- Email: [email protected]
A digital method of measuring the gonial angle on radiographs for forensic age estimation
Author’s Accepted Manuscript A Digital Method of Measuring the Gonial Angle on Radiographs for Forensic Age Estimation Ashith B. Acharya
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PII: DOI: Reference:
S2212-4780(17)30002-3 http://dx.doi.org/10.1016/j.jofri.2017.09.002 JOFRI265
To appear in: Journal of Forensic Radiology and Imaging Received date: 23 January 2017 Revised date: 8 September 2017 Accepted date: 18 September 2017 Cite this article as: Ashith B. Acharya, A Digital Method of Measuring the Gonial Angle on Radiographs for Forensic Age Estimation, Journal of Forensic Radiology and Imaging, http://dx.doi.org/10.1016/j.jofri.2017.09.002 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 galley proof before it is published in its final citable 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.
A Digital Method of Measuring the Gonial Angle on Radiographs for Forensic Age Estimation
Ashith B. Acharya, BDS, GDFO Department of Forensic Odontology, S.D.M. College of Dental Sciences and Hospital, Sattur, Dharwad – 580009, Karnataka, India.
Corresponding author: Dr. Ashith B. Acharya Associate Professor and Head Department of Forensic Odontology S.D.M. College of Dental Sciences and Hospital Sattur, Dharwad – 580009 Karnataka, India Tel: +91-836-2468142 (Ext. 115) Fax: +91-836-2467612 E-mail: [email protected]
Sources of support: None
Conflicts of interest: None
Abstract Objective: Age estimation has important legal ramifications and assessing it, particularly in living adults, can prove challenging on occassion. This paper explores the use of gonial angle 1
in age estimation, applying a new digital method which may be suitable in elderly subjects when many/all teeth are missing. Materials and Methods: A commercially available and ubiquitous software was used to measure the gonial angle on digital orthopantomograms from 100 subjects (48 males and 52 females; age range 18−89 years) which was subjected to linear regression analysis. Results: The correlation coefficient for the gonial angle on the right side (r = 0.25) was greater than that for the left side (r = 0.23). Both correlations were statistically significant (p < 0.05). The regression equations derived were tested on a holdout sample (n = 17; age range 21−71 years) and revealed a mean absolute difference of approximately ±14 years for the two regression equations. Conclusion: Although the gonial angle may not consistently change with an increase in chronologic age, the digital method proposed here may be one of few options available for use in the elderly with minimal or no teeth seeking retirement benefits, and may be applied as a method of last resort in geriatric age prediction.
Keywords:
Age
assessment;
Mandibular
angle;
Radiographic
measurement;
Orthopantomogram; Adobe® Photoshop®
Introduction The law is known to necessitate age estimation in postmortem reconstructive identification as well as in living subjects with no valid birth records, and several parts of the body such as the metacarpals, long bones, clavicle, jaws and the teeth may be used towards this end. This is based on the ~15 years forensic odontology experience this author has had in Nepal and India combined, rendering opinion on the age of living and dead human subjects— both children and adults—in over 125 cases. However, in 2013, two edentate subjects were referred for age assessment for determining if they had reached the threshold of 60 years and were eligible to claim retirement benefits, resulting in an unusual situation wherein forensic 2
‘dental’ age estimation was required but the teeth were missing. A search for alternative parameters of age estimation in these cases led to an exploration of the use of the mandibular gonial angle, which may be conveniently assessed on radiographs by trained dentists. This may also be applied in postmortem age estimation since there can be cases wherein only the mandible is recovered (Fig. 1). The gonial angle is considered to be obtuse at birth and, as teeth are added and growth takes place during childhood, it becomes more acute.1 According to Jensen and Palling,2 with old age the angle increases to between 120 and 150, becoming more similar to the ‘infantile angle’ of 135 to 150. The principal motivation for this study was a lack of gonial angle age estimation standards for Indians and an objective to develop regression formulae for the purpose. Although a recent study has examined the gonial angle in the people of this country, no regression equation per se was published in that paper.3 Traditionally, the angle on dry mandible specimens has been measured using a mandibulometer, as illustrated in Oettlé et al.1 (Fig. 2). However, several studies exist wherein the angle has been measured on radiographs.3,4 Considering the present author’s experience of forensic age estimation referrals of edentate living subjects undertaken on radiographs, a conscious decision was made to evaluate the angle on orthopantomograms (OPTs). The aim was to determine the correlation of the derived measurements on the OPTs and chronologic age, and apply the obtained regression equations on a holdout sample to determine their accuracy/error rate in age estimation. Towards this end, a digital method was developed using a widely used and commercially available software program.
Materials and Methods Material 3
The material comprised of 100 digital OPTs from as many subjects (48 males and 52 females) whose ages ranged from 18 to 89 years (average = 42.3 years) (Table 1). All digital OPTs were obtained from records available in S.D.M. College of Dental Science’s Department of Oral Medicine & Radiology, and were previously taken on patients who were referred to the department for diverse oral diagnostic reasons. The digital OPTs were acquired using a Kodak 9000 3D Extraoral Imaging System (Kodak Dental Systems, PracticeWorks Inc., Atlanta, USA).
Measurement of Gonial Angle The right and left gonial angle on digital OPT is measured as follows: 1. The digital OPT is opened in Adobe Photoshop 7.0.1 software programme (Adobe Systems Inc., Mountain View, CA) and the ‘Measure Tool’ (hidden below the ‘Eyedropper Tool’ in the Photoshop Toolbox) selected (boxed) (Fig. 3). Note that the ‘Measure Tool’ is renamed as ‘Ruler Tool’ in newer versions of Photoshop. 2. Clicking ‘Arbitrary’ reveals the Rotate Canvas dialog (Fig. 4, boxed), which shows the amount of rotation (in degrees) required to orient the lower border of the mandible horizontally; the dialog also specifies whether the rotation must be done clock-wise (CW) or counter clock-wise (CCW). In Fig. 4, rotating the radiograph by 29.5 achieves this. Click ‘OK’ (Fig. 4, boxed) to obtain this degree of rotation. 3. Once the digital OPT is rotated, press ‘Ctrl’ and ‘R’ (‘Command’ and ‘R’ for Macintosh systems) together to activate Photoshop’s in-built ‘rulers’ (the white borders with ruler markings on the upper and left sides of the digital OPT image window in Fig. 5). Using the mouse/touchpad, click the cursor within the ‘rulers’ on the upper border of the image and drag onto the image. A horizontal line, referred to as a ‘guide’, is created (line in Fig. 5; the line color may differ depending on the settings of the Photoshop software). This 4
line/guide must be positioned on the horizontally orientated lower border of the body of the mandible. One can move the guide to the desired location using the ‘Move Tool’ on Photoshop’s toolbox (Fig. 5, encircled) or by holding down the ‘Ctrl’ key (‘Command’ key for Macintosh systems) and positioning the cursor on the guide and then and dragging it. 4. Next, the ‘Measure Tool’ is used to draw a line along the posterior border of ramus (this line must touch the posterior border at the level of the condyle and above the mandibular angle—see Fig. 6). The ‘Measure Tool’ must be used to draw the line from top-to-bottom for the subject’s left ramus and bottom-to-top for the subject’s right ramus (this is to avoid an angle that is exceedingly acute). Note the angle ‘A’ on the Options Bar (Fig. 6, encircled). If the angle depicted has a negative sign (−130, as seen in Fig. 6), the sign should be disregarded (i.e., the absolute value only, viz., 130 is considered).
Statistical Analysis To ascertain the strength of correlation of the gonial angles to chronologic age, as well as develop age estimation formulas, the data was subjected to linear regression analysis with the right and left angles taken as independent variables and actual age as dependent variable. The gonial angle for the right and left sides were also subjected to a paired t-test to determine potential statistical differences between the two sides. Since some believe that the gonial angle decreases from childhood to adulthood, followed by an increase with progression towards old age,1,2 quadratic and cubic regression analyses—both of which are curve estimations—were undertaken to determine if they produced stronger correlations (higher R values) than the linear regression analysis. The regression formulas developed were applied on a holdout/test sample (n = 17) to ascertain their potential accuracy and error rates in real-life scenarios. The holdout sample 5
comprised of subjects whose age ranged from 21 to 71 years (average = 41.8 years) and included 10 females and seven males. The difference between the estimated and actual age (the ‘error’) was determined for each subject in the holdout sample, and the mean absolute difference (MAD) calculated. The absolute difference is the difference between the estimated and actual age devoid of a positive or negative sign (the ‘unsigned’ value). For example, the actual age of test subject no. 10 was 46 years and the estimated age was 41.27 years using the right gonial angle; the error here is −4.73 years but the negative sign is discarded and only its absolute value (viz., 4.73) is considered in the calculation. The MAD, therefore, is the average magnitude of difference in a set of estimates and has previously been used as a measure of accuracy of age estimation methods.5,6 Although the more commonly used standard error of the estimate (SEE) produced from regression analyses gives an indication of the expected error rate, there is an inherent bias since it is based on the training dataset (n = 100, in this study)7 and does not necessarily reflect the error in an independent test sample or forensic casework. Hence, the MAD was used since it may represent the error more objectively; the SEE was also calculated separately for the test dataset to compare it with the MAD. To assess potential intra- and inter-observer variation, the gonial angle (right and left sides) was re-measured on 15 randomly selected digital OPTs. The measurements were made six months after the primary measurements were completed (for intra-observer variation). Potential differences between the two sets of recordings by the principal examiner and between the principal examiner and second examiner were assessed using the paired t-test. Lastly, an independent samples t-test was performed to assess potential statistically significant sex differences in the gonial angle (right and left sides were assessed separately). While the regression analyses and paired t-tests were performed on an SPSS 17.0 statistical software program (SPSS Inc., Chicago, IL; now IBM Corp., Armonk, NY), the 6
MAD was derived on an MS Office Excel spreadsheet (Office 2011, Microsoft Corp., Redmond, WA). This study was approved by the Institutional Ethical Committee (certificate IRB No. 2015/S/FO/01, dated 6 November 2015).
Results The paired t-test for determining potential intra-observer differences showed statistically insignificant differences between the primary measurements and the repetitions by the same examiner (p > 0.05) for both the right and left gonial angles (t-values of −1.5 and 0.06, respectively) as well as measurements made by the second examiner (p > 0.05; t-values of 1.22 and 1.51 for right and left sides, respectively). The mean of the gonial angle was 120.6 for the right side and 120.9 for the left side. The paired t-test for determining possible statistical differences between the left and right sides revealed none (t-value = −0.49; p > 0.05). The independent samples t-test to assess potential sex differences in the right and left gonial angle also showed statistically insignificant differences (p > 0.05; t-value = 1.21 and 1.68 for right and left sides, respectively). The linear, quadratic and cubic regression analyses revealed little or no difference between each other in terms of correlation and, hence, the latter two are not commented on further. The correlation coefficient for the gonial angle on the right side (r = 0.245) was greater than that for the left side (r = 0.226). Both correlations were statistically significant (p < 0.05). The linear regression equations derived and their SEEs are depicted in Table 2. The application of these equations on the holdout sample (n = 17) revealed an MAD that approximated ±14 years (Table 2). Discussion
7
The results of the present study show that there is a low albeit statistically significant correlation (p < 0.05) between age and the gonial angle which marginally decreases as the former increases (Fig. 7). The results also show that the angle on the right side was slightly more strongly correlated to age than on the left side. However, this did not translate to any practical improvements in terms of (lower) error rates in age estimation (Table 2), with all MADs hovering around ±14 years (the SEEs were approximately ±15.8 years). In fact, the right–left measurement differences per se were statistically insignificant, similar to that observed in Larheim and Svanaes9 and Al-Shamout et al.10 As in the present study, Upadhyay et al.3 too observed a “definite decrease” in the gonial angle with an increase in age; however, the decrease was statistically insignificant in their study. On the other hand, Al-Shamout et al.10 found that the gonial angle increases with age while others have reported a lack of recognizable change in the gonial angle with age.1,11−14 It therefore appears that the age-related changes which occur in the gonial angle may not be regular. It is believed that masticatory muscles change with age, decrease in their contractile activity, with a reduction in muscle density and masseter and medial pterygoid muscles undergo greater age-related decreases because of their insertion into the region of the gonial angle;15 according to Merrot et al.,16 increase in the mandibular angle in the elderly edentate may be explained by imbalance between the elevator and depressor muscles of the mandible, “as a function of the elevator muscles or by the absence of the molar buttress”. Therefore, while gonial angle change with age may partly be physiologic, it is also influenced by tooth loss and, therefore, the correlation between it and age may be low to moderate, as evidenced in the results of this paper. At the same time, no sex differences appear to exist in the gonial angle, as seen by the statistically insignificant malefemale difference (p > 0.05). With respect to the approach used herein, the author believes that the angle measured in the present study is similar to that obtained for dry mandible specimens using a 8
mandibulometer, as illustrated in Oettlé et al.1 (Fig. 2). The planes drawn and delineated using the rotation options and guides in Photoshop were such that the ‘horizontal’ plane in the digital OPTs—which contacted the inferior border of the mandible—was the standard horizontal plane used in traditional methods, while the planes drawn along the posterior border of the mandibular ramus corresponds to the ‘rameal’ or the movable wing of the mandibulometer, which comes in contact with the posterior surface of the ramus at the condyle and inferiorly above the angle.1 Also, the ‘tangent’ drawn along the inferior border lies close to its posterior region since, in the traditional method, the vertical pressure is applied on the “left second molar tooth or its cavity”1 (p. 506) and that portion is likely to contact the horizontal plane of the mandibulometer. These constitute the “standard” horizontal and rameal planes and the angle formed between these is recorded as the gonial angle.1 The measurement of the gonial angle using two ‘tangents’—one drawn on the inferior border of the mandible, and another along the posterior border of the condyle and ramus— has also been used in a previous study of orthopantomographic gonial angle measurement.4 A conscious decision was taken to undertake the study on OPTs and not lateral cephalograms because of the interference of the superimposed images appearing on the latter, potentially undermining reliable measurements of the gonial angle.4 This disadvantage is not encountered in OPTs. It is also believed that the gonial angle can be determined more easily on an OPT than in a lateral cephalogram.4 No statistical difference was found in the gonial angle measurements taken on the two types of radiographs,4 which was also the case with Matilla et al.17 and Altonen et al.18 Moreover, an important advantage of using OPTs is that they are often taken as part of routine examination of patients to serve as a tool for oral diagnostic purposes. In fact, Larheim and Svanaes9 report that the gonial angle measured on an OPT is nearidentical to that assessed on a dried mandible, implying that this may be applied both in the 9
living and postmortem skeletal contexts. But, as stated earlier in this paper, a primary objective of this study was to apply the results on living subjects, especially individuals with few or no teeth and who may require age estimation for claiming retirement benefits (mostly ≥60 years in the Indian context). This may be done using the software and method discussed above. To obtain gonial angle readings, other software programs may also be used (e.g., KODAK Dental Imaging Software, KODAK Dental Systems, PracticeWorks Inc., Atlanta, USA), however, the intention of using Photoshop in this study was to develop a method that can be used on a relatively ubiquitous image editing program, and regardless of access to specific dental radiographic software. Of course, the negative effect of ionizing radiation on living persons is well documented and no radiographs should be taken beyond the examination range recommend in scientific recommendations.19 X-ray examination of the dentition (including the OPTs used in this study) may be considered as falling within this “examination range.” Nevertheless, the author recognizes that when ionizing radiation is applied, local regulations must be observed; from a scientific viewpoint, the ‘minimization principle’—which requires to perform each examination with as much radiation dose saving approach as possible and to dispense any exposure that is not mandatory—is to be followed.19 It is also noteworthy that children and adolescents are believed to be considerably more sensitive than adults to carcinogenic risks of ionizing radiation.20 Ramsthaler et al.20 cites several studies that suggest that the long-term risk of cancer in terms of mortality as a result of ionizing radiation was approximately 12–15% per Sievert of radiation exposure for young children, as against 5–9% or less for adults such as those included in this study. Therefore, the risk of radiography posed to adults (such as those used in this study) is about half that encountered in children. In fact, Ramsthaler et al.20 deduce that, theoretically, the health risks that could ensue due to radiation emitted from an OPT exposure are “100 times smaller than 10
other everyday risks, such as the use of a car or public transportation.”20 In general, it is considered acceptable to use radiographs—including OPTs—for age estimation so long as one ensures optimization of the procedures used and minimizing the risks.20
Conclusions A digital method is proposed for measuring the gonial angle for age estimation, which has particular use in living geriatric subjects. The findings reveal a statistically significant but low correlation to age, with relatively large error rates in age estimation. The author recognizes that the changes in the gonial angle may not be consistent with chronologic age. Therefore, the gonial angle needs to be used guardedly as a parameter of estimating age, and perhaps as a method of last resort in the absence of teeth or when other more robust and reliable techniques are unavailable for use.
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Acknowledgments The author wishes to thank Prof. C. Bhasker Rao, former Principal, and Prof. Srinath L. Thakur, Principal, and the Management of S.D.M. College of Dental Sciences and Hospital, for their support to research in forensic odontology. The author also wishes to acknowledge the assistance of Dr. Kruthika Guttal in radiograph collection and clarifications on the radiographic appearance of the mandible on OPTs, and measurement of angle using Kodak Dental Imaging software.
References 1. Oettlé AC, Becker PJ, de Villiers E, et al. The influence of age, sex, population group, and dentition on the mandibular angle as measured on a South African sample. Am J Phys Anthropol. 2009;139(4):505–511. 2. Jensen E, Palling M. The gonial angle. Am J Orthod. 1954;40:120–133. 3. Upadhyay RB, Upadhyay J, Agrawal P, et al. Analysis of gonial angle in relation to age, gender, and dentition status by radiological and anthropometric methods. J Forensic Dent Sci. 2012;4(1):29–33. 4. Shahabi M, Ramazanzadeh B-A, Mokhber N. Comparison between the external gonial angle I panoramic radiographs and lateral cephalograms of adult patients with Class I malocclusion. J Oral Sci. 2009;51(3):425–429. 5. Spalding KL, Buchholz BA, Bergman LE, et al. Age written in teeth by nuclear tests. Nature 2005;437:333–334. 6. Acharya AB, Vimi S. Effectiveness of Bang and Ramm’s formulae in age assessment of Indians from dentin translucency length. Int J Legal Med. 2009;123:483–488.
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7. Giles E, Klepinger LL. Confidence intervals for estimates based on linear regression in forensic anthropology. J Forensic Sci. 1988;33:1218–1222. 8. Solheim T, Sundnes PK. Dental age estimation of Norwegian adults – a comparison of different methods. Forensic Sci Int. 1980;16(1):7–17. 9. Larheim TA, Svanaes DB. Reproducibility of rotational panoramic radiography: Mandibular linear dimensions and angles. Am J Orthod Dentofac Orthop. 1986;90:45–51. 10. Al-Shamout R, Ammoush M, Alrbata R, et al. Age and gender differences in gonial angle, ramus height and bigonial width in dentate subjects. Pakistan Oral Dent J. 2012;32(1):81–87. 11. Keen JA. A study of the angle of the mandible. J Dent Res. 1945;24:77–86. 12. Israel H. The failure of aging or loss of teeth to drastically alter mandibular angle morphology. J Dent Res. 1973;52:83–90. 13. Raustia AM, Salonen MA. Gonial angles and condylar and ramus height of the mandible in complete denture wearers—a panoramic radiograph study. J Oral Rehabil. 1997;24(7):512–516. 14. Ceylan G, Yaníkoglu N, Yílmaz AB, Ceylan Y. Changes in the mandibular angle in the dentulous and edentulous states. J Prosthet Dent. 1998;80(6):680–684. 15. Hannam AG, Wood WW. Relationships between the size and spatial morphology of human masseter and medial pterygoid muscles, the craniofacial skeleton, and jaw biomechanics. Am J Phys Anthropol. 1989;80:429–45. 16. Merrot O, Vacher C, Merrot S, Godlewski G, Frigard B, Goudot P. Changes in the edentate mandible in the elderly. Surg Radiol Anat. 2005;27(4):265–70. 17. Mattila K, Altonen M, Haavikko K. Determination of the gonial angle from the orthopantomogram. Angle Orthod. 1977;47(2):107–110. 18. Altonen M, Haavikko K, Mattila K. Developmental position of lower third molar in 13
relation to gonial angle and lower second molar. Angle Orthod. 1977;47(4):249–255. 19. Schmeling A, Grundmann C, Fuhrmann A, Kaatsch HJ, Knell B, Ramsthaler F, Reisinger W, Riepert T, Ritz-Timme S, Rösing FW, Rötzscher K, Geserick G. Criteria for age estimation in living individuals. Int J Legal Med. 2008;122(6):457–60. 20. Ramsthaler F, Proschek P, Betz W, Verhoff MA. How reliable are the risk estimates for X-ray examinations in forensic age estimations? A safety update. Int J Legal Med. 2009;123(3):199–204.
Legends for Figures Figure 1 The recovery of a single, isolated, mandible is not uncommon in forensic, anthropological and archaeological cases.
Figure 2 A dry mandible specimen placed on a ‘mandibulometer’ for reading its gonial angle (Reprinted from Oettlé AC, Becker PJ, de Villiers E, et al. The influence of age, sex, population group, and dentition on the mandibular angle as measured on a South African sample. Am J Phys Anthropol. 2009;139(4):505–511, with permission of Wiley).
Figure 3
14
The ‘Measure Tool’ (or ‘Ruler Tool’), which is hidden below the ‘Eyedropper Tool’ in the Photoshop Toolbox (red box), is selected; the tangent drawn using the ‘Measure Tool’ along the lower border of the body of the mandible is also seen (white line).
Figure 4 To horizontally orient the tangent drawn using the ‘Measure Tool’, go to Image>Rotate Canvas>Arbitrary, click on the latter and click ‘OK’ in the Rotate Canvas dialog box.
Figure 5 Once Photoshop’s in-built ‘Ruler’ is activated by typing ‘Ctrl’ and ‘R’ (‘Command’ and ‘R’ for Macintosh systems), the cursor is clicked within the ‘Ruler’ and dragged to create a guide (blue line). This guide is placed on the horizontally orientated lower border of the body of the mandible; adjustments to the position of the guide may be made using the ‘Move Tool’ (encircled in black).
Figure 6 The ‘Line Tool’ (hidden below the ‘Rectangle Tool’) (red box) is used to draw a line (white line) over the ‘Guide’ along the lower border of the body of the mandible. Using the ‘Measure Tool’, a line is drawn along the posterior border of ramus. ‘A’ on the Options Bar reveals the angle (circled in black); if the angle depicted has a negative sign, the sign should be disregarded.
Figure 7 Scatter plot showing correlation of the left gonial angle (in degrees) to age (in years) and the linear regression line. 15
Table 1 Age and Sex Distribution of the Orthopantomograms Used for Measuring the Gonial Angles Age Group (years) Male Female Total 16 15 31 1830 6 14 20 3140 8 7 15 4150 9 7 16 5160 >60 9 9 18 Total 48 52 100
16
Table 2 Linear Regression Equations for Age Estimation Using the Right and Left Gonial Angle, with the Respective Standard Error of the Estimate (SEE) Derived for the Reference Sample (n = 100) and the Mean Absolute Difference (MAD) Obtained for Test Sample (n = 17) Gonial Angle Regression Equation SEE MAD (± year) (± year) Right 15.77 14.22 Age = 107.234 + (–0.538 Right Gonial Angle) Left 15.84 13.98 Age = 100.920 + (–0.484 Left Gonial Angle)
Highlights
The paper proposes a new digital method of age estimation by measuring gonial angle
Statistically significant (p < 0.05) albeit low correlation (~r = 0.25) was obtained
Error of ±14 years in age estimation was produced for gonial angle
The suggested digital method may be applied when no other alternatives are available
The method has application in elderly living subjects but should be used guardedly
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www.elsevier.com/locate/jofri
PII: DOI: Reference:
S2212-4780(17)30002-3 http://dx.doi.org/10.1016/j.jofri.2017.09.002 JOFRI265
To appear in: Journal of Forensic Radiology and Imaging Received date: 23 January 2017 Revised date: 8 September 2017 Accepted date: 18 September 2017 Cite this article as: Ashith B. Acharya, A Digital Method of Measuring the Gonial Angle on Radiographs for Forensic Age Estimation, Journal of Forensic Radiology and Imaging, http://dx.doi.org/10.1016/j.jofri.2017.09.002 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 galley proof before it is published in its final citable 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.
A Digital Method of Measuring the Gonial Angle on Radiographs for Forensic Age Estimation
Ashith B. Acharya, BDS, GDFO Department of Forensic Odontology, S.D.M. College of Dental Sciences and Hospital, Sattur, Dharwad – 580009, Karnataka, India.
Corresponding author: Dr. Ashith B. Acharya Associate Professor and Head Department of Forensic Odontology S.D.M. College of Dental Sciences and Hospital Sattur, Dharwad – 580009 Karnataka, India Tel: +91-836-2468142 (Ext. 115) Fax: +91-836-2467612 E-mail: [email protected]
Sources of support: None
Conflicts of interest: None
Abstract Objective: Age estimation has important legal ramifications and assessing it, particularly in living adults, can prove challenging on occassion. This paper explores the use of gonial angle 1
in age estimation, applying a new digital method which may be suitable in elderly subjects when many/all teeth are missing. Materials and Methods: A commercially available and ubiquitous software was used to measure the gonial angle on digital orthopantomograms from 100 subjects (48 males and 52 females; age range 18−89 years) which was subjected to linear regression analysis. Results: The correlation coefficient for the gonial angle on the right side (r = 0.25) was greater than that for the left side (r = 0.23). Both correlations were statistically significant (p < 0.05). The regression equations derived were tested on a holdout sample (n = 17; age range 21−71 years) and revealed a mean absolute difference of approximately ±14 years for the two regression equations. Conclusion: Although the gonial angle may not consistently change with an increase in chronologic age, the digital method proposed here may be one of few options available for use in the elderly with minimal or no teeth seeking retirement benefits, and may be applied as a method of last resort in geriatric age prediction.
Keywords:
Age
assessment;
Mandibular
angle;
Radiographic
measurement;
Orthopantomogram; Adobe® Photoshop®
Introduction The law is known to necessitate age estimation in postmortem reconstructive identification as well as in living subjects with no valid birth records, and several parts of the body such as the metacarpals, long bones, clavicle, jaws and the teeth may be used towards this end. This is based on the ~15 years forensic odontology experience this author has had in Nepal and India combined, rendering opinion on the age of living and dead human subjects— both children and adults—in over 125 cases. However, in 2013, two edentate subjects were referred for age assessment for determining if they had reached the threshold of 60 years and were eligible to claim retirement benefits, resulting in an unusual situation wherein forensic 2
‘dental’ age estimation was required but the teeth were missing. A search for alternative parameters of age estimation in these cases led to an exploration of the use of the mandibular gonial angle, which may be conveniently assessed on radiographs by trained dentists. This may also be applied in postmortem age estimation since there can be cases wherein only the mandible is recovered (Fig. 1). The gonial angle is considered to be obtuse at birth and, as teeth are added and growth takes place during childhood, it becomes more acute.1 According to Jensen and Palling,2 with old age the angle increases to between 120 and 150, becoming more similar to the ‘infantile angle’ of 135 to 150. The principal motivation for this study was a lack of gonial angle age estimation standards for Indians and an objective to develop regression formulae for the purpose. Although a recent study has examined the gonial angle in the people of this country, no regression equation per se was published in that paper.3 Traditionally, the angle on dry mandible specimens has been measured using a mandibulometer, as illustrated in Oettlé et al.1 (Fig. 2). However, several studies exist wherein the angle has been measured on radiographs.3,4 Considering the present author’s experience of forensic age estimation referrals of edentate living subjects undertaken on radiographs, a conscious decision was made to evaluate the angle on orthopantomograms (OPTs). The aim was to determine the correlation of the derived measurements on the OPTs and chronologic age, and apply the obtained regression equations on a holdout sample to determine their accuracy/error rate in age estimation. Towards this end, a digital method was developed using a widely used and commercially available software program.
Materials and Methods Material 3
The material comprised of 100 digital OPTs from as many subjects (48 males and 52 females) whose ages ranged from 18 to 89 years (average = 42.3 years) (Table 1). All digital OPTs were obtained from records available in S.D.M. College of Dental Science’s Department of Oral Medicine & Radiology, and were previously taken on patients who were referred to the department for diverse oral diagnostic reasons. The digital OPTs were acquired using a Kodak 9000 3D Extraoral Imaging System (Kodak Dental Systems, PracticeWorks Inc., Atlanta, USA).
Measurement of Gonial Angle The right and left gonial angle on digital OPT is measured as follows: 1. The digital OPT is opened in Adobe Photoshop 7.0.1 software programme (Adobe Systems Inc., Mountain View, CA) and the ‘Measure Tool’ (hidden below the ‘Eyedropper Tool’ in the Photoshop Toolbox) selected (boxed) (Fig. 3). Note that the ‘Measure Tool’ is renamed as ‘Ruler Tool’ in newer versions of Photoshop. 2. Clicking ‘Arbitrary’ reveals the Rotate Canvas dialog (Fig. 4, boxed), which shows the amount of rotation (in degrees) required to orient the lower border of the mandible horizontally; the dialog also specifies whether the rotation must be done clock-wise (CW) or counter clock-wise (CCW). In Fig. 4, rotating the radiograph by 29.5 achieves this. Click ‘OK’ (Fig. 4, boxed) to obtain this degree of rotation. 3. Once the digital OPT is rotated, press ‘Ctrl’ and ‘R’ (‘Command’ and ‘R’ for Macintosh systems) together to activate Photoshop’s in-built ‘rulers’ (the white borders with ruler markings on the upper and left sides of the digital OPT image window in Fig. 5). Using the mouse/touchpad, click the cursor within the ‘rulers’ on the upper border of the image and drag onto the image. A horizontal line, referred to as a ‘guide’, is created (line in Fig. 5; the line color may differ depending on the settings of the Photoshop software). This 4
line/guide must be positioned on the horizontally orientated lower border of the body of the mandible. One can move the guide to the desired location using the ‘Move Tool’ on Photoshop’s toolbox (Fig. 5, encircled) or by holding down the ‘Ctrl’ key (‘Command’ key for Macintosh systems) and positioning the cursor on the guide and then and dragging it. 4. Next, the ‘Measure Tool’ is used to draw a line along the posterior border of ramus (this line must touch the posterior border at the level of the condyle and above the mandibular angle—see Fig. 6). The ‘Measure Tool’ must be used to draw the line from top-to-bottom for the subject’s left ramus and bottom-to-top for the subject’s right ramus (this is to avoid an angle that is exceedingly acute). Note the angle ‘A’ on the Options Bar (Fig. 6, encircled). If the angle depicted has a negative sign (−130, as seen in Fig. 6), the sign should be disregarded (i.e., the absolute value only, viz., 130 is considered).
Statistical Analysis To ascertain the strength of correlation of the gonial angles to chronologic age, as well as develop age estimation formulas, the data was subjected to linear regression analysis with the right and left angles taken as independent variables and actual age as dependent variable. The gonial angle for the right and left sides were also subjected to a paired t-test to determine potential statistical differences between the two sides. Since some believe that the gonial angle decreases from childhood to adulthood, followed by an increase with progression towards old age,1,2 quadratic and cubic regression analyses—both of which are curve estimations—were undertaken to determine if they produced stronger correlations (higher R values) than the linear regression analysis. The regression formulas developed were applied on a holdout/test sample (n = 17) to ascertain their potential accuracy and error rates in real-life scenarios. The holdout sample 5
comprised of subjects whose age ranged from 21 to 71 years (average = 41.8 years) and included 10 females and seven males. The difference between the estimated and actual age (the ‘error’) was determined for each subject in the holdout sample, and the mean absolute difference (MAD) calculated. The absolute difference is the difference between the estimated and actual age devoid of a positive or negative sign (the ‘unsigned’ value). For example, the actual age of test subject no. 10 was 46 years and the estimated age was 41.27 years using the right gonial angle; the error here is −4.73 years but the negative sign is discarded and only its absolute value (viz., 4.73) is considered in the calculation. The MAD, therefore, is the average magnitude of difference in a set of estimates and has previously been used as a measure of accuracy of age estimation methods.5,6 Although the more commonly used standard error of the estimate (SEE) produced from regression analyses gives an indication of the expected error rate, there is an inherent bias since it is based on the training dataset (n = 100, in this study)7 and does not necessarily reflect the error in an independent test sample or forensic casework. Hence, the MAD was used since it may represent the error more objectively; the SEE was also calculated separately for the test dataset to compare it with the MAD. To assess potential intra- and inter-observer variation, the gonial angle (right and left sides) was re-measured on 15 randomly selected digital OPTs. The measurements were made six months after the primary measurements were completed (for intra-observer variation). Potential differences between the two sets of recordings by the principal examiner and between the principal examiner and second examiner were assessed using the paired t-test. Lastly, an independent samples t-test was performed to assess potential statistically significant sex differences in the gonial angle (right and left sides were assessed separately). While the regression analyses and paired t-tests were performed on an SPSS 17.0 statistical software program (SPSS Inc., Chicago, IL; now IBM Corp., Armonk, NY), the 6
MAD was derived on an MS Office Excel spreadsheet (Office 2011, Microsoft Corp., Redmond, WA). This study was approved by the Institutional Ethical Committee (certificate IRB No. 2015/S/FO/01, dated 6 November 2015).
Results The paired t-test for determining potential intra-observer differences showed statistically insignificant differences between the primary measurements and the repetitions by the same examiner (p > 0.05) for both the right and left gonial angles (t-values of −1.5 and 0.06, respectively) as well as measurements made by the second examiner (p > 0.05; t-values of 1.22 and 1.51 for right and left sides, respectively). The mean of the gonial angle was 120.6 for the right side and 120.9 for the left side. The paired t-test for determining possible statistical differences between the left and right sides revealed none (t-value = −0.49; p > 0.05). The independent samples t-test to assess potential sex differences in the right and left gonial angle also showed statistically insignificant differences (p > 0.05; t-value = 1.21 and 1.68 for right and left sides, respectively). The linear, quadratic and cubic regression analyses revealed little or no difference between each other in terms of correlation and, hence, the latter two are not commented on further. The correlation coefficient for the gonial angle on the right side (r = 0.245) was greater than that for the left side (r = 0.226). Both correlations were statistically significant (p < 0.05). The linear regression equations derived and their SEEs are depicted in Table 2. The application of these equations on the holdout sample (n = 17) revealed an MAD that approximated ±14 years (Table 2). Discussion
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The results of the present study show that there is a low albeit statistically significant correlation (p < 0.05) between age and the gonial angle which marginally decreases as the former increases (Fig. 7). The results also show that the angle on the right side was slightly more strongly correlated to age than on the left side. However, this did not translate to any practical improvements in terms of (lower) error rates in age estimation (Table 2), with all MADs hovering around ±14 years (the SEEs were approximately ±15.8 years). In fact, the right–left measurement differences per se were statistically insignificant, similar to that observed in Larheim and Svanaes9 and Al-Shamout et al.10 As in the present study, Upadhyay et al.3 too observed a “definite decrease” in the gonial angle with an increase in age; however, the decrease was statistically insignificant in their study. On the other hand, Al-Shamout et al.10 found that the gonial angle increases with age while others have reported a lack of recognizable change in the gonial angle with age.1,11−14 It therefore appears that the age-related changes which occur in the gonial angle may not be regular. It is believed that masticatory muscles change with age, decrease in their contractile activity, with a reduction in muscle density and masseter and medial pterygoid muscles undergo greater age-related decreases because of their insertion into the region of the gonial angle;15 according to Merrot et al.,16 increase in the mandibular angle in the elderly edentate may be explained by imbalance between the elevator and depressor muscles of the mandible, “as a function of the elevator muscles or by the absence of the molar buttress”. Therefore, while gonial angle change with age may partly be physiologic, it is also influenced by tooth loss and, therefore, the correlation between it and age may be low to moderate, as evidenced in the results of this paper. At the same time, no sex differences appear to exist in the gonial angle, as seen by the statistically insignificant malefemale difference (p > 0.05). With respect to the approach used herein, the author believes that the angle measured in the present study is similar to that obtained for dry mandible specimens using a 8
mandibulometer, as illustrated in Oettlé et al.1 (Fig. 2). The planes drawn and delineated using the rotation options and guides in Photoshop were such that the ‘horizontal’ plane in the digital OPTs—which contacted the inferior border of the mandible—was the standard horizontal plane used in traditional methods, while the planes drawn along the posterior border of the mandibular ramus corresponds to the ‘rameal’ or the movable wing of the mandibulometer, which comes in contact with the posterior surface of the ramus at the condyle and inferiorly above the angle.1 Also, the ‘tangent’ drawn along the inferior border lies close to its posterior region since, in the traditional method, the vertical pressure is applied on the “left second molar tooth or its cavity”1 (p. 506) and that portion is likely to contact the horizontal plane of the mandibulometer. These constitute the “standard” horizontal and rameal planes and the angle formed between these is recorded as the gonial angle.1 The measurement of the gonial angle using two ‘tangents’—one drawn on the inferior border of the mandible, and another along the posterior border of the condyle and ramus— has also been used in a previous study of orthopantomographic gonial angle measurement.4 A conscious decision was taken to undertake the study on OPTs and not lateral cephalograms because of the interference of the superimposed images appearing on the latter, potentially undermining reliable measurements of the gonial angle.4 This disadvantage is not encountered in OPTs. It is also believed that the gonial angle can be determined more easily on an OPT than in a lateral cephalogram.4 No statistical difference was found in the gonial angle measurements taken on the two types of radiographs,4 which was also the case with Matilla et al.17 and Altonen et al.18 Moreover, an important advantage of using OPTs is that they are often taken as part of routine examination of patients to serve as a tool for oral diagnostic purposes. In fact, Larheim and Svanaes9 report that the gonial angle measured on an OPT is nearidentical to that assessed on a dried mandible, implying that this may be applied both in the 9
living and postmortem skeletal contexts. But, as stated earlier in this paper, a primary objective of this study was to apply the results on living subjects, especially individuals with few or no teeth and who may require age estimation for claiming retirement benefits (mostly ≥60 years in the Indian context). This may be done using the software and method discussed above. To obtain gonial angle readings, other software programs may also be used (e.g., KODAK Dental Imaging Software, KODAK Dental Systems, PracticeWorks Inc., Atlanta, USA), however, the intention of using Photoshop in this study was to develop a method that can be used on a relatively ubiquitous image editing program, and regardless of access to specific dental radiographic software. Of course, the negative effect of ionizing radiation on living persons is well documented and no radiographs should be taken beyond the examination range recommend in scientific recommendations.19 X-ray examination of the dentition (including the OPTs used in this study) may be considered as falling within this “examination range.” Nevertheless, the author recognizes that when ionizing radiation is applied, local regulations must be observed; from a scientific viewpoint, the ‘minimization principle’—which requires to perform each examination with as much radiation dose saving approach as possible and to dispense any exposure that is not mandatory—is to be followed.19 It is also noteworthy that children and adolescents are believed to be considerably more sensitive than adults to carcinogenic risks of ionizing radiation.20 Ramsthaler et al.20 cites several studies that suggest that the long-term risk of cancer in terms of mortality as a result of ionizing radiation was approximately 12–15% per Sievert of radiation exposure for young children, as against 5–9% or less for adults such as those included in this study. Therefore, the risk of radiography posed to adults (such as those used in this study) is about half that encountered in children. In fact, Ramsthaler et al.20 deduce that, theoretically, the health risks that could ensue due to radiation emitted from an OPT exposure are “100 times smaller than 10
other everyday risks, such as the use of a car or public transportation.”20 In general, it is considered acceptable to use radiographs—including OPTs—for age estimation so long as one ensures optimization of the procedures used and minimizing the risks.20
Conclusions A digital method is proposed for measuring the gonial angle for age estimation, which has particular use in living geriatric subjects. The findings reveal a statistically significant but low correlation to age, with relatively large error rates in age estimation. The author recognizes that the changes in the gonial angle may not be consistent with chronologic age. Therefore, the gonial angle needs to be used guardedly as a parameter of estimating age, and perhaps as a method of last resort in the absence of teeth or when other more robust and reliable techniques are unavailable for use.
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Acknowledgments The author wishes to thank Prof. C. Bhasker Rao, former Principal, and Prof. Srinath L. Thakur, Principal, and the Management of S.D.M. College of Dental Sciences and Hospital, for their support to research in forensic odontology. The author also wishes to acknowledge the assistance of Dr. Kruthika Guttal in radiograph collection and clarifications on the radiographic appearance of the mandible on OPTs, and measurement of angle using Kodak Dental Imaging software.
References 1. Oettlé AC, Becker PJ, de Villiers E, et al. The influence of age, sex, population group, and dentition on the mandibular angle as measured on a South African sample. Am J Phys Anthropol. 2009;139(4):505–511. 2. Jensen E, Palling M. The gonial angle. Am J Orthod. 1954;40:120–133. 3. Upadhyay RB, Upadhyay J, Agrawal P, et al. Analysis of gonial angle in relation to age, gender, and dentition status by radiological and anthropometric methods. J Forensic Dent Sci. 2012;4(1):29–33. 4. Shahabi M, Ramazanzadeh B-A, Mokhber N. Comparison between the external gonial angle I panoramic radiographs and lateral cephalograms of adult patients with Class I malocclusion. J Oral Sci. 2009;51(3):425–429. 5. Spalding KL, Buchholz BA, Bergman LE, et al. Age written in teeth by nuclear tests. Nature 2005;437:333–334. 6. Acharya AB, Vimi S. Effectiveness of Bang and Ramm’s formulae in age assessment of Indians from dentin translucency length. Int J Legal Med. 2009;123:483–488.
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7. Giles E, Klepinger LL. Confidence intervals for estimates based on linear regression in forensic anthropology. J Forensic Sci. 1988;33:1218–1222. 8. Solheim T, Sundnes PK. Dental age estimation of Norwegian adults – a comparison of different methods. Forensic Sci Int. 1980;16(1):7–17. 9. Larheim TA, Svanaes DB. Reproducibility of rotational panoramic radiography: Mandibular linear dimensions and angles. Am J Orthod Dentofac Orthop. 1986;90:45–51. 10. Al-Shamout R, Ammoush M, Alrbata R, et al. Age and gender differences in gonial angle, ramus height and bigonial width in dentate subjects. Pakistan Oral Dent J. 2012;32(1):81–87. 11. Keen JA. A study of the angle of the mandible. J Dent Res. 1945;24:77–86. 12. Israel H. The failure of aging or loss of teeth to drastically alter mandibular angle morphology. J Dent Res. 1973;52:83–90. 13. Raustia AM, Salonen MA. Gonial angles and condylar and ramus height of the mandible in complete denture wearers—a panoramic radiograph study. J Oral Rehabil. 1997;24(7):512–516. 14. Ceylan G, Yaníkoglu N, Yílmaz AB, Ceylan Y. Changes in the mandibular angle in the dentulous and edentulous states. J Prosthet Dent. 1998;80(6):680–684. 15. Hannam AG, Wood WW. Relationships between the size and spatial morphology of human masseter and medial pterygoid muscles, the craniofacial skeleton, and jaw biomechanics. Am J Phys Anthropol. 1989;80:429–45. 16. Merrot O, Vacher C, Merrot S, Godlewski G, Frigard B, Goudot P. Changes in the edentate mandible in the elderly. Surg Radiol Anat. 2005;27(4):265–70. 17. Mattila K, Altonen M, Haavikko K. Determination of the gonial angle from the orthopantomogram. Angle Orthod. 1977;47(2):107–110. 18. Altonen M, Haavikko K, Mattila K. Developmental position of lower third molar in 13
relation to gonial angle and lower second molar. Angle Orthod. 1977;47(4):249–255. 19. Schmeling A, Grundmann C, Fuhrmann A, Kaatsch HJ, Knell B, Ramsthaler F, Reisinger W, Riepert T, Ritz-Timme S, Rösing FW, Rötzscher K, Geserick G. Criteria for age estimation in living individuals. Int J Legal Med. 2008;122(6):457–60. 20. Ramsthaler F, Proschek P, Betz W, Verhoff MA. How reliable are the risk estimates for X-ray examinations in forensic age estimations? A safety update. Int J Legal Med. 2009;123(3):199–204.
Legends for Figures Figure 1 The recovery of a single, isolated, mandible is not uncommon in forensic, anthropological and archaeological cases.
Figure 2 A dry mandible specimen placed on a ‘mandibulometer’ for reading its gonial angle (Reprinted from Oettlé AC, Becker PJ, de Villiers E, et al. The influence of age, sex, population group, and dentition on the mandibular angle as measured on a South African sample. Am J Phys Anthropol. 2009;139(4):505–511, with permission of Wiley).
Figure 3
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The ‘Measure Tool’ (or ‘Ruler Tool’), which is hidden below the ‘Eyedropper Tool’ in the Photoshop Toolbox (red box), is selected; the tangent drawn using the ‘Measure Tool’ along the lower border of the body of the mandible is also seen (white line).
Figure 4 To horizontally orient the tangent drawn using the ‘Measure Tool’, go to Image>Rotate Canvas>Arbitrary, click on the latter and click ‘OK’ in the Rotate Canvas dialog box.
Figure 5 Once Photoshop’s in-built ‘Ruler’ is activated by typing ‘Ctrl’ and ‘R’ (‘Command’ and ‘R’ for Macintosh systems), the cursor is clicked within the ‘Ruler’ and dragged to create a guide (blue line). This guide is placed on the horizontally orientated lower border of the body of the mandible; adjustments to the position of the guide may be made using the ‘Move Tool’ (encircled in black).
Figure 6 The ‘Line Tool’ (hidden below the ‘Rectangle Tool’) (red box) is used to draw a line (white line) over the ‘Guide’ along the lower border of the body of the mandible. Using the ‘Measure Tool’, a line is drawn along the posterior border of ramus. ‘A’ on the Options Bar reveals the angle (circled in black); if the angle depicted has a negative sign, the sign should be disregarded.
Figure 7 Scatter plot showing correlation of the left gonial angle (in degrees) to age (in years) and the linear regression line. 15
Table 1 Age and Sex Distribution of the Orthopantomograms Used for Measuring the Gonial Angles Age Group (years) Male Female Total 16 15 31 1830 6 14 20 3140 8 7 15 4150 9 7 16 5160 >60 9 9 18 Total 48 52 100
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Table 2 Linear Regression Equations for Age Estimation Using the Right and Left Gonial Angle, with the Respective Standard Error of the Estimate (SEE) Derived for the Reference Sample (n = 100) and the Mean Absolute Difference (MAD) Obtained for Test Sample (n = 17) Gonial Angle Regression Equation SEE MAD (± year) (± year) Right 15.77 14.22 Age = 107.234 + (–0.538 Right Gonial Angle) Left 15.84 13.98 Age = 100.920 + (–0.484 Left Gonial Angle)
Highlights
The paper proposes a new digital method of age estimation by measuring gonial angle
Statistically significant (p < 0.05) albeit low correlation (~r = 0.25) was obtained
Error of ±14 years in age estimation was produced for gonial angle
The suggested digital method may be applied when no other alternatives are available
The method has application in elderly living subjects but should be used guardedly
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