ABSTRACT
This investigation aims to assess the accuracy with which cobalt-chromium clasp are made and the degree to which they are still functioning after periods of wear of one month and six months. Two groups of clasps were made; the clasps in one group had a taper form; the clasps in the other group were uniform in cross-section. The force required to deflect each clasp by 0.25mm was ascertained using the Instron Universal Testing Machine [Instron Ltd High Wycombe, Bucks, England]. An apparatus for cyclic deflection of clasps was designed. Clasps were deflected by 0.25mm 240 times [representing one month's wear] and a further 1200 times [a total of six month's wear] and their permanent deformation was measured using electronic calipers. It was found that the force required to deflect clasps of apparently identical design and dimension was very variable. Permanent deformation of clasps occurred within one month and further deformation occurred the end of six months. The clasps of uniform cross section were more resistant to permanent deformation. It is concluded that cast cobalt chromium clasps are inconsistent in performance and may not be functioning as retainers after a short priod of denture wear in the mouth