|Neonatal Line assessment among Milwaukee County Institution Grounds (MCIG) perinates to determine viability.
Paper presented at the 80th annual meeting of the Society for American Archaeology, San Francisco, 15 – 19 April 2015.
Emily Mueller Epstein, Brianne E. Charles, and Brooke L. Drew
A sample of perinatal individuals recovered from the Milwaukee County Institution Grounds Cemetery (ca. 1890-1920) includes broken teeth (Figure 1). We evaluated these teeth for the presence of the neonatal line to differentiate stillborn individuals from those that died following live birth (Figure 2). Our research is nondestructive. We compare the results of the neonatal line analysis to the distribution of stillborn and live births documented in the MCIG burial record and City of Milwaukee vital records.
We present the two distinct analytical events that structured the outcome of this study in chronological order. First, we describe the project-related age estimation methods and the results that prompted our interest in assessing juvenile dentition for the presence of NNL. Both analyses require distinct reviews of dental development.
Dental development related to project-related age estimation methods
Dental development is considered the most accurate means of estimating juvenile age at death for a variety of reasons, but most notably because the timing of dental development is less susceptible to environmentally based variability than other parts of the musculoskeletal system (White 2000: 385) (Figure 3). We briefly review the dental developmental sequence following Hilson (1996) to provide background to the project-related age estimation methods. The
The cellular matrix required for tooth formation organizes during late embryonic development. At around the 14th fetal week, tissues that will eventually become enamel and dentin assume a bell-shape and cellular division proceeds respectively in opposite directions on either side of what becomes the dentalenamel junction (DEJ). During cellular maturation occurs, hard enamel tissue formation proceeds appositionally from the cusp to the cervical margin. The whole process occurs first for the incisors, then the first molars, second incisors, canines, and then the second molars. By the 30th week of fetal development, the first permanent molars have developed cuspids.
Project-related analyses: Methods and results
We used four different methods to estimate age via dental remains during project related analyses (Figure 4). Those methods considered enamel mineralization, dental formation, and eruption (Lysel et al. 1962 as described in Scheuer and Black 2000; Moorrees et al. 1963a, 1963b; Sunderland, et al. 1987; Ubelaker 1989). With exception for Ubelaker (1987 et al.), estimated dental age methods were not intended to yield results for individuals between Mid-fetal and neonatal development, though the method is based on a compilation of formation and eruption data collected from American Indians and other “non-white” populations. We also applied Ubelaker’s (1989) widely used method to increase the comparability of our results with those from other sites. Once the non-metric dental assessments are complete, the lowest and highest ages returned from any of the four methods form the combined estimated age range and the average of those two ages is used to assign the individual to a developmental category.
Results of the project related dental age estimates indicate Infants, Neonates, and Fetuses, respectively, outranked all other Developmental Categories (Figure 5). Burials with indeterminate dental age assessments lacked the preservation required for assignment to a developmental category.
Enamel development relevant to NNL study methods
In this study, we investigated 133 dentitions categorized as fetal and neonatal for the presence of the neonatal line (Figure 6). This study complements our other efforts to close the gap in estimating dental age during the perinatal period (Charles and Epstein 2015). We review NNL development to provide a context for the NNL study methods.
The neonatal line is the first accentuated Brown Striae of Retzius (Hilson 1996)(Figure 7). Brown retzius lines are hypoplasias that result in more obvious striae due to disrupted enamel deposition. The NNL develops in the deciduous dentition and first permanent molar due to the stress of birth. However, the NNL is quickly covered by the additional enamel layers. Linear enamel hypoplasias (LEH) are also stress related disruptions affecting enamel deposition. However, LEH are evident within the perykimata, those enamel layers that encircle and terminate on a deciduous or permanent tooth’s surface (Figure 8a.). Observing the NNL requires a natural or sectioned tooth along the transverse or radial plane (Figure 8b.).
The NNL is clearly visible in teeth prepared for histological assessment (e.g., Smith and Avishai 2005)(Figure 9a). Tafforeau and Smith (2008) completed a non-destructive NNL assessment on fossil hominid teeth using x-ray synchrotron microtomography. In our efforts, however, we used a relatively low-tech dissection microscope and recorded images with a mounted AmScope 10 megapixel camera. We discovered, however, the iPhone 5C produced images with superior clarity. The neonatal line is clearly visible in dentition radially broken as a result of natural taphonomic processes with 40x magnification (Figure 9b).
NNL Study Methods and Results
For each of the 133 burials, we reviewed the project-related dental inventory and dental age assessment data (Figure 10). We assessed naturally broken teeth via microscopy since destructive analyses of burials recovered during the 2013 excavations are not allowed. Burials lacking broken teeth received indeterminate assessment results, as did those with unclear enamel histology.
Presence of the neonatal line is observed as a clear change in enamel tissue radiating from the marginal ridges, just above the cervicoenamel junction (CEJ)(Figure 11 and 12). Burials exhibiting evidence for the neonatal line total 60. The absence of the NNL is evident in these images by a complete regularity in the enamel tissue. Burials lacking evidence for a NNL total 17 (Figure 13).
Burials exhibiting burned enamel tissues total 44. Some teeth exhibit a strong NNL despite the thermally altered enamel (Figure 14a). In others, heat caused the enamel tissues to crack and separate from the enamel-dentine junction (EDJ), changes associated with temperatures ranging between 300˚ and 500˚ C (Fairgreive 2008:147)(Figure 14b). Prior to the microscopic analysis of enamel tissues, we identified only four burials with evidence for thermal alteration. Curiously, juveniles burials exhibiting evidence for burned enamel were recovered from unburned wooden coffins.
Results indicate 30 fetal, 25 neonates and 1 infant could not be assessed for NNL due to a number of factors including lack of transverse or radial breaks, dentition present only in the alveolar crypt, or remarkably poor dental preservation. Of the remaining specimens, 17 fetal burials were reassigned into the Neonatal category, 7 neonates were reassigned as Fetal, and the classification of the 12 infants was confirmed (Figure 15).
We compared the new Fetal and Neonatal values to those recorded in the historic records (Figure 16). Drew transcribed and compiled the Milwaukee County Coroner’s reports referencing burial at the MCIG Paupers’ Cemetery and the MCIG Burial record into a single database. Historic data query results suggest the possible number of fetuses and neonates buried at the MCIG Pauper’s Cemetery total of 1,377. Results of the NNL study indicate a greater portion of individuals survived birth to die as neonates than the reverse, which is what the historic records show. However, orders of magnitude separate the study sample size from the population size recorded during the late nineteenth and early twentieth century.
Our study demonstrates a non-destructive and low-cost method for assessing naturally broken dentition of perinates for the presence of the NNL (Figure 17). Microscopy enhanced the visibility of burned enamel tissues, causing a marked increase in the number of burials exhibiting burned skeletal tissues. The NNL study presented here allowed us to close the age gap inherent in the project related analyses, but see also Charles and Epstein (2015). As a result of this research, we reclassified a total of seventeen individuals and found the distribution of the fetal and neonatal age groups proportional to the distribution indicated in the historical records. The NNL assessment results provide another data point for integrated skeletal identification efforts by Drew (2012) and Richards (1997), which link historical records, archaeological context, and skeletal data.
Dr. Patricia B. Richards, MCIG Principle Investigator, UWM CRMS Assistant Director, and MCIG SAA Symposium organizer.
Dr. Lynne Goldstein, Discussant
UWM Graduate School travel grants.
Works Cited (Figure 19)
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