The Utility of Dental Cementum Increment Analysis for Estimating Season-of-Death in Naturally Decomposed Skeletons
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Determining the season-of-death (i.e. spring/summer or fall/winter) from human remains has significant implications for forensic anthropological and bioarchaeological investigations. In forensic anthropology, determining the season-of-death may greatly increase the accuracy of estimating the postmortem interval (PMI) in human remains. In bioarchaeology, knowing the season-of-death may contribute to the understanding of mortuary patterns, mortality periods, and identify changes in human behavior over time.
Dental cementum increment analysis (DCIA), also known as cementochronology, is the microscopic examination of the alternating mineralized layers in dental cementum, the part of the tooth root that anchors the tooth to the bone. These layers are laid down incrementally twice a year and resemble the cross-section of a tree. Theoretically, under the microscope one bright ring represents the growth season (spring/summer) and one opaque ring represents the dormant season (fall/winter). Based on this theory, Wedel (2007) used DCIA to estimate the season-of-death with 99% accuracy in a sample of teeth extracted from living individuals. If Wedel (2007) is validated and the season-of- death can accurately be estimated in a sample of known individuals who decomposed in a natural environment, then this method will greatly improve the estimation of PMI in forensic contexts.
The following study used DCIA to validate Wedel (2007) to determine if band translucency can effectively estimate season-of-death in human remains using a known date-of-death skeletal collection of individuals that have undergone natural decomposition processes similar to those examined by forensic anthropologists and bioarchaeologists. Additionally, causal factors for the appearance of cementum annulations in human teeth were investigated.
The results of two separate observations of 24 individuals show that there is not a strong relationship between the translucency of the band and the season-of-death as would be expected using methods outlined by Wedel (2007). In the first observation, no difference was found between the band translucency of individuals who died in the spring/summer and fall/winter, and bands were identified correctly in only 60% of the sample. In the second observation, individuals who died in the spring/summer were more likely to exhibit an opaque band, while those who died in the fall/winter were more likely to exhibit a bright band. Correctly correlating the bands to the actual season-of-death in the second observation only occurred in 18% of the sample. Intraobserver error tests determined that estimating the season-of-death based on the translucency of the outer cementum increment yielded results only slightly greater than those achieved by chance. That is, if one were to simply guess the outer band, the results would be about the same.
To investigate the impact of diet on cementum deposition and to ensure the method of preparation was valid, DCIA was tested on a sample of 9 wild deer and 2 domestic dogs. These results indicate there is a correlation between season and cementum deposition, but the extent of this relationship is poorly understood. However, it is unlikely diet plays as significant a role as implied by Lieberman (1994), since domestic mammals lack seasonal variation in diet. Stress factors related to cause-of-death were ruled out as possible confounding variables in this study, but periodontal disease and cementum diagenesis remain questionable limitations. It is likely that the age of the individual is the biggest influence on the clarity of the outer band, and; therefore, the ability of the investigator to estimate the season-of-death.
At this time DCIA is not recommended for use in forensic practice on individuals over fifty years of age; however, with a greater understanding of the biological basis for cementum deposition and the effects of degeneration on the outer band, the method described by Wedel (2007) shows promise for its utility in young humans and wild or domestic non-human mammals.