Identification through X-ray fluorescence analysis of dental restorative resin materials: a comprehensive study of noncremated, cremated, and processed-cremated individuals

Tooth-colored restorative materials are increasingly being placed in the practice of modern dentistry, replacing traditional materials such as amalgam. Many restorative resins have distinct elemental compositions that allow identification of brand. Not only are resins classifiable by elemental content, but they also survive extreme conditions such as cremation. This is of significance to the forensic odontologist because resin uniqueness adds another level of certainty in victim identification, especially when traditional means are exhausted. In this three-part study, unique combinations of resins were placed in six human cadavers (total 70 restorations). Simulated ante-mortem dental records were created. In a blind experiment, a portable X-ray fluorescence (XRF) unit was used to locate and identify the resin brands placed in the dentition. The technique was successful in location and brand identification of 53 of the restorations, which was sufficient to enable positive victim identification among the study group. This part of the experiment demonstrated the utility of portable XRF in detection and analysis of restorative materials for victim identification in field or morgue settings. Identification of individuals after cremation is a more difficult task, as the dentition is altered by shrinkage and fragmentation, and may not be comparable with a dental chart. Identification of processed cremains is a much greater challenge, as comminution obliterates all structural relationships. Under both circumstances, it is the nonbiological artifacts that aid in identification. Restorative resin fillings can survive these conditions, and can still be named by brand utilizing elemental analysis. In a continuation of the study, the cadavers were cremated in a cremation retort under standard mortuary conditions. XRF was again used to analyze retrieved resins and to identify the individuals based on restorative materials known to exist from dental records. The cremains were then processed and the analysis was repeated to determine whether restorative resins could be found under this extreme condition. Under both circumstances, sufficient surviving resin material was found to distinguish positively each individual in the study group. This study showed the utility of XRF as an analytical tool for forensic odontology and also the significance of the role of restorative resins in victim identification, even after cremation.     

Analytical survey of restorative resins by SEM/EDS and XRF: databases for forensic purposes

Frequently in forensic cases, unknown substances must be identified. Automated databases can ease the burden of comparison as materials may be compared against many known standards in a relatively short period of time. It has been shown that dental resins can be named according to brand or brand group even in conditions as harsh as cremation. Databases are already in use for many materials, but no such database exists for dental resins. Thus, two databases were generated. One utilized a laboratory-based method, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), in conjunction with the Spectral Library Identification and Classification Explorer (SLICE) software. The other was based on portable X-ray fluorescence (XRF). The ability to perform database comparison with portable instrumentation can thus be brought directly to the field. Both the SLICE and XRF databases were evaluated by testing unknown resins. EDS is a well-established technique and the SLICE program was demonstrated to be a good tool for unknown resin identification. Portable XRF is a relatively new instrument in this regard and its databases have been constructed mostly for metal alloy comparison and environmental soil testing. However, by creation of a custom spectral library, it was possible to distinguish resin brand and bone and tooth from other substances.     

Ultraviolet illumination as an adjunctive aid in dental inspection

Tooth-colored resin fillings have become increasingly popular as restorative materials. Their presence in the dentition presents a challenge to the clinician and the forensic odontologist, as detection of the fillings can be difficult both visually and radiographically. As they necessarily form part of the unique dentition of an individual, recognition of the resins is important for forensic identification. Alternative light sources have been used with success in various fields of forensic science. In recent years small LED flashlights emitting at specific wavelengths in the ultraviolet light (UV) range have been developed. Their low cost, small size, and ready availability makes their use practical in both forensic dental inspection and clinical settings. UV inspection is of interest because enamel, dentin and dental materials all have differing fluorescent properties when illuminated by UV light. It was one goal of this research to quantitatively assess the fluorescence properties of modern restorative resins in order to predict their behavior during inspection using UV illumination. The second goal was to demonstrate practical use of UV in dental inspection with examples of how different materials fluoresce. Quantitative measurements were obtained for optical emission wavelength and intensity for 15 modern resins using a spectrophotometer. Results indicated that resin brands fluoresce at different wavelengths and with varying intensities. Practical use and comparison of the flashlights revealed that the most useful excitation wavelengths for resin detection were in the UVA range (365 and 380 nm). Porcelain restorations and composite resin fillings exhibited different responses to these two wavelengths and thus use of both is recommended for forensic dental inspection.     

Detection and classification of composite resins in incinerated teeth for forensic purposes

The great demand for esthetic restorations has resulted in placement of large numbers of composite resin fillings. The popularity of these materials is reflected in the quantity and variety of resin brands currently on the market. The ability to distinguish resin brands can aid in positive identification of burn victims, assuming that appropriate dental records exist. Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) was used to characterize the structure and composition of 10 modern resins. The structure of each resin was unique to manufacturer, and elemental analysis allowed separation into distinct groups. These 10 resins were also placed in extracted teeth and incinerated at 900 degrees C for 30 min, simulating near cremation conditions. The resins were identifiable by SEM/EDS after incineration, and the elemental composition remained almost unchanged. The data produced are immediately useful for resin identification in forensics, and comparative analysis can be readily performed using standard equipment. This work represents the initial stage of database generation.     

Forensic applications of pyrolysis capillary gas chromatography

A simple system of pyrolysis capillary gas chromatography has been used to improve discrimination and long-term reproducibility in the analysis of polymers particularly alkyd based paints typically encountered in forensic casework. This involved the coupling of a Pye Curie-point pyrolyser to the inlet port of a capillary gas chromatograph operated in the splitless mode. Examples of pyrograms demonstrating improved differentiation of alkyd paints, and also examples of other architectural and automotive paints, automobile rubbers, adhesives, polyurethane foams and fibres are shown.