Cranial suture closure as an age indicator: A review

Forensic Science International 307 (2020) 110111

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Forensic Science International journal homepage: www.elsevier.com/locate/forsciint

Review Article

Cranial suture closure as an age indicator: A review Sittiporn Ruengdita , D. Troy Caseb , Pasuk Mahakkanukrauhc,d,e,* a

Department of Forensic Medicine, Faculty of Medicine, Chiang Mai University, Chiang Mai, 50200, Thailand Department of Sociology and Anthropology, North Carolina State University, Campus Box 8107, Raleigh, NC 27695-8107, USA c Department of Anatomy, Faculty of Medicine, Chiang Mai University, Chiang Mai, 50200, Thailand d Forensic Osteology Research Center, Faculty of Medicine, Chiang Mai University, 50200, Thailand e Excellence Center in Osteology Research and Training Center (ORTC), Chiang Mai University, Chiang Mai, 50200, Thailand b

A R T I C L E I N F O

A B S T R A C T

Article history: Received 4 July 2019 Received in revised form 24 November 2019 Accepted 4 December 2019 Available online 26 December 2019

Cranial suture closure has been recognized for over a century as a useful trait for age estimation. Although this indicator has become a standard feature of age assessment protocols in skeletal remains, serious questions have been raised about its reliability. This article attempts to provide a comprehensive review of cranial suture closure as an age indicator from several perspectives, including its anatomy and history, as well as issues relating to validation, statistics, and the potential of technological advancements to improve outcomes. We further suggest a path forward for the use of cranial suture closure as an estimator of age. Although its unreliability has been widely reported, cranial suture closure still appears to have value as an aging method, and it is hoped that the information contained in this article can serve as a stepping stone toward more effective use of this indicator. The cranium is often more durable than other skeletal elements in both archaeological and forensic circumstances, so maximizing the effectiveness of cranial indicators is an important goal. It is hoped that recent advancements in technology and in analytical approaches to the cranial sutures could breathe some new life into this feature as an indicator of age. © 2019 Elsevier B.V. All rights reserved.

Keywords: Age estimation Suture closure Forensic anthropology

Contents 1. 2.

3. 4. 5. 6. 7. 8. 9.

Anatomy of cranial sutures and their closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . History of cranial suture closure as an age indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cranial Sutures before “Todd and Lyon 1924” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Pioneering study of Todd and Lyon (1924) on age estimation from cranial suture closure studies . . . . . 2.2. Studies on age estimation using cranial suture closure after Todd and Lyon Mckern and Stewart (1957) 2.3. Cranial sutures as an age Indicator: The perspective from the European school . . . . . . . . . . . . . . . . . . . . . . . . . Meindl and Lovejoy (1985) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alternative cranial suture sites as age predictors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Validation studies on published age estimation methods using cranial suture closure . . . . . . . . . . . . . . . . . . . . Why cranial suture closure is still used even though its reliability is questioned . . . . . . . . . . . . . . . . . . . . . . . . Development of statistical analytical techniques and cranial suture closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advanced techniques for cranial suture examination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion and path forward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CRediT authorship contribution statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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1. Anatomy of cranial sutures and their closure * Corresponding author at: Department of Anatomy, Faculty of Medicine, Chiang Mai University, Chiang Mai, 50200, Thailand. E-mail addresses: [email protected] (S. Ruengdit), [email protected] (D. Troy Case), [email protected] (P. Mahakkanukrauh). http://dx.doi.org/10.1016/j.forsciint.2019.110111 0379-0738/© 2019 Elsevier B.V. All rights reserved.

The skull is composed of 22 bones (excluding three pairs of ear ossicles and the hyoid). Most of these bones develop through intramembranous ossification, while only the base of the skull

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develops by means of endochondral ossification. Between each adjacent cranial bone, the two bones interlock by means of a saw tooth, or zipper-like articulation called a suture. Sutures are composed of fibrous tissue that joins the cranial bones together. During craniofacial development, sutures are the main sites of bone growth along the margins of the cranial bones, especially during periods of rapid growth. Twenty-four (24) of these sutures (Fig. 1) have been studied and reported in the forensic osteological literature [1–4]. During normal postnatal development, some sutures remain open and some close according to as yet undefined molecular mechanisms. Suture formation seems to be regulated by growth factor signaling along the osteogenic fronts of the adjacent bones [5,6]. Sutures can develop between bone edges in the midline, between two adjacent bones, and at the sites of overlapping bone plates that approach each other at different levels. This latter circumstance can result in overlapping sutures, such as the squamosal suture [7–9]. Suture morphology derives from the interactions of three different tissues: sutural mesenchyme, osteogenic fronts, and the dura mater [10]. Sutural mesenchyme begins the process by differentiating and depositing extracellular matrix which is then mineralized. During development of the sutures, the sutural mesenchymes are separated by the intervening bones into an outer ectoperiosteal layer and an inner dura mater [11]. Signals from the dura mater are more important during the prenatal period. They regulate suture patency. Osteogenic fronts are dominant in the postnatal period [10]. Any disturbances in the signaling pathways can cause very severe defects, such as cranial disfigurement. These factors and environmental effects probably influence cranial structure throughout life [9]. Studies have reported that molecular mechanisms regulate suture closure. Disturbance occurring with this mechanism could result in malfunction of suture patency and fusion [12]. Craniosynostosis, or premature suture is a pathological condition related to the suture closure timing. Early closure of single sutures leads to variation in suture closure pattern [13–15].

Consequently, this condition would most definitely cause an important bias in age estimation based on suture closure. Cranial bone growth during neurocranium development involves intramembranous bone growth with a separate ossification center for each of the primordial cranial bones. The osteogenic fronts at the cranial bone edge approximate one another and suture formation is initiated as the bone fronts abut or overlap one another [11,16]. The edges of these adjacent cranial bones develop into cranial suture sites, with the distance between adjacent bone margins and the timing of cranial bone fusions and suture obliteration regulated by the dura mater [5]. In humans, the end point of cranial vault growth occurs with fusion of associated bones in the third decade of life. In contrast, in the facial region, the bones may remain separated by fibrous tissue until the seventh or eighth decade of life [5], although there is some disagreement about the timing of these events based on previous studies [2,17–19]. Besides the factors related to cranial bone development, other factors, such as hormones, biomechanical force, and diet have also been proposed as important variables in cranial bone development and suture maintenance [20,21]. For example, estrogen has been reported to be one of the factors that plays a role in the development of the cranial suture complex [20]. James and colleagues (2009) suggested that signals derived from estrogen may be associated with suture fusion in the mouse, by affecting osteoblast differentiation. Additionally, misinterpretation of suture closure that could lead to error in estimating age may be caused by trauma. Diastasis, or linear fractures that pass into a suture line and interrupt the weaker interdigitation between the cranial bones or that widen the original open suture could make observers misread the fracture as an open-like suture [22,23]. Additionally, post-mortem trauma caused by burning or freezing can result in heat-induced fractures [22,24]. This kind of fractures can also mimic unfused stages of cranial sutures. The relationship between cranial bone growth at the bone edge and suture patency plays an important role in mechanisms of suture closure. The biological mechanisms that regulate cranial

Fig. 1. Examples of cranial sutures studied in major publications. These include ectocranial (top left, middle, and bottom right), endocranial (bottom left) aspects (coronal, sagittal, and lambdoidal sutures), suture locations (A: bregma, B: midcoronal, C: anterior sagittal, D: obelion, E: lambba, F: midlambdoid, G: pterion, H: sphenofrontal), facial sutures (top right: I denotes frontonasal, J denotes nasomaxillary sutures), and maxillary sutures (bottom right: K and L denote anterior median and transverse palatine sutures, respectively).

S. Ruengdit et al. / Forensic Science International 307 (2020) 110111

edge growth and suture patency remain unclear. Therefore, uncertain intrinsic factors coupled with poorly understood extrinsic factors, such as biomechanical force or diet, might lead to the variation that has been reported in terms of cranial suture closure. 2. History of cranial suture closure as an age indicator Age estimation among adults has been the subject of research for nearly a century. Obliteration of cranial sutures was among the first areas of the skeleton targeted for age estimation in adults, and has received considerable attention since it was first proposed [1,3,25–30]. However, this method of age estimation has been replaced by other methods that appear to be more accurate. Recently, a survey of forensic anthropologists who routinely do forensic anthropology casework was conducted to determine which methods are used preferentially for age estimation [31]. The results revealed that the Suchey-Brooks method [32] which utilizes the pubic symphysis was the preferred approach (over 95 %) for estimating age. The second preference (92.2 %) was the Iscan et al. method [33–36], that examines the sternal end of the fourth rib, as well as the Lovejoy et al. method (92.2 %) which evaluates changes on the auricular surface of the ilium [37]. Although cranial sutures [30] were the second least preferred method (61.2 %), a majority of forensic anthropologists still use this method, with some caution, when other age indicators are not available. 2.1. Cranial Sutures before “Todd and Lyon 1924” Cranial sutures and their relationship to age were a topic of discussion in the literature long before Todd and Lyon began their studies [1,38–40]. Some of these observations, such as that cranial sutures obliterate earlier in individuals of African ancestry (Gratiolet, 1856, cited in [1]) have been contradicted by more recent research, but several observations from this early period have been confirmed. Fallopius and Eustachius (mid-1500s, cited in [1]), for example, observed that the sagittal suture is normally the first to initiate closure, and Topinard (1885, cited in [1]) demonstrated that there was a sequence to cranial suture closure, beginning with the sagittal suture, then the coronal suture, and finally the squamosal suture quite a bit later. Researchers also noted that closure began at different times on the endo- and ecto-cranial surfaces [39], suggested that the sutures be divided into segments for study (Broca, 1861; Frederic, 1906, cited in [1]) and questioned the ability of endocranial or ectocranial suture closure to indicate the age of any skull with an error rate of less than 10–15 years (Ribbe, 1885; Frederic, 1906, cited in [1]). These observations provided an important basis for the landmark studies conducted by Todd and Lyon [1]. 2.2. Pioneering study of Todd and Lyon (1924) on age estimation from cranial suture closure studies In the 1920s, Todd and Lyon [1,25–27] published a series of research articles on cranial suture closure. They argued that theirs was the first study to conduct a systematic analysis of cranial suture closure with proper materials and methods. They suggested that an appropriate sample must represent the population to be studied, that information on sex and ancestry must be known, and that the crania must be cut to enable endocranial examination. Their studies then became fundamental for researchers, both as a basis for knowledge on the topic, and as a target of criticism, leading to vigorous debate and a number of follow-up investigations on cranial suture closure and its relationship to age estimation in the early years of physical anthropology.

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The works of Todd and Lyon were an examination of endo- and ectocranial sutures on White and Black male crania of known age. Crania of doubtful age were rejected from the study. The vault, circum-meatal region, and accessory sutures, a new method of grouping the sutures, were proposed and inspected. Each suture was divided into segments and a five-scale scoring method (0–4) was applied to evaluate the degree of suture closure. Additionally, in Todd and Lyon’s (1924) study, there was a procedure for sample elimination that was emphasized, and later criticized by many researchers (e.g. [17,18,30]. Crania that were considered to be accelerated or retarded in their suture closure progression were rejected from the study, effectively removing outliers. Then, the closure trend was examined and found to display a substantial relationship between age and suture closure. This trend was finally proposed as the modal pattern of suture union. The rejected crania were classified into a group showing abmodal suture progress. Besides the crania with abmodal suture progress, those for which age information did not fit with ages obtained from the postcranial skeleton, or which seemed to be doubtful, were also discarded. This has led to a justified criticism of sampling bias [30]. Furthermore, lapsed union was firstly observed and defined as a characteristic of sutures which failed to unite due to the heaping up of bone tissue along the margins of the unclosed portion. It was treated as equivalent to a closed suture; however, this has led to confusion and caused some error in the evaluations of previous researchers who interpreted this characteristic as an open suture [30]. Todd and Lyon also found that lapsed union was more common on the ectocranial surface than the endocranial aspect, and suggested that ectocranial sutures were unreliable indicators of age because of considerable individual variation. Todd and Lyon’s (1924) suture closure trend is described in Table 1. The authors proposed that the closure trend displays three main characteristics, which are commencement of closure, rapid closure progress, and complete closure. Also, Todd and Lyon (1924) demonstrated clearly that some suture segments had their own pattern of closure independent from the others and that sutures on different areas of the cranium varied in closure pattern with differences ranging from slight to extreme. This variation in pattern made the cranial sutures potentially valuable for age estimation. Although Todd and Lyon (1924) suggested that sutures show a definite closure trend related to age, they recognized that it was unwise to rely solely on suture closure as an age indicator because of individual variability. More recent researchers agree that it is preferable to utilize suture closure in conjunction with other skeletal age markers [2,41–43]. Researchers nowadays still favor the use of endocranial sutures over ectocranial sutures as an age indicator [42,44]. Todd and Lyon also found that the endocranial and ectocranial aspects of each suture followed the same pattern of progress, except in the case of the coronal, sphenofrontal, and the inferior part of the mastooccipital suture [25,26], as well as the same pattern of rapid closure [25,26]. No clear differences in the age at closure were found between the Black and White samples, though this could be the result of their system of excluding abmodal skulls [17,18,30,45], which persisted in these follow-up studies. The study of Black males did find that the progress of suture closure in Black males was more erratic and that fewer sutures showed complete closure throughout life than in the White male sample. The primary contribution of Todd and Lyon [1,25–27] was not a reliable method for age estimation in human skeletons, but rather a comprehensive study of a large number of sutures, on both the ectocranial and endocranial surfaces, and in two groups of different geographic ancestry. Despite the unfortunate decision to reject crania that did not seem to fit the pattern of age progression found in the majority, these studies contributed a number of important

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Table 1 Pattern of endocranial suture closure according to the study of Todd and Lyon (1924). Stages of Beginning and Complete Union (ectocranial) Suture

Age

Indicator

Sagittal Spheno-frontal Coronal (except pteric part) Pteric part (coronal suture) Lambdoidal (except asteric part) Asteric part Masto-occipital Sagittal Coronal (except pteric part) Pteric part (coronal suture) Lambdoidal Masto-occipital (inf) Spheno-frontal Spheno-parietal Masto-occipital (sup and middle) Spheno-temporal (inf) Spheno-temporal (sup) Sagittal Coronal (except pteric part) Squamous Parieto-mastoid (ant) Parieto-mastoid (post) Pteric part (coronal suture) Lambdoidal (except asteric part) Lambdoidal (asteric part) Masto-occipital (sup and middle) Masto-occipital (inf) Spheno-temporal (inf) Spheno-temporal (sup) Spheno-parietal Spheno-parietal Spheno-frontal Masto-occipital (inf) Masto-occipital (sup and middle) Parieto-mastoid (post) Squamous Parieto-mastoid (ant) Spheno-temporal (sup)

22 22 24 26 26 26 26 26 26-29 26-29 26-29 26-30 26-30 29 30 30 30 31 38 Late 30s Late 30s Late 30s 41 42 47 50 50 50 50 50 Early 60s 65 70 80 80 or over Rare Rare Extremely rare

Begins fusion Begins fusion Begins fusion Begins fusion Begins fusion Begins fusion Begins fusion Rapid progress Rapid progress Rapid progress Rapid progress Rapid progress Rapid progress Begins fusion Begins fusion Begins fusion Begins fusion Complete Complete Begins fusion Begins fusion Begins fusion Complete Complete Complete Rapid progress Rapid progress Rapid progress Rapid progress Rapid progress Complete Complete Complete Complete Complete Complete Complete Complete

findings about variability in the timing of cranial suture closure, about the relationship between endo- and ecto-cranial sutures, and about the general way in which sutures progress from open to closed that made it possible for later researchers to develop methods for age estimation from cranial sutures. Unfortunately, the practice of excluding skulls for failure to fit the pattern of others means that their results could not be used effectively for age estimation as the true breadth of the error associated with any estimates was unknown. 2.3. Studies on age estimation using cranial suture closure after Todd and Lyon Mckern and Stewart (1957) After the pioneering studies of Todd and Lyon in the 1920s, Mckern and Stewart [2] examined the cranial sutures of 375 skeletal remains of American soldiers who died in the Korean War. All of these soldiers were male. They studied a new group of sutures, termed the facial sutures, expecting to provide additional information about cranial suture closure. Vault sutures were also examined to obtain more information on this sample. Subdivision of vault sutures for examination followed [45], including the addition of more of the coronal suture in an area called pars stephanica. A five-scale scoring system (0–4) was applied to evaluate closure progress. Although facial sutures seemed to have a closure trend that was more closely associated with biological age than the vault sutures, the trend was not considered reliable

enough for application to age estimation. Additionally, a combination of scores obtained from all sutures for each individual was utilized in a regression analysis. This was the first clear attempt at developing a systematic method of age estimation from the cranial sutures. The attempt failed, however, because the trend of closure found in the study was not clear enough to support the estimation of age among unknown individuals (Table 2). Therefore, the authors concluded that this kind of age indicator was unreliable even as a circumstantial marker of age [2]. However, the conclusion drawn from Mckern and Stewart’s study was probably affected by the composition of the sample in their study, which was strongly biased toward very young individuals and had a relatively narrow age range (17–50 years) overall [41,46,47]. The mean age of the samples in this study was 23 years, but most sutures in most individuals do not even begin fusing until 40 years of age or older. 3. Cranial sutures as an age Indicator: The perspective from the European school After Todd and Lyon [1,25–27] published the results of their pioneering study as a series of articles in the 1920s, Acsadi and Nemeskeri [28] published a study of age estimation utilizing cranial sutures based on a skeletal collection of Hungarian individuals (Table 2). The sample of 352 crania was examined both endocranially and ectocranially. It appeared to the authors that closure of the sutures progressed slowly from the internal side to the external surface. Therefore, the authors decided to focus only on endocranial sutures. Sixteen endocranial suture segments were evaluated for their closure applying Martin’s (1957) five-point scale (0–4) (as cited in [28]). The average closure scores for each individual—the closure index—was computed. This closure index was then analyzed in order to provide a regression model for estimating age. The Acsadi and Nemeskeri technique [28] added the suture scores together and then divided by five, while Meindl and Lovejoy would later simply add the numbers and use the total as a composite score [30]. In either case, this represents an improvement in technique by utilizing information from multiple sutures simultaneously instead of focusing on them individually. A table showing the mean age and mean deviation corresponding with the closure index was proposed for predicting age from unknown skulls [28]. Years later, Perizonius [29] extended Ascadi and Nemeskeri’s [28] work by conducting a study on 256 crania from Amsterdam (Table 2). His aim was to validate the Acsadi and Nemeskeri method on another population sample. This study not only attempted to test the previous method, but also proposed a new one by developing two new suture closure indices. One was a mean closure index calculated from ten suture segments, which showed a closure progression that was significantly correlated with known age. This was obtained from the young subsample group (20–49 years). The other was an index computed from selected suture segments from the old age group (50–99 years). Selecting the suture segments that are most indicative of age for a particular age group represented another improvement to age estimation efficiency. The study pointed out that the endocranial suture index using all 16 suture segments had a strong positive correlation (r = 0.67) with the ages of the young individuals as did the index obtained from the young subsample group (r = 0.70). Furthermore, the closure index (based on only 10 segments) derived from the old age group had a low but significant correlation with old individuals (r = 0.26). This finding suggested that specific cranial suture segments might provide greater estimation accuracy with particular age groups. However, an independent, efficient age indicator was necessary as a criterion for classifying unknown crania into some age group, such as “younger” or “more than 50

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Table 2 Summary of important findings for each cranial suture, suture location, or segment. Stages of Beginning and Complete Union Suture

Age

Indicator (fusion)

Correlation coefficient (r)

Incisive [3] Incisive [3] Palatine (post-med) [3] Sagittal (ecto) [2] Palatine (trans) [3] Coronal (ecto) [2] Palatine (ant-med) [3] Palatine (post-med) [3] Lambdoidal (ecto) [2] Coronal [2] Lambdoidal [2] Obelion [23] Pterion [23] Lambda [23] Sphenofrontal [23] Midlambdoid [23] Sagittal (ant) [23] Midcoronal [23] Bregma [23] Obelion [23] Sphenotemporal (inf) [23] Sagittal (ant) [23] Pterion [23] Lambda [23] Sphenofrontal [23] Sphenotemporal (sup) [23] Midlambdoid [23] Palatine (ant-med) [3] Sphenotemporal (inf) [23] Palatine (transverse) [3] Coronal (endo) [22] Sagittal (endo) [22] Lambdoidal (endo) [22] Coronal (ecto) [22] Sagittal (ecto) [22] Lambdoidal (ectoo) [22]

16 20 22 24 25 26 27 27 27 28 29 36 36 39 39 41 41 43 44 45 46 47 49 50 51 53 53 54 55 59 NA NA NA NA NA NA

Begins Completes Begins Begins Begins Begins Begins Completes Begins Completes Completes Begins Begins Begins Begins Begins Begins Begins Begins Completes Begins Completes Completes Completes Completes Begins and Completes Completes Completes Completes Completes NA NA NA NA NA NA

NA NA NA NA NA NA NA NA NA NA NA 0.37 0.51 0.43 0.43 0.43 0.35 0.38 0.38 0.34 0.34 0.35 0.51 0.43 0.43 0.29 0.43 NA 0.34 NA 0.24 0.11 0.14 0.23 0.09 0.03

years” so that the appropriate indicators could be applied to crania of unknown age [29]. Although the Perizonius [29] modification of Ascadi and Nemeskeri’s [28] work was published before the classic work of Meindl and Lovejoy [30] it had less impact on the field, at least based on citation counts. This may be due to the use of endocranial sutures, which tend to close first and therefore may be less useful on older individuals, and which requires removal of the skullcap to use successfully. The use of endocranial sutures is still recommended as a basis for estimating young adults in a well-known standards manual for biological anthropologists —“Standards for data collection from human skeletal remains” [48] as these sutures show a high correlation with age [42], however, the three endocranial sutures recommended are based on the work of Todd and Lyon [1] while Acsadi and Nemeskeri [28] are mentioned only in the introductory paragraph and are not included as a source for the recommended method. In contrast, both endo-and ecto-cranial suture closure – [30,40,49,28] has been recommended as an age indicator if only the cranium is found [50], but it must be applied only for age assignment into broad age categories since the current methods provide extremely wide age intervals due to inter- and intra-individual variability. 4. Meindl and Lovejoy (1985) In 1985, Meindl and Lovejoy [30] proposed a new approach to age-at-death estimation using cranial suture closure. A sample of 236 crania from the Hamann-Todd Collection were examined with a specific focus on 10 suture sites on the ectocranial surface which

were later categorized into lateral-anterior and vault suture groups. Ectocranial sutures were selected because they tend to close at older ages and this was thought to be more relevant in forensic circumstances. An important contribution of this study was an explicit approach to data collection for the purposes of age estimation. An area of one centimeter surrounding a specific suture location was investigated for each of the 10 sites. A four-point scale scoring method (0–3), rather than the five-point scale used by previous researchers, was developed for evaluating suture closure. A combination of scores by simply adding the scores obtained from each suture site was also analyzed in order to provide more accurate age predictors. The lateral anterior sutures and vault sutures were treated as separate indicators. For the lateral anterior sutures, the composite score had a higher correlation with age (r = 0.57) than that of the vault sutures (r = 0.50) and was considered to represent the best combination of sutures for age estimation. The effect of ancestry and sex on closure of the sutures was also investigated. It should be noted that this was the first time that sex was taken into account in the development of a new aging method based on the cranial sutures. Meindl and Lovejoy determined that sex and ancestry had no significant effect on the estimation of age using either the lateral-anterior or vault suture systems. However, sex differences in suture closure progression showing males more advanced than females had been discussed in a previous validation study [17]. Sex based variation in suture closure progression is rare, however, and many other studies have found no sex differences in the rate of suture closure [1,3,4,28,29]. It is probably safe, therefore, to assume a similar progression between the sexes in

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most populations. Meindl and Lovejoy also suggested that these methods could be used on Black and White individuals without adjusting for geographic ancestry. However, later studies have argued that differences in suture closure patterns can be found between these two ancestral groups [44]. Meindl and Lovejoy [30] brought a clear methodology to age estimation from the cranial sutures, one that could be used in either a forensic or archaeological context. The use of various small suture segments seemed to improve the results, and despite earlier findings that the endocranial sutures were easier to score and showed a more consistent closure progression, use of the ectocranial sutures in this method had the advantage of not requiring the cranium to be cut. However, estimation accuracy using this method was poor, making the technique more valuable for physical anthropologists studying archaeological skeletons that only needed to be categorized as young, middle, or old adult, and less valuable in a forensic context where a narrower age range is much more beneficial for individual identification. 4.1. Alternative cranial suture sites as age predictors Although most of the past studies of cranial suture aging have been focused on the cranial vault sutures, or sutures along the lateral sides of the skull, a few studies have attempted to employ other cranial sutures to predict age-at-death with some success (e.g. [3,4,51]). Mann and colleagues [51] conducted a preliminary study on closure progression with age based on the maxillary sutures. Thirty-six skeletal remains of White individuals were evaluated for degree of maxillary suture closure. The sutures were classified into four locations: incisive (IN), anterior median palatine (AMP), transverse palatine (TP), and posterior median palatine (PMP). A general pattern of closure was found beginning in the teens and ending in the 50 s. Incisive was the first to begin obliteration, prior to adulthood, while PMP was the next suture to complete closure during an individual’s 20 s. Transverse palatine was the next to close and AMP was the last to show evidence of complete closure during the fifth decade of life. Incisive and TP started to close from the lateral side and progressed toward the midline of the maxilla. Closure of the anterior and posterior median palatine progressed from posterior to anterior. In 1991, Mann and colleagues [3] extended their work with a larger sample by examining maxillary sutures from 186 Black and White skeletons. Obliteration of each of the four maxillary sutures was examined (Table 2). Sex and ancestry were also considered for their effects on suture obliteration. The authors suggested that males showed more evidence of obliteration than females at any given age, contrary to most findings from the other cranial sutures; therefore, sex should be considered when applying these sutures as age indicators. In addition, the general pattern of suture obliteration was consistent with their earlier study [51], with incisive being the first maxillary suture to obliterate (at an average age of ca. 20 years), followed by PMP. The next was TP and the last to obliterate was AMP (at an average age of 54 years). The study revealed that geographic ancestry had little effect on the closure of maxillary sutures, while sex had to be taken into account when applying these features for estimation. Although closure of sutures in males appeared to be more advanced than in females at any given age, females presented more accurate age prediction than males. Females exhibited 59 % correct estimates within 10 years while only 34 % prediction accuracy was obtained from the male samples. A test sample was also examined by one of the authors and by an experienced forensic anthropologist. The results indicated consistency in scoring between the observers.

Two other sutures have been studied individually for their utility as age indicators. The frontosphenoidal suture was examined both endocranially and ectocranially by Dorandeu et al. [52] on 290 autopsy cases and found to show an age progression but one with a very wide 95 % prediction range of 23 years. The frontonasal suture was examined both endocranially and ectocranially by Alesbury et al. [4] on 522 crania but found to have low utility as an age indicator because of a low correlation with age at death (R2 = 0.11). From all studies mentioned in the earlier sections, some important ideas can be gleaned. Endocranial sutures appear to show a closer association with age than those on the ectocranial aspect, although most of the ectocranial sutures close later and may be more suitable in the oldest age groups. In terms of sutural groups, vault sutures demonstrate the weakest association with age. In addition, suture segments seem to show a stronger correlation with age than whole sutures (Table 2 and 3). Furthermore, combination of multiple suture elements provides better age estimates than treatment of each suture or segment individually. Finally, there appears to be a sex-related effect on aging accuracy for some sutures, but African- versus Europeanancestry seems to have little effect on results. 5. Validation studies on published age estimation methods using cranial suture closure After the early years of age estimation method development, questions of method efficiency on populations other than those on which the method was developed were raised. Due to new legal requirements related to the Daubert ruling, in which error rates of age estimation methods had to be demonstrated for the target skeletal samples, attempts were made to validate age estimation methods described in the earlier section of this review. These studies provide some insight into the interpopulation applicability of cranial suture aging methods. Error rates for age estimation methods were presented in several ways in previous studies. Bias and inaccuracy were among the commonly reported values used to estimate the error rate. The study of Lovejoy et al. [53] was the earliest to introduce the use of bias and inaccuracy. According to their study, error in estimating age referred to the difference between estimated age and actual age. Bias was defined as the mean over- or under-prediction while definition of inaccuracy was the average absolute error of age estimation for each individual, without reference to over- or underaging. Bias and inaccuracy obtained from validation studies of cranial suture aging methods on different ancestral groups are tabulated in Table 3. Bias can be less than zero (< 0) indicating underestimation of age, equal to zero ( = 0) which refers to equivalent cases of both under- and over-estimation, or greater than zero (> 0) suggesting overestimation of age. The highest degree of underestimation of age was found in the validation study using the Meindl and Lovejoy vault suture method on Hungarian skeletal samples [54] (Table 3). This bias derived from estimation of individuals’ ages in a group of skeletons aged 81–100 years old (40 cases). This result is not surprising, because most of the cranial age indicators listed in Table 2 show an average age of complete closure for the Meindl and Lovejoy (1985) suture segments at age 55 or younger. On the contrary, the greatest degree of overestimation of age was shown in Ruengdit et al.’s (2018) study [55] that tested the Mann method on Thai crania. Bias and inaccuracy were reported for each age cohort of samples in the study. It is important to note that the range of bias and inaccuracy presented in Table 3 lists the highest degree of underestimation of age (< 0) to the greatest overestimation (> 0) considering all age cohorts considered in the study. Careful review of original studies is recommended if one needs to thoroughly compare previous age

Table 3 Validation study on published age estimation methods using cranial suture closure. Method used

Suture location

Author

Sample

Collection

r

Bias

Inaccuracy

Mean age

Acsadi and Nemeskeri (1970)

Endocranial vault

Perizonius [22] Key et al. [35] Galera et al. [40]

256 125 408 555 238

University of Amsterdam Spitalfields, London Terry

0.17-0.67* – 0.37-0.66*

-*** – –

– – –

– Not significantly different –

Semmelweis University

0.44*

(-23.63) - 10.88

8.32-23.63

Chiang Mai University Terry

0.26-0.35** 0.33-0.52*

(-27.1) – 18.7 –

0.6-26.2 –

Increased with the following phases Slightly higher than those found by Acsadi and Nemeskeri. – –

Municipal University of Amsterdam Spitalfields, London

0.15-0.44* 0.54-0.96*

– –

– –

Wolff et al. [44]

Acsadi and Nemeskeri (1970)

Endocranial vault Ectocranial vault

Ruengdit et al. [45] Galera et al. [40]

Meindl and Lovejoy (1985)

Ectocranial vault

Perizonius [22] Key et al. [35]

0.33-0.50

–

–

Wolff et al. [44]

Semmelweis University

0.21*

(-45.57) - 8.95

4.35-45.57

Gocha et al. [46] Ruengdit et al. [45] Key et al. [35]

74 Thais 170 Thais 125 Europeans

Khon Kaen University Chiang Mai University Spitalfields, London

– 0.23** 0.54-0.91*

(-39.6) - 10.54 (-42.0) - 8.5 –

2.5-39.6 5.7-42.0 –

Galera et al. [40]

Terry

0.35-0.53

–

–

Young system

Gocha et al. [46] Ruengdit et al. [45] Key et al. [35]

408 Whites 555 Blacks 69 Thais 169 Thais 25 Europeans

Khon Kaen University Chiang Mai University Spitalfields, London

– 0.29** –

(-34.2) - 9.1 (-40.0) - 12.7 –

3.0-34.2 5.2-40.0 –

Old system

Key et al. [35]

101 Europeans

Spitalfields, London

–

–

–

Endocranial vault Ectocranial vault Endocranial vault Maxillary

Galera et al. [40]

408 Whites 555 Blacks

Terry

Ruengdit et al. [45]

173 Thais

Chiang Mai University

0.37-0.64 0.34-0.50 0.42-0.65 0.30**

– – – (-23.5) - 32.3

– – – 6.3-32.3

Ectocranial vault

Masset (1982) Baker (1984) Mann (1991)

– Significantly higher than that of original study – No increase with increasing phases – – Significantly higher than that of original study – – – Shows pattern of increasing age with increasing closure score No pattern of increasing age with increasing closure score – – – –

S. Ruengdit et al. / Forensic Science International 307 (2020) 110111

Terry

Lateral-anterior

Perizonius (1984)

161 Thais 408 Whites 555 Blacks 256 Amsterdam 150 Europeans 408 Whites 555 Blacks 239 Hungarians

Galera et al. [40]

Meindl and Lovejoy (1985)

Amsterdam Europeans Whites Blacks Hungarians

*

Correlation coefficient (r) obtained from the correlation between actual age and closure score. Range of correlation coefficient represents all coefficient derived from all subsamples (categorized by sexes, age, ancestry, or group of sutures) resented in each study. ** Correlation coefficient obtained from the correlation between actual age and estimated age. *** Not applicable in the study.

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estimation studies because bias (and inaccuracy) were reported using different age cohorts, which may also have had different numbers of individuals in each age cohort. Furthermore, overestimation of age in young individuals and underestimation of age in old individuals commonly occurred in most studies. Besides bias and inaccuracy, correlation coefficients (r) are among the most commonly reported statistics in cranial suture aging validation studies. This statistic is used in order to describe the relationship between actual age and stage of suture closure or actual age and estimated age. The highest correlation coefficient (r = 0.96) presented in Table 3 was obtained by calculating the Spearman rank correlation between the actual age of individuals in the Spatialfields sample from London [42] and the closure score for the midlambdoid suture based on the Meindl and Lovejoy vault suture method. Interestingly, this seems to be the highest correlation coefficient between actual age and suture closure among both original and validation studies. By contrast, the lowest correlation coefficient was found for the relationship between mean ectocranial closure stages of the coronal suture based on the Acsadi and Nemeskeri method and the actual age of Amsterdam individuals aged 40–99 years old using Spearman rank correlation analysis [29]. In addition, descriptive statistics of individuals’ ages in each closure stage based on each method were also used to compare results for the original and validation studies. According to Table 3, the mean age for each closure stage obtained from most validation studies was likely to be higher than that of the original study. Conversely, there were several studies that reported similar mean ages in each closure stage to that reported in the original study; however, there were also studies that had no pattern of increasing mean age of individuals with increasing closure stage. As shown in Table 3, the age distribution of the skeletal samples in the original studies affected the estimated age of the target samples in the validation studies. The Acsadi and Nemeskeri method along with the Meindl and Lovejoy method seem to underestimate the age when applied to other populations. This is probably caused by the difference between the age distribution of the samples from these two original studies which were younger than those of the validation studies. Hence, the estimated age of the target samples was mimicked by the original sample’s age distribution. Researchers should be aware of this, particularly when dealing with skeletons that are likely to be old based on other skeletal observations. 6. Why cranial suture closure is still used even though its reliability is questioned Cranial suture closure has been studied for over a century, yet many researchers have argued that it is unreliable as an age indicator [17,19,42,43,45,56]. Although research suggests that endocranial sutures are more reliable in estimating age than ectocranial sutures, Brooks [17] suggested more than half a century ago that suture closure, both ectocranial and endocranial, has to be used with caution – only as supportive evidence for other age indicators – because of its poor relationship to age, especially in females. However, many researchers still recommend cranial suture closure for skeletal age estimation, if only in conjunction with other methods of aging [17,30,40,41,57], and a majority of forensic anthropologists still use it in casework [31]. Crania are often the best preserved parts of the skeleton in both archaeological and forensic contexts, and are sometimes the only part of the skeleton recovered [17,40,41]. If cranial sutures are to be used, then it is important to identify the best possible approaches for a particular case or circumstance.

7. Development of statistical analytical techniques and cranial suture closure Nawrocki [58] developed a multifactorial method of age estimation using cranial suture closure. The study used a combination of ectocranial, endocranial, and palatine sutures to create age estimation equations. Stepwise regression analysis was also performed to select the suture locations that provide the most accurate information on age among all considered suture segments. One hundred individuals from the Terry Collection were examined. Twenty-seven suture locations were considered using Meindl and Lovejoy [30] and Mann et al. [3,51] methods. Correlation coefficients for these equations, indicating the relationship between the sum of all considered suture scores and actual age, were relatively high (r = 0.72). In addition, equations for subgroups of the sample were reported in order to provide more appropriate equations under certain circumstances, based on ancestry and sex. Consequently, stepwise regression analysis was conducted to develop accurate estimation equations with only a few suture positions required. An important finding was that the age distribution of the sample used to develop the method considerably affected the mean error of estimation when applied to the test sample. A test sample with a similar age distribution to the reference sample used to develop the method would provide a lower mean error than a sample that has a relatively different age composition to that of the reference sample. A few years later, Zambrano [59] conducted research to extend the previous work of Nawrocki [58]. Fourteen (14) equations derived from Nawrocki’s study were tested on 388 skeletons identified as recently deceased individuals of European ancestry. Inaccuracy and bias were computed and showed greater values than the ones reported in Nawrocki’s study [58]. The most important result was that the bias was negative, indicating systematic age underestimation. This inaccuracy and bias decreased, however, when the test sample was culled to obtain an age distribution that better matched the mean age of the Terry Collection sample from which Nawrocki produced his equations. These results suggested that Nawrocki’s equations can be applied to modern samples in forensic medicine, assuming the user is aware of the age distribution of the reference sample [59]. The most recent statistical approach that has now been widely applied by researchers for developing age estimation methods is what Boldsen and colleagues [41] call “transition analysis”. Transition analysis is an approach that focuses on the timing of the transition from one stage of skeletal morphology to the next stage. This concept can be applied to any skeletal traits that can be arranged into an invariant series of senescent stages [41]. However, it is difficult to pinpoint when a skeletal trait has transitioned from one stage to the next. Therefore, it is necessary to consider a transition distribution and then fit the transition analysis model using the maximum likelihood method [60]. Boldsen and colleagues suggested that instead of using a point estimate for age, or a fixed age interval, the probability density function Pr(a|cj) should be taken into account. Pr(a|cj) is the probability that a person died at age a given that the person had skeletal trait presenting characteristics cj, where cj is the set of skeletal traits observed in the j-th skeleton in the sample. These estimates, however, can be affected by the age composition of the reference sample. This problem can be solved if cj is regressed on a. Consequently, Pr(cj|a) is obtained and an age estimate can be derived by applying Bayes’ theorem. In addition, a uniform or informative prior distribution is applied in Bayesian analysis. Transition analysis was developed using data on the pubic symphysis, auricular surface of the ilium, and cranial sutures of known-age skeletal samples from the Terry Collection at the

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Smithsonian Institution. A user-friendly computational program (ADBOU) was also provided to allow easy application of this method [61]. In addition, an updated scoring system that allows individual parts of pubic symphysis, auricular surface of the ilium, and cranial sutures to be used has also been published [41]. This method has been validated in several populations. A validation study on South African samples revealed 92 % accuracy for the transition analysis approach to cranial suture closure [62]. However, the high accuracy (92 %) from the test on South African samples derived from the relatively wide range of estimate (30–95 years) that mostly covers the adult life span [62]. Thus, precision of estimation in terms of age estimated range has to be considered. Transition analysis has been extensively used in the past decade, and applied to various age indicators; for example, the pubic symphysis [60,63,64], first rib [65], dental wear and dental translucency [66,67], and the medial clavicle [68]. It has also been used in the investigation of human rights cases [64]. These statistical approaches (from regression to transition analysis) have been developed in order to apply methods that are appropriate for data that includes considerable variation, such as the timing of cranial suture closure. Development of statistical methods used for cranial suture closure has been investigated alongside other age estimation methods. Transition analysis represents an important advance, because it avoids the problem of bias based on the age distribution of the reference sample used to develop the method, leading to an estimated age more appropriate to the population group from which the target unknown remains derive. 8. Advanced techniques for cranial suture examination In terms of alternative methods for examining cranial suture closure specifically, computed tomography (CT) is one application that has been considered because of its ability to produce high quality images of sutures. Post-mortem CT (PMCT) has been introduced and is routinely utilized in the field of forensic anthropology. PMCT has been applied to the cranium in order to study cranial morphology, measurements, pathology, and trauma in many studies, including biological anthropology of ancient and modern skeletal remains [69–72], and for biological profile research in forensic anthropology [73–76]. Focusing on biological profile research using PMCT, several studies have recently examined specific age indicators using this technology, such as the pelvis, clavicles, premolars, the spheno-occipital synchondrosis, first ribs, fourth ribs, and thyroid cartilage [77–83]. Besides these features, several studies have investigated closure of sutures by means of PMCT [84–87]. Harth and colleagues [88] conducted an early study on closure of the sutures using sectional images obtained from CT scans. The authors examined vault sutures scanned from the skullcaps of cadavers during the autopsy process. Flat-panel CT was used in order to maximize the resolution of the suture images [88]. A year later, Obert, Harth, and their team developed age estimation methods from their original work in 2009 [86]. Instead of using conventional statistics (e.g. regression analysis) they applied an extrema approach. Flat-panel tomography was applied in order to obtain high resolution cross-sectional images of cranial sutures. Two-hundred twenty-one (221) calottes from individuals in autopsy cases were scanned and 14 cranial suture segments in each calotte were evaluated for their degree of closure. The study revealed no statistically significant influence from sex. Intra- and inter-observer error were also computed and exhibited an acceptable intraobserver agreement, as well as agreement among three observers. This indicated that the approach can be useful in estimating age at death.

9

Additionally, Chiba et al. [85] reported on a study of sagittal suture scans from Japanese cadavers using multi-detector CT (MDCT). They selected this modality because it is commonly used in many forensic medicine departments. They found a positive correlation between age and degree of closure observed from CT sectional images (r = 0.71-0.85). It should be noted this age-related correlation range is higher than those mentioned in the earlier section based on visual examination of the sutures alone (see Table 2). Recently, a study by Boyd et al. [84], evaluated the utility of CT for examining degree of cranial suture closure. Cross-sectional CT images of five cranial suture positions – lambda, as well as both left and right midcoronal and midlambda, were obtained from 231 autopsy samples. The study revealed good correlation (0.60) between the degree of suture closure and age. Furthermore, no statistically significant differences were found between CT scan parameters nor between the left and right sides. Interobserver error was also analyzed and showed substantial agreement between two observers, indicating that the scoring method, applied to cross-sectional CT images, was reproducible. The use of CT provides more detail about suture closure. Characteristics of suture closure can be examined in cross-section allowing the examiners to evaluate closure of both ecto- and endo-cranial sutures at the same time. This approach could provide new information about the obliteration of sutures that might improve the efficiency of its use as an age indicator. Although CT is routinely used for forensic casework in some countries, such as Japan and certain European countries, it is quite expensive to utilize CT forensically in developing countries that might have only one or two CT scanners in one hospital or institute. Thus, CT scanning as a means of assessing age in cranial sutures shows promise, but its applicability may be limited by the number of forensic specialists with access to the requisite equipment. 9. Conclusion and path forward Over the century that cranial suture closure has been investigated for its utility as an age indicator, it would appear that the critics who have argued for the unreliability of cranial sutures as estimators of age have mostly won. The relationship between suture closure and age is so erratic in some studies that fluctuating bias, high inaccuracy, and wide ranges of estimated ages make cranial sutures appear to be fairly useless in forensic contexts. However, this tendency of many sutures to provide erratic information about age does not mean that cranial suture closure is completely useless for age estimation. Evidence has shown that cranial suture closure can have a relatively good relationship with age and low levels of inaccuracy when the right sutures are used in combination within particular age groups. This suggests that cranial suture closure can still serve as supportive evidence when evaluated in conjunction with other more reliable age indicators that could narrow down the age of unknown individuals to a particular age group. Advanced statistical or mathematical approaches such as those outlined above can assist in making use of these data for age estimation. Forensic anthropologists clearly agree, as over 60 % of them still consider cranial sutures as part of their toolkit for age estimation. Previous research has taught us much about cranial sutures and their association with age. We know that endocranial sutures appear to perform more consistently than ectocranial sutures for age estimation, and that the issue of “lapsed union” can be problematic for scoring closure among ectocranial vault sutures. We know that most of the commonly used suture segments complete fusion at ages averaging between 20 and 60, suggesting that this is the optimal age range for cranial sex estimation

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(c.f. Table 2). A few suture segments do reach ages above 60, such as endocranial closure of the sagittal suture at above age 70, and endocranial portions of the parietomastoid and masto-occipital with reported ages of 80 or above (Table 1), and these may be helpful in identifying older individuals. We know that the cranial vault sutures perform more poorly overall than the circummeatal and lateral-anterior sutures. We know that the age distribution of the reference sample on which a method is developed can have an influence on age estimates, so this distribution should be considered carefully when developing new methods, or a technique like transition analysis should be applied to the resulting data to reduce the impact of this reference sample bias. We also know that combining suture segments together into composite scores or applying specific suture segments to particular age groups may improve outcomes, and that application of statistics such as stepwise regression can avoid redundancy of information and reduce the number of suture segments necessary to estimate an age when using composite scores. Finally, there is evidence that at least some sutures initiate closure endocranially first, then complete closure ectocranially. To the extent that there is a significant time lag between commencement and final closure, this information may also prove useful in age estimation work on the cranium. In the future, imaging technology and artificial intelligence methods may provide some hope for improvements in the outcomes of cranial suture closure aging methods. Although examination of cranial suture closure has been attempted using imaging technology; such as computed tomography, the approach still requires more clearly-defined protocols. One possibility in this arena is micro-CT, because this kind of CT provides higher resolution than that obtained from MDCT which has been used in many studies thus far. Higher image resolution could provide more detail about suture closure characteristics not visible at the surface. Also, traditional statistical methods such as linear regression might not be appropriate for suture closure which shows much variation in different age groups. Age is certainly not the only contributing factor that regulates the suture closure mechanism. However, it still shows a significant relationship with suture closure. Assessment of this relationship through artificial intelligence approaches such as machine learning may be an alternative answer for use of cranial suture closure data. Although the unreliability of suture closure as a stand-alone aging method has been widely reported, most of the suture locations with the poorest results are vault sutures. There are alternative suture locations that have received less attention; for instance, the sutures on the cranial base and the facial sutures. Study of cranial suture closure as an age indicator is not quite dead. There is still room for development if we can answer the following questions: (1) Are we looking at the right suture locations? (2) How do we obtain a “true” measure of suture closure? Which kinds of methods or tools can provide this? And finally, (3) which kinds of analytical methods are most appropriate for gaining the most information from suture closure? CRediT authorship contribution statement Sittiporn Ruengdit: Conceptualization, Writing - original draft. D. Troy Case: Writing - review & editing, Visualization. Pasuk Mahakkanukrauh: Writing - review & editing, Supervision, Project administration, Funding acquisition. Acknowledgements We would like to thank the Excellence in Osteology Research and Training Center (ORTC) with partially supported by Chiang Mai University. Most important, the authors realize the persons who

donated their bodies for the improvement of education and research. References [1] T.W. Todd, D. Lyon, Endocranial suture closure. Its progress and age relationship. Part I.—adult males of white stock, Am. J. Phys. Anthropol. 7 (3) (1924) 325–384. [2] T.W. McKern, T.D. Stewart, Skeletal Age Changes in Young American Males Analysed From the Standpoint of Age Identification, DTIC Document, 1957. [3] R.W. Mann, R.L. Jantz, W.M. Bass, P.S. Willey, Maxillary suture obliteration: a visual method for estimating skeletal age, J. Forensic Sci. 36 (3) (1991) 781–791. [4] H.S. Alesbury, D.H. Ubelaker, R. Bernstein, Utility of the frontonasal suture for estimating age at death in human skeletal remains*, J. Forensic Sci. 58 (1) (2013) 104–108. [5] L.A. Opperman, T.M. Sweeney, J. Redmon, J.A. Persing, R.C. Ogle, Tissue interactions with underlying dura mater inhibit osseous obliteration of developing cranial sutures, Dev. Dyn. 198 (4) (1993) 312–322. [6] D.A. Roth, J.P. Bradley, J.P. Levine, H.F. McMullen, J.G. McCarthy, M.T. Longaker, Studies in cranial suture biology: part II. Role of the dura in cranial suture fusion, Plast. Reconstr. Surg. 97 (4) (1996) 693–699. [7] V. Johansen, S.H. Hall, Morphogenesis of the mouse coronal suture, Cells Tissues Organs 114 (1) (1982) 58–67. [8] J.A. Furtwängler, S.H. Hall, L.K. Koskinen-Moffett, Sutural morphogenesis in the mouse calvaria: the role of apoptosis, Cells Tissues Organs 124 (1-2) (1985) 74–80. [9] K. Wolff, E. Hadadi, Z. Vas, A novel multidisciplinary approach toward a better understanding of cranial suture closure: the first evidence of genetic effects in adulthood, Am. J. Hum. Biol. 25 (6) (2013) 835–843. [10] H.-J. Kim, D. Rice, P.J. Kettunen, I. Thesleff, FGF-, BMP-and Shh-mediated signalling pathways in the regulation of cranial suture morphogenesis and calvarial bone development, Development 125 (7) (1998) 1241–1251. [11] V. Kokich, Biology of Sutures, Craniosynostosis: Diagnosis, Evaluation, and Management, (1986) . [12] M. Beederman, E.M. Farina, R.R.J.G. Reid, Diseases, Molecular basis of cranial suture biology and disease: osteoblastic and osteoclastic perspectives, Genes Dis. 1 (1) (2014) 120–125. [13] L.R. French, I.T. Jackson, L.J.J.Joce. Melton III, A population-based study of craniosynostosis, J. Clin. Epidemiol. 43 (1) (1990) 69–73. [14] J. Hukki, P. Saarinen, M. Kangasniemi, Single Suture Craniosynostosis: Diagnosis and Imaging, Craniofacial Sutures, Karger Publishers, 2008, pp. 79–90. [15] S. Singer, C. Bower, P. Southall, J.J.Ajomg. Goldblatt, Craniosynostosis in Western Australia, 1980–1994: a population-based study, Am. J. Med. Genet. 83 (5) (1999) 382–387. [16] M.M. Cohen Jr, Sutural biology and the correlates of craniosynostosis, Am. J. Med. Genet. 47 (5) (1993) 581–616. [17] S.T. Brooks, Skeletal age at death: the reliability of cranial and pubic age indicators, Am. J. Phys. Anthropol. 13 (4) (1955) 567–597. [18] W. Cobb, The Age Incidence of Suture Closure, Anat. Rec., WILEY-LISS DIV JOHN WILEY & SONS INC, 605 THIRD AVE, NEW YORK, NY, 1955 10158-0012, pp. 277-277. [19] I. Hershkovitz, B. Latimer, O. Dutour, L.M. Jellema, S. Wish-Baratz, C. Rothschild, B.M. Rothschild, Why do we fail in aging the skull from the sagittal suture? Am. J. Phys. Anthropol. 103 (3) (1997) 393–399. [20] A.W. James, A.A. Theologis, S.A. Brugmann, Y. Xu, A.L. Carre, P. Leucht, K. Hamilton, K.S. Korach, M.T. Longaker, Estrogen/estrogen receptor alpha signaling in mouse posterofrontal cranial suture fusion, PLoS One 4 (9) (2009) e7120. [21] Z. Sun, E. Lee, S.W. Herring, Cranial sutures and bones: growth and fusion in relation to masticatory strain, Anat. Rec. A 276 (2) (2004) 150–161. [22] P. Saukko, B. Knight, Knight’s Forensic Pathology, fourth edition, CRC press, 2015. [23] A.H. Ross, S.M. Abel, The Juvenile Skeleton in Forensic Abuse Investigations, Springer, 2011. [24] E.J. Pope, O.J.Jo.F.S. Smith, Identification of traumatic injury in burned cranial bone: an experimental approach, J. Forensic Sci. 49 (3) (2004) JFS2003286-10. [25] T.W. Todd, D. Lyon, Suture closure—its progress and age relationship. Part IV.— ectocranial closure in adult males of Negro stock, Am. J. Phys. Anthropol. 8 (2) (1925) 149–168. [26] T.W. Todd, D. Lyon, Cranial suture closure. Its progress and age relationship. Part III.—endocranial closure in adult males of Negro stock, Am. J. Phys. Anthropol. 8 (1) (1925) 47–71. [27] T.W. Todd, D. Lyon, Cranial suture closure. Its progress and age relationship. Part II.—ectocranial closure in adult males of white stock, Am. J. Phys. Anthropol. 8 (1) (1925) 23–45. [28] G. Acsádi, J. Nemeskéri, History of Human Life Span and Mortality, Akadémiai Kiadó, 1970. [29] W.R.K. Perizonius, Closing and non-closing sutures in 256 crania of known age and sex from Amsterdam (a.d. 1883–1909), J. Hum. Evol. 13 (2) (1984) 201–216. [30] R.S. Meindl, C.O. Lovejoy, Ectocranial suture closure: a revised method for the determination of skeletal age at death based on the lateral-anterior sutures, Am. J. Phys. Anthropol. 68 (1) (1985) 57–66.

S. Ruengdit et al. / Forensic Science International 307 (2020) 110111 [31] H.M. Garvin, N.V. Passalacqua, Current practices by forensic anthropologists in adult skeletal age estimation, J. Forensic Sci. 57 (2) (2012) 427–433. [32] S. Brooks, J.M. Suchey, Skeletal age determination based on the os pubis: a comparison of the Acsádi-Nemeskéri and Suchey-Brooks methods, Hum. Evol. 5 (3) (1990) 227–238. _ [33] M.Y. Işcan, S.R. Loth, R.K. Wright, Racial variation in the sternal extremity of the rib and its effect on age determination, J. Forensic Sci. 32 (2) (1987) 452–466. [34] M.Y. Işcan, S.R. Loth, R.K. Wright, Metamorphosis at the sternal rib end: a new method to estimate age at death in white males, Am. J. Phys. Anthropol. 65 (2) (1984) 147–156. [35] M.Y. Iscan, S.R. Loth, R.K. Wright, Age estimation from the rib by phase analysis: white females, J. Forensic Sci. 30 (3) (1985) 853–863. [36] M.Y. Işcan, S.R. Loth, Determination of age from the sternal rib in white females: a test of the phase method, J. Forensic Sci. 31 (3) (1986) 990–999. [37] C.O. Lovejoy, R.S. Meindl, T.R. Pryzbeck, R.P. Mensforth, Chronological metamorphosis of the auricular surface of the ilium: a new method for the determination of adult skeletal age at death, Am. J. Phys. Anthropol. 68 (1) (1985) 15–28. [38] T. Dwight, The closure of the cranial sutures as a sign of age, Boston Med. Surg. J. 122 (17) (1890) 389–392. [39] F. Parsons, C. Box, The relation of the cranial sutures to age, J. Anthropol. Inst. Gt. Britain Ireland 35 (1905) 30–38. [40] C. Masset, Age Estimation On The Basis Of Cranial Sutures, Age Markers In The Human Skeleton, (1989) , pp. 71–103. [41] J.L. Boldsen, G.R. Milner, L.W. Konigsberg, J.W. Wood, Transition analysis: a new method for estimating age from skeletons, Cambridge Studies In Biological And Evolutionary Anthropology, (2002) , pp. 73–106. [42] C.A. Key, L.C. Aiello, T. Molleson, Cranial suture closure and its implications for age estimation, Int. J. Osteoarchaeol. 4 (3) (1994) 193–207. [43] D. Sahni, I. Jit, Sanjeev Neelam, Time of closure of cranial sutures in northwest Indian adults, Forensic Sci. Int. 148 (2–3) (2005) 199–205. [44] V. Galera, D.H. Ubelaker, L.-A.C. Hayek, Comparison of macroscopic cranial methods of age estimation applied to skeletons from the Terry Collection, J. Forensic Sci. 43 (5) (1998). [45] R. Singer, Estimation of age from cranial suture closure. A report on its unreliability, J. Forensic Med. 1 (1) (1953) 52–59. [46] J.-P. Bocquet-Appel, C. Masset, Farewell to paleodemography, J. Hum. Evol. 11 (4) (1982) 321–333. [47] B.M. Usher, Reference samples: the first step in linking biology and age in the human skeleton, Cambridge Studies In Biological And Evolutionary Anthropology, (2002) , pp. 29–47. [48] J.E. Buikstra, D.H. Ubelaker, Standards for Data Collection From Human Skeletal Remains, (1994) . [49] R.K. Baker, The Relationship of Cranial Suture Closure and Age Analyzed in a Modern MULTI-rACIAL Sample of Males and Females, California State University, Fullerton, Ann Arbor, 1984 pp. 121-121. [50] E. Cunha, E. Baccino, L. Martrille, F. Ramsthaler, J. Prieto, Y. Schuliar, N. Lynnerup, C. Cattaneo, The problem of aging human remains and living individuals: a review, Forensic Sci. Int. 193 (1–3) (2009) 1–13. [51] R.W. Mann, S.A. Symes, W. Bass, Maxillary suture obliteration: aging the human skeleton based on intact or fragmentary maxilla, J. Forensic Sci. 32 (1) (1987) 148–157. [52] A. Dorandeu, B. Coulibaly, M.-D. Piercecchi-Marti, C. Bartoli, J. Gaudart, E. Baccino, G. Leonetti, Age-at-death estimation based on the study of frontosphenoidal sutures, Forensic Sci. Int. 177 (1) (2008) 47–51. [53] C.O. Lovejoy, R.S. Meindl, R.P. Mensforth, T.J. Barton, Multifactorial determination of skeletal age at death: a method and blind tests of its accuracy, Am. J. Phys. Anthropol. 68 (1) (1985) 1–14. [54] K. Wolff, Z. Vas, P. Sótonyi, L.G. Magyar, Skeletal age estimation in Hungarian population of known age and sex, Forensic Sci. Int. 223 (1-3) (2012) 374.e1–374.e8. [55] S. Ruengdit, S. Prasitwattanaseree, K. Mekjaidee, A. Sinthubua, P. Mahakkanukrauh, Age estimation approaches using cranial suture closure: a validation study on a Thai population, J. Forensic Leg. Med. 53 (2018) 79–86. [56] R. Powers, 84. The disparity between known age and age as estimated by cranial suture closure, Man 62 (1962) 52–54. [57] J.S. Johnson, A comparison of age estimation using discriminant function analysis with some other age estimations of unknown skulls, J. Anat. 121 (Pt 3) (1976) 475–484. [58] S.P. Nawrocki, Regression Formulae for Estimating Age at Death From Cranial Suture Closure, Forensic Osteology: Advances in the Identification of Human Remains, Charles C. Thomas, Springfield, 1998, pp. 276–292. [59] C.J. Zambrano, Evaluation of Regression Equations Used to Estimate Age at Death From Cranial Suture Closure, MS Thesis, University of Indianapolis, Indianapolis, IN, 2005. [60] L.W. Konigsberg, N.P. Herrmann, D.J. Wescott, E.H. Kimmerle, Estimation and evidence in forensic anthropology: age-at-death, J. Forensic Sci. 53 (3) (2008) 541–557. [61] G.R. Milner, J.L. Boldsen, Transition analysis: a validation study with knownage modern American skeletons, Am. J. Phys. Anthropol. 148 (1) (2012) 98–110. [62] N. Jooste, E. L’Abbé, S. Pretorius, M. Steyn, Validation of transition analysis as a method of adult age estimation in a modern South African sample, Forensic Sci, Int. 266 (580) (2016) e1–580 e7.

11

[63] G.E. Berg, Pubic bone age estimation in adult women, J. Forensic Sci. 53 (3) (2008) 569–577. [64] E.H. Kimmerle, R.L. Jantz, L.W. Konigsberg, J.P. Baraybar, Skeletal estimation and identification in American and East European populations, J. Forensic Sci. 53 (3) (2008) 524–532. [65] E.A. DiGangi, J.D. Bethard, E.H. Kimmerle, L.W. Konigsberg, A new method for estimating age-at-death from the first rib, Am. J. Phys. Anthropol. 138 (2) (2009) 164–176. [66] D.A. Prince, L.W. Konigsberg, New formulae for estimating age-at-death in the Balkans utilizing Lamendin’s dental technique and Bayesian analysis, J. Forensic Sci. 53 (3) (2008) 578–587. [67] D.A. Prince, E.H. Kimmerle, L.W. Konigsberg, A bayesian approach to estimate skeletal age-at-Death utilizing dental wear, J. Forensic Sci. 53 (3) (2008) 588–593. [68] N. Langley-Shirley, R.L. Jantz, A bayesian approach to age estimation in modern americans from the clavicle*, J. Forensic Sci. 55 (3) (2010) 571–583. [69] J. Appleby, G.N. Rutty, S.V. Hainsworth, R.C. Woosnam-Savage, B. Morgan, A. Brough, R.W. Earp, C. Robinson, T.E. King, M. Morris, Perimortem trauma in King Richard III: a skeletal analysis, Lancet 385 (9964) (2015) 253–259. [70] A. Balzeau, D. Grimaud-Hervé, E. Indriati, T. Jacob, Computer tomography scanning of Homo erectus crania Ngandong 7 from Java: internal structure, paleopathology and post-mortem history, Berkala Llmu Kedokteran 35 (3) (2003) 133–140. [71] F. Cesarani, M.C. Martina, A. Ferraris, R. Grilletto, R. Boano, E.F. Marochetti, A.M. Donadoni, G. Gandini, Whole-body three-dimensional multidetector CT of 13 Egyptian human mummies, Am. J. Roentgenol. 180 (3) (2003) 597–606. [72] Z. Hawass, S.N. Saleem, Mummified daughters of King Tutankhamun: archeologic and CT studies, Am. J. Roentgenol. 197 (5) (2011) W829–W836. [73] M. Akhlaghi, K. Bakhtavar, A. Kamali, J. Maarefdoost, A. Sheikhazad, F. Mousavi, S.H.S. Anary, E. Sheikhazadi, The diagnostic value of anthropometric indices of maxillary sinuses for sex determination using CT-scan images in Iranian adults; A cross-sectional study, J. Forensic Leg. Med. (2017). [74] A.L. Brough, B. Morgan, C. Robinson, S. Black, C. Cunningham, C. Adams, G.N. Rutty, A minimum data set approach to post-mortem computed tomography reporting for anthropological biological profiling, Forensic Sci. Med. Pathol. 10 (4) (2014) 504–512. [75] Sd.S. Rocha, D.Ld.P. Ramos, Md.G.P. Cavalcanti, Applicability of 3D-CT facial reconstruction for forensic individual identification, Pesquisa Odontológica Brasileira 17 (1) (2003) 24–28. [76] A. Sakuma, M. Ishii, S. Yamamoto, R. Shimofusa, K. Kobayashi, H. Motani, M. Hayakawa, D. Yajima, H. Takeichi, H. Iwase, Application of postmortem 3D-CT facial reconstruction for personal identification, J. Forensic Sci. 55 (6) (2010) 1624–1629. [77] H. Aboshi, T. Takahashi, T. Komuro, Age estimation using microfocus X-ray computed tomography of lower premolars, Forensic Sci. Int. 200 (1) (2010) 35–40. [78] R.B. Bassed, C. Briggs, O.H. Drummer, Analysis of time of closure of the sphenooccipital synchondrosis using computed tomography, Forensic Sci. Int. 200 (1) (2010) 161–164. [79] K.D. Dang-Tran, F. Dedouit, F. Joffre, D. Rougé, H. Rousseau, N. Telmon, Thyroid cartilage ossification and multislice computed tomography examination: a useful tool for age assessment? J. Forensic Sci. 55 (3) (2010) 677–683. [80] F. Dedouit, S. Bindel, D. Gainza, A. Blanc, F. Joffre, D. Rougé, N. Telmon, Application of the iscan method to two-and three-dimensional imaging of the sternal end of the right fourth rib, J. Forensic Sci. 53 (2) (2008) 288–295. [81] G. Moskovitch, F. Dedouit, J. Braga, D. Rougé, H. Rousseau, N. Telmon, Multislice computed tomography of the first rib: a useful technique for bone age assessment, J. Forensic Sci. 55 (4) (2010) 865–870. [82] D. Schulze, U. Rother, A. Fuhrmann, S. Richel, G. Faulmann, M. Heiland, Correlation of age and ossification of the medial clavicular epiphysis using computed tomography, Forensic Sci. Int. 158 (2) (2006) 184–189. [83] A. Wade, A. Nelson, G. Garvin, D.W. Holdsworth, Preliminary radiological assessment of age-related change in the trabecular structure of the human Os pubis, J. Forensic Sci. 56 (2) (2011) 312–319. [84] K.L. Boyd, C. Villa, N. Lynnerup, The use of CT scans in estimating age at death by examining the extent of ectocranial suture closure, J. Forensic Sci. 60 (2) (2015) 363–369. [85] F. Chiba, Y. Makino, A. Motomura, G. Inokuchi, S. Torimitsu, N. Ishii, A. Sakuma, S. Nagasawa, H. Saitoh, D. Yajima, M. Hayakawa, Y. Odo, Y. Suzuki, H. Iwase, Age estimation by multidetector CT images of the sagittal suture, Int. J. Legal Med. 127 (5) (2013) 1005–1011. [86] S. Harth, M. Obert, F. Ramsthaler, C. Reuß, H. Traupe, M.A. Verhoff, Ossification Degrees of cranial sutures determined with flat-panel computed tomography: narrowing the age estimate with extrema, J. Forensic Sci. 55 (3) (2010) 690–694. [87] M. Obert, C. Schulte-Geers, R.L. Schilling, S. Harth, M. Kläver, H. Traupe, F. Ramsthaler, M.A. Verhoff, High-resolution flat-panel volumetric CT images show no correlation between human age and sagittal suture obliteration— independent of sex, Forensic Sci. Int. 200 (1) (2010) e1–180 180, e12. [88] S. Harth, M. Obert, F. Ramsthaler, C. Reuß, H. Traupe, M.A. Verhoff, Estimating age by assessing the ossification degree of cranial sutures with the aid of FlatPanel-CT, Leg. Med. 11 (2009) S186–S189.