Potential of proton microbeam in the study of dental composites. 1. Micro-PIXE mapping of Ca, Zr, Ba and Yb

In recent studies, PIXE and ERDA showed a high potential for dental composites [1, 2]. However, wide-beam IBA techniques can not explore the biomaterials' granular structure, which requires microbeam methods to be accounted for.
In this report we applied proton μPIXE for mapping the major elements in dental composites, with the aim of evaluating the method's potential. A flat sample with a smooth surface (~ 1 mm thick) of the composite previously labeled IV.a [1,2] was prepared by photopolymerization on a glass plate. Measurements were carried out at the Rossendorf nuclear microprobe with a 3.1 MeV proton beam focused to a spot of ~3 μm. Five areas ~250 x 250 μrn located ~0.5-2 mm apart of each other were mapped on the flat specimen at ~4 μm resolution. The μPIXE maps of Ca, Zr, Ba and Yb clearly evidenced the granular structure of the composite. The mineral particles revealed a polydisperse size distribution and different compositions. Thus while most mineral particles were Ca-rich and not larger than ~8 μm, a small number of much larger inclusions were seen, with size in the ~16-60 μm range and with high levels of Zr, Ba and Yb. Generally the maps of the elements were complementary, but some apparent deviations from this rule were seen in the different areas. This suggests that the mixture of mineral particles may show some degree of heterogeneity visible in the sample on a ~1 mm scale, which is comparable to the diameter of a dental filling. Therefore μPIXE mapping gives structural insight on the dental composites, potentially relevant for the study of their properties and behavior in the oral environment.
[1] E.A. Preoteasa et al., Nucl. Instr. and Meth. in Phys. Res. B 189 (2002) 426-430.
[2] E.A. Preoteasa et al., Anal. Bioanal. Chem. 379 (2004) 825-841.