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(MSL)
[1–6] [PREPRINTER stage]
Med Sci Law OnlineFirst, published on March 22, 2015 as doi:10.1177/0025802415575415
Original article
A new approach to sex estimation using the mandibular canine index
Medicine, Science and the Law 0(0) 1–6 ! The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0025802415575415 msl.sagepub.com
Ana Margarida Silva1, Maria Lurdes Pereira1,2, ´ lvaro Azevedo1,2 and So´nia Gouveia3,4, Joa˜o Nuno Tavares5,6, A Ineˆs Morais Caldas1,7
Abstract Rao et al.’s mandibular canine index (MCI) is a simple odontometric method which uses the mandibular canine as the key to sex estimation. This index is defined as the ratio between the right canine mesiodistal dimension and the mandibular canine arch width. The aim of this study was to contribute to sex estimation using dental techniques by analysing the MCI efficiency, and to propose a new approach for its use. Measurements were taken from 120 plaster casts (70 females) in the 16–30 year age group. Although statistically significant sexual dimorphism was observed in both the mesiodistal dimension and the mandibular canine arch width, the MCI showed a low accuracy in sex classification (54.2% correct identifications). This accuracy was improved to 64.2% using receiver operating characteristics curve analysis. Yet, despite the better accuracy, these results reinforce the idea that the MCI may not be particularly useful in sex prediction, since it may not reflect the same degree of sexual dimorphism as its absolute measures. Keywords forensic sciences, forensic odontology, human identification, odontometry, sex estimation, ROC curve analysis, mandibular canine index
Introduction
the teeth,9 but it can also reflect three-dimensional measurements and weight/mass assessment.10 Mandibular canines have been called the ‘keyteeth’ in human identification.11–15 They consistently exhibit the greatest sex difference among all human teeth, being less affected than others by periodontal diseases. They are frequently the last teeth to be extracted, and also bear a greater chance of surviving severe trauma.3,4,13,14,16 Thus, the mandibular canines are frequently used for human identification, and
Teeth are known for being the most resistant structures of the human body and thus play a major role in identifying skeletal remains. The use of dental techniques has been reported as very useful in human identification, and has been used to determine the sex of skeletal remains. Sex estimation refers to the study of the biological and physiological features that define men and women, whereas gender estimation refers to the social roles, behaviours, activities and attributes given by a society as being appropriate for 1 Faculdade de Medicina Denta´ria da Universidade do Porto, Portugal men and women.1 Previously, the use of several body 2 EPIUnit - Instituto de Sau´de Pu´blica da Universidade do Porto, parameters (e.g. craniofacial morphology and pelvic Portugal 3 measurements) was reported to allow an accuracy Instituto de Engenharia Electro´nica e Informa´tica de Aveiro, Universidade de Aveiro (IEETA/UA), Portugal ranging from 96% to 100% in sex estimation.2,3 4 Centro de Investigac¸a˜o e Desenvolvimento em Matema´tica e However, it is not uncommon to recover only partial Aplicac¸o˜es (CIDMA/UA), Universidade de Aveiro, Portugal human remains, or fragmentary skull and pelvic 5 Departamento de Matema´tica da Faculdade de Cieˆncias da bones.4 In such cases, teeth can be especially useful, Universidade do Porto, Portugal 6 since they are known to resist a great variety of physCentro de Matema´tica da Universidade do Porto (CMUP/UP), Portugal ical, chemical and biological insults. 7 CENCIFOR, Centro de Cieˆncias Forenses, Portugal It has been stated that teeth have a high degree of 5 sexual dimorphism. In general, men have bigger teeth Corresponding author: than female.6,7 Yet, these data are not consensual, and Ineˆs Morais Caldas, Faculdade de Medicina Denta´ria da Universidade do 8 reverse dimorphism has also been found. Sexual Porto, Rua Dr. Manuel Pereira da Silva, 4200-393 Porto, Portugal. Email: [email protected] dimorphism relies on differences in the diameter of Downloaded from msl.sagepub.com at DICKENSON SCHOOL OF LAW on May 26, 2015
XML Template (2015) [19.3.2015–11:24am] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/MSLJ/Vol00000/150004/APPFile/SG-MSLJ150004.3d
(MSL)
[1–6] [PREPRINTER stage]
2 Rao’s mandibular canine index (MCI) is often used as the methodology for sex estimation, being known for its simplicity and inexpensive application.17 However, there is no consensus on the suitability of the MCI in sex estimation, as different authors have reached different conclusions.2,3,16,17 This study therefore aims to contribute to sex estimation using dental techniques, assessing the reliability and applicability of the MCI in sex prediction.
Materials and methods
Medicine, Science and the Law 0(0) mesiodistal dimensions of mandibular canines, the inter-canine arch width and the MCI was calculated, and possible sex differences were evaluated using the ttest with the Bonferroni correction (multiplying the pvalue by the number of comparisons). Due to the lack of normality of the data and the approximation of the sampling distribution of the sampling mean to a normal distribution for sufficiently large samples (a consequence of the central limit theorem), non-parametric comparison of the groups was also conducted using the Mann–Whitney U-test, which led to the same statistical conclusions as the parametric testing. The level of global significance used was 5%. Statistical analysis was performed using IBM SPSS Statistics v20.0 software and Microsoft Office Excel 2007. This study was evaluated and approved by the Ethical Board of the Faculty of Dental Medicine of University of Porto, Portugal. Since the cast models were made anonymously, no informed consent form was required.
One hundred and twenty plaster casts of patients attending the residency clinic of the Faculty of Dental Medicine of University of Porto, Portugal, were studied. Cast models belonged to 70 females and 50 males, ranging in age from 16 to 30 years old. Inclusion criteria were Portuguese population affinity, no signs of periodontal disease (evaluated in the cast models by a measurement inferior to 3 mm from the cement enamel junction to the cast reproduction of gingival tissues), anterior teeth free from caries Results or any dental treatment and teeth well aligned, with no interdental spacing or open-bite. Cronbach’s coefficient alpha was evaluated as >0.9 All measurements were performed using a digital for all variables (0.94 for d33, 0.97 for d43 and 0.93 caliper (PaleoTech Concepts) with a maximum absofor d3343), thus indicating high internal consistency lute error of 0.5 mm. Caliper beaks were placed along of the measurements. In fact, pairwise correlations the long axis of the tooth. The mesiodistal (MD) between the 14 repeated measurements were >0.85 dimension was considered as the greatest distance for all variables and all cases. Furthermore, there between contact points on the mandibular canine were no relevant measurement deviations: from the crown proximal surfaces, d43 for the right canine 42 repeated measurements (three measurements and d33 for the left. The mandibular canine arch from 14 casts for each variable), >90% of the measwidth was measured as the distance between the tips urements in both d33 and d43 had a maximum absoof the mandibular canines (d3343). These measurelute difference of 0.5 mm (i.e. the measurement ments were repeated in 14 randomly selected casts resolution), while 90% of the d3343 measurements within a 24-hour interval with a second observer in had an absolute difference of 41mm. order to evaluate intra- and inter-observer variability. In order to compare the accuracy of the MCI standInternal consistency of the measurements was ard in Portuguese and Indian samples, probability assessed using Cronbach’s coefficient alpha. function density graphs were plotted (Figure 1). It Measurements were also validated by pairwise comcan be observed that in the Portuguese population, parison from Spearman’s non-parametric correlations density graphs for males and females overlap almost and maximum absolute differences. completely, pointing to the low discrimination power As proposed by Rao et al.,17 the MCI was then of the MCI. Furthermore, Rao’s cut-off point seems inadequate to distinguish males and females. The optiobtained by calculating the ratio of the MD dimenmal cut-off value (0.282) allowed a sensitivity value of sion of right mandibular canine (d43) and the 94% and a specificity value of 25.7% to be obtained, inter-canine width (d3343). Additionally, a cut-off indicating that 94% of males were correctly classified, value – the MCI standard – was determined following whereas only 25.7% of females were assessed accurthe formula: [(Mean Male MCI–SD)þ(Mean Female ately. The accuracy of the MCI standard in sex predicMCIþSD)]/2. Casts with MCI values up to this cuttion in different population samples is depicted in off value were reported as female, whereas MCI Table 1. It can be observed that Rao’s MCI performvalues above this limit were reported as male. The ance in an Indian population is quite high (85.9%), MCI standard performance in several studies was although two recent studies in other Indian populacompared.3,16–19 tions observed lower performance values (50.7% and In order to compare the accuracy of the MCI 72.0%). In a French population, in which more similastandard in Portuguese and Indian samples, probabilrities with Portuguese population are expected, the ity function density graphs were plotted. The performMCI performed slightly better (62.9%). ance of alternative cut-offs in sex determination was A ROC curve analysis was used to assess the optiexplored using receiver operating characteristic mal cut-off for identifying males using the MCI. (ROC) curve analysis. Descriptive statistics of the Downloaded from msl.sagepub.com at DICKENSON SCHOOL OF LAW on May 26, 2015
XML Template (2015) [19.3.2015–11:24am] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/MSLJ/Vol00000/150004/APPFile/SG-MSLJ150004.3d
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[1–6] [PREPRINTER stage]
Silva et al.
3
Figure 1. Probability density function of mandibular canine index (MCI) values in (a) the Portuguese sample and (b) the Indian sample from Rao et al.18 for a comprehensive comparison of the data. Figure (1b) was inspired by figure 2 in Rao et al.18 for visual comparison.
Table 1. Standard MCI accuracy in sex prediction reported in literature studies, obtained from different population samples. Males
Females
Total
Standard MCI
Population
Number
%
Number
%
Number
%
0.282a 0.27418 0.24419 0.2562 0.26921
Portuguese Indian Indian Indian French
47/50 322/382 51/103 78/100 133/214
94.0 84.3 49.51 78.0 62.15
18/70 336/384 52/100 66/100 134/210
25.7 87.5 52.0 66.0 63.81
65/120 658/766 103/203 144/200 267/424
54.2 85.9 50.7 72.0 62.9
a Calculated for the present sample. MCI: mandibular canine index.
Usually, the MCI standard is obtained using the right Discussion mandibular canine mesiodistal dimension. However, as it was unknown if a better performance in sex preDetermining a person’s sex is crucial part of human diction could be achieved using the right or left manidentification. Dental techniques are often used for dibular canine, the MCI standard using the left this purpose due to the extraordinary resistance of mandibular canine was also determined (Figure 2). teeth to hazardous factors, enabling dental techniques Figure 2 illustrates that no relevant differences in to be used in situations where other methodologies MCI performance were observed either using d43 or cannot be used. Although the use of DNA has d33. Furthermore, the area under the ROC curve has become common due to its robust results, the fact is a value inferior to 0.75 (0.685) showing a moderate that biological samples are not always available or performance in establishing sex classification. suitable for DNA fingerprinting. However, according However, the sex estimation results using the cut-off to Acharya and Mainali,20 teeth should not be used as determined by the ROC curve analysis (0.303) were the sole indicator of sex, even though studies indicate better than those obtained using the MCI standard they are a good adjunct for sex estimation. (Table 2). The canine teeth have been routinely used for Table 3 depicts the canine dimensions, canine manhuman identification purposes because they have dibular arch width and the MCI. All measurements shown the greatest degree of sexual dimorphism were larger in males, and the observed mean differacross numerous populations.4,5,6,9,21–24 Besides, ences were statistically significant (p < .05). they are the most resistant teeth in the human Downloaded from msl.sagepub.com at DICKENSON SCHOOL OF LAW on May 26, 2015
XML Template (2015) [19.3.2015–11:24am] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/MSLJ/Vol00000/150004/APPFile/SG-MSLJ150004.3d
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[1–6] [PREPRINTER stage]
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Medicine, Science and the Law 0(0)
dentition, which has led to their use alone in sex estimation.11–15,21 Compared to other teeth, canines present higher level of survival and undergo less wear.24 The reliability of Rao’s MCI methodology is perhaps well illustrated in this study by the near inexistence of
Figure 2. Receiver operating characteristic curve for the assessment of optimal cut-off values for identifying males using the MCI standard from the right mandibular canine (solid line) and the left mandibular canine (dashed). The marks identify the optimal cut-off values in each case.
inter- and intra-observer differences, and data consistent with those from other authors.5,24 A significant relationship was found between sex and canine dimensions as well as between sex and the MCI, which is also in agreement with data from other studies.4,17,22,24 Furthermore, significant differences in the MD width were found, and teeth measurements were systematically wider in men, which has also been found in previous studies.4,13–15,21,25–29 With regard to the MCI standard value for sex determination, contrary to Rao’s study,17 the best cut-point (0.282) performed poorly in sex estimation, identifying 94% of males but only 25.7% of females. This could be explained by population differences, supporting the theory that specific population data should be used for this assessment.7 Rao’s study was carried out in an Indian sample, in which females exhibited MCI values much lower than those of males, with little overlap of frequency curves and with small and similar standard deviation values for males and females in histograms with the normal setting (see Figure 1). In the present sample from the Portuguese population, females exhibited MCI values much higher than Indian females and quite similar to Portuguese (and Indian) males, resulting in a much bigger overlap of frequency curves (see Figure 1). As stated before, these differences may relate to population features,7 but other factors such as the environmental may also have an influence. For instance, a secular trend could be responsible for the changes. Rao’s investigation was conducted in the
Table 2. Standard MCI accuracy in sex prediction in current sample calculated using Rao’s guidelines and ROC curve analysis. Males
Rao’s guidelines ROC curve analysis
Females
Total
Teeth
Standard MCI
Number
%
Number
%
Number
%
43 33 43 33
0.282 0.282 0.303 0.303
47/50 47/50 36/50 36/50
94.0 94.0 72.0 72.0
18/70 17/70 41/70 40/70
25.7 24.3 58.6 57.1
65/120 64/120 77/120 76/120
54.2 53.3 64.2 63.3
ROC: receiver operating characteristic.
Table 3. Descriptive statistics of the canine dimensions, inter-canine width and MCI.
MCI Mandibular right canine (d43) Mandibular left canine (d33) Mandibular arch width (d3343)
Sex
n
Mean (mm)SD
Range (mm)
pa
Male Female Male Female Male Female Male Female
50 70 50 70 50 70 50 70
0.31 0.02 0.30 0.02 8.64 0.59 7.63 0.49 8.64 0.56 7.70 0.48 27.55 1.86 25.42 1.69
0.26–0.37 0.26–0.38 7.00–10.00 6.50–8.50 7.00–10.00 6.50–8.50 23.50–35.00 21.00–28.50
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Med Sci Law OnlineFirst, published on March 22, 2015 as doi:10.1177/0025802415575415
Original article
A new approach to sex estimation using the mandibular canine index
Medicine, Science and the Law 0(0) 1–6 ! The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0025802415575415 msl.sagepub.com
Ana Margarida Silva1, Maria Lurdes Pereira1,2, ´ lvaro Azevedo1,2 and So´nia Gouveia3,4, Joa˜o Nuno Tavares5,6, A Ineˆs Morais Caldas1,7
Abstract Rao et al.’s mandibular canine index (MCI) is a simple odontometric method which uses the mandibular canine as the key to sex estimation. This index is defined as the ratio between the right canine mesiodistal dimension and the mandibular canine arch width. The aim of this study was to contribute to sex estimation using dental techniques by analysing the MCI efficiency, and to propose a new approach for its use. Measurements were taken from 120 plaster casts (70 females) in the 16–30 year age group. Although statistically significant sexual dimorphism was observed in both the mesiodistal dimension and the mandibular canine arch width, the MCI showed a low accuracy in sex classification (54.2% correct identifications). This accuracy was improved to 64.2% using receiver operating characteristics curve analysis. Yet, despite the better accuracy, these results reinforce the idea that the MCI may not be particularly useful in sex prediction, since it may not reflect the same degree of sexual dimorphism as its absolute measures. Keywords forensic sciences, forensic odontology, human identification, odontometry, sex estimation, ROC curve analysis, mandibular canine index
Introduction
the teeth,9 but it can also reflect three-dimensional measurements and weight/mass assessment.10 Mandibular canines have been called the ‘keyteeth’ in human identification.11–15 They consistently exhibit the greatest sex difference among all human teeth, being less affected than others by periodontal diseases. They are frequently the last teeth to be extracted, and also bear a greater chance of surviving severe trauma.3,4,13,14,16 Thus, the mandibular canines are frequently used for human identification, and
Teeth are known for being the most resistant structures of the human body and thus play a major role in identifying skeletal remains. The use of dental techniques has been reported as very useful in human identification, and has been used to determine the sex of skeletal remains. Sex estimation refers to the study of the biological and physiological features that define men and women, whereas gender estimation refers to the social roles, behaviours, activities and attributes given by a society as being appropriate for 1 Faculdade de Medicina Denta´ria da Universidade do Porto, Portugal men and women.1 Previously, the use of several body 2 EPIUnit - Instituto de Sau´de Pu´blica da Universidade do Porto, parameters (e.g. craniofacial morphology and pelvic Portugal 3 measurements) was reported to allow an accuracy Instituto de Engenharia Electro´nica e Informa´tica de Aveiro, Universidade de Aveiro (IEETA/UA), Portugal ranging from 96% to 100% in sex estimation.2,3 4 Centro de Investigac¸a˜o e Desenvolvimento em Matema´tica e However, it is not uncommon to recover only partial Aplicac¸o˜es (CIDMA/UA), Universidade de Aveiro, Portugal human remains, or fragmentary skull and pelvic 5 Departamento de Matema´tica da Faculdade de Cieˆncias da bones.4 In such cases, teeth can be especially useful, Universidade do Porto, Portugal 6 since they are known to resist a great variety of physCentro de Matema´tica da Universidade do Porto (CMUP/UP), Portugal ical, chemical and biological insults. 7 CENCIFOR, Centro de Cieˆncias Forenses, Portugal It has been stated that teeth have a high degree of 5 sexual dimorphism. In general, men have bigger teeth Corresponding author: than female.6,7 Yet, these data are not consensual, and Ineˆs Morais Caldas, Faculdade de Medicina Denta´ria da Universidade do 8 reverse dimorphism has also been found. Sexual Porto, Rua Dr. Manuel Pereira da Silva, 4200-393 Porto, Portugal. Email: [email protected] dimorphism relies on differences in the diameter of Downloaded from msl.sagepub.com at DICKENSON SCHOOL OF LAW on May 26, 2015
XML Template (2015) [19.3.2015–11:24am] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/MSLJ/Vol00000/150004/APPFile/SG-MSLJ150004.3d
(MSL)
[1–6] [PREPRINTER stage]
2 Rao’s mandibular canine index (MCI) is often used as the methodology for sex estimation, being known for its simplicity and inexpensive application.17 However, there is no consensus on the suitability of the MCI in sex estimation, as different authors have reached different conclusions.2,3,16,17 This study therefore aims to contribute to sex estimation using dental techniques, assessing the reliability and applicability of the MCI in sex prediction.
Materials and methods
Medicine, Science and the Law 0(0) mesiodistal dimensions of mandibular canines, the inter-canine arch width and the MCI was calculated, and possible sex differences were evaluated using the ttest with the Bonferroni correction (multiplying the pvalue by the number of comparisons). Due to the lack of normality of the data and the approximation of the sampling distribution of the sampling mean to a normal distribution for sufficiently large samples (a consequence of the central limit theorem), non-parametric comparison of the groups was also conducted using the Mann–Whitney U-test, which led to the same statistical conclusions as the parametric testing. The level of global significance used was 5%. Statistical analysis was performed using IBM SPSS Statistics v20.0 software and Microsoft Office Excel 2007. This study was evaluated and approved by the Ethical Board of the Faculty of Dental Medicine of University of Porto, Portugal. Since the cast models were made anonymously, no informed consent form was required.
One hundred and twenty plaster casts of patients attending the residency clinic of the Faculty of Dental Medicine of University of Porto, Portugal, were studied. Cast models belonged to 70 females and 50 males, ranging in age from 16 to 30 years old. Inclusion criteria were Portuguese population affinity, no signs of periodontal disease (evaluated in the cast models by a measurement inferior to 3 mm from the cement enamel junction to the cast reproduction of gingival tissues), anterior teeth free from caries Results or any dental treatment and teeth well aligned, with no interdental spacing or open-bite. Cronbach’s coefficient alpha was evaluated as >0.9 All measurements were performed using a digital for all variables (0.94 for d33, 0.97 for d43 and 0.93 caliper (PaleoTech Concepts) with a maximum absofor d3343), thus indicating high internal consistency lute error of 0.5 mm. Caliper beaks were placed along of the measurements. In fact, pairwise correlations the long axis of the tooth. The mesiodistal (MD) between the 14 repeated measurements were >0.85 dimension was considered as the greatest distance for all variables and all cases. Furthermore, there between contact points on the mandibular canine were no relevant measurement deviations: from the crown proximal surfaces, d43 for the right canine 42 repeated measurements (three measurements and d33 for the left. The mandibular canine arch from 14 casts for each variable), >90% of the measwidth was measured as the distance between the tips urements in both d33 and d43 had a maximum absoof the mandibular canines (d3343). These measurelute difference of 0.5 mm (i.e. the measurement ments were repeated in 14 randomly selected casts resolution), while 90% of the d3343 measurements within a 24-hour interval with a second observer in had an absolute difference of 41mm. order to evaluate intra- and inter-observer variability. In order to compare the accuracy of the MCI standInternal consistency of the measurements was ard in Portuguese and Indian samples, probability assessed using Cronbach’s coefficient alpha. function density graphs were plotted (Figure 1). It Measurements were also validated by pairwise comcan be observed that in the Portuguese population, parison from Spearman’s non-parametric correlations density graphs for males and females overlap almost and maximum absolute differences. completely, pointing to the low discrimination power As proposed by Rao et al.,17 the MCI was then of the MCI. Furthermore, Rao’s cut-off point seems inadequate to distinguish males and females. The optiobtained by calculating the ratio of the MD dimenmal cut-off value (0.282) allowed a sensitivity value of sion of right mandibular canine (d43) and the 94% and a specificity value of 25.7% to be obtained, inter-canine width (d3343). Additionally, a cut-off indicating that 94% of males were correctly classified, value – the MCI standard – was determined following whereas only 25.7% of females were assessed accurthe formula: [(Mean Male MCI–SD)þ(Mean Female ately. The accuracy of the MCI standard in sex predicMCIþSD)]/2. Casts with MCI values up to this cuttion in different population samples is depicted in off value were reported as female, whereas MCI Table 1. It can be observed that Rao’s MCI performvalues above this limit were reported as male. The ance in an Indian population is quite high (85.9%), MCI standard performance in several studies was although two recent studies in other Indian populacompared.3,16–19 tions observed lower performance values (50.7% and In order to compare the accuracy of the MCI 72.0%). In a French population, in which more similastandard in Portuguese and Indian samples, probabilrities with Portuguese population are expected, the ity function density graphs were plotted. The performMCI performed slightly better (62.9%). ance of alternative cut-offs in sex determination was A ROC curve analysis was used to assess the optiexplored using receiver operating characteristic mal cut-off for identifying males using the MCI. (ROC) curve analysis. Descriptive statistics of the Downloaded from msl.sagepub.com at DICKENSON SCHOOL OF LAW on May 26, 2015
XML Template (2015) [19.3.2015–11:24am] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/MSLJ/Vol00000/150004/APPFile/SG-MSLJ150004.3d
(MSL)
[1–6] [PREPRINTER stage]
Silva et al.
3
Figure 1. Probability density function of mandibular canine index (MCI) values in (a) the Portuguese sample and (b) the Indian sample from Rao et al.18 for a comprehensive comparison of the data. Figure (1b) was inspired by figure 2 in Rao et al.18 for visual comparison.
Table 1. Standard MCI accuracy in sex prediction reported in literature studies, obtained from different population samples. Males
Females
Total
Standard MCI
Population
Number
%
Number
%
Number
%
0.282a 0.27418 0.24419 0.2562 0.26921
Portuguese Indian Indian Indian French
47/50 322/382 51/103 78/100 133/214
94.0 84.3 49.51 78.0 62.15
18/70 336/384 52/100 66/100 134/210
25.7 87.5 52.0 66.0 63.81
65/120 658/766 103/203 144/200 267/424
54.2 85.9 50.7 72.0 62.9
a Calculated for the present sample. MCI: mandibular canine index.
Usually, the MCI standard is obtained using the right Discussion mandibular canine mesiodistal dimension. However, as it was unknown if a better performance in sex preDetermining a person’s sex is crucial part of human diction could be achieved using the right or left manidentification. Dental techniques are often used for dibular canine, the MCI standard using the left this purpose due to the extraordinary resistance of mandibular canine was also determined (Figure 2). teeth to hazardous factors, enabling dental techniques Figure 2 illustrates that no relevant differences in to be used in situations where other methodologies MCI performance were observed either using d43 or cannot be used. Although the use of DNA has d33. Furthermore, the area under the ROC curve has become common due to its robust results, the fact is a value inferior to 0.75 (0.685) showing a moderate that biological samples are not always available or performance in establishing sex classification. suitable for DNA fingerprinting. However, according However, the sex estimation results using the cut-off to Acharya and Mainali,20 teeth should not be used as determined by the ROC curve analysis (0.303) were the sole indicator of sex, even though studies indicate better than those obtained using the MCI standard they are a good adjunct for sex estimation. (Table 2). The canine teeth have been routinely used for Table 3 depicts the canine dimensions, canine manhuman identification purposes because they have dibular arch width and the MCI. All measurements shown the greatest degree of sexual dimorphism were larger in males, and the observed mean differacross numerous populations.4,5,6,9,21–24 Besides, ences were statistically significant (p < .05). they are the most resistant teeth in the human Downloaded from msl.sagepub.com at DICKENSON SCHOOL OF LAW on May 26, 2015
XML Template (2015) [19.3.2015–11:24am] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/MSLJ/Vol00000/150004/APPFile/SG-MSLJ150004.3d
(MSL)
[1–6] [PREPRINTER stage]
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Medicine, Science and the Law 0(0)
dentition, which has led to their use alone in sex estimation.11–15,21 Compared to other teeth, canines present higher level of survival and undergo less wear.24 The reliability of Rao’s MCI methodology is perhaps well illustrated in this study by the near inexistence of
Figure 2. Receiver operating characteristic curve for the assessment of optimal cut-off values for identifying males using the MCI standard from the right mandibular canine (solid line) and the left mandibular canine (dashed). The marks identify the optimal cut-off values in each case.
inter- and intra-observer differences, and data consistent with those from other authors.5,24 A significant relationship was found between sex and canine dimensions as well as between sex and the MCI, which is also in agreement with data from other studies.4,17,22,24 Furthermore, significant differences in the MD width were found, and teeth measurements were systematically wider in men, which has also been found in previous studies.4,13–15,21,25–29 With regard to the MCI standard value for sex determination, contrary to Rao’s study,17 the best cut-point (0.282) performed poorly in sex estimation, identifying 94% of males but only 25.7% of females. This could be explained by population differences, supporting the theory that specific population data should be used for this assessment.7 Rao’s study was carried out in an Indian sample, in which females exhibited MCI values much lower than those of males, with little overlap of frequency curves and with small and similar standard deviation values for males and females in histograms with the normal setting (see Figure 1). In the present sample from the Portuguese population, females exhibited MCI values much higher than Indian females and quite similar to Portuguese (and Indian) males, resulting in a much bigger overlap of frequency curves (see Figure 1). As stated before, these differences may relate to population features,7 but other factors such as the environmental may also have an influence. For instance, a secular trend could be responsible for the changes. Rao’s investigation was conducted in the
Table 2. Standard MCI accuracy in sex prediction in current sample calculated using Rao’s guidelines and ROC curve analysis. Males
Rao’s guidelines ROC curve analysis
Females
Total
Teeth
Standard MCI
Number
%
Number
%
Number
%
43 33 43 33
0.282 0.282 0.303 0.303
47/50 47/50 36/50 36/50
94.0 94.0 72.0 72.0
18/70 17/70 41/70 40/70
25.7 24.3 58.6 57.1
65/120 64/120 77/120 76/120
54.2 53.3 64.2 63.3
ROC: receiver operating characteristic.
Table 3. Descriptive statistics of the canine dimensions, inter-canine width and MCI.
MCI Mandibular right canine (d43) Mandibular left canine (d33) Mandibular arch width (d3343)
Sex
n
Mean (mm)SD
Range (mm)
pa
Male Female Male Female Male Female Male Female
50 70 50 70 50 70 50 70
0.31 0.02 0.30 0.02 8.64 0.59 7.63 0.49 8.64 0.56 7.70 0.48 27.55 1.86 25.42 1.69
0.26–0.37 0.26–0.38 7.00–10.00 6.50–8.50 7.00–10.00 6.50–8.50 23.50–35.00 21.00–28.50
