The neonatal line is quite broad in most individuals, indicating a disruption in tooth formation that lasts longer than one day. Scientists have wondered whether a difficult birth process leads to darker or broader neonatal lines. Current evidence appears to be mixed. Infants born after an operative intervention due to complications had the thickest neonatal lines. However, another study of children did not find that these lines varied among children born different ways.
My hunch is that the discrepancies between these two studies may relate to the difficulty of preparing sections for microscopic analysis, which often involves a combination of skill and luck. It turns out that nonhuman primate infants also have neonatal lines in their teeth, as do other mammals.
They appear in the first molars of free-living wild primates, as well as in captive ones, and many show strongly marked birth lines. This is interesting because nonhuman primates appear to have a more mild labor and delivery process than humans. Their babies pass through the birth canal with much less difficulty than large-brained human babies. However, this line does allow scientists to determine whether individuals survived the birth process. One example is an investigation of ritualized human sacrifice in Carthage , an ancient Phoenician city in Northern Africa.
The teeth of 50 young infants buried in ceramic urns were assessed via microscopic study to determine if they were stillborn, or if they survived long enough to record growth after the neonatal line. Apparently half of the individuals did not preserve this marker, which means that they were unlikely to have lived long enough to be sacrificed. The research team concluded that, while occasional practices of this grisly ritual may have influenced historical reports, the prevalence of very young children in ancient Mediterranean funerary contexts is more likely due to stillbirths or infectious diseases during early infancy.
Another remarkable use of the neonatal line is the determination of whether an infant was born prematurely. Dean and Birch sectioned the teeth, located the neonatal line of each twin, and counted the number of days these teeth had been forming prior to birth.
A widened neonatal line has been associated with a complicated delivery, neonatal difficulties at birth, maternal complications at birth, infant birthweight and short gestation length. The present study measured the width of the neonatal line in a sample of forty-five primary teeth collected from Canadian children. Birth history information was gathered through in depth interviews with the mothers of children donating teeth.
Statistical testing was carried out to determine if significant differences exist in neonatal line width between groups of children with respect to birth trauma, neonatal health, maternal health and term at birth. Neonatal line represents the first enamel formed after birth and it separates prenatal enamel from postnatal enamel. A similar hypomineraralized line can be seen in dentin also, but the mineralization pattern and the non-reparative nature of enamel make the neonatal line in enamel more distinct and reliable than the one in dentin.
Since the deciduous tooth germs and the first permanent molar begin calcifying by the fifth lunar month 20 th week in utero , and the mineralization continues for some period of time after birth, all these teeth posses neonatal line.
As it forms a precise line of demarcation between prenatal and post natal enamel indicating the time of birth, the presence of neonatal line in a developing tooth indicates a live birth and a separate existence. The neonatal line was identified in the enamel of all the developing tooth germs which were subjected to the microscopic study indicating the baby was born alive and it had a separate existence. The scalloped pattern of neonatal line seen in canines and molars under both light and polarized microscope may be explained in terms of the shape of the terminal secretary end piece of the ameloblasts.
Similar scalloping can be noticed on the superficial surface of the enamel in the decalcified section where the ameloblasts can be seen lodged within the concave margins [ Figure 4 ].
In the ground sections of incisors, the neonatal line that appeared as a straight line under light microscope showed scalloping under SEM. But in the developing first molar from a one and a half year old boy and in the fully developed deciduous molars which were used as controls, the neonatal line was rather straight.
Based on these observations, it was understood that as mineralization progresses, neonatal line which initially appears as a scalloped line, straightens out and becomes distinct as more and more layers of enamel gets deposited over it.
The estimation of period of survival of an infant in the perinatal period using neonatal line as the line of reference seems to be more accurate as it gives the exact age of the baby in days. The exact timing of enamel formation is always the same for a given individual, though it shows slight variation between individuals and species.
In the present study, the six days of post natal survival estimated from the cross striation count was found to be accurate as the chronological age of the baby was available for comparison. The main limitation of using neonatal line for the assessment of postnatal survival of infants is that most of the infanticides occur immediately after birth, but a couple of days of survival are necessary before the neonatal lines could be detected.
As per the evidence from contemporary literature, neonatal lines can be demonstrated with light microscope only if considerable thickness of post natal enamel deposition takes place. In practice, that means the baby should survive for a period of around 3 weeks for the neonatal line to be visible.
The detection of the neonatal line depends on various factors like the axis of the tooth section, section thickness, and the light source used and also, the absence of this line is not an indication of still birth.
According to Whittaker and MacDonald,[ 1 ] it should be possible to distinguish postnatal enamel from prenatal enamel within a day or two after birth under SEM. Though SEM examination of the ground sections of tooth germs in our study also showed the presence of neonatal line, the period of survival of the baby could not be determined using SEM, as the enamel rods were not clearly visible. Neonatal line and its significance in establishing the period of separate existence could be used as a proof, if required, in substantiating the criminal nature of infanticide.
More accurate and earliest detection of this line particularly within hours after death by means of advanced techniques could rewrite this supplementary evidence of possible infanticide into substantial evidence and more studies need to be done in this direction.
Source of Support: Nil. Conflict of Interest: None declared. National Center for Biotechnology Information , U. J Forensic Dent Sci. Author information Copyright and License information Disclaimer. Address for correspondence: Dr. E-mail: ni. This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.
This article has been cited by other articles in PMC. Abstract Background: The presence of neonatal line indicates live birth and it is possible to estimate the exact period of survival of the infant in days by measuring the amount of postnatal hard tissue formation, and thus can be an evidence to the brutal act of infanticide. Materials and Methods: Primary tooth germs of both the arches were removed from the sockets of an infant who died few days after birth.
Results: The ground sections of all the developing tooth germs showed the presence of neonatal line and the analysis of enamel showed six distinct cross striations along the enamel rod length indicating the period of survival of the baby to be six days which was later confirmed with the hospital records. Conclusion: Neonatal line could be used as an evidence of infanticide.
Keywords: Infanticide, live birth, postnatal survival, neonatal line. Introduction The brutal act of neonaticide, especially targeted against newborn female babies is a common practice in India. Study background Body of a full term baby who died six days after birth in our hospital due to respiratory distress was donated to the Department of Anatomy.
Aim of the study To demonstrate the presence of neonatal line in the developing primary tooth germs of a new born baby who died in the perinatal period using light, polarized and scanning electron microscope SEM. Read what you need to know about our industry portal bionity.
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