Potential of ERDA for analysis and depth profiles of light elements in dental composites

In the elemental analysis of dental composites, XRF and PIXE failed to detect low Z elements. The light elements from these biomaterials can be detected, however, by various ion beam analysis techniques. Among them, elastic recoil detection analysis (ERDA) is a fairly new method for simultaneous analysis of light and medium mass elements at the surface and for the determination of their depth profile. In view of evaluating the potential of ERDA for the analysis of dental composites, Tetric Ceram (Vivadent) was chosen because it contains many light elements, i.e. H, C, N, O, F, Al, Si. A flat surface sample was prepared as for XRF and PIXE. The ERDA measurements were carried out using a van de Graaff tandem accelerator. The projectiles were 80 MeV 63 Cu10+ ions. The detector was a compact ΔE(gas)-E(solid) telescope. The angles of incidence and exit were 75 angle relative to the sample normal. The ΔE-E spectrum evidenced H, B, C, N, O, F, Na, Al and Si. The elements' total energy spectra were analyzed with our program SURFAN , showing the relative atomic concentrations H : B : C : N : O : F : Na : Al : Si, to be in the ratios 0.8 : 0.1 : 0.8 : 0.03 : 1.4 : 0.18 : 0.004 : 0.09 : 0.4. Levels of the organic H and C were high, while Si dominated the inorganic elements, followed by F, B and Al. The ratios H/C and B/Al were equal to ∼1. Levels of N (organic) and Na (inorganic) were low. Oxygen high level came both from the organic polymer and the inorganic particles. The ratios between elements concentrations were not uniform within the depth of 1-1.5 μm penetrated by the 63 Cu10+ ion beam, evidencing depth profiles by deviations of the experimental energy spectra with respect to the theoretical calculations for homogenous distributions. Thus H, C, N were increased for a depth of ∼0.25-0.35 μm, Al and Si decreased for ∼ 0.35-0.40 μm, and F decreased for ∼ 0.2 μm. This showed the local concentrations near surface to be higher for the organic polymer and lower for the inorganic phase, the latter showing a faster decrease for F than for Al and Si. The near surface opposite trends of the organic/inorganic phases indicates competition between their filling factors within a depth equal to the mean radius of the inorganic particles, where additional interstitial space becomes available and is filled by the polymer. A mean radius of 0.35 μm specified by the producer supports this view. The more abrupt decrease of F suggests a smaller mean size of the YbF3 crystals than of the Al, Si-containing particles. (authors)