Fig. (1) Principal phases during the preparation of the samples. (a) A prismatic model was first built with impression chalk within which different nails were inserted. Thermoplastc resin disks were heated with the Biostar System (b) and inserted into the model at a pressure of 4.1 atm so as to reproduce the dimension of the nail head (c). After being shaped and once the cooling was completed, the discs were removed (d). The discs were finally cut with a milling cutter in many different squares (d-e) the surface of which was then polished (f).