Effects of clasp retention forces and abrasion on different cast crowns.

STATEMENT OF PROBLEM Dental alloys have different mechanical properties compared with enamel. However, few studies have been conducted to determine the effects of the retention forces of clasps when applied on different cast crowns. PURPOSE The purpose of this study was to evaluate the retention forces of cast circumferential clasps made of cobalt-chromium alloy on complete cast crowns made of cobalt-chromium (CC group) and gold-silver-palladium (AC group) alloys, and to observe their abrasion patterns. MATERIAL AND METHODS Two groups of specimens were fabricated (n=5) and subjected to repeated insertion-removal tests (100 to 15,000 cycles). The mean values of removal forces at 100, 400, 800, 1500, 4500, 7500, 10,000, and 15,000 cycles, and their corresponding change rates compared with the initial 100 cycles' retention were determined. The differences between the 2 groups were analyzed by 2-way repeated measures analysis of variance at 100, 7500, and 15,000 cycles. The surfaces of specimens were observed with scanning electron microscopy. RESULTS There were significant differences between the CC and AC groups in retention forces (P<.05). Clasp retention showed a descending trend for cobalt-chromium alloy crowns from the initial value, which decreased by 29.9% after 15,000 insertion-removal cycles. A sharp increase in retention could be observed in the AC group, which rose by 99.7% ultimately. The worn surfaces of the gold-silver-palladium crowns showed different wear patterns compared with the cobalt-chromium alloy crowns. CONCLUSIONS The results indicate that cobalt-chromium alloy crowns and gold-silver-palladium alloy crowns perform differently when cobalt-chromium alloy clasps are designed as retainers for partial removable dental prostheses. Crown designs should be changed, depending on the retainer and clasp materials for partial removable dental prostheses abutment teeth.