Testing Discriminant Functions for Sex Determination from Deciduous Teeth*,†

Are deciduous upper molars and lower canines useful for sex estimation?

OBJECTIVE

This paper investigates whether deciduous upper molars and lower canines have sexual dimorphic features, exploring these teeth' dimensions and the presence of Zuckerkandl's tubercle and Carabelli's cusp on the first and second upper molars.

DESIGN

We analyzed 64 pairs of dental plaster casts from 34 females and 30 males aged between 3 and 12 years. We measured the first and second deciduous upper molars and the lower deciduous canines (maximum mesiodistal and buccolingual length), and we registered the presence of the Zuckerkandl's tubercle and the Carabelli's cusp on the first and second upper molars, respectively.

RESULTS

Regarding the differentiation between sexes using Carabelli's cusp and Zuckerkandl's tubercle, the classification was not independent of Carabelli's cusp presence only for tooth 65 (p = 0.035). In all other teeth, whether for Carabelli's cusp or Zuckerkandl's tubercle, their presence was similar for both sexes. There were statistically significant differences between sexes (p < 0.05) for the buccolingual measurements of both upper second molars, the first right upper molar, and the right canine. The developed model allowed for a 64.1% accuracy in sex estimation.

CONCLUSIONS

The study suggests that while Carabelli's cusp and Zuckerkandl's tubercle in upper deciduous molars don't consistently differ between sexes, tooth size, particularly the buccolingual measurements of certain teeth, including upper deciduous molars and lower canines, may provide a more reliable criterion for sex estimation. The developed model depicted moderate accuracy, underscoring the need for a multifactorial approach when estimating sex from skeletal remains. It suggests that while dental features can contribute to sex estimation, they should be used in conjunction with other skeletal or molecular markers to improve accuracy.

Human bony labyrinth as a sex indicator in subadults

Due to the durability and good preservation of the petrous bone in archaeological and forensic contexts, the value of the inner ear as a sex indicator has been evaluated in various studies. Previous findings suggest that the morphology of the bony labyrinth is not stable in the postnatal period. In this study, we aim to assess the sexual dimorphism of the bony labyrinth via analysis of computed tomography (CT) data obtained from 170 subadults (birth to 20 y.o.) and test whether the postnatal changes of the bony labyrinth affect the level of dimorphism in the inner ear. A set of 10 linear measurements of 3D labyrinth models as well as 10 size and shape indices were analyzed. Sexually dimorphic variables were used to produce sex estimation formulae with discriminant function analysis. The produced formulae allowed for the correct classification of up to 75.3 % of individuals aged from birth to 15 years old. Sexual dimorphism was not significant for individuals between 16 and 20 years of age. This study suggests that the morphology of the subadult bony labyrinth exhibits significant sexual dimorphism in individuals under 16 years of age, which can aid the forensic identification process. Although postnatal growth of the temporal bone seems to affect the level of sexual dimorphism present in the inner ear, the formulae created in this study could be used as an additional tool for sex estimation of subadult (<16 y.o.) remains.

Sexual dimorphism in deciduous tooth crown size: Variability within and between groups

OBJECTIVES

Sexual dimorphism in deciduous tooth crown size is often used to identify sex in sub-adults from archeological sites and forensic settings. Yet sexual dimorphism in deciduous dental attributes is less well documented than in permanent teeth. This analysis was conducted to document variation in sexual dimorphism within and between a global sample of populations.

METHODS

Mean deciduous tooth crown size was culled from published literature, yielding a sample of 37 groups. Mean mesiodistal (MD) and buccolingual (BL) crown dimensions are the basis for computing percent sexual dimorphism [(M/F-1) * 100]. Three analyses were conducted: (1) a statistical analysis of mean % sex dimorphism (%SD) within and between populations, (2) an evaluation of rank-ordered %SD by tooth, and (3) an assessment of intergroup patterns in degree of sexual dimorphism. Univariate tests of significance, correlation and regression, and multivariate cluster analysis were used.

RESULTS

Mean %SD is low overall (1.77) for 26 groups and the level of dimorphism is not significantly different for MD (1.68) and BL (1.72) dimensions. The most sexual dimorphic deciduous teeth include incisor, canine and molar tooth types, while in the permanent dentition canines are consistently most sexual dimorphic. Global variation in sexual dimorphism of deciduous tooth size is low with little inter-ethnic variation.

CONCLUSIONS

Sexual dimorphism in crown size is lower and more variably expressed than in permanent teeth. Differences may relate to developmental, chromosomal, and hormonal factors. Degree of sexual dimorphism is not associated with ethnicity in this global sample.

Testing the cross-applicability of juvenile sex estimation from diaphyseal dimensions

Sex estimation is a crucial component of the biological profile. Stull et al. (2017) have proposed a promising juvenile sex estimation method using long bone measurements taken from a South African sample, providing relatively high classification accuracies and made easy to use via the KidStats web-based app. In this study, we test the models developed by Stull et al. (2017) on an external historic population from Lisbon, Portugal, in order to determine whether the models can be reliably applied to archeological and forensic populations outside of the original population sample. The study sample consisted of 102 individuals (45 females and 57 males) aged under 13 years at death from the Lisbon identified skeletal collection. Measurements from these individuals were used to test the flexible discriminant analysis (FDA) models given by Stull et al. (2017). Allocation accuracies were calculated for boys and girls and children over and under 2 years separately and combined. Our findings show that the models developed by Stull et al. (2017) yield poor accuracy when applied to our external population and thus can potentially be misapplied on archeological skeletal remains or forensic remains of unknown origin. A number of statistical issues may explain why models fail to be transportable or even generalizable, namely multicollinearity, model overfitting and overly optimist bootstrapped cross-validation rates. It is also likely that population differences in size and sexual size dimorphism also affected the applicability of the models. We emphasize the importance of externally validating prediction models, particularly if they are intended to be applied across populations. Our study addresses Stull and co-worker's request for further validation of the method on populations outside of South Africa, as the models cannot be confidently applied in the field until it has been externally validated.

Sexing the bony labyrinth: A morphometric investigation in a subadult and adult Belgian identified sample

In forensic anthropology, sex estimation is a fundamental step in assessing individual biological profiles when analyzing human skeletons. Yet, current methods are not reliable enough to allow an accurate sex identification of highly fragmented, burnt, or subadult remains. This paper aims to investigate sexual dimorphism of the bony labyrinth on both identified subadult and adult individuals. The bony labyrinth is of particular interest for sex estimation since it is alleged to complete size and maturation pre-pubertally and is located inside the petrous part of the temporal bone which protects it from taphonomic processes. The study was performed on 93 CT scans of identified individuals from two Belgian osteological collections (19-20th century) and from current pediatric images (Erasme hospital, Brussels). Linear and angular measurements were taken on 2D slices of right bony labyrinths. Intra- and interobservers error measurements were calculated. Statistical tests were used to unravel any morphological variations between subadult and adult bony labyrinths and to highlight differences between females and males, separately in subadults and adults. Linear discriminant functions were established by cross-validation and tested on an independent sample from Belgium. Some measurements were significantly different between subadults and adults, and between females and males within both subadult and adult samples. Univariate functions achieved 72.7% in subadults and 68.4% in adults whereas multivariate equations increased accuracy respectively up to 84.9% and 78.4%. This study entails promising results to design a sex estimation method suitable for fragmented and/or subadult remains. Further metric approaches are needed to explore bony labyrinth sexual dimorphism.

Sex estimation by tooth dimension in a contemporary Spanish population

AIM

Sex determination is a fundamental step in the biologic profile reconstruction of unknown individuals. Teeth are frequently recovered intact, even in case of natural or mass disasters, fires, crashes or accidents. Therefore, they are very valuable in sex determination in a forensic and anthropological context. The objective of this study is to identify a method for sex determination using the mesio-distal widths of permanent teeth, in a contemporary Spanish sample.

METHOD

The mesio-distal dimensions of permanent teeth were obtained from study casts derived from patients seeking treatment at the orthodontic clinic of the Universidad Europea de Valencia. A total of 210 patients were included in the study group after applying the inclusion and exclusion criteria. The mean age of the subjects was 14.48±2.78 in males and 14.71±2.69 in females. A Principal Component Analysis (PCA) was performed from the logarithm of the dental widths. Then, a Logistic Regression Model (LRM) was used to assess the statistical significance of the relations among the components and the sex of an individual.

RESULTS

Based on the indicators Average Tooth Dimension (ADT), Canines to the Rest of the dentition Ratio (CRR) and Lower to Upper Canine Ratio (LUCR) a predictive equation was obtained in order to determine the sex of an unknown individual. The global accuracy of the method was 76.2%. If a simpler model is used based only on the LUCR indicator the accuracy reached would be of 65.7%. The global accuracy of the method in a validation group proved to be 70%.

CONCLUSIONS

The use of tooth dimension can be a considered a valuable complementary tool to use in sex determination in a Spanish contemporary population.

A systematic review of odontological sex estimation methods

BACKGROUND

In human identification sex estimation plays an important role in the search for ante-mortem data.

AIM

To systematically review studies describing and testing/validating methods of odontological sex estimation. The set research question was: What odontological sex estimation method is the most accurate?

MATERIALS AND METHODS

An electronic search until November 29th 2016 was performed in 5 databases: MEDLINE/PubMed, Cochrane, SciELO, LILACS and Grey literature. The PRISMA guidelines were used. Studies were assessed and included based on the reported data. In particular data criteria were set regarding the considered population, sample size, age range, sex estimation method, type of statistical analysis and study outcome. The extracted data enabled to classify the included studies. Meta-analysis was used to compare the study outcomes per obtained study group.

RESULTS

The established search string detected 4720 studies. 103 were considered eligible after review of title, abstract and full-text. The odontological sex estimation methods were classified based on dental metric and non-metric measurements (n=65), cephalometric analysis (n=13), frontal and maxillary sinuses (n=5), cheiloscopy (n=4), palatal features (n=3) and biochemical analysis of teeth (n=13). Teeth measurements for sex estimation were mainly performed on casts (n=34), followed by skeletal remains (n=13), medical imaging (n=5), intraoral measurements/ photography (n=4), and cascades of the above (n=4).

CONCLUSION

The variety of published odontological sex estimation methods highlights the importance of sex estimation in human identification. Biochemical analysis of teeth proved to be the most accurate method, but in forensic practice, a need to select the most appropriate evidence based odontological sex estimation method exists.

Sex estimation based on deciduous and permanent dentition in a contemporary Spanish population

Sex estimation of skeletal remains with satisfactory allocation accuracy represents an essential step in reconstructing the biological profile of unknown individuals in archaeological research and forensic practice. Teeth are among the most frequently recovered physical elements of an individual that remain after death due to their hardness, durability, and resistance to postmortem insults. This study was based on the deciduous and permanent dentition of 269 individuals (150 males and 119 females) from the Granada osteological collection of identified infants, young children, and adults (Granada, Spain). Mesiodistal, buccolingual, and diagonal crown and cervical diameters of both dentitions were measured, and logistic regression analyses were performed to create equations for sex discrimination. The results show that the first and second deciduous molars and the permanent canines are the teeth with the greatest sexual dimorphism, providing percentages of correct assignment of sex between 78.1 and 93.1% in deciduous dentition and between 79.4 and 92.6% in permanent teeth, depending on the dimensions used. The results indicate that this method may be applicable as an adjunct with other accepted procedures for sex estimation when fragmentary skeletal remains are encountered in archaeological excavations and in forensic contexts.

Sexual dimorphism of the bony labyrinth: a new age-independent method

Currently in physical anthropology there is a need for reliable methods of sex estimation for immature individuals and highly fragmented remains. This study develops a sex estimation technique from discriminant function analysis of the bony labyrinth as it matures before puberty and can survive taphonomic conditions that would destroy most other skeletal material. The bony labyrinth contains the organs of hearing and balance. For this reason biologists and paleoanthropologists have undertaken research in this area to understand evolutionary changes in locomotion. Prior studies have found clear differences between species, but within-species variation has not been satisfactorily investigated. 3D segmentations of the left and right labyrinths of 94 individuals from a Cretan collection were generated and measured. Mean measurements of height, width, size, and shape indices were analyzed for sexual dimorphism, bilateral asymmetry, and measurement error. Significant sexual dimorphism was detected for several measurements. For sex estimation, the single best variable was the radius of curvature of the posterior semicircular canal, which achieved 76% accuracy. Two multivariate functions increased accuracy to 84%. Although these equations are less accurate than equations for complete long bones and crania, they appear to be as accurate as or better than other techniques for sexing immature individuals and temporal bones.