In forensics, it is critical to determine the time since death, also known as the post-mortem interval (PMI). A whole range of approaches for its estimation have been applied. These include visual analysis, histopathology, molecular biology, Raman microspectroscopy, and other imaging techniques. However, real challenges still exist in determining the so-called “late interval”, where death has occurred seven or more days prior.
There are potential advantages to using dental tissues in the determination of PMI, such as them being sheltered within the mouth, and being resistant to the decomposition processes of skeletonization and putrefaction. However, despite these factors, there is yet to be an approach that can accurately predict PMI using dental tissues.
A recent study showed how information obtained from dental samples using micro-CT – a technique already widely applied in dentistry laboratory studies – could help improve the accuracy of PMI estimation.
A matter of time
The researchers, led by Ahmet Altan at the Tokat Gaziosmanpaşa University in Turkey, divided 60 female rats into six groups. After death, one group were studied immediately, and the remaining five groups were placed in a sheltered garden, exposed to a mean temperature of 25°C for periods of time ranging from seven to 90 days. Each group was studied at the end of each respective time period. The mandibles were dissected, and soft tissue removed prior to micro-CT analysis.
The researchers studied enamel abrasion and cement abrasion. They found that at the first three time points – 0 hours, 7 days, and 15 days – there was no significant difference in enamel abrasion. However, at 30 days and beyond, they saw significant differences. Mean enamel abrasion at 30 days was 0.006 mm, but at 60 days and 90 days, it was 0.024 mm, a fourfold increase.
The researchers also found that the longest time point was associated with significant differences in mineral density.
There were no significant differences in cement abrasion at any of the time points, nor were there differences in enamel or cement thickness.
The most accurate knowledge
The team, who reported their findings in the International Journal of Legal Medicine, highlight the accuracy of micro-CT for providing qualitative and quantitative results with high-resolution images.
Micro-CT has already been widely applied in dental research to investigate factors such as root canal morphology, enamel thickness, mineral density, enamel abrasion, and dentin levels. All dental structures and tissues can be explored with micro-CT and it can also be used with very small samples, the researchers note.
“Micro-CT, which provides the most accurate knowledge regarding the hard tissues in the body, would be extremely beneficial in PM imaging of the bone and teeth,” they say.
In this study, they were able to show that, although enamel thickness was unaltered, enamel abrasion did increase significantly over time. They also say that the change in mineral density observed for the longest time period is a novel finding.
“The evident decline of the mineral density in the teeth of all animals after 3 months post-death is a new parameter for PMI investigation,” say the researchers. “Compared with other research studies, micro-CT investigation in terms of mineral density is easy and allows the storage of specimens for future, nondestructive, and different analyses.”
The authors say that future research is needed to determine if enamel abrasion and mineral density could be useful parameters for PMI. This will also require confirmation in various environmental conditions such as extremes of heat and cold, and in water submersion.
A novel technology
The team carried out their experiments using the Bruker SkyScan 1275 micro-CT system. The SkyScan 1275 offers high levels of automation with simple push-button operation while also delivering advanced X-ray technology. Rapid scanning time coupled to a powerful GPU allows for fast image acquisition, making this the ideal tool for research and industrial settings.
To further enhance throughput, the system can accept an automatic sample changer which allows for up to 16 samples of 50mm diameter or eight up to 96mm. This delivers a streamlined but flexible solution, as samples can be changed at any time while the scanning sequence is running. The scanning protocol can also be adjusted for each individual sample.
Akbulut N, Çetin S, Bilecenoğlu B, et al. The micro-CT evaluation of enamel-cement thickness, abrasion, and mineral density in teeth in the postmortem interval (PMI): new parameters for the determination of PMI. Int J Legal Med 2019; doi: 10.1007/s00414-019-02104-2.