Amino acid dating forensic science

Relation of Age Estimation and Forensic Science Age estimation is important in the field of Methods vs Racemization of Amino Acids/ Radiocarbon Dating.
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The tooth crown was cut away from the root at the level of the cervical line and incubated in 10 n NaOH at room temperature in a water bath sonicator Branson Every 24 h NaOH was replaced, and the non-enamel structures were removed mechanically using an odontologic electric drill.

What Is Forensic Carbon 14 Dating?

Purified enamel was then washed three times with ddH 2 O, 1 resubmersed in 10 n NaOH, and placed again into the sonicator water bath. This procedure was repeated every day for 3—5 days until all dentin and soft structures were stripped from the enamel. The enamel was then rinsed several times in ddH 2 O and dried at room temperature overnight. Ten teeth were processed separately using a modified, simplified protocol.

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For these teeth, the crown was also separated from the root of the tooth, although this time the entire crown was washed in ddH 2 O and crushed using a liquid nitrogen-filled cryogenic impact grinder SPEX Freezer Mill. A fine powder was obtained using a standard program with a run time of 15 min. The enamel, crushed teeth, and the whole crown were weighed and kept sealed in a glass tube until pretreated for AMS analysis. Aliquots of the enamel samples were placed in culture tubes for pretreatment to remove the surface carbon that may have coated the enamel between formation and analysis.

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Because the carbon content of enamel is 0. Enamel samples were immersed in 1. Powdered samples react vigorously in 1. The acid pretreatment was designed to remove the outer surface of the enamel that was exposed to the harsh alkali environment earlier without dissolving too much of the enamel. Base always contains some carbonate that can potentially exchange with the enamel during the preparation step.

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Furthermore, alkali solutions remove CO 2 from the atmosphere and produce carbonate and bicarbonate in solution that can precipitate. Each dried enamel sample was broken into 5—10 pieces, placed in an individual single use reactor, and again weighed to the nearest 0. The acid etching method dissolves a couple milligrams of exterior enamel surface in a mg enamel sample. The evolved CO 2 was purified, trapped, and reduced to graphite in the presence of iron catalyst in individual reactors 14 , Background values were controlled by consistently following procedures, frequently baking sample tubes, periodically cleaning rigs, and maintaining a clean laboratory The operation is similar to that described by Guilderson et al.

Enamel samples are usually full-size and contemporary, so analysis times are relatively rapid, generally less than 5 min.

Corrections for background contamination introduced during AMS sample preparation are made by establishing the contributions from contemporary and fossil carbon following published procedures 21 , The enamel samples are organized in groups of 10—14 unknowns bracketed by primary standards with one primary standard in the middle of the group.

The secondary standards, primary standards, and group of unknowns are measured consecutively as a cycle. Upon completion of a cycle, the set of primary standards, secondary standards, and unknown samples is measured again until desired precision is achieved. A typical group of 14 enamel samples is measured completely in 2—3 h.

All 14 C data are reported using the F 14 C fraction modern nomenclature developed for postbomb data The average age at which enamel formation is completed for each specific tooth has been determined previously and is dependent on the tooth number and gender of the person 3 , 4 , 10 , If the sex of a person is unknown, the average time for enamel completion for males and females is calculated.

The 14 C concentration measured in the tooth enamel is plotted onto a curve of atmospheric 14 C against time to determine the year of enamel synthesis and date of birth of the individual. The time in years taken for the enamel to form is subtracted from the year obtained to give an estimated date of birth Fig. Calibrated ages were obtained by using the CALIbomb Levin data set where the smoothing in years was set at 1. In CALIbomb, these values are predicted using a straight line from prebomb values to For these age ranges, values from the Hua and Barbetti 26 were used.

Application of combined analysis of radiocarbon and aspartic acid racemization on four teeth collected from homicide case. Three teeth with relatively short enamel laydown times showed no bomb spike-derived 14 C in the enamel. However, the fourth tooth, an upper jaw third molar with a much longer enamel formation period, did and matched atmospheric 14 C levels equating to This indicates a birth date of By adding the average age red dashed line estimated from the racemization analysis, the year of death was calculated red vertical line to be DOB , date of birth.

If it is not obvious whether an individual is born before or after the peak of the bomb tests, then two teeth with different enamel laydown times need to be analyzed; this will distinguish whether the 14 C measurement relates to the rising or falling part of the curve 4. Additional studies by Cook et al. Because determining which side of the bomb peak a person falls has previously been demonstrated, we do not include the analysis of two teeth for this purpose here but have rather chosen the age range appropriate to the known date of birth of the individual. In the summer of , hunters found a human skeleton covered by a tarpaulin in a Swedish forest.

Forensic examination revealed that the person had been shot in the back of his skull. Although the skeleton was almost complete, the consultant forensic anthropologist could not determine the deceased age with any precision but stated that it was a male and suggested he had been about 30—40 years old at the time of death. The anthropologist further estimated that the body had been dead for less than 15 years. Four teeth were extracted and subjected to both 14 C analysis and aspartic acid racemization as described previously. Teeth from individuals with dates of birth ranging from through aged 13—70 years were analyzed see supplemental Table 1.

Regression analysis of date of birth estimations using radiocarbon dating of tooth enamel and aspartic acid racemization analysis of crown dentin reveal a strong correlation between the two methods for teeth formed during and after the period of bomb testing Fig. Although both methods are in good agreement with each other, radiocarbon dating offered more precise age estimations than aspartic acid racemization analysis.

Radiocarbon analysis of tooth enamel from nine Swedish individuals 10 teeth , where the date of birth was known, yielded a 14 C-based date of birth estimation accuracy of 1. Two teeth that were formed prior to the period of nuclear weapon testing showed prebomb radiocarbon values. Aspartic acid racemization analysis of crown dentin using the same teeth yielded an average error of age estimation of 6. Teeth from an additional 22 individuals were also analyzed: As in the first round, radiocarbon dating gave a more precise estimate of chronological age than aspartic acid racemization analysis radiocarbon dating age estimate precision was 0.

An analysis of all cases demonstrated the average age estimate precision of radiocarbon dating to be 1. Teeth from the same number of individuals were studied for each method; however, three individuals analyzed for radiocarbon dating showed prebomb levels of radiocarbon in their enamel. As such, one can only conclude that the said individual is born at least x number of years before the beginning of the bomb pulse where x indicates the enamel laydown time.

In all cases where the analyzed tooth was formed before the period of nuclear bomb testing, AMS readings indicated prebomb radiocarbon values. For details regarding each case, see Table I and supplemental Table 1.

Amino acid dating - Wikipedia

The two 14 C cases giving prebomb values are omitted. Analysis of the whole crushed crown as opposed to purified enamel also results in precise date of birth estimation Table II. Crushing the complete tooth crown significantly simplifies the processing needed for radiocarbon analysis and cuts the preprocessing time down to 15 min. Four teeth from an ongoing homicide case in Sweden were analyzed for enamel radiocarbon content as well as aspartic acid racemization of crown dentin. Radiocarbon analysis showed that three of the teeth, with enamel laydown times ranging from 2. One tooth, a third molar from the upper jaw tooth number 48 , did contain bomb carbon in the enamel.

Given that the enamel laydown time for this tooth is 13 years, the victim's date of birth was estimated at Because no exact date of death is known for this case, it is not possible using radiocarbon analysis alone to determine the chronological age of the victim. Aspartic acid racemization analysis of crown dentin from the same four teeth indicated that the victim was Combining the age of the victim with the date of birth, it is possible to estimate the date of death as being The resistance of teeth to environmental influence makes them particularly valuable in the forensic setting.

Teeth can remain intact for an appreciable time and allow for an odontologic identification of even very old skeletons provided ante-mortem data are available. Furthermore, no exchange of carbon will take place in the enamel of the mature tooth during life and generally not after death, making mature permanent teeth particularly suitable for radiocarbon analysis.

We show that both aspartic acid racemization and AMS radiocarbon analyses can be performed on a single tooth and that the combined analysis can provide information about the year of birth and year of death of an individual. Both methods correlate well. In this study, we analyzed almost double the number of individuals reported in the first study and made minor adjustments to the methods. We now report an average absolute error of date of birth estimation of 1. Aspartic acid racemization analysis of dentin also allowed for a fair prediction of the age of the person with a precision comparable to that reported previously for a review, see Ref.

Both methods have strengths and limitations. The radiocarbon birth dating method can tell the birth date of the person regardless of the time of death. However, the time window for this analysis is limited to subjects born after the early s because the calculations are based on the measurement of bomb pulse-derived 14 C. For older subjects, analysis of third molars if available may be necessary to detect bomb carbon because of the delay in their enamel laydown time.

This is well illustrated by the described homicide case. Four teeth were analyzed for enamel radiocarbon content with enamel laydown time ranging from 2. Although no radiocarbon could be detected in the three teeth with the shortest enamel laydown period 2. From this, we could deduce that the victim was born in Aspartic acid racemization analysis of the four teeth estimated the victim to be Despite Interpol contacts, this person was never identified. The police do have an idea of who this person might be, a foreigner believed to be in his forties who was suspected for having set fire to a restaurant in but then disappeared.

The results of the radiocarbon and aspartic acid racemization analyses provide additional support for this theory and illustrate how combining both methodologies can provide precise and valuable information to assist police authorities. Aspartic acid racemization analysis of dentin provides information about the chronological age of an individual at death because the chemical conversion from the l -enantiomer to the d -enantiomer will typically stop completely after death.

Thus, analysis is independent of the calendar years in which the person was born and died. To determine these calendar years, other methods must be used, and usually the only alternative is to estimate the post-mortem interval. The wide window for this interval given by the experienced anthropologist in the homicide case serves as an example of the difficulties this often poses. One advantage of aspartic acid racemization analysis is that it is independent of the bomb spike and hence can be used for age determination of subjects born long before the beginning of aboveground nuclear weapon testing.

Several factors, however, will affect the precision of this method. Because the racemization process is basically a function of temperature and time, teeth are exposed to different ambient temperatures depending on their location.

Age Estimation in Forensic Sciences

They suggest that in elderly individuals racemization in teeth that have been situated deep in the oral cavity for a long time and thus are exposed to higher ambient temperatures are more influenced by the environment than by the period of tooth formation. Selection of which tooth to analyze may therefore yield different results depending on the age of the individual. The types of teeth best suited for racemization analysis are single rooted teeth such as mandibular incisors or mandibular premolars 13 , In these teeth, all the dentin can be easily collected, and test results have shown that analysis using whole dentin yields a more accurate age estimate than analysis using only part of the dentin The age estimation precision reported here for aspartic acid racemization of dental enamel was conducted on an assortment of teeth and would most likely have been significantly higher if mandibular single rooted teeth had been available and used for analysis.

In addition, some of the teeth were collected from teenagers where complete root formation may not have been completed.


In such cases, it is impossible to collect whole dentin, resulting in poorer age estimation as described above. In the ideal situation, the same type of teeth to be used for age estimation analysis should be used as standards to obtain the best precision For the radiocarbon analysis, we expedited the standard extraction procedure reported previously 4 by using an electric odontological drill to remove dentin. Hence, enamel could typically be isolated within 4 days. The freezing mill used to crush teeth may turn out to be an even more attractive alternative to more rapidly obtain a birth dating.

It should be pointed out that age determination is particularly important to limit the search for possible missing person matches and that this information may be badly needed in the early phase of an investigation whether it concerns a crime or a mass disaster. Because radiocarbon analysis also gave good precision with the crushed teeth where the whole crown was ground down, we conclude that the exchange of carbon between the dentin within the crown and the environment typically is negligible.