Comparative Study Of The Retention Of Vitallium2000plus And Nobilium2000 Cast Clasps In The Simulated 3-year Clinical Use

Objective:In order to study the effects of Vitallium2000 plus and Nobilium2000 cast clasps by simulating clasp removal and wear by patients,the change trend of the retaining force of the clasp during the cycle was studied,observed the morphological changes of the inner surface of the clasp after cyclic clasp.In order to provide a reference for the clinical design and clasp material selection.Methods:1.The standard wax model of the mandibular first molar was used as the primary abutment,an inverted concave meter was determined to be 0.25 mm and 0.5mm.In order to specify the orientation of the clasp,the near central support concave and the vertical guide planes were prepared on the parallel milling apparatus,twenty metal abutments were made by lost wax casting method,conventional embedded,casting,sandblasting,grinding and polishing.Twenty standard metal abutments for mandibular first molars were randomly divided into 4 groups;2.Design and print wax clasp ring by computer aided(CAD)method,the clasps were designed with two undercut depths of 0.25 mm and 0.50 mm,according to the designed data printed wax clasp,three-arm clasp is cast by losing wax method,to ensure the consistency of the sample,the clasp is not polished,only sandblasted.The experimental group used Vitallium2000 plus c the designed data,whereas the control group used Nobilium2000.A total of 4 groups were set(each group five clasps);3.The universal mechanical testing machine simulated cycle test.Each clasp was removed for 5000 times in a cycle,and the initial retaining force of the clasp was recorded.Then the retaining force was measured for 500 times in a cycle,and the microstructure changes of the clasp were observed by SEM after the cycle;4.Student’s t-test and linear correlation analysis were used for statistical processing of the data;5.Before the cycle fatigue test,all specimens were examined by magnifying glasses and scanning electron microscope.Results:1.The retention force of the two materials is negatively correlated with the number of cycles;2.Clasps made of same material,the retentive force of 0.50 mm undercut depths is greater than that of 0.25mm;3.Under the 0.25 mm undercut,the retention force of Vitallium2000 plus clasps is grater than the Nobilium2000 clasps,the difference has statistical significance(p<0.001),Under the 0.50 mm undercut,the retention force of Vitallium2000 plus clasps is grater than the Nobilium2000 clasps,the difference has statistical significance(p=0.003),after cycle,the retention force of Vitallium2000 plus clasps is greater than the Nobilium2000 clasps,the difference has statistical significance(p<0.001);4.Scanning electron microscopy(SEM)showed that there were wear marks on the inner surface of the clasp after cycle.The wear marks were mainly concentrated in the tip1/3 of the clasp,but no cracks were found.Conclusions:1.Vitallium2000 plus and Nobilium2000 cast clasps can maintain ideal retentive force at 0.25 mm and 0.5mm undercut depth in the long-term use;2.Nobilium2000 generally has a lower retentive force than Vitallium2000 Plus,there is no difference in the stability of retention force between the two materials.