Age Estimation in Forensic Sciences

Age determination of unknown human bodies is important in the setting of a crime investigation or a mass disaster because the age at death, birth date, and year of death as well as gender can guide investigators to the correct identity among a large number of possible matches. Traditional morphological methods used by anthropologists to determine age are often imprecise, whereas chemical analysis of tooth dentin, such as aspartic acid racemization, has shown reproducible and more precise results. In this study, we analyzed teeth from Swedish individuals using both aspartic acid racemization and radiocarbon methodologies. The rationale behind using radiocarbon analysis is that aboveground testing of nuclear weapons during the cold war (1955–1963) caused an extreme increase in global levels of carbon-14 (14C), which has been carefully recorded over time. Forty-four teeth from 41 individuals were analyzed using aspartic acid racemization analysis of tooth crown dentin or radiocarbon analysis of enamel, and 10 of these were split and subjected to both radiocarbon and racemization analysis. Combined analysis showed that the two methods correlated well (R2 = 0.66, p < 0.05). Radiocarbon analysis showed an excellent precision with an overall absolute error of 1.0 ± 0.6 years. Aspartic acid racemization also showed a good precision with an overall absolute error of 5.4 ± 4.2 years. Whereas radiocarbon analysis gives an estimated year of birth, racemization analysis indicates the chronological age of the individual at the time of death. We show how these methods in combination can also assist in the estimation of date of death of an unidentified victim. This strategy can be of significant assistance in forensic casework involving dead victim identification. Age determination of unknown human bodies is important in the setting of a crime investigation or a mass disaster because the age at death, birth date, and year of death as well as gender can guide investigators to the correct identity among a large number of possible matches. Traditional morphological methods used by anthropologists to determine age are often imprecise, whereas chemical analysis of tooth dentin, such as aspartic acid racemization, has shown reproducible and more precise results. In this study, we analyzed teeth from Swedish individuals using both aspartic acid racemization and radiocarbon methodologies. The rationale behind using radiocarbon analysis is that aboveground testing of nuclear weapons during the cold war (1955–1963) caused an extreme increase in global levels of carbon-14 (14C), which has been carefully recorded over time. Forty-four teeth from 41 individuals were analyzed using aspartic acid racemization analysis of tooth crown dentin or radiocarbon analysis of enamel, and 10 of these were split and subjected to both radiocarbon and racemization analysis. Combined analysis showed that the two methods correlated well (R2 = 0.66, p < 0.05). Radiocarbon analysis showed an excellent precision with an overall absolute error of 1.0 ± 0.6 years. Aspartic acid racemization also showed a good precision with an overall absolute error of 5.4 ± 4.2 years. Whereas radiocarbon analysis gives an estimated year of birth, racemization analysis indicates the chronological age of the individual at the time of death. We show how these methods in combination can also assist in the estimation of date of death of an unidentified victim. This strategy can be of significant assistance in forensic casework involving dead victim identification. The identification of human bodies, where there are no clues as to the identity from circumstantial data, poses a difficult problem to the investigator. The determination of age and sex of the body can be crucial to the investigator to limit the search for individuals that could possibly match missing person lists and therefore minimize efforts involving very unlikely alternatives. Whereas gender today can be determined with DNA methods, age determination is not as straightforward. Age estimation in children and adolescents often depends on morphological methods, such as radiological examination of skeletal and dental development. In adults, however, age estimation based on these methods is much less accurate. Current methods of age estimation include simple, yet less precise morphological methods (such as evaluation of dental or skeletal morphology) or more complex, yet more accurate laboratory methods (such as racemization of aspartic acid in dentin or tooth enamel or radiocarbon dating of tooth enamel). Both of the latter methods result in high precision age estimation. Analysis based on morphological methods can yield age estimation error margins of greater than ±10 years (for reviews, see Refs. 1Ritz-Timme S. Cattaneo C. Collins M.J. Waite E.R. Schütz H.W. Kaatsch H.J. Borrman H.I. Age estimation: the state of the art in relation to the specific demands of forensic practise.Int. J. Legal Med. 2000; 113: 129-136Crossref PubMed Scopus (389) Google Scholar and 2Waite E.R. Collins M.J. Ritz-Timme S. Schutz H.W. Cattaneo C. Borrman H.I. A review of the methodological aspects of aspartic acid racemization analysis for use in forensic science.Forensic Sci. Int. 1999; 103: 113-124Crossref PubMed Scopus (52) Google Scholar), whereas precise methods such as aspartic acid racemization and radiocarbon analysis report accuracies of ±3 and ±1–2 years, respectively (3Cook G.T. Dunbar E. Black S.M. Xu S. A preliminary assessment of age at death determination using the nuclear weapons testing 14C activity of dentine and enamel.Radiocarbon. 2006; 48: 305-310Crossref Scopus (42) Google Scholar, 4Spalding K.L. Buchholz B.A. Bergman L.E. Druid H. Frisén J. Forensics: age written in teeth by nuclear tests.Nature. 2005; 437: 333-334Crossref PubMed Scopus (158) Google Scholar, 5Helfman P.M. Bada J.L. Aspartic acid racemization in tooth enamel from living humans.Proc. Natl. Acad. Sci. U.S.A. 1975; 72: 2891-2894Crossref PubMed Scopus (270) Google Scholar, 6Helfman P.M. Bada J.L. Aspartic acid racemisation in dentine as a measure of ageing.Nature. 1976; 262: 279-281Crossref PubMed Scopus (303) Google Scholar, 7Ohtani S. Yamamoto T. Strategy for the estimation of chronological age using the aspartic acid racemization method with special reference to coefficient of correlation between D/L ratios and ages.J. Forensic Sci. 2005; 50: 1020-1027Crossref PubMed Google Scholar). As such, aspartic acid racemization and radiocarbon dating currently represent the methods of choice for precise age estimation. Assessment of age using aspartic acid racemization methodology was first described in 1975 by Helfman and Bada (5Helfman P.M. Bada J.L. Aspartic acid racemization in tooth enamel from living humans.Proc. Natl. Acad. Sci. U.S.A. 1975; 72: 2891-2894Crossref PubMed Scopus (270) Google Scholar) and has since been widely used in forensic age estimation. During the course of aging, l-forms of amino acids are transformed by racemization to the d-forms. At a temperature of +25 °C, it would take ∼100,000 years for all l-forms of amino acids present in living tissues to undergo complete racemization to the d-amino acid form (5Helfman P.M. Bada J.L. Aspartic acid racemization in tooth enamel from living humans.Proc. Natl. Acad. Sci. U.S.A. 1975; 72: 2891-2894Crossref PubMed Scopus (270) Google Scholar). Thus, the extent of racemization of amino acids may be used to estimate the age of various tissues. Of all stable amino acids, aspartic acid has one of the fastest racemization rates and is therefore the amino acid most commonly used for age estimation. Rates of change of l-form amino acids to d-forms are influenced by various factors, such as temperature, humidity, pH, etc. Because of the continuous formation and removal or degradation of amino acids, tissues with low metabolic rates provide better age estimates than those with high metabolic rates. With this in mind, teeth are the tissue of choice for age estimation analysis. If the post-mortem interval is long, bones and teeth may be all the forensic expert can work with. Aspartic acid racemization analysis for the purpose of age estimation has been performed on both tooth enamel and crown dentin with analysis of crown dentin shown to yield more accurate age estimation than dental enamel (5Helfman P.M. Bada J.L. Aspartic acid racemization in tooth enamel from living humans.Proc. Natl. Acad. Sci. U.S.A. 1975; 72: 2891-2894Crossref PubMed Scopus (270) Google Scholar, 6Helfman P.M. Bada J.L. Aspartic acid racemisation in dentine as a measure of ageing.Nature. 1976; 262: 279-281Crossref PubMed Scopus (303) Google Scholar). These results have been repeated by several investigators, and typically a high correlation between aspartic acid racemization and age has been (for a see 7Ohtani S. Yamamoto T. Strategy for the estimation of chronological age using the aspartic acid racemization method with special reference to coefficient of correlation between D/L ratios and ages.J. Forensic Sci. 2005; 50: 1020-1027Crossref PubMed Google Scholar). these overall not all report the of and (for a see 2Waite E.R. Collins M.J. Ritz-Timme S. Schutz H.W. Cattaneo C. Borrman H.I. A review of the methodological aspects of aspartic acid racemization analysis for use in forensic science.Forensic Sci. Int. 1999; 103: 113-124Crossref PubMed Scopus (52) Google Scholar). In radiocarbon analysis of tooth enamel is a described in K.L. Buchholz B.A. Bergman L.E. Druid H. Frisén J. Forensics: age written in teeth by nuclear tests.Nature. 2005; 437: 333-334Crossref PubMed Scopus (158) Google and yet to be by the forensic amino acid racemization radiocarbon dating of enamel the date of birth of an the date of death is also chronological age can be Radiocarbon dating of dental enamel has been used with very high precision to determine the date of birth of and unidentified individuals (3Cook G.T. Dunbar E. Black S.M. Xu S. A preliminary assessment of age at death determination using the nuclear weapons testing 14C activity of dentine and enamel.Radiocarbon. 2006; 48: 305-310Crossref Scopus (42) Google Scholar, 4Spalding K.L. Buchholz B.A. Bergman L.E. Druid H. Frisén J. Forensics: age written in teeth by nuclear tests.Nature. 2005; 437: 333-334Crossref PubMed Scopus (158) Google Scholar). The rationale of the method is to determine the year of tooth formation based on levels of radiocarbon present in tooth or carbon-14 (14C), is in the by with in the are and are to form is the of 14C levels in the been stable for several of years to all of nuclear weapons during the of the cold war (1955–1963) the of in the H. of radiocarbon in and in the PubMed Scopus Google Scholar, of radiocarbon from nuclear tests.Nature. PubMed Scopus Google Scholar). nuclear testing was at a levels of 14C in the and the as a result of a 14C levels in the have been with a of years. 14C levels have not because of has a of 14C has of the to with large and Because radiocarbon is all living this as the an of the years. radiocarbon are in the of are in whereas and form over a of a the because is from the in to and the because are The date of formation of a tissue can be estimated from the by these in and the 14C with the formation can over several years in M.J. to chronological age assessment based on dental Sci. Int. 2000; PubMed Scopus Google Scholar, The of the Scholar). radiocarbon analysis of tooth the limit of enamel formation has been used the time enamel this of 14C from the to the body B.A. K.L. of birth determination using radiocarbon dating of dental PubMed Scopus Google Scholar). from Swedish individuals with a date of birth and chronological age were analyzed using both aspartic acid racemization of dentin and radiocarbon analysis of Radiocarbon analysis of enamel precise date of birth and because the date of of all teeth was the chronological age could also be A showed that chronological age was more estimated using radiocarbon dating of dental enamel than with analysis of aspartic acid racemization of In an Swedish where the identity we how both can be to provide important as to the year of birth of the the estimated age of the person at the time of death, and the estimated date of death. The precision of radiocarbon dating of tooth enamel to determine the year of birth of an individual is a forensic for to use to the of possible in the of the the date of death be well radiocarbon analysis can be used in with aspartic acid racemization analysis of tooth dentin to provide year of death and chronological age of the victim. Forty-four teeth were from dental in with the of all date of date of birth and and gender were This and for tooth used in the are shown in teeth to an were by the Swedish in this date of birth and date of death were not In where aspartic acid racemization analysis of dentin and radiocarbon analysis of enamel were performed on the of the tooth and the complete were used for aspartic acid racemization, and the of the crown was for radiocarbon analysis. The aspartic acid racemization analysis was performed to a described S. Yamamoto T. Strategy for the estimation of chronological age using the aspartic acid racemization method with special reference to coefficient of correlation between D/L ratios and ages.J. Forensic Sci. 2005; 50: 1020-1027Crossref PubMed Google Scholar). were by the teeth with a low dentin were carefully from the with the and the dentin was with in and for the dentin were in an and 10 of the was used as the for determination of the racemization and were by using a and The of the was in in and with The of was to the of and the racemization was as the chronological age on the and the racemization on the we the by the where the racemization is the chronological and is the racemization estimate the chronological we the age on the and the racemization on the and the by the The estimated age was by the in this with that of the to be a the method of racemization see S. Yamamoto T. Age estimation by amino acid racemization in human Forensic Sci. 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Forensics: age written in teeth by nuclear tests.Nature. 2005; 437: 333-334Crossref PubMed Scopus (158) Google Scholar, M.J. to chronological age assessment based on dental Sci. Int. 2000; PubMed Scopus Google Scholar, The of the Scholar). If the sex of a person is the time for enamel for and is The 14C in the tooth enamel is a of 14C time to determine the year of enamel and date of birth of the The time for the enamel to form is from the year to an estimated date of birth and were by using the where the in years was at 1.0 and error was 14C tooth enamel that between and the was not In these are using a from to these age from the and of 14C for and age Scopus Google Scholar) were for and aspartic acid formation acid racemization from absolute from absolute at in a If it is not an individual is or the of the two teeth with enamel to be this the 14C to the or of the K.L. Buchholz B.A. Bergman L.E. Druid H. Frisén J. Forensics: age written in teeth by nuclear tests.Nature. 2005; 437: 333-334Crossref PubMed Scopus (158) Google Scholar). by (3Cook G.T. Dunbar E. Black S.M. Xu S. A preliminary assessment of age at death determination using the nuclear weapons testing 14C activity of dentine and enamel.Radiocarbon. 2006; 48: 305-310Crossref Scopus (42) Google Scholar) also show that radiocarbon analysis on the of the tooth dentin and also one to determine an individual is on the or of the Because which of the a person has been we not include the analysis of two teeth for this purpose have the age to the date of birth of the In the of a human by a in a Swedish Forensic examination that the person been in the of the was the forensic could not determine the age with precision that it was a and been years at the time of death. The estimated that the body been dead for less than years. teeth were and subjected to both 14C analysis and aspartic acid racemization as described teeth from a of 41 Swedish individuals were analyzed for aspartic acid racemization radiocarbon analysis. from individuals with of birth from were analyzed and are in and and aspartic acid racemization of an formation acid year of or or or in a analysis of date of birth using radiocarbon dating of tooth enamel and aspartic acid racemization analysis of crown dentin a correlation between the two methods for teeth during and the of testing both methods are in good with radiocarbon dating more precise age than aspartic acid racemization analysis. Radiocarbon analysis of tooth enamel from Swedish individuals where the date of birth was a date of birth estimation of years = teeth that were to the of nuclear testing showed radiocarbon Aspartic acid racemization analysis of crown dentin using the teeth an error of age estimation of years = from an individuals were also individuals were analyzed using radiocarbon dating of enamel to estimate date of birth and were teeth from individuals analyzed using aspartic acid racemization analysis As in the first radiocarbon dating a more precise estimate of chronological age than aspartic acid racemization analysis dating age estimate precision was years = with the aspartic acid racemization age estimation of years = analysis of all the age estimate precision of radiocarbon dating to be 1.0 years = 0.6 = and of aspartic acid racemization to be 5.4 years = = from the number of individuals were for however, individuals analyzed for radiocarbon dating showed levels of radiocarbon in As such, one can that the individual is at number of years the of the where indicates the enamel time. In all where the analyzed tooth was the of nuclear radiocarbon Analysis of the crown to also results in precise date of birth estimation the complete tooth crown the for radiocarbon analysis and the time to good date of birth estimation was also for one tooth crown subjected to analysis and analysis of tooth formation of tooth tooth in a teeth from an in were analyzed for enamel radiocarbon as well as aspartic acid racemization of crown Radiocarbon analysis showed that of the with enamel from to years, were of that the victim was in or a from the number in the that the enamel time for this tooth is years, the date of birth was estimated at Because no date of death is for this it is not possible using radiocarbon analysis to determine the chronological age of the victim. Aspartic acid racemization analysis of crown dentin from the teeth that the victim was years at the time of death. the age of the victim with the date of birth, it is possible to estimate the date of death as ± years and The of teeth to in the forensic can for an time and for an identification of very are no of take in the enamel of the tooth during and not death, teeth for radiocarbon analysis. We show that both aspartic acid racemization and radiocarbon can be performed on a tooth and that the analysis can provide the year of birth and year of death of an Both methods The of radiocarbon analysis of enamel for year of birth determination has been to show a high precision with an estimation error of years K.L. Buchholz B.A. Bergman L.E. Druid H. Frisén J. Forensics: age written in teeth by nuclear tests.Nature. 2005; 437: 333-334Crossref PubMed Scopus (158) Google Scholar). In this study, we analyzed the number of individuals in the first and to the We report an absolute error of date of birth estimation of 1.0 years. Aspartic acid racemization analysis of dentin also for a of the age of the person with a precision to that (for a see 2Waite E.R. Collins M.J. Ritz-Timme S. Schutz H.W. Cattaneo C. Borrman H.I. A review of the methodological aspects of aspartic acid racemization analysis for use in forensic science.Forensic Sci. Int. 1999; 103: 113-124Crossref PubMed Scopus (52) Google Scholar). Both methods have and The radiocarbon birth dating method can the birth date of the person of the time of death. the time for this analysis is to the because the are based on the of analysis of may be to because of the in enamel time. This is well by the described teeth were analyzed for enamel radiocarbon with enamel time from to years. no radiocarbon could be in the teeth with the enamel the analysis of a tooth time of showed radiocarbon in the tooth we could that the victim was in Aspartic acid racemization analysis of the teeth estimated the victim to be years at the time of death, the date of death at this person was The have an of this person a to be in was for to a in The results of the radiocarbon and aspartic acid racemization provide for this and how both can provide precise and to assist Aspartic acid racemization analysis of dentin the chronological age of an individual at death because the chemical from the to the typically death. Thus, analysis is of the years in which the person was and determine these years, methods be and the is to estimate the post-mortem The for this interval by the in the as an of the this often of aspartic acid racemization analysis is that it is of the and can be used for age determination of the of aboveground nuclear factors, however, the precision of this Because the racemization is a of temperature and teeth are to on S. Yamamoto T. in the D/L aspartic acid ratios in dentin among of teeth from the individual and estimated J. Legal Med. PubMed Scopus Google Scholar) that racemization rates between the tooth in that in individuals racemization in teeth that have been in the for a time are to are more influenced by the than by the of tooth of which tooth to may therefore yield results on the age of the The of teeth for racemization analysis are teeth such as or S. Yamamoto T. Age estimation by amino acid racemization in human Forensic Sci. Scopus Google Scholar, S. Yamamoto T. in the D/L aspartic acid ratios in dentin among of teeth from the individual and estimated J. Legal Med. PubMed Scopus Google Scholar). In these all the dentin can be and results have shown that analysis using dentin a more accurate age estimate than analysis using of the dentin S. racemization ratios in dentin from a Google Scholar). The age estimation precision for aspartic acid racemization of dental enamel was on an of teeth and would most have been teeth been and used for analysis. In of the teeth were from where complete formation may not have been In such it is to dentin, in age estimation described In the the of teeth to be used for age estimation analysis be used as to the precision S. Yamamoto T. Age estimation by amino acid racemization in human Forensic Sci. Scopus Google Scholar). the radiocarbon we the K.L. Buchholz B.A. Bergman L.E. Druid H. Frisén J. Forensics: age written in teeth by nuclear tests.Nature. 2005; 437: 333-334Crossref PubMed Scopus (158) Google Scholar) by using an to enamel could typically be The used to teeth may to be an more to more a birth be that age determination is important to limit the search for possible missing person and that this may be in the of an investigation it a crime or a mass Because radiocarbon analysis also good precision with the teeth where the crown was we that the of between the dentin the crown and the typically is This has also been shown by aspartic acid racemization of crown dentin S. racemization ratios in dentin from a Google Scholar). of these however, showed a a low We not have a good for this than that have because of an in the or dental the crown was Age estimation in all teeth was excellent absolute 1.0 The of the radiocarbon method described is to in the years. for this are as The of the teeth in the has over because of more of and to The to radiocarbon for This that a number of unknown dead bodies are to have teeth The precision of analysis that a of enamel be for analysis. We have shown that radiocarbon dating of tooth enamel an precise estimation of an date of the date of tooth aspartic acid racemization age of death. The combination of these to the forensic and to determine the identity and time of death of unidentified We this strategy to in and in the identification work with mass are to the and individuals in this with