Concentraciones de elementos traza y microscopía multifotónica en dientes humanos para la estimación de la edad

Abstract

The estimation of age is one of the most complex problems to solve in Forensic Sciences, due to the lack of consensus and precision of the methods, both in living and deceased people, its determination in many occasions is crucial in the resolution of the cases. The methodology described in the scientific literature for its estimation is numerous, mainly in bones and teeth. The choice of the most appropriate methods in each case is crucial, as is compliance with medical, ethical and legal principles. Nowadays, dental pieces have become a fundamental tool in both Anthropology and Forensic Dentistry, mainly in case where the subject can not be identified visually or by other means, since the teeth are more resistant to extreme situations such as natural disasters, accidents, fires, etc. in comparation with bones that can suffer a greater number of alterations. Dentine is, due to its unique and singular nature, a suitable biological matrix for the study for the long-term deposition of the elements. It has an elemental stability of its structure and at the same time an important dynamism and diversity in its composition. The general objective of this thesis was analysed by using different instrumental techniques, the chemical changes that occur in the human teeth over the years, in order to extend and improve the existing methods for age estimation. The first objective was to investigate in Spanish population, a total of 25 trace elements in 150 healthy coronal dentines, molars and premolars. The teeth were classified into three age groups, by sex and by tooth type. The elements analysed were grouped into essential or potentially essential and toxic or potentially toxic, and they were detected in the following order of concentration Ca > P > Mg > Na > S > K > Sr > Zn > Ba > Fe > B > Ti > Mn > Cr > Ni > Cu > Co > Se > V, and the toxic: Al > Pb > Sn > Li > As > Cd. The techniques used were Inductively Couple Plasma Mass Spectromety (ICP-MS) and Inductively Couple Plasma Optical Emission Spectromety (ICP-MS). The second objective was to determine the estimation of age through 11 teeth, using the techniques of multiphoton microscopy: Two Photon Excitation Fluorescence (TPEF) and Second Harmonic Generation (SHG). Firstly, from the comparison of both signals obtained (ratio) and with the obtaining of the AGIN and SAAID (Age Index). Secondly, by varying the size of the tubules present in the dentine. Sodium, potassium, barium, nickel and cobalt are the essential elements that show variability according to sex. Sodium and cobalt were higher in women. Lead was the only toxic element significantly higher in men. Both types of teeth, molars and premolars, are suitable for the study of trace elements in dentine. Of the 25 elements analysed, ten were significantly correlated with age, of which three are toxic (Pb, Sn and Li) or potentially toxic and seven essential (Sr, Mg, S, K, Zn, Ba, B). Their average concentrations were significantly higher as the age range increased, with the exception of B and Zn. The toxic elements lead, lithium and tin correlate significantly and positively with each other and with the essential elements which increase significantly with age (Sr, Mg, S, K, Zn, Ba, B). Lead is the element that best explains age as a function of its concentrations in dentine using a logarithmic regression model. Enamel only provides a TPEF signal, while dentine shows TPEF and SHG signals, the latter due to the presence of collagen. There are no significant differences between the ratio of TPEF/SHG signals from local areas and global dentine, with a correlation between both close to 1. Therefore, it is not necessary to perform an analysis with local multiphoton microscopy, a global analysis being sufficient. We observe that the ratio between the two multiphoton signals (TPEF/SHG) increases progressively and significantly from 18 to 50 years of age, as do the SAAID values due to the decreases in collagen present in dentine over the years. Both parameters remain more stable after this age. On the other hand, the increase in the size of the dentine tubules observed by SHG, indicates an increase in age, probably due to the increase in the mineral component and the reduction of collagen fibres. Between the younger and older subjects there is a 65% increase in the size of the dentine tubules. Trace elements analysis and multiphoton microscopy in human dentine are effective complementary tools for age estimation, being of particular importance in different circumstances in the medical-forensic field. Key words: Age estimation; trace element; tooth; ICP-MS; ICP-OES; multiphoton microscopy; forensic.