Study On Elastic Limit And Cyclic Fatigue Test Of Resin Clasp And The Abrasion On The Tooth Surface

Objective:(1)To investigate the best cross section design of Aulen elastic resin clasp and the best retentive undercut depth; (2) Compare the retention force of resin clasp and cobalt-chrominum alloy cast clasp in cyclic fatigue test and learn the attenuation of retention force; (3)To investigate the abrasion on the tooth surface in cyclic fatigue test.Methods:30 resin straight clasps made into 3 groups by different types were subjected to compression-deformation test in the universal material test machine,the elastic deformation limit and relevant enclasp forces were got, after the data produced from the machine were analyzed by a serial of software, combine the clinical conditions and choose a best type.Then another 10 resin clasps and 10 Co-Cr clasps were made to engage one of two retentive undercut depths (0.25mm or 0.50mm).The force required to remove the clasps was measured using the universal testing machine.Meanwhile the distance between the tips of each clasp was measured before and after the cyclic fatigue test. Data were subjected to ANOVA and LSD-t, followed by repeated measures analysis of variance.Lastly a resin clasp and a Co-Cr clasp were made according to the best clinical design, a cyclic fatigue test on the crown of extracted tooth was evaluated using the universal testing machine,we scan the friction area before and after the cyclic fatigue test using the electron microscope and compared the situation of abrasion.Results:(1)The elastic deformation limit of all resin straight clasps is 1.488-1.824mm, and the relevant enclasp forces is 2.182-2.345N. When the deformation is 0.25mm, there is no significant difference between A group and B group, also between B group and C group, but there is significant difference between A group and C group;When the deformation is 0.50mm, there is significant difference between A group and B group, also between A group and B group,but there is no significant difference between B group and C group. (2)All of the clasps experienced a decrease in retentive force measurements before and after the cyclic fatigue test, the greatest decrease was found in Co-Cr,0.50mm group with the figure of 6.937N, and the smallest was found in resin,0.25mm group.Before and after the cyclic fatigue test, there is no significance found in the retentive force of resin clasps, while significant differences were found in the retentive force of Co-Cr clasps.The distance between the tips of Co-Cr group is lager than resin group.(3)Both clasps on the extracted tooth experienced a significance decrease in retentive force measurements before and after the cyclic fatigue test. When using resin clasp, the electron microscope picture of the tooth surface shows that there are no obvious grooves.When using Co-Cr clasp, the electron microscope picture of the tooth surface shows that the original texture can not be seen, but there are many grooves.Conclusions:(1)When Aulen elastic resin is used as clasp, the best design is the cross section is like a hemicycle,width is 2.5mm, depth is 1.3mm, and the coning is 0.8,which is suitable to engage the retentive undercut depths of 0.50mm. (2) Resin clasp can afford less retention force than Co-Cr clasp, but the retention force of resin clasp decreased slowly in clinical use,instead, two or more resin clasps can be used or other retention methods can be combined together. (3)The abrasion of resin clasp on the tooth surface is less than the Co-Cr clasp.