Predictive accuracy of sexing the mandible by ramus flexure

Shape variation and sex differences of the adult human mandible evaluated by geometric morphometrics

In cases of osseous defects, knowledge of the anatomy, and its age and sex-related variations, is essential for reconstruction of normal morphology. Here, we aimed at creating a 3D atlas of the human mandible in an adult sample using dense landmarking and geometric morphometrics. We segmented 50 male and 50 female mandibular surfaces from CBCT images (age range: 18.9-73.7 years). Nine fixed landmarks and 510 sliding semilandmarks were digitized on the mandibular surface, and then slid by minimizing bending energy against the average shape. Principal component analysis extracted the main patterns of shape variation. Sexes were compared with permutation tests and allometry was assessed by regressing on the log of the centroid size. Almost 49 percent of shape variation was described by the first three principal components. Shape variation was related to width, height and length proportions, variation of the angle between ramus and corpus, height of the coronoid process and inclination of the symphysis. Significant sex differences were detected, both in size and shape. Males were larger than females, had a higher ramus, more pronounced gonial angle, larger inter-gonial width, and more distinct antegonial notch. Accuracy of sexing based on the first two principal components in form space was 91 percent. The degree of edentulism was weakly related to mandibular shape. Age effects were not significant. The resulting atlas provides a dense description of mandibular form that can be used clinically as a guide for planning surgical reconstruction.

Biomechanical Implications of Mandibular Flexion on Implant-Supported Full-Arch Rehabilitations: A Systematic Literature Review

BACKGROUND

Mandibular flexion (MF) is a complex biomechanical phenomenon, which involves a deformation of the mandible, due mainly to the contraction of the masticatory muscles, and it can have numerous clinical effects. The deformation of the lower jaw caused by mandibular flexion is generally very small, and it is often overlooked and considered irrelevant from a clinical point of view by many authors; however, it should be important to remember that median mandibular flexure (MMF) has a multifactorial aetiology. The main aim of the current systematic review is to highlight the different factors that can increase MF in order to help clinicians identify patients to whom they should pay more attention. As a secondary outcome, we wanted to analyse the preventive measures and suitable techniques to be adopted to minimise the negative effects of this phenomenon on oral fixed rehabilitations.

METHODS

The review, which was carried out in accordance with the "Preferred Reporting Items for Systematic reviews and Meta-Analyses" (PRISMA) flowchart, was recorded in the "International Prospective Register of Systematic Reviews" (PROSPERO). As research questions, "Patient/Population, Intervention, Comparison and Outcomes" (PICO) questions were employed. Using the ROBINS-I technique, the risk of bias in non-randomised clinical studies was evaluated.

RESULTS

The initial electronic search identified over 1300 potential articles, of which 54 studies were included in this systematic review. Information regarding the relationship between MF and individual factors, mandibular movements, impression taking, and fixed rehabilitations were obtained.

CONCLUSIONS

The studies included in this systematic review showed that MF is greater during protrusive movements, in the posterior areas of the lower jaw, and in patients with brachial facial type, greater jaw length; small gonial angle; and less density, length, and bone surface of the symphysis. The biomechanical effects of mandibular flexion on fixed restorations are debated. Prospective clinical and radiological observational studies should be conducted to evaluate the potential short-, medium-, and long-term consequences of MF.

Clinical Influence of Mandibular Flexure on Oral Rehabilitation: Narrative Review

AIM

The current paper aims to review mandibular flexure and its clinical implications in the field of oral rehabilitation. Mandibular flexure is a deformity of the mandible, which occurs during jaw movements.

METHODS AND MATERIALS

An electronic database search was conducted using the PRISM model, with a total of 49 articles included.

RESULTS

Mandibular flexure affects various stages of oral rehabilitation treatments. Effects of mandibular flexure are more significant in periodontal patients, and in implant-supported restorations, compared to natural teeth, due to differences in the force absorption by the periodontal ligament. Various adjustments must be made to the prosthodontic framework to enable long-term survival of the restorative treatments.

CONCLUSIONS

Dental practitioners should pay attention to the following: (1) digital impressions are preferred over conventional; (2) mouth opening should be kept to a minimum (as possible, up to 10-20 mm) while also avoiding any anterior movements of the mandible (protrusion); (3) the number of abutment teeth should be kept to a minimum; (4) structures in the lower jaw should be splitted; (5) non-rigid connectors should be used to reduce the effort exerted; (6) in periodontal patients, the preference is for short-span restorations and non-rigid connectors; (7) in implant-supported restorations, it is preferable to divide the framework into two or three segments, utilizing rigid materials with a low elastic modulus. There is no agreement in the literature about the preferred location of the implants in the jaw.

Comparison of data mining algorithms for sex determination based on mastoid process measurements using cone-beam computed tomography

Purpose

The mastoid region is ideal for studying sexual dimorphism due to its anatomical position at the base of the skull. This study aimed to determine sex in the Iranian population based on measurements of the mastoid process using different data mining algorithms.

Materials and Methods

This retrospective study was conducted on 190 3-dimensional cone-beam computed tomographic (CBCT) images of 105 women and 85 men between the ages of 18 and 70 years. On each CBCT scan, the following 9 landmarks were measured: the distance between the porion and the mastoidale; the mastoid length, height, and width; the distance between the mastoidale and the mastoid incision; the intermastoid distance (IMD); the distance between the lowest point of the mastoid triangle and the most prominent convex surface of the mastoid (MF); the distance between the most prominent convex mastoid point (IMSLD); and the intersecting angle drawn from the most prominent right and left mastoid point (MMCA). Several predictive models were constructed and their accuracy was compared using cross-validation.

Results

The results of the t-test revealed a statistically significant difference between the sexes in all variables except MF and MMCA. The random forest model, with an accuracy of 97.0%, had the best performance in predicting sex. The IMSLD and IMD made the largest contributions to predicting sex, while the MMCA variable had the least significant role.

Conclusion

These results show the possibility of developing an accurate tool using data mining algorithms for sex determination in the forensic framework.

Examination of new parameters for sex determination of mandible using Japanese computer tomography data

OBJECTIVE

In the field of forensic science, sex discrimination of skeletons is an important identification item for personal identification. The individual sex discrimination method using skeletons includes a determination method using measurement values and a macroscopic form observation method. Both methods have advantage and disadvantage. In this study, we used the homologous model technique and principal component (PC) analysis to determine gender difference from morphology of the mandible.

METHODS AND MATERIALS

45 patients (23 males and 22 females) of CT imaging for tooth extraction from January 2018 to March 2019 at department of oral surgery, Osaka Medical College. The mean age was 43.1 ± 14.6. Patients with less than 14 remaining teeth were excluded because the number of remaining teeth may affect the shape of the mandible. 3D images were constructed, and 20 landmarks plotting on the 3D model surfaces. We generated template models of the mandible consisting of approximately 8434 polygons. The template model automatically fitted into the individually scanned point cloud of the mandible by minimising external and internal energy functions. As described above, the mandibles were constructed for each sample by using the Homologous Body Modeling software (HBM, Digital Human Technology, Inc.) and the mHBM-Rugle (Medic Engineering Corporation). The mandibles were analysed using the PCA.

RESULTS

The contribution of the most important PC was found to be 27.2%. 12 PCs explained over 75% of the total variance. That is, it was able to express 75% or more of the mandible expression with 12 PCs. A significant difference between male and female was observed in the first PCs (Wilcoxon test, p < 0.05). Visualising the result of the first PC showed that the mandibular branch of male was larger than that of female, and the mandible angle was overhanging outside.

CONCLUSION

This method is a combination of the determination method using the previous measurement values and the determination using macroscopic observation, and is considered to be innovative method.

Geometric morphometric analysis of sexual dimorphism in the mandible from panoramic X-ray images

The human mandible is routinely utilised as part of the assessment of biological identity in forensic anthropological and odontological practice. The research introduces a novel geometric morphometric technique to investigate and quantify shape variation in the morphology of the mandibular corpus and ascending ramus and consequently highlights the potential for forensic purposes. Human mandibles from digital clinical orthopantomogram X-ray images, based on a sample of 50 male and 50 female adults from a modern Italian population, were examined. Three fixed landmarks were applied to the symphysis and condyle and 50 semi-landmarks re-sampled along the inferior corpus and the posterior ramus. Symmetrical reflection was applied yielding 200 configurations of 53 landmarks. Shape analyses were undertaken via: Procrustes superimposition; principal components analysis to investigate patterns of variation; classification using linear discriminant analysis with leave-one-out cross-validation; partial least squares (PLS) to test for structural modularity; and finally, retitle page sampling and re-analysis following PLS to optimize shape classification criteria. Stepwise re-sampling of landmarks reached an optimum cross-validated classification of 94.0% based on 25 landmarks; the results are strongly significant and suggest that the shape relationship between the mandibular corpus and ramus offers significant potential for forensic identification purposes using this method.

The morphology of the human mandible: A computational modelling study

Cephalometric methods have been used to evaluate morphometric measurements of the mandible and quantify sex-related anatomical features; however, most studies to date employ a limited set of location-specific measurements without considering the entire three-dimensional anatomy of the mandible. The aims of this study were to develop statistical shape models (SSMs) of partially edentulous male and female mandibles to evaluate inter-subject morphological variability and secondly to assess the effectiveness of discrete clinical morphometric measurements in prediction of complete three-dimensional mandible geometry. Computed tomography images of forty partially edentulous female and twenty-five male subjects were obtained, and SSM developed using mesh fitting, rigid body registration and principal component analysis. Analysis of female and male SSMs showed that the variation along their first principal components was size-related. Sex-differentiating pure shape variations were found along the first principal component of size-normalised SSM and were observed to be most prominent in the symphysis and posterior ramus regions of the mandible. Seven morphometric measurements were found to characterise female and male shape prediction optimally. The capability to rapidly generate accurate patient-specific shape-predictive models of the mandible may be useful for implant development and pre-operative planning, particularly in the absence of bony structures following trauma or tumour resection.

Sex estimation using computed tomography of the mandible

Sex estimation of skeletal parts is of great value even in the DNA era. When computed tomography (CT) facilities were introduced to forensic institutes, new possibilities for sex estimation emerged. The aim of this study was to develop a CT-based method for sex estimation using the mandible. Twenty-five CT-based measurements of the mandible were developed and carried out on 3D reconstructions (volume rendering) and cross sections of the lower jaw of 438 adult individuals (214 males and 224 females). Intraobserver and interobserver variances of the measurements were examined using intraclass correlation coefficient (ICC) analysis. Five discriminant functions were developed using different states of completeness of the mandible. The success rates of these equations were cross validated twice. The measurements were found to be highly reliable (for intraobserver 0.838 < ICC < 0.995 and for interobserver 0.71 < ICC < 0.996). For a complete mandible, the correct classification rate was 90.8%. For incomplete mandibles, the correct classification rates varied from 72.9 to 85.6%. Cross-validation tests yielded similar success rates, for the complete mandible 89% and for the incomplete mandible 67.5 to 89%. We concluded that CT techniques are appropriate for estimating sex based on the mandible size and shape characteristics. Suggested discriminant functions for sex estimation are given with data on the correct classification rates.

Accuracy of mandibular measurements of sexual dimorphism using stabilizer equipment

The objective of this investigation was to compare the accuracy of mandibular measurements using a stabilizer (MS) with gold standard computed tomography (GS) images. Sixty mandibles were studied. Werth TomoScope HV Compact® was used to obtain CT images (GS), and the MS was also used. Analysis of the CT scans was performed using the VG Studio Max software® (Volume Graphics GmbH, Heidelberg, Germany), and MS was used after the proper positioning of the mandible. Descriptive and paired t test measures were used, and a ROC curve was calculated, as well as sensibility and specificity. MedCalc and STATA 13.0® were used (95% level of significance). Bicondylar breadth, bicoronoid breadth and minimum ramus breadth reached the highest concordance correlation coefficients at 0.99 (0.99-1.00), 0.99 (0.99-1.00) and 1.00 (0.99-1.00), respectively. Comparing observers with GS, the lowest accuracy was noted for the maximum mandibular length [0.59 (0.45-0.69), 0.64 (0.51-0.74)], the breadth of the right (0.14 (0.04-0.23), 0.14 (0.004-0.24)) and left mandibular body [0.14 (0.03-0.24), 0.16 (0.05-0.26)], and the right [0.58 (0.45-0.69), 0.63 (0.51-0.73) and left (0.59 (0.45-0.70), 0.59 (0.46-0.69)] mandibular angle. Various measurements exhibited good sensibility for males using MS: maximum mandibular length (78.12), bicondylar breadth (78.12), left mandibular notch breadth (84.37), and the left height of the mandibular body at the mental foramen (75.00). High specificity in discriminating females was observed for the left maximal ramus height (85.19), mandibular length (85.71), bicoronoid breadth (96.43), right height of the mandibular body at the mental foramen (82.19), bimental breadth (78.57), breadth right (92.86) and left (96.43) mandibular body, minimum ramus breadth (89.29), and left mandibular angle (85.71). MS was able to discriminate sexual dimorphism.

Radiographic Blind Test of Curvature of the Posterior Border of the Mandibular Ramus as a Morphological Indicator of Gender

PURPOSE

Curvature of the posterior border of the mandibular ramus at the occlusal plane has been described as a morphological trait for males. Controversy over the accuracy of this method remains among researchers; studies employing similar methods report accuracy rates for successful gender identification ranging from 59% to 99%. This blind study assessed evaluators' ability to determine gender based on the presence or absence of curvature of the posterior margin of the mandibular ramus through panoramic radiographs.

MATERIALS AND METHODS

Randomly selected panoramic radiographs were obtained from The Ohio State University College of Dentistry for 413 adult male (M) and female (F) subjects. Two evaluators separately assigned ratings using a similar method to the Loth and Henenberg methodology to each subject on the right and left sides of mandibular rami. The ratings were based upon three criteria: (1) presence of curvature at the occlusal plane (M), (2) presence of curvature but not at the occlusal plane (F), and (3) lack of curvature (F). Pearson exact chi-squared test was used to evaluate the statistical strength of the ratings.

RESULTS

The evaluators were only in agreement for both the right and left rami in roughly two-thirds (66.8%) of cases when there was no excessive tooth loss (ETL); however, the inter-observer agreement improved to 82.1% for those rami associated with ETL. Inter-observer agreement occurred in 72.9% of female rami and in only 64.4% of male rami.

CONCLUSION

The results of this study indicated that assessment of posterior border curvature of  mandibular rami through panoramic radiographs was not a reliable indicator of gender and was further plagued by unacceptably high levels of inter-observer disagreement.

Gender-Related Differences in Pelvic Morphometrics of the Retriever Dog Breed

This study presents the results from a morphometric analysis of 52 dry Retriever dog pelvic bones (30 male, 22 female). A total of 20 parameters were measured using an osteometric board and digital vernier caliper. Six parameters were found to be significantly higher (P < 0.05) in males than in females, while one parameter was significantly higher (P < 0.05) in females than in males. However, none of the measured parameters demonstrated clear cut-off values with no intersect between males and females. Therefore, we generated a stepwise discriminant analysis from all 20 parameters in order to develop a possible working equation to discriminate gender from a dog pelvic bone. Stepwise discriminant analysis was used to create a discrimination function: Y = [82.1*PS/AII] - [50.72*LIS/LI] - [23.09*OTD/SP] + [7.69*SP/IE] + [6.52*IC/OW] + [7.67*ISA/OW] + [20.77*AII/PS] + [504.71*OW/ISA] - [90.84*PS/ISA] - [148.95], which showed an accuracy rate of 86.27%. This is the first study presenting an equation/function for use in discriminating gender from a dog's pelvic measurements. The results can be used in veterinary forensic anthropology and also show that a dog's pelvis presents sexual dimorphisms, as in humans.

Clinical importance of median mandibular flexure in oral rehabilitation: a review

The mandible has a property to flex inwards around the mandibular symphysis with change in shape and decrease in mandibular arch width during opening and protrusion of the mandible. The mandibular deformation may range from a few micrometres to more than 1 mm. The movement occurs because of the contraction of lateral pterygoid muscles that pulls mandibular condyles medially and causes a sagittal movement of the posterior segments. This movement of mandible can have a profound influence on prognosis and treatment outcome for various restorative, endodontics, fixed, removable and implant-related prosthesis. The review unfolds the causes, importance and clinical implications of median mandibular flexure in oral rehabilitation. This review also highlights the appropriate preventive measures and techniques that should be adopted by clinicians to minimise the effect of flexural movement of the jaw during oral rehabilitation. This would not only help clinicians to achieve a good prosthesis with accurate fit and longevity but also maintain the health of the surrounding periodontal or periimplant gingival tissues and bone.

Osteometric analysis for sexing of modern sternum - an autopsy study from South India

Estimation of sex is considered as one of the essential parameters in forensic anthropology and requires foremost attention in the analysis of commingled and unidentified remains. In India, there is a paucity of population specific morphometric standards for identifying sex from unknown human remains in different population groups. The present research is an osteometric analysis to study the sexual dimorphism of the sternum of South Indian origin using statistical considerations. The study sample constituted of adult autopsied sternums of known age and sex. Five linear measurements (length of the manubrium, mesosternum, manubrium and mesosternum together, and width at 1st and at 3rd sternebra) were examined during the study. Three indices (manubrio-corpus Index, ratio of the length of the mesosternum and manubrium, and sternubrial-width index) were computed from the length and width measurements of the sternum. Statistical analysis was done using SPSS computer software and Student's t-test was applied to find the sex differences in these variables. While statistically significant sex differences were observed for all the five linear measurements of the sternum, none of the sternal indices showed statistically significant sex differences. Discriminant function and logistic regression analysis were performed to derive the predicting models for estimation of sex from the different variables. The predictability of sternal measurements in sexing using univariate models ranged between 67.5% for the width at 3rd sternebra and 74.4% for the combined length of manubrium and mesosternum. The classification accuracy rates of sternal measurements were observed to be higher when multivariate analysis was performed. Length of manubrium and mesosternum together along with width at 1st sternebra yielded maximum accuracy of 79.5% (discriminant function analysis) and 81.2% (logistic regression analysis) in sexing of male and female sternum. The present research concludes that the application of sternum in sex estimation should be restricted to cases when other more reliable bones for sexing are not available to the investigators.

Sex determination of human mandible using metrical parameters

INTRODUCTION

Determination of sex from an unknown human bone is an important role in forensic and anthropology field. The mandible is the largest and hardest facial bone, that commonly resist post mortem damage and forms an important source of information about sexual dimorphism.

AIM

To determine the sex of unknown human adult mandible using metrical parameters.

MATERIAL AND METHODS

A random collection of 250 dry, complete, undamaged human adult mandibles of South Indian population were subjected to metrical parameters like Bigonial breadth, Bicondylar breadth and Mandibular length using Mandibulometer and Vernier caliper.

STATISTICAL ANALYSIS USED

The data's were expressed as Mean ± SD and then analyzed by t-test by using SPSS software. Discriminating point and limiting points were also calculated.

RESULTS

The mandibular length, bigonial breadth and bicondylar breadth showed significant statistical gender difference.

CONCLUSION

The present study revealed that the sex of human mandible can be assessed by using metrical parameters as an additional tool to establish the identity of a person.

Sex determination using mandibular ramus flexure: a preliminary study on Indian population

Determination of sex by morphological assessment has been one of the oldest approaches in forensic anthropology. Loth and Henneberg(6) introduced a morphological trait "Mandibular Ramus Flexure" for sex identification with a high accuracy of 99% in African Blacks. However, the population specificity of sexually dimorphic features is well known. The purpose of this study is to test the reliability of this trait in Indian population. A total number of 112 adult mandibles (88 males and 24 females) were studied from the Department of Forensic Medicine, Institute of Medical Sciences, Banaras Hindu University, India. The mandibles were scored according to the original method by two observers in three different sessions. This was done to test inter and intra-observer errors in identifying the trait. The result shows that this trait can be used to diagnose sex with an average accuracy of upto 82%. Though, inter and intra-observer errors were present but could be minimized with extended practice. So, the trait has the potential to be relied upon as a single morphological trait for determination of sex in Indian population.

The Watinglo mandible: a second terminal Pleistocene Homo sapiens fossil from tropical Sahul with a test on existing models for the human settlement of the region

This paper analyses a fossil human mandible, dated to circa 10ka, from Watinglo rockshelter on the north coast of Papua New Guinea. The fossil is metrically and morphologically similar to male mandibles of recent Melanesians and Australian Aborigines. It is distinguished from Kow Swamp and Coobool Creek male mandibles (Murray Valley, terminal Pleistocene) by being smaller and having different shape characteristics, as well as smaller teeth and a slower rate of tooth wear. It pairs with the Liang Lemdubu female (Late Glacial Maximum, Aru Islands) in suggesting that the morphology of the terminal Pleistocene inhabitants of tropical Sahul was gracile compared to their contemporaries within the southern Murray drainage. An explanatory scenario for this morphological contrast is developed in the context of the Homo sapiens early fossil record, Australasian mtDNA evidence, terminal Pleistocene climatic variation, and the possibility of multiple entry points into Sahul.

Recommendations for the forensic diagnosis of sex and age from skeletons

In both diagnostic fields a two-stage strategy is recommended: to first use "field" methods that are quick and easy but more imprecise and then "laboratory" methods that are time consuming but more precise. In preparing skeletal work, individuality of a skeleton should be checked, traces of diseases sought and time since death assessed. For sexing non-adults, the field methods are tooth mineralisation, long bone length and a few morphological skull and pelvis characteristics, for adults it is the morphology of pelvis and skull, and for both age groups the advanced laboratory method is molecular biology. For ageing non-adults the methods are mineralisation of teeth, long bone length and epiphysis development. For ageing adults the advanced laboratory method is aspartic acid racemisation. Less accurate laboratory methods are cement ring counts and histology of bones and teeth. Quick morphological methods using the pubic symphysis and other traits in combinations follow. Finally, cranial sutures and tooth number give a quick and rough impression. For the selection of a method and the assessment of its value the stochastic error produced for the reference sample is the decisive criterion; it should also be used to assess the reliability of a single diagnosis. Prerequisites for all work with skeletons are not only a complete knowledge of the relevant biology as well as specific techniques but also initial detailed instructions and with forensic applications, personal experience.