• Kesinee Pattanachareon D.D.S.
• Parnupong Wongthai BSc., D.D.S.(Hons.), M.S., Diplomate, Thai Board of Prosthodontics

Objective The aim of this study was to investigate properties and fatigue resistance of cobaltchromium
alloy cast circumferential clasps recycled in different mixing ratios by weight between used
alloy and new alloy.

Materials and methods Forty-five circumferential clasp samples made from cobalt-chromium alloy
were divided into 3 groups (n=15 per group): 100% new alloy; 50% used alloy mixed with 50% new
alloy; and 100% used alloy, which the used alloy was utilized only once. Ten samples per group were
subjected to the bending test until fractured and data were recorded. The remaining 5 samples per
group were subjected to cyclic deflection. The preset value of 0.25 mm was used to simulate the clasp
deflection during insertion and removal of the removable partial denture over the undercut of the
abutment, until a 0.1 mm permanent deformation occurred vertically. The number of loading cycles of
each sample was recorded. One-way analysis of variance and LSD multiple comparison tests were
used to compare the results of the 3 groups.

Results The 100% new alloy cast clasps showed significantly higher mean loads at yield point,
modulus of elasticity and loads required for 0.25 mm deflection compared to the 100% used alloy cast
clasps (p < 0.05), but showed no significant difference from those of the 50% used alloy mixed with
50% new alloy cast clasps. The mean fatigue resistance of the 100% new alloy cast clasps (8,457
cycles) was significantly higher than the 50% used alloy and 50% new alloy cast clasps (5,479 cycles)
and the 100% previously used alloy cast clasps (2,880 cycles) respectively (p < 0.05).

Conclusion Recycle of cobalt-chromium alloy in the higher ratio of the used alloy reduces the
properties and fatigue resistance of the cast clasp.

(CU Dent J. 2010;33:185-196)