AbstractsMedical & Health Science

The purpose of this in-vitro study was to compare the retention of circlet (E) clasps and back action clasps against three different abutment surface materials (enamel, composite, CAD/CAM ceramic crown) during long-term simulation of attachment and detachment, and to measure the loss of retention and wear after 16,000 simulated cycles of attachment-detachment. Forty-eight models were constructed by placing either an upper first premolar or a metal die inside a metal rectangular block. Models were divided according to the abutment teeth into three groups. Group GI consisted of 16 unrestored human premolars with sound enamel. Group GII had 16 premolars re-contoured buccally using composite resin. Group GIII had 16 metal dies (duplicated from a human premolar) covered by CAD/CAM all-ceramic crowns. On the models, E-circlet (E) and back-action (B) clasps were constructed to engage the model's teeth. Removal and insertion cycling of clasps was carried out for 250, 500, 1,000, 2,000, 4,000, 8,000, and 16, 000 cycles by using a chewing simulator. The retention force of each clasp was measured before cycling and at different intervals by using universal testing machine. An acrylic replica was made for each abutment retention surface before and after cycling. Each replica was examined by SEM, and the wear areas were measured. The data was analyzed statistically using 1-way ANOVA, 2-way ANOVA, and Mann-Whitney tests. No significant differences in retention of either clasp were found between the three abutment material surfaces. However, there was a significant decrease in retention force of the circlet (E) clasp between 1,000 and 2,000 cycles but not the back action clasp. There were no significant differences in retention loss after 16,000 cycles (P≥0.05) of both clasps (E, B) on the three abutment materials (enamel, composite resin, CAD/CAM ceramic crown). There were significant differences among the wear areas of the abutment surface of the six subgroups (P≤0.05). Within the limitations of this study, the following conclusions were drawn: 1) The back action clasp maintains its retention force for a longer period than the circlet (E) clasp. 2) Composite resin contouring of teeth seems to be a viable technique for creating retention for the RPD clasps because there was no significant difference between the 3 abutment materials regarding their retention forces at different intervals (P0.05). 3) The difference in design between circlet E-clasps and back action clasps had no significant effect on the loss of retention force after 16,000 cycles. 4) Using different abutment surfaces for clasp retention had no significant effect on the amount of retention loss after 16,000 cycles. 5) The composite resin contoured teeth showed more wear than the enamel and ceramic by the action of E and back action clasps. However, E-clasps caused more wear on the abutment materials than back action clasps. Das Ziel dieser In-vitro-Studie war es, die Retention von E-Klammern und Back-Aktion-Klammern auf auf drei Materialien zu…