The Distribution and Biogenic Origins of Zinc in the Mineralised Tooth Tissues of Modern and Fossil Hominoids: Implications for Life History, Diet and Taphonomy

Zinc is incorporated into enamel, dentine and cementum during tooth growth. This work aimed to distinguish between the processes underlying Zn incorporation and Zn distribution. These include different mineralisation processes, the physiological events around birth, Zn ingestion with diet, exposure to the oral environment during life and diagenetic changes to fossil teeth post-mortem. Synchrotron X-ray Fluorescence (SXRF) was used to map zinc distribution across longitudinal polished ground sections of both deciduous and permanent modern human, great ape and fossil hominoid teeth. Higher resolution fluorescence intensity maps were used to image Zn in surface enamel, secondary dentine and cementum, and at the neonatal line (NNL) and enamel-dentine-junction (EDJ) in deciduous teeth. Secondary dentine was consistently Zn-rich, but the highest concentrations of Zn (range 197-1743 ppm) were found in cuspal, mid-lateral and cervical surface enamel and were similar in unerupted teeth never exposed to the oral environment. Zinc was identified at the NNL and EDJ in both modern and fossil deciduous teeth. In fossil specimens, diagenetic changes were identified in various trace element distributions but only demineralisation appeared to markedly alter Zn distribution. Zinc appears to be tenacious and stable in fossil tooth tissues, especially in enamel, over millions of years.

Assessment of physiological disturbances during pre- and early postnatal development based on microscopic analysis of human deciduous teeth from the Late Epipaleolithic site of Shubayqa 1 (Jordan)

OBJECTIVES

To study pre- and early postnatal tooth formation and to analyze the effects of physiological disturbances on enamel and dentin formation in deciduous teeth of infants from the Late Epipaleolithic (Natufian) site Shubayqa 1.

MATERIALS AND METHODS

Ten deciduous teeth from six infants (ages at death between 21 and 239 days) were analyzed by light and scanning electron microscopy.

RESULTS

Marked prism cross-striations and an abnormal wavy course of the prisms were recorded in pre- and postnatal enamel of all analyzed teeth. Single or multiple accentuated incremental lines were observed in prenatal enamel of nine teeth and in postnatal enamel of eight teeth. Accentuated Andresen lines and broader zones exhibiting an enhanced calcospheritic pattern were recorded in the pre- and postnatally formed dentin of nine teeth.

DISCUSSION

The structural abnormalities in the pre- and postnatally formed enamel of the infants are considered indicative of chronic stress that negatively affected the activity of secretory ameloblasts. The structural aberrations in pre- and postnatal dentin denote that odontoblasts were also affected by this stress. The presence of single or multiple accentuated incremental lines in pre- and postnatal enamel is interpreted as reflecting (short-term) impacts of higher intensity superimposed on the chronic stress. Our findings suggest compromised maternal health affecting the late fetus and compromised health in newborns. Although limited by the small number of analyzed individuals, the present study contributes to the knowledge of maternal and early infant health conditions in Late Epipaleolithic populations.

Using teeth as tools: Investigating the mother-infant dyad and developmental origins of health and disease hypothesis using vitamin D deficiency

OBJECTIVES

With a growing interest in the mother-infant dyad and the Developmental Origins of Health and Disease hypothesis among biological and medical anthropologists, this study set out to provide all the information required to evaluate if mineralization defects in dentine might be caused by vitamin D deficiency in the critical first 1000 days of life.

MATERIALS AND METHODS

Information was compiled on dentine formation in utero to approximately 18 years, and a method for determining the location of the neonatal line in dentine was devised, allowing the assessment of the prenatal and early life period. Re-evaluation of previously analyzed teeth (n = 61) was undertaken with detailed examination of n = 5/22 first permanent molars forming in the prenatal and critical early life periods.

RESULTS

First permanent molars and all deciduous teeth give information on intrauterine development and on the first 1000 days postnatally providing a direct window on maternal and fetal health. Three archaeological individuals had interglobular dentine that formed prenatally suggesting that their mothers experienced vitamin D deficiency at the time dentine was forming and all other individuals had a deficiency during the first 1000 days of life. Conditions that could cause systemic mineralization defects were determined, and in each, case they were found to be consistent with vitamin D deficiency.

DISCUSSION

The neonatal line serves as a clear baseline for determining prenatal and postnatal events, particularly those related to vitamin D, calcium, and phosphate metabolism, and can be used to investigate the maternal-infant dyad for both past and present communities.

Those who died very young-Inferences from δ15 N and δ13 C in bone collagen and the absence of a neonatal line in enamel related to the possible onset of breastfeeding

OBJECTIVES

Stable isotope analysis has often been used in neonatal remains from archeological contexts to investigate the presence of a signal of breastfeeding and weaning in past populations. Tooth histology on the other hand might be used as an indicator of birth survival. This pilot study aimed to investigate the feasibility of using stable nitrogen (δ¹⁵ N) and carbon (δ¹³ C) isotope values from neonatal bone collagen to elucidate if values deviating from the adult female average could indicate breastfeeding and co-occur with the presence of a neonatal line (NNL). The combination of these independent indicators might be useful in clarifying the fate of individuals who died around birth.

MATERIALS AND METHODS

Bone collagen from 21 archeological human and animal specimens was extracted and analyzed via mass-spectrometry for δ¹⁵ N and δ¹³ C. A verification of the stable isotope results was undertaken using tooth histology on three individuals who were investigated for the presence of a NNL as an indicator of live birth and short survival.

RESULTS

The biological age of the human samples varied between 8.5 lunar months (Lm) and 2 postnatal months (Pm) of age. All except one individual exhibited elevated δ¹⁵ N values compared to the female average. The histological analyses revealed no NNL for this and two further individuals (n = 3).

DISCUSSION

The results indicate that elevated nitrogen values of very young infants relative to a female average in archeological contexts are not necessarily associated with a breastfeeding onset signal, and therefore cannot be used exclusively as a proxy of birth survival. The elevation might be possible due to various reasons; one could be nutritional, in particular maternal stress during pregnancy or a metabolic disorder of mother and/or her child. In those cases, the evaluation of a NNL might reveal a false breastfeeding signal as seen for two individuals in our sample who have elevated nitrogen values despite the fact no NNL could be observed. Overall, our data support the growing awareness that bone collagen δ¹⁵ N values of neonates/infants should not be used as a proxy for breastfeeding or birth survival on its own.

Neonatal line as a linear evidence of live birth: Estimation of postnatal survival of a new born from primary tooth germs

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. Ground sections were made with hard tissue microtome. Decalcified sections were made from the crown of primary right mandibular canine and the sections were stained with hematoxylin and eosin. To visualize the neonatal line, the sections were subjected to light mocroscopy, polarized microscopy and scanning electron microscopy. A developing permanent molar from a one and a half year old boy and ten fully developed deciduous molars were used as controls.

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. Accurate detection of neonatal line with advanced techniques could rewrite this supplementary evidence of infanticide into substantial evidence.

The developmental clock of dental enamel: a test for the periodicity of prism cross-striations in modern humans and an evaluation of the most likely sources of error in histological studies of this kind

Dental tissues contain regular microscopic structures believed to result from periodic variations in the secretion of matrix by enamel- and dentine-forming cells. Counts of these structures are an important tool for reconstructing the chronology of dental development in both modern and fossil hominids. Most studies rely on the periodicity of the regular cross-banding that occurs along the long axis of enamel prisms. These prism cross-striations are widely thought to reflect a circadian rhythm of enamel matrix secretion and are generally regarded as representing daily increments of tissue. Previously, some researchers have argued against the circadian periodicity of these structures and questioned their use in reconstructing dental development. Here we tested the periodicity of enamel cross-striations--and the accuracy to which they can be used--in the developing permanent dentition of five children, excavated from a 19th century crypt in London, whose age-at-death was independently known. The interruption of crown formation by death was used to calibrate cross-striation counts. All five individuals produced counts that were strongly consistent with those expected from the independently known ages, taking into account the position of the neonatal line and factors of preservation. These results confirm that cross-striations do indeed reflect a circadian rhythm in enamel matrix secretion. They further validate their use in reconstructing dental development and in determining the age-at-death of the remains of children whose dentitions are still forming at the time of death. Significantly they identify the most likely source of error and the common difficulties encountered in histological studies of this kind.