Study I: The materials tested were NiTi (54%Ni, 46%Ti, Unitec, U.S.A), stainless steel AISI 316 LVM (12%Ni, 18%Cr, 68%Fe, 2%Mo, Sandvik, Sweden), ASTM Grade 2 commercially pure titanium (TISTO GmbH, Düsseldorf, Germany), white soft paraffin (white soft paraffin is a semi-solid mixture of hydrocarbons obtained from petroleum and bleached) and a composite material known as Silux Plus® (Bisfenol-A-diglyidylmetacrylate 15-20%, triethylglycoldimetacrylate 15-20%, aluminoxide <1%, amorphic siliconoxide 50-60%, 3- metacryloxidepropyltrimetoxisilan <7%, Silux Plus, 3M, USA) Metal test discs of 6x7 mm were taken from a large bar by turning on a lathe. The composite material was prepared using a rubber mould. The surface preparation consisted of electrolytic polishing for stainless steel and water sanding for titanium and NiTi (waterproof silicon carbide paper FEPA P#2400).
Studies II and III: The tested materials were vacuum-melted, drawn and fully annealed NiTi (56 % nickel by weight, 44 % titanium by weight, Af = - 10 ˚C, NiTi Development Co., USA), AO/ASIF stainless steel (Synthes GmbH, Switzerland), and AO/ASIF Ti-6Al-4V alloy (90 % titanium by weight, 6 % aluminium by weight, 4 % vanadium by weight, Synthes GmbH, Switzerland).
Identical round test implants were taken from a longer wire by mechanically cutting. The implants used in both studies were 1.8 mm in diameter and 6 mm in length. The cut ends of the implants were rounded using water-cooled grinding (silicon carbide paper FEPA P#800, Struers, Denmark). The material surfaces were as received: stainless steel was electrolytically polished, NiTi and Ti-6Al-4V were received in a mechanically ground condition.
Study IV: The NiTi and stainless steel materials and surface preparations were as in the studies II and III. Implants of 1.8x18 mm were taken from a longer wire by mechanically cutting, and the cut ends of the implants were rounded as previously.
The test discs and implants were all degreased with 70 % ethanol, washed with an ultrasonic vibrobath and autoclaved (30 min., 121˚C) before the procedures.