Qualitative assessment of microstructure and Hertzian indentation failure in biocompatible glass ionomer cements

Discs of biocompatible glass ionomer cements were prepared for Hertzian indentation and subsequent fracture analyses. Specifically, 2 × 10 mm samples for reproducing bottom-initiated radial fracture, complemented by 0.2 × 1 mm samples for optimal resolution with X-ray micro tomography (μCT), maintaining dimensional ratio. The latter allowed for accurate determination of volumetric-porosity of the fully cured material, fracture-branching through three Cartesian axes and incomplete bottom-initiated cracking. Nanocomputed tomography analyses supported the reliability of the μCT results. Complementary 2-dimensional fractographic investigation was carried out by optical and scanning electron microscopies on the larger samples, identifying fracture characteristics. The combined 3-D qualitative assessment of microstructure and fractures, complemented by 2-D methods, provided an increased understanding of the mechanism of mechanical failure in these cements. Specifically, cracks grew to link pores while propagating along glass-matrix interfaces. The methodological development herein is exploitable on related biomaterials and represents a new tool for the rational characterisation, optimisation and design of novel materials for clinical service.

[Wiskott-Aldrich syndrome in a hetrozygous woman]

The authors report a case of a 20-year old woman, with all the characteristics of the Wiskott-Aldrich-syndrome. The main signs of the disease were recurrent infections, eczema, thrombocytopenia and mild mucosal bleeding. The size of platelets was reduced. Storage pool disease was based on the abnormal platelet aggregation and the lack of dense bodies shown by electronmicroscopic examination. The disturbances of the lymphocytes, neutrophils and monocytes, which resulted in immunodeficiency, could be proven by the immunological tests. This X-linked recessive disorder appeared with typical signs in a heterozygous carrier woman. According to our knowledge, no similar case has been reported before.