*2.1. Study Protocol*

The contact surfaces of the samples were subjected to different surface machining techniques such as polishing, milling, sandblasting (so-called traditional methods), and plasma-electrolyte processing. The traditional method of surface machining was carried out using a milling cutter NTI 060. 14.2 mm (NTI, Alfeld, Germany), a sandblasting machine (Bego Easyblast, Bremen, Germany) using sand (Renfert Cobra, Hilzingen, Germany) with particles size 125, 90, 50 µm at 0.25 MPa air-abrasion pressure approximately 10 mm from the sample surface during 60 s.

After surfacing, the samples were labeled. Then morphological and elemental analyses were carried out. After that samples with ceramic layers were manufactured. Shear strength was determined for joint samples.
