Since 1979, we have been reported that the metal bonding denture base resin had many advantages when we used in the prosthetic field. However unexpected fractures of the wire clasp were frequently observed within the shorter clinical period than commonly. Cantilever type repeating bending tests were carried out to search for whether the use of this resin caused the wire fracture or not. Two types of test pieces, straight and crank-like, were fabricated by the φ0.9 mm Co-Cr wrought wire and two heat cured resins, META-DENT and ACRON. Repeating bending stresses were loaded at 10 mm left from the fulcrum. Bending cycles required to the fracture of test pieces made of adhesive resin are one-half time as many as the conventional in both two types. It was considered that these differences caused by the space between wire and resin. Test pieces intentionally proposed 0.3 mm space between wire and resin showed remarkable resistances to the wire fracture. When the stress was loaded at 12 mm, the bending strengh also increased. Test pieces with φ1.0mm wrought wire were also tested, however the fracture resistance did not increased. It was recognized that the wire
