Retention Force Attenuation Of Two Clasps And Surface Abrasion Of The Cr-Co Crowns

0bjective：To establish a evaluation system of clasp cyclic fatigue test andinvestigate the the retention force changes of Cr-Co alloy T bar clasps and MoCr-Co T bar clasps on Cr-Co crowns， and the surface abrasion of thecrowns,respectively in or without saliva soak conditions during one year。Methods：Standard crowns were made，and using Cr-Co alloy and Mo Cr-Co tomade standard T bar clasps。T bar clasps and Cr-Co crowns were fixed on instrontesting machine. A repeated of1800times of placement and removal were carriedout，on0.25mm，0.5mm undercut depth and in or without saliva soak conditions，simulating one year of clinical use。 The atenuation curves of the maximum values ofthe retention force were evaluated。The surface abrasion of the crowns contact withthe T bar clasps was scanned before and after the test by the electron microscope。Results：The retention force attenuation of every clasp accord with the logarithmattenuation law。The equations were Y=15.091-2.290lgX in the group of Cr-Co alloyclasp on0.25mm undercut depth without saliva soak condition。The equations were Y=16.197-2.310lgX in the group of Mo Cr-Co clasp on0.25mm undercut depthwithout saliva soak condition。The equations were Y=21.170-4.727lgX in the groupof Cr-Co alloy clasp on0.5mm undercut depth without saliva soak condition。Theequations were Y=21.862-4.663lgX in the group of Mo Cr-Co clasp on0.5mmundercut depth without saliva soak condition。 The equations wereY=14.677-2.522lgX in the group of Cr-Co alloy clasp on0.25mm undercut depth insaliva soak condition。The equations were Y=15.794-2.450lgX in the group of MoCr-Co clasp on0.25mm undercut depth in saliva soak condition。The equations wereY=20.166-4.795lgX in the group of Cr-Co alloy clasp on0.5mm undercut depth insaliva soak condition。The equations were Y=21.133-4.852lgX in the group of MoCr-Co clasp on0.5mm undercut depth in saliva soak condition。Scanning electronmicroscopy showed in the same condition, there was less surface abrasion in MoCr-Co T bar group。Conclusion：The logarithm attenuation law is observed in the T bar clasps made of Mo Cr-Co and Cr-Co alloy。The Mo Cr-Co clasp is superior to maintain theretention force than the Cr-Co clasp。The surface abrasion of the crown for the MoCr-Co bar clasp is less slight compared with that for the Cr-Co alloy bar clasp。Theundercut depth of0.25mm is within the elastic limit of Cr-Co alloy and Mo Cr-Co,and the undercut depth of0.5mm is beyond the elastic limit of Cr-Co alloy and MoCr-Co. On a specific undercut depth the retention force attenuation of clasp insaliva soak condition is mroe than the same kind of clasp without saliva soakcondition...