(39a) Radiopaque flame-made Ta2O5/SiO2 nanoparticles with controlled refractive index and transparency

Dental fillings made of composite organic monomers and ceramic fillers (particles) are used for tooth shaded dental restoration of anterior lesions and small - medium sized defects in the posterior region. This is a result of the excellent esthetic properties of these fillings as well as health concerns with amalgam fillings regarding mercury release. Therefore, the relation of filler properties to composite characteristics such as radiopacity, tensile strength, hardness, shrinkage, wear and transparency have been intensively studied in the last few years. Mixed Ta₂O₅-containing SiO₂ powders with high specific surface area, controlled refractive index, transparency and crystallinity were prepared by flame spray pyrolysis as fillers for dental composites. The production rate ranged from 6.7 ? 100 g/h in a lab scale reactor. The effect of the Ta-precursor, the solvent, the total metal concentration and the Ta-content were studied by nitrogen adsorption, x-ray diffraction, light microscopy, HRTEM, DIFTS analysis, as well as the composite transparency within a polymer matrix of dimethylacrylate for dental restoration applications. Filler properties such as transparency, crystallinity and Ta-dispersion in the SiO₂ matrix altered the composite performance. Ta₂O₅ crystallites and a low Ta-dispersion within the SiO₂ matrix decreased the filler and composite transparency. Powders with identical specific surface area, refractive index and Ta₂O₅-loading (24 wt%) showed a wide range of composite transparencies from 33 ? 78 % depending on filler properties. Fillers with an amorphous structure, a high Ta-dispersion and a matching refractive index with the polymer matrix showed the highest composite transparency of 86 % for a 16.5 wt% filler loading including 35 wt% Ta₂O₅ giving an optimal radiopacity.