicts of interest.

   References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]

  [Table 1], [Table 2]


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