- Email: [email protected]
The Influence of the Mandibular Gonial Angle on the Incidence of Mandibular Angle Fracture—A Radiomorphometric Study
Accepted Manuscript The influence of mandibular gonial angle on the incidence of mandibular angle fracture – a radiomorphometric study P. Elavenil, MDS, MBA, FAM, Reader, J. Pooja, BDS, Intern, B. Sasikala, MDS, Reader, S. Shanmugasundaram, MDS, MBA, Professor, V.B. Krishnakumar Raja, MDS, Professor & Head, S. Dilip, MDS, Professor PII:
S0278-2391(16)30750-9
DOI:
10.1016/j.joms.2016.08.016
Reference:
YJOMS 57405
To appear in:
Journal of Oral and Maxillofacial Surgery
Received Date: 6 July 2016 Revised Date:
7 August 2016
Accepted Date: 8 August 2016
Please cite this article as: Elavenil P, Pooja J, Sasikala B, Shanmugasundaram S, Krishnakumar Raja V, Dilip S, The influence of mandibular gonial angle on the incidence of mandibular angle fracture – a radiomorphometric study, Journal of Oral and Maxillofacial Surgery (2016), doi: 10.1016/ j.joms.2016.08.016. 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.
ACCEPTED MANUSCRIPT
The influence of mandibular gonial angle on the incidence of mandibular angle fracture – a radiomorphometric study Authors
2. Pooja J ,BDS- Interna 3. Sasikala B, MDS – Readera 4. Shanmugasundaram S, MDS, MBA –Professora 5. Krishnakumar Raja VB, MDS – Professor & Heada
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Institute of affiliation:
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6. Dilip S, MDS –Professorb
Department of Oral & Maxillofacial Surgerya,
Department of Orthodontics & Dentofacial Orthopaedicsb,
Ramapuram Campus,
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Ramapuram, Chennai.
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SRM Dental College & Hospital,
Corresponding Author:
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P. Elavenil, MDS, MBA, FAM
Department of Oral & Maxillofacial Surgery, SRM Dental College & Hospital Ramapuram Campus, Ramapuram, Chennai – 600089 Email: [email protected] Mobile: +91 98412 54653
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1. Elavenil P, MDS, MBA,FAM – Readera
ACCEPTED MANUSCRIPT Abstract Purpose: The aim of this radiomorphometric study was to analyse the association between mandibular gonial angle and risk of mandibular angle fracture. Methods: A retrospective analysis of medical records and radiographs of patients treated for mandibular fractures was done. The exposure studied was presence of high gonial angle
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while the outcome was fracture of the mandibular angle. The mandibular gonial angle (G) and mandibular height at the angle (MHA) were measured using the FACAD software. Data obtained was analysed using statistical software (S.P.S.S. Version 16, IBM Corp).
Results: The study sample comprised of 210 mandibular fractures; 70 mandibular angle
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fractures and 140 non-angle fractures. The Mean gonial angle in patients with mandibular angle fractures was 126.8+/-7.9 degrees, which was 4.5 degrees more than in patients with
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other mandibular fractures (p=0.0001). Patients with high gonial angle were 11.77 times more likely to sustain an angle fracture than subjects with normal or low gonial angles (Adjusted Odds ratio of 11.77, 95% confidence interval, 3.65 - 37.94, P<0.001). There was also a statistically significant reduction in the mandibular height at angle in patients with high gonial angle (P=0.0001).
Conclusion: The study demonstrates that people with high gonial angle are at an increased
Keywords
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risk for angle fracture and presents the related clinical implications.
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displacement
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Gonial angle, mandibular angle fracture, fracture biomechanics, fracture
ACCEPTED MANUSCRIPT INTRODUCTION Fractures of the mandibular angle are common in occurrence 1, 2. The higher incidence has been attributed to the curvature at the angle region 3, 4, presence of impacted third molar 5, 6 and height of mandible at the angle 7. The poor quality of bone at the angle region has also been demonstrated as a cause of fracture 8 .However the impact of the
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mandibular growth pattern-the vertical or horizontal growth, on the incidence of angle fracture has not been studied so far. One of the important anthropometric features which describes the mandibular growth pattern is the mandibular gonial angle 9, 10. It refers to the angle which is formed by the ramus line (RL) and the mandibular line
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(ML), where RL is the tangent to the posterior border of the mandible and ML is the lower border of the mandible through the gnathion 11,12 (Fig-1). The gonial angle may
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be assessed clinically 13 or radiographically 14 by manual 12 & digital methods 15. In an individual, though the right and left gonial angles are the same 11, 16 the normal gonial angle varies according to ethnicity, sex and age 17, 18. Based on the gonial angle, individuals may be classified as high, normal and low angle 19 or vertical, normal and horizontal growers respectively 20. Numerous studies have established a positive correlation between gonial angle and bony architecture at the mandibular angle region . Further, a high gonial angle has been associated with lower bite forces and reduced
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cortical thickness. On the basis of the existing literature, this study was designed to determine any possible correlation between high gonial angle and incidence of
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mandibular angle fracture, in Indian population.
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MATERIALS AND METHODS:Study design and Sample
To analyse the research question, a retrospective cohort study was designed using data of consecutive patients who underwent treatment for mandibular fractures between 2009 and 2015, at our institute. The Institutional Review Board approval was obtained and the study was performed in concordance with the current standards recommended for the reporting of observational studies (STROBE statement). 210 Orthopantomograms (OPG) demonstrating mandibular fractures were selected for the study from patient records. Inclusion and Exclusion Criteria
ACCEPTED MANUSCRIPT The inclusion criteria for selection of sample comprised of pre-operative, digital OPGs of patients with mandibular fractures, between the ages of 20 and 50. The OPGs with poor picture quality & resolution were excluded from the study. Also OPGs demonstrating completely edentulous state or pathological changes like cystic lesions, osteoporosis etc. were omitted. Patients with panfacial trauma were also not considered for the study.
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Variables and data collection
The predictor variable was the presence or absence of high gonial angle while the primary outcome variable was the presence or absence of mandibular angle fracture. A radiographic
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diagnosis of angle fracture was made when the fracture line was located posterior to the second molar, along the curvature connecting the body of mandible and posterior border of
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ramus 22.
The data for descriptive analysis was derived from medical records and included the following; age & sex of the patient, side of fracture, presence or absence of impacted mandibular third molar and displacement of fracture fragments.
The study sample was segregated based on the anatomic distribution of fracture as
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Parasymphysis, Body, Angle and Condyle fractures. For data analysis, the sample was broadly classified into 2 groups; Angle fractures and Non -angle fractures (Parasymphysis, Body, and Condyle). The pre-operative OPGs were digitally calibrated to 1:1 ratio taking into consideration the magnification index provided by the manufacturer. This was further
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confirmed clinically, using the pre-operative dental models of the respective patients. The mesio-distal width of the last standing molar on the fracture side was measured on the dental
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cast and was compared with the dimensions on the OPG to confirm the magnification error. The following parameters were measured using FACAD orthosurgical tracing software
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(Fig-1).
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Gonial angle (G) in degrees: The three point angular measurement of the gonial angle was determined by digitally calculating the angular measurement formed by the points connecting Articulare (Ar), Gonion (Go) and Menton (Mn). The normal range for gonial angle was fixed as 121.8 degrees +/- 6.2, based on norms specific to our study population
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. Any value above 128
degrees was considered high gonial angle and below 115.6 degrees was marked low gonial angle.
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Measurement of mandibular height at angle (MHA) in millimeters. This was measured from the root apex of the impacted third molar to the inferior border of the mandible 24 (line a-b).
Data analysis Data obtained from the study was analysed using statistical software (S.P.S.S. Version 16,
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IBM Corp). Qualitative variables in the study were compared using Pearson’s Chi Square Test and quantitative variables with one way ANOVA test. Statistical significance was set at P value of <0.05 for the study. Risk assessment modelling was used to assess relationships between high gonial angle and risk of angle fracture (relative risk and odds ratio). The
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confounding effect of presence of an impacted third molar on angle fracture was adjusted using a logistic regression model. A P value of <0.05 was considered statistically significant.
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RESULTS:-
The study sample included 210 OPGs with mandibular fractures involving 85% males and 25% females. The mean age of patients with mandibular fractures was 29.31+/-7.62. The distribution of fractures based on the anatomic site was Angle fractures (70) and Non angle fractures (140) (Fig-2). The presence of impacted third molars was a significant 88.6% within
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the angle fracture group and 39% in the non-angle fracture group (P = 0.0001). The fracture wise distribution of gonial angle is shown in Fig-3; The Mean gonial angle of patients in the angle fracture group was 126.8+/-7.9 degrees which was 4.5 degrees more than
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the non- angle group (Mean = 122.3+/-4.9 degrees, P = 0.0001) (Table1) Within the angle fracture group, 51% of the patients had high gonial angles (Fig-4) (P=0.795)
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with a mean of 133+/-3.4 degrees, 33% had normal gonial angles (Mean 123.3+/-2.3) and 16% had low gonial angles (Mean 113.6+/-3.6). Relationship between gonial angle and fracture of mandibular angle: The analysis of data from table 2 indicates that there is a significant association between high gonial angle and incidence of angle fracture. Subjects with
high gonial angles had an
unadjusted 10.3 fold increase in risk for angle fracture over subjects with normal or low gonial angles (Relative risk - 10.3; 95 % confidence interval, 1.8 to 2.7, P<0.0001). Subjects with high gonial angles were also statistically associated with an 11.77 times increased chance for angle fracture (Adjusted Odds ratio of 11.77, 95% confidence interval, 3.65 - 37.94, P<0.001)
ACCEPTED MANUSCRIPT when compared with subjects without high gonial angles. The odds ratio was adjusted for the confounding variable of presence of impacted teeth by using a logistic regression model. The data also demonstrated that there was a reduction in mean mandibular height at the angle with increase in gonial angle (P = 0.029); measuring 20.3+/-3.9mm for low, 19.9+/-3.6mm for normal and 18+/-2.5mm for high gonial angles (Fig-5). With regards to fracture
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displacement, 58.3% of the high gonial angle patients, 25% of the normal and 16.7% of the low gonial angle patients showed displacement of the fracture fragments. However this
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observation was statistically not significant (P = 0.112).
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DISCUSSION:-
The preponderance of mandibular angle fractures has been greatly attributed to the anatomic weakness of the angle region due to its curvature and change in the osseous grain pattern. Several studies have demonstrated that factors like impacted third molars, reduced mandibular height and poor bone quality weaken the mandibular angle further and lead to many fold increase in the risk of fracture. However no study has been reported so far, describing the
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impact of gonial angle on the structural integrity of the angle region and its influence on the bio-dynamics of angle fracture.
This retrospective study demonstrates a greater incidence of angle fractures in patients with
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high gonial angle thus emphasising its importance in the pathogenesis of angle fracture. The rationale behind this finding could be attributed to the characteristic variations in muscle
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physiology and bony architecture associated with changes in gonial angle. Gonial angle is an important anthropometric feature which contributes to facial esthetics and bio-dynamics of masticatory musculature. In practice, Gonial angle is assessed by radiographic analysis. Though lateral cephalogram is the preferred radiograph used to determine gonial angle, OPGs were used for this study as they are the established norm of assessing angle fractures and were the only available data. The accuracy of OPG in assessing gonial angle has been established by Bhullar et al25 Studies also indicate that OPGs provide more precise measurement of the gonial region because they do not demonstrate overlap of structures (right and left angles) as seen in a lateral cephalograms 25, 26. For this study, accurate measurement of gonial angle was ensured, by calibrating and measuring the OPGs digitally.
ACCEPTED MANUSCRIPT Also, since the gonial angle varies with ethnicity, the gonial angle of the study sample was measured and compared with the established anthropometric standards specific for the Indian population 17. In individuals with high gonial angle or vertical growers, CT 27 and ultrasonographic 28 studies have established presence of masticatory muscles with relatively smaller cross sectional 21
and longer moment arm as compared to normal and low angled individuals
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thickness
(Table-3). As the gonial angle increases from 90 to 150 degrees, the moment arm of load lengthens by 115% and the mechanical advantage of masticatory muscles especially temporalis and masseter reduces by 55%9. Roberta et al performed 3 dimensional anatomic
Similar observations were made by Patricia et al
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dissections using ultrasonography which confirmed the aforesaid radiological findings. also in a study involving children. The
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characteristic muscle morphology in a high angle individual generates relatively lower bite forces or masticatory load which in turn results in reduced cortical bone thickness at the mandibular angle region. Thus the mandibular cortical bone width is thinner in hyperdivergent (high angle) cases than the hypo divergent
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. This feature is also reflected in the
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thickness of the associated alveolar bone . Further, it has been established that the height of the mandible at the ramus and angle region in high angle cases is lesser, as compared to 33, 34, 35
. Similarly, our study revealed comparatively shorter mandibular
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normal individuals
height in high gonial angle cases which may be a contributory factor to the higher incidence of angle fractures. The study also demonstrates that subjects with high gonial angles are 11.77
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times more likely to have an angle fracture than subjects with normal or low gonial angles. Theoretically the displacement of fracture fragments is dependent on the fracture line and the
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extent of muscle pull. In the sample studied, all the fractures were unfavourable and hence displacement was likely to be present. More displacement was expected to be seen in mandibles with low gonial angle due to the higher muscle forces and the inverse for high angle cases. However in this study, the displacement was found to be more in high angle individuals. This may be attributed to the fact that the anatomical height of the mandible at the angle and body regions were found to be significantly less in high angle mandibles making less resistant to displacing forces . Studies indicate that the propensity of the mandible to fracture increases when the mandibular height is less than 19mm which is further confirmed by our results
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. Nevertheless, the degree of displacement of fracture fragments in relation
to the gonial angle was not analysed in this study.
ACCEPTED MANUSCRIPT The results of this study not only indicate a potential risk factor in the pathogenesis of angle fractures but also have noteworthy clinical implications. They highlight the following clinical problems in managing mandibular angle fractures in high angle cases; (1) reduced bone stock at the angle (2) reduced cortical bone thickness & hence compromised screw anchorage and (3) more prevalence of displaced fracture fragments. Considering the findings of the study, the
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following objectives may be considered while planning for osteosynthesis in high angle mandibular fractures (a) achieving better anchorage in the form of extra screws and (b) using rigid fixation to accommodate for the reduced bone stock and increased tendency to be displaced. When using mono-cortical fixation for high angle mandibles, the unit cortical
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anchorage per screw may be significantly lower. Hence to provide the same degree of stability the number of screws used for fixation may need to be increased. Further, the loss of screw anchorage may be minimised by using Locking plates. The greater displacement of fracture
additional plates
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fragments observed in high angle individuals also necessitates rigid fixation in the form of . High angle individuals involved in contact sports may be encouraged to
wear protective gears to prevent fracture of mandibular angle.
The merits of the study include; (i) use of anthropometric standards (gonial angle) which were specific to Indian population, thus increasing the validity of the study (ii) selection of sample
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consisting of uniform age group and (iii) Calibration of OPGs and digital calculation of the gonial angle which reduces the investigator’s error and ensures accuracy in measurements. The presence of impacted third molars in this sample is a variable that cannot be controlled in
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a retrospective study involving trauma. However, this confounding has been adjusted adequately by statistical means. A multi centric study with a larger homogenous sample, a
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“matched case control trial” or an in-vitro Finite Element Model (FEM) study analysing models with different gonial angles may add more knowledge to this correlation. In conclusion, individuals with high gonial angle are at a greater risk of sustaining mandibular angle fractures. The fracture fragments in such individuals also demonstrate greater displacement which may necessitate a modification in fixation methods.
Conflict of Interest: None Ethical Clearance: Not required
ACCEPTED MANUSCRIPT Patient Consent: Not required All authors have viewed the manuscript and agreed to the submission
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Acknowledgements The authors wish to acknowledge the contribution of Prof Krishnaraj Rajaram and Prof & Head, Ravi Kannan of Department of Orthodontics and Dentofacial Orthopaedics towards
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conduct of the study and manuscript preparation.
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4. Takada H, Abe S, Tamatsu Y, Mitarashi S, Saka H, Ide Y: Three
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ACCEPTED MANUSCRIPT 12. Upadhay RB,Upadhyay J, Agrawal P, Rao NN: Analysis of gonial angle in relation to age, gender, and dentition status by radiological and anthropometric methods. J Forensic dent sci 4(1): 29–33, 2012 13. St. John D, Mulliken JB, Kaban LB, PadwaBL: Anthropometric analysis of mandibular asymmetry in infants with deformational posterior plagiocephaly. J Oral
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Radiography Have the Power to Identify the Gonial Angle in Orthodontics? ScientificWorldJournal 1-4, 2014
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18. Rupa KR, Chatra L, Shenai P, Veena KM, Rao PK, Prabhu RV, Kushraj T, Shetty P, Hameed S: Gonial angle and ramus height as sex determinants: A radiographic pilot study. J Cranio Max Dis 4: 111-6, 2015 19. Rubika J, Felicita AS, SivambigaV: Gonial Angle as an Indicator for the Prediction of Growth Pattern. World J Dent 6(3):161 – 163, 2015
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21. Van Spronsen PH, Weijs WA, Valk J, Prahl-Andersen B, VanGinkel FC:A Comparison of Jaw Muscle Cross-sections of Long-face and Normal Adults. J Dent Res 71: 1279 -1285, 1992
22. Tevepaugh DB, Dodson TB: Are mandibular third molars a risk factor for angle fractures? A retrospective cohort study. J Oral MaxillofacSurg 53: 646, 1995
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ACCEPTED MANUSCRIPT 25. Bhullar MK, Uppal AS, Kochhar GK, Chachra S, Kochhar AS: Comparison of gonial angle determination from cephalograms and orthopantomogram. Indian J Dent 5(3): 123–126, 2014 26. Shahabi M, Ramazanzadeh BA, Mokhber N: Comparison between the external gonial angle in panoramic radiographs and lateral cephalograms of adult patients with Class I
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malocclusion. J Oral Sci 51(3): 425-429, 2009 27. Ariji Y, Kawamata A, Yoshida K, Sakuma S, Nawa H, Fujishita H, Ariji E.: Threedimensional morphology of the masseter muscle in patients with mandibular prognathism. Dentomaxillofac Radiol 29: 113 -118, 2000
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28. Kiliaridis S, Kälebo P: Masseter Muscle Thickness Measured by Ultrasonography and its Relation to Facial Morphology. J Dent Res 70(9): 1262-1265, 1991 29. Weijis WA, Hillen B: Relationships between masticatory muscle cross sections and
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skull shape. J Dent Res 63(9): 1154-1157, 1984
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31. Ono A, Motoyoshi M, Shimizu N: Cortical bone thickness in the buccal posterior
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region for orthodontic mini-implants. Int. J. Oral MaxillofacSurg 37:334–340, 2008 32. Sharma NS, Shrivastav SS, Hazarey PV: Relationships among Types of Growth Patterns, Buccolingual Molar Inclination and Cortical Bone Thickness of the Mandible: A CT Scan Study. J IndOrthodSoc 46(2): 59-64, 2012
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33. Horner KA, Behrents RG, Kim KB, Buschang PH: Cortical bone and ridge thickness of hyperdivergent and hypodivergent adults. Am J Orthod Dentofacial Orthop
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ACCEPTED MANUSCRIPT Tables
Table -1 Summary of outcome variables
85.7 76.7 90.2 86.7
14.3 23.3 9.8 13.3
88.6 13.3 11.9 16.9
11.4 86.7 88.1 83.1
88.9 0.590
11.1
12.5 0.0001
87.5
Table 2 – Risk Assessment Angle fracture Present
Angle fracture Absent
Total
36 34 70
7 133 140
43 164 210
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High gonial angle Present Absent Total
Impacted Teeth Presence Absence in % in %
Mean Gonial Angle ( in degrees) 126.8+/-7.9 123.4+/-4.2 121.7+/-7.7 122.2+/-5.2
Mean Mandibular Height at Angle ( in mm) 19.0+/-3.3 21.3+/-1.4 21.6+/-1.9 21.9+/-1.4
122.0+/-3.5 0.0001
22.0+/-1.1 0.0001
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Gender Female in %
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Condyle Body Parasymphysi s Symphysis Significance (p value)
Male %
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Anatomical Site of fracture ANGLE NON-ANGLE
Relative risk -10.3(95 %confidence interval, 1.8 to 2.7), P<0.0001
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Adjusted Odds ratio - 11.77 (95% confidence interval, 3.65 - 37.94), P<0.001
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Table 3- Differences between high and low angle patients FEATURES Gonial angle Facial divergence Growth Pattern Muscle load arm Moment arm Mechanical advantage (Temporalis & masseter) Bite force Mandibular cortical width Mandibular ramus height
HIGH ANGLE Large (increased) Hyperdivergent Vertical Lengthened Longest Decreased
LOW ANGLE Small(decreased) Hypodivergent Horizontal Reduced Shortest Increased
Lesser Higher Decreased
Greater Lower Increased
ACCEPTED MANUSCRIPT Captions to Illustrations Fig 1: Orthopantomogram demonstrating (1) measurement of gonial angle(G) and (2) Mandibular height at angle (MHA) RL- Ramus line ML-Mandibular line
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a-b- Mandibular height at angle
Fig-2: Distribution of mandibular fractures according to anatomic site
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Fig-3: Fracture site-wise distribution of patients with high, normal and low gonial angles Fig-4: Distribution of gonial angles in angle fracture group
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Fig-5: Distribution of height of mandible compared between different gonial angles
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S0278-2391(16)30750-9
DOI:
10.1016/j.joms.2016.08.016
Reference:
YJOMS 57405
To appear in:
Journal of Oral and Maxillofacial Surgery
Received Date: 6 July 2016 Revised Date:
7 August 2016
Accepted Date: 8 August 2016
Please cite this article as: Elavenil P, Pooja J, Sasikala B, Shanmugasundaram S, Krishnakumar Raja V, Dilip S, The influence of mandibular gonial angle on the incidence of mandibular angle fracture – a radiomorphometric study, Journal of Oral and Maxillofacial Surgery (2016), doi: 10.1016/ j.joms.2016.08.016. 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.
ACCEPTED MANUSCRIPT
The influence of mandibular gonial angle on the incidence of mandibular angle fracture – a radiomorphometric study Authors
2. Pooja J ,BDS- Interna 3. Sasikala B, MDS – Readera 4. Shanmugasundaram S, MDS, MBA –Professora 5. Krishnakumar Raja VB, MDS – Professor & Heada
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Institute of affiliation:
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6. Dilip S, MDS –Professorb
Department of Oral & Maxillofacial Surgerya,
Department of Orthodontics & Dentofacial Orthopaedicsb,
Ramapuram Campus,
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Ramapuram, Chennai.
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SRM Dental College & Hospital,
Corresponding Author:
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P. Elavenil, MDS, MBA, FAM
Department of Oral & Maxillofacial Surgery, SRM Dental College & Hospital Ramapuram Campus, Ramapuram, Chennai – 600089 Email: [email protected] Mobile: +91 98412 54653
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1. Elavenil P, MDS, MBA,FAM – Readera
ACCEPTED MANUSCRIPT Abstract Purpose: The aim of this radiomorphometric study was to analyse the association between mandibular gonial angle and risk of mandibular angle fracture. Methods: A retrospective analysis of medical records and radiographs of patients treated for mandibular fractures was done. The exposure studied was presence of high gonial angle
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while the outcome was fracture of the mandibular angle. The mandibular gonial angle (G) and mandibular height at the angle (MHA) were measured using the FACAD software. Data obtained was analysed using statistical software (S.P.S.S. Version 16, IBM Corp).
Results: The study sample comprised of 210 mandibular fractures; 70 mandibular angle
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fractures and 140 non-angle fractures. The Mean gonial angle in patients with mandibular angle fractures was 126.8+/-7.9 degrees, which was 4.5 degrees more than in patients with
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other mandibular fractures (p=0.0001). Patients with high gonial angle were 11.77 times more likely to sustain an angle fracture than subjects with normal or low gonial angles (Adjusted Odds ratio of 11.77, 95% confidence interval, 3.65 - 37.94, P<0.001). There was also a statistically significant reduction in the mandibular height at angle in patients with high gonial angle (P=0.0001).
Conclusion: The study demonstrates that people with high gonial angle are at an increased
Keywords
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risk for angle fracture and presents the related clinical implications.
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displacement
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Gonial angle, mandibular angle fracture, fracture biomechanics, fracture
ACCEPTED MANUSCRIPT INTRODUCTION Fractures of the mandibular angle are common in occurrence 1, 2. The higher incidence has been attributed to the curvature at the angle region 3, 4, presence of impacted third molar 5, 6 and height of mandible at the angle 7. The poor quality of bone at the angle region has also been demonstrated as a cause of fracture 8 .However the impact of the
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mandibular growth pattern-the vertical or horizontal growth, on the incidence of angle fracture has not been studied so far. One of the important anthropometric features which describes the mandibular growth pattern is the mandibular gonial angle 9, 10. It refers to the angle which is formed by the ramus line (RL) and the mandibular line
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(ML), where RL is the tangent to the posterior border of the mandible and ML is the lower border of the mandible through the gnathion 11,12 (Fig-1). The gonial angle may
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be assessed clinically 13 or radiographically 14 by manual 12 & digital methods 15. In an individual, though the right and left gonial angles are the same 11, 16 the normal gonial angle varies according to ethnicity, sex and age 17, 18. Based on the gonial angle, individuals may be classified as high, normal and low angle 19 or vertical, normal and horizontal growers respectively 20. Numerous studies have established a positive correlation between gonial angle and bony architecture at the mandibular angle region . Further, a high gonial angle has been associated with lower bite forces and reduced
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cortical thickness. On the basis of the existing literature, this study was designed to determine any possible correlation between high gonial angle and incidence of
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mandibular angle fracture, in Indian population.
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MATERIALS AND METHODS:Study design and Sample
To analyse the research question, a retrospective cohort study was designed using data of consecutive patients who underwent treatment for mandibular fractures between 2009 and 2015, at our institute. The Institutional Review Board approval was obtained and the study was performed in concordance with the current standards recommended for the reporting of observational studies (STROBE statement). 210 Orthopantomograms (OPG) demonstrating mandibular fractures were selected for the study from patient records. Inclusion and Exclusion Criteria
ACCEPTED MANUSCRIPT The inclusion criteria for selection of sample comprised of pre-operative, digital OPGs of patients with mandibular fractures, between the ages of 20 and 50. The OPGs with poor picture quality & resolution were excluded from the study. Also OPGs demonstrating completely edentulous state or pathological changes like cystic lesions, osteoporosis etc. were omitted. Patients with panfacial trauma were also not considered for the study.
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Variables and data collection
The predictor variable was the presence or absence of high gonial angle while the primary outcome variable was the presence or absence of mandibular angle fracture. A radiographic
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diagnosis of angle fracture was made when the fracture line was located posterior to the second molar, along the curvature connecting the body of mandible and posterior border of
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ramus 22.
The data for descriptive analysis was derived from medical records and included the following; age & sex of the patient, side of fracture, presence or absence of impacted mandibular third molar and displacement of fracture fragments.
The study sample was segregated based on the anatomic distribution of fracture as
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Parasymphysis, Body, Angle and Condyle fractures. For data analysis, the sample was broadly classified into 2 groups; Angle fractures and Non -angle fractures (Parasymphysis, Body, and Condyle). The pre-operative OPGs were digitally calibrated to 1:1 ratio taking into consideration the magnification index provided by the manufacturer. This was further
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confirmed clinically, using the pre-operative dental models of the respective patients. The mesio-distal width of the last standing molar on the fracture side was measured on the dental
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cast and was compared with the dimensions on the OPG to confirm the magnification error. The following parameters were measured using FACAD orthosurgical tracing software
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(Fig-1).
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Gonial angle (G) in degrees: The three point angular measurement of the gonial angle was determined by digitally calculating the angular measurement formed by the points connecting Articulare (Ar), Gonion (Go) and Menton (Mn). The normal range for gonial angle was fixed as 121.8 degrees +/- 6.2, based on norms specific to our study population
17
. Any value above 128
degrees was considered high gonial angle and below 115.6 degrees was marked low gonial angle.
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Measurement of mandibular height at angle (MHA) in millimeters. This was measured from the root apex of the impacted third molar to the inferior border of the mandible 24 (line a-b).
Data analysis Data obtained from the study was analysed using statistical software (S.P.S.S. Version 16,
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IBM Corp). Qualitative variables in the study were compared using Pearson’s Chi Square Test and quantitative variables with one way ANOVA test. Statistical significance was set at P value of <0.05 for the study. Risk assessment modelling was used to assess relationships between high gonial angle and risk of angle fracture (relative risk and odds ratio). The
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confounding effect of presence of an impacted third molar on angle fracture was adjusted using a logistic regression model. A P value of <0.05 was considered statistically significant.
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RESULTS:-
The study sample included 210 OPGs with mandibular fractures involving 85% males and 25% females. The mean age of patients with mandibular fractures was 29.31+/-7.62. The distribution of fractures based on the anatomic site was Angle fractures (70) and Non angle fractures (140) (Fig-2). The presence of impacted third molars was a significant 88.6% within
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the angle fracture group and 39% in the non-angle fracture group (P = 0.0001). The fracture wise distribution of gonial angle is shown in Fig-3; The Mean gonial angle of patients in the angle fracture group was 126.8+/-7.9 degrees which was 4.5 degrees more than
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the non- angle group (Mean = 122.3+/-4.9 degrees, P = 0.0001) (Table1) Within the angle fracture group, 51% of the patients had high gonial angles (Fig-4) (P=0.795)
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with a mean of 133+/-3.4 degrees, 33% had normal gonial angles (Mean 123.3+/-2.3) and 16% had low gonial angles (Mean 113.6+/-3.6). Relationship between gonial angle and fracture of mandibular angle: The analysis of data from table 2 indicates that there is a significant association between high gonial angle and incidence of angle fracture. Subjects with
high gonial angles had an
unadjusted 10.3 fold increase in risk for angle fracture over subjects with normal or low gonial angles (Relative risk - 10.3; 95 % confidence interval, 1.8 to 2.7, P<0.0001). Subjects with high gonial angles were also statistically associated with an 11.77 times increased chance for angle fracture (Adjusted Odds ratio of 11.77, 95% confidence interval, 3.65 - 37.94, P<0.001)
ACCEPTED MANUSCRIPT when compared with subjects without high gonial angles. The odds ratio was adjusted for the confounding variable of presence of impacted teeth by using a logistic regression model. The data also demonstrated that there was a reduction in mean mandibular height at the angle with increase in gonial angle (P = 0.029); measuring 20.3+/-3.9mm for low, 19.9+/-3.6mm for normal and 18+/-2.5mm for high gonial angles (Fig-5). With regards to fracture
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displacement, 58.3% of the high gonial angle patients, 25% of the normal and 16.7% of the low gonial angle patients showed displacement of the fracture fragments. However this
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observation was statistically not significant (P = 0.112).
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DISCUSSION:-
The preponderance of mandibular angle fractures has been greatly attributed to the anatomic weakness of the angle region due to its curvature and change in the osseous grain pattern. Several studies have demonstrated that factors like impacted third molars, reduced mandibular height and poor bone quality weaken the mandibular angle further and lead to many fold increase in the risk of fracture. However no study has been reported so far, describing the
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impact of gonial angle on the structural integrity of the angle region and its influence on the bio-dynamics of angle fracture.
This retrospective study demonstrates a greater incidence of angle fractures in patients with
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high gonial angle thus emphasising its importance in the pathogenesis of angle fracture. The rationale behind this finding could be attributed to the characteristic variations in muscle
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physiology and bony architecture associated with changes in gonial angle. Gonial angle is an important anthropometric feature which contributes to facial esthetics and bio-dynamics of masticatory musculature. In practice, Gonial angle is assessed by radiographic analysis. Though lateral cephalogram is the preferred radiograph used to determine gonial angle, OPGs were used for this study as they are the established norm of assessing angle fractures and were the only available data. The accuracy of OPG in assessing gonial angle has been established by Bhullar et al25 Studies also indicate that OPGs provide more precise measurement of the gonial region because they do not demonstrate overlap of structures (right and left angles) as seen in a lateral cephalograms 25, 26. For this study, accurate measurement of gonial angle was ensured, by calibrating and measuring the OPGs digitally.
ACCEPTED MANUSCRIPT Also, since the gonial angle varies with ethnicity, the gonial angle of the study sample was measured and compared with the established anthropometric standards specific for the Indian population 17. In individuals with high gonial angle or vertical growers, CT 27 and ultrasonographic 28 studies have established presence of masticatory muscles with relatively smaller cross sectional 21
and longer moment arm as compared to normal and low angled individuals
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thickness
(Table-3). As the gonial angle increases from 90 to 150 degrees, the moment arm of load lengthens by 115% and the mechanical advantage of masticatory muscles especially temporalis and masseter reduces by 55%9. Roberta et al performed 3 dimensional anatomic
Similar observations were made by Patricia et al
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dissections using ultrasonography which confirmed the aforesaid radiological findings. also in a study involving children. The
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characteristic muscle morphology in a high angle individual generates relatively lower bite forces or masticatory load which in turn results in reduced cortical bone thickness at the mandibular angle region. Thus the mandibular cortical bone width is thinner in hyperdivergent (high angle) cases than the hypo divergent
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. This feature is also reflected in the
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thickness of the associated alveolar bone . Further, it has been established that the height of the mandible at the ramus and angle region in high angle cases is lesser, as compared to 33, 34, 35
. Similarly, our study revealed comparatively shorter mandibular
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normal individuals
height in high gonial angle cases which may be a contributory factor to the higher incidence of angle fractures. The study also demonstrates that subjects with high gonial angles are 11.77
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times more likely to have an angle fracture than subjects with normal or low gonial angles. Theoretically the displacement of fracture fragments is dependent on the fracture line and the
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extent of muscle pull. In the sample studied, all the fractures were unfavourable and hence displacement was likely to be present. More displacement was expected to be seen in mandibles with low gonial angle due to the higher muscle forces and the inverse for high angle cases. However in this study, the displacement was found to be more in high angle individuals. This may be attributed to the fact that the anatomical height of the mandible at the angle and body regions were found to be significantly less in high angle mandibles making less resistant to displacing forces . Studies indicate that the propensity of the mandible to fracture increases when the mandibular height is less than 19mm which is further confirmed by our results
7,36
. Nevertheless, the degree of displacement of fracture fragments in relation
to the gonial angle was not analysed in this study.
ACCEPTED MANUSCRIPT The results of this study not only indicate a potential risk factor in the pathogenesis of angle fractures but also have noteworthy clinical implications. They highlight the following clinical problems in managing mandibular angle fractures in high angle cases; (1) reduced bone stock at the angle (2) reduced cortical bone thickness & hence compromised screw anchorage and (3) more prevalence of displaced fracture fragments. Considering the findings of the study, the
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following objectives may be considered while planning for osteosynthesis in high angle mandibular fractures (a) achieving better anchorage in the form of extra screws and (b) using rigid fixation to accommodate for the reduced bone stock and increased tendency to be displaced. When using mono-cortical fixation for high angle mandibles, the unit cortical
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anchorage per screw may be significantly lower. Hence to provide the same degree of stability the number of screws used for fixation may need to be increased. Further, the loss of screw anchorage may be minimised by using Locking plates. The greater displacement of fracture
additional plates
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fragments observed in high angle individuals also necessitates rigid fixation in the form of . High angle individuals involved in contact sports may be encouraged to
wear protective gears to prevent fracture of mandibular angle.
The merits of the study include; (i) use of anthropometric standards (gonial angle) which were specific to Indian population, thus increasing the validity of the study (ii) selection of sample
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consisting of uniform age group and (iii) Calibration of OPGs and digital calculation of the gonial angle which reduces the investigator’s error and ensures accuracy in measurements. The presence of impacted third molars in this sample is a variable that cannot be controlled in
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a retrospective study involving trauma. However, this confounding has been adjusted adequately by statistical means. A multi centric study with a larger homogenous sample, a
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“matched case control trial” or an in-vitro Finite Element Model (FEM) study analysing models with different gonial angles may add more knowledge to this correlation. In conclusion, individuals with high gonial angle are at a greater risk of sustaining mandibular angle fractures. The fracture fragments in such individuals also demonstrate greater displacement which may necessitate a modification in fixation methods.
Conflict of Interest: None Ethical Clearance: Not required
ACCEPTED MANUSCRIPT Patient Consent: Not required All authors have viewed the manuscript and agreed to the submission
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Acknowledgements The authors wish to acknowledge the contribution of Prof Krishnaraj Rajaram and Prof & Head, Ravi Kannan of Department of Orthodontics and Dentofacial Orthopaedics towards
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conduct of the study and manuscript preparation.
ACCEPTED MANUSCRIPT References 1. Lee JT, Dodson TB: The effect of mandibular third molar presence and position on the risk of an angle fracture. Int J OralMaxillofac Surg 58(4): 394 – 98, 2000 2. Perez R, Oeltjen JC, Thaller SR: A Review of Mandibular Angle Fractures. Craniomaxillofac Trauma Reconstr 4(2): 69–72, 2011
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3. Yadav S, Tyagi S, Puri N, Kumar P, Kumar P: Qualitative and quantitative
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4. Takada H, Abe S, Tamatsu Y, Mitarashi S, Saka H, Ide Y: Three
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5. Meisami T, Sojat A, Sàndor GKB, Lawrence HP, Clokie CML: Impacted third molars and risk of angle fracture. Int J OralMaxillofac Surg 31(2):140–144, 2002 6. Fuselier JC, Ellis EE, Dodson TB: Do mandibular third molars alter the risk of angle fracture? J Oral MaxillofacSurg 60(5):514-8, 2002
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7. Subbaiah MT, Ponnuswamy IA, David MP: Relationship between mandibular angle fracture and state of eruption of mandibular third molar: A digital radiographic study. J Indian Acad Oral Med Radiol 27:35-41, 2015 8. Precious DS: Trauma and Reconstruction, an Issue of Oral and Maxillofacial Surgery
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Clinics. Edition: 6. Canada: 21 – 22, 2013 9. Throckmorton G, Finn RA, Bell WH: Biomechanics of differences in lower facial
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Height. Am J Orthod 6(80): 90106-2, 1980
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ACCEPTED MANUSCRIPT 12. Upadhay RB,Upadhyay J, Agrawal P, Rao NN: Analysis of gonial angle in relation to age, gender, and dentition status by radiological and anthropometric methods. J Forensic dent sci 4(1): 29–33, 2012 13. St. John D, Mulliken JB, Kaban LB, PadwaBL: Anthropometric analysis of mandibular asymmetry in infants with deformational posterior plagiocephaly. J Oral
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Radiography Have the Power to Identify the Gonial Angle in Orthodontics? ScientificWorldJournal 1-4, 2014
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18. Rupa KR, Chatra L, Shenai P, Veena KM, Rao PK, Prabhu RV, Kushraj T, Shetty P, Hameed S: Gonial angle and ramus height as sex determinants: A radiographic pilot study. J Cranio Max Dis 4: 111-6, 2015 19. Rubika J, Felicita AS, SivambigaV: Gonial Angle as an Indicator for the Prediction of Growth Pattern. World J Dent 6(3):161 – 163, 2015
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21. Van Spronsen PH, Weijs WA, Valk J, Prahl-Andersen B, VanGinkel FC:A Comparison of Jaw Muscle Cross-sections of Long-face and Normal Adults. J Dent Res 71: 1279 -1285, 1992
22. Tevepaugh DB, Dodson TB: Are mandibular third molars a risk factor for angle fractures? A retrospective cohort study. J Oral MaxillofacSurg 53: 646, 1995
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ACCEPTED MANUSCRIPT 25. Bhullar MK, Uppal AS, Kochhar GK, Chachra S, Kochhar AS: Comparison of gonial angle determination from cephalograms and orthopantomogram. Indian J Dent 5(3): 123–126, 2014 26. Shahabi M, Ramazanzadeh BA, Mokhber N: Comparison between the external gonial angle in panoramic radiographs and lateral cephalograms of adult patients with Class I
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malocclusion. J Oral Sci 51(3): 425-429, 2009 27. Ariji Y, Kawamata A, Yoshida K, Sakuma S, Nawa H, Fujishita H, Ariji E.: Threedimensional morphology of the masseter muscle in patients with mandibular prognathism. Dentomaxillofac Radiol 29: 113 -118, 2000
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28. Kiliaridis S, Kälebo P: Masseter Muscle Thickness Measured by Ultrasonography and its Relation to Facial Morphology. J Dent Res 70(9): 1262-1265, 1991 29. Weijis WA, Hillen B: Relationships between masticatory muscle cross sections and
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31. Ono A, Motoyoshi M, Shimizu N: Cortical bone thickness in the buccal posterior
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region for orthodontic mini-implants. Int. J. Oral MaxillofacSurg 37:334–340, 2008 32. Sharma NS, Shrivastav SS, Hazarey PV: Relationships among Types of Growth Patterns, Buccolingual Molar Inclination and Cortical Bone Thickness of the Mandible: A CT Scan Study. J IndOrthodSoc 46(2): 59-64, 2012
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33. Horner KA, Behrents RG, Kim KB, Buschang PH: Cortical bone and ridge thickness of hyperdivergent and hypodivergent adults. Am J Orthod Dentofacial Orthop
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35. Al-Jabrah O: Association of type 2 diabetes mellitus with the reduction of mandibular residual ridge among edentulous patients using panoramic radiographs. Csaz Stomatol 1: 61-68, 2011 36. Bailey BJ, Johnson JT, Shawn D: Head & Neck Surgery—otolaryngology. Volume: 1. Newlands; 2006: 969 – 971. 37. Cillo JE, Ellis E III. Management of bilateral mandibular angle fractures with combined rigid and non-rigid fixation. J Oral MaxillofacSurg 72(1):106-111, 2014
ACCEPTED MANUSCRIPT Tables
Table -1 Summary of outcome variables
85.7 76.7 90.2 86.7
14.3 23.3 9.8 13.3
88.6 13.3 11.9 16.9
11.4 86.7 88.1 83.1
88.9 0.590
11.1
12.5 0.0001
87.5
Table 2 – Risk Assessment Angle fracture Present
Angle fracture Absent
Total
36 34 70
7 133 140
43 164 210
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High gonial angle Present Absent Total
Impacted Teeth Presence Absence in % in %
Mean Gonial Angle ( in degrees) 126.8+/-7.9 123.4+/-4.2 121.7+/-7.7 122.2+/-5.2
Mean Mandibular Height at Angle ( in mm) 19.0+/-3.3 21.3+/-1.4 21.6+/-1.9 21.9+/-1.4
122.0+/-3.5 0.0001
22.0+/-1.1 0.0001
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Gender Female in %
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Condyle Body Parasymphysi s Symphysis Significance (p value)
Male %
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Anatomical Site of fracture ANGLE NON-ANGLE
Relative risk -10.3(95 %confidence interval, 1.8 to 2.7), P<0.0001
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Adjusted Odds ratio - 11.77 (95% confidence interval, 3.65 - 37.94), P<0.001
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Table 3- Differences between high and low angle patients FEATURES Gonial angle Facial divergence Growth Pattern Muscle load arm Moment arm Mechanical advantage (Temporalis & masseter) Bite force Mandibular cortical width Mandibular ramus height
HIGH ANGLE Large (increased) Hyperdivergent Vertical Lengthened Longest Decreased
LOW ANGLE Small(decreased) Hypodivergent Horizontal Reduced Shortest Increased
Lesser Higher Decreased
Greater Lower Increased
ACCEPTED MANUSCRIPT Captions to Illustrations Fig 1: Orthopantomogram demonstrating (1) measurement of gonial angle(G) and (2) Mandibular height at angle (MHA) RL- Ramus line ML-Mandibular line
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a-b- Mandibular height at angle
Fig-2: Distribution of mandibular fractures according to anatomic site
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Fig-3: Fracture site-wise distribution of patients with high, normal and low gonial angles Fig-4: Distribution of gonial angles in angle fracture group
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Fig-5: Distribution of height of mandible compared between different gonial angles
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