Wear of Telescopic CAD/CAM zirconia and High-noble Metal Copings for Overdenture Retention

Objectives: Patient's satisfaction and adequate function of removable partial dentures [RPD] highly depend on the retention of the prosthesis. A telescopic overdenture is retained by secondary crowns that cover tooth-supported fixed copings. The retention of telescopic crowns [TC] depends on material, design and fit of the framework over the copings. The aim of this in-vitro-study is to compare different materials and designs of telescopic crowns. Methods: 3 groups each containing 5 specimens were tested (n=15): 1. Zirconia copings [ZC] with non-precious metal TC and gold friction-pins, 2. high-noble metal copings (0°) and TC [T] and 3. high-noble metal copings (6°) and TC [K]. A canine-supported mandibular overdenture was constructed. Each system was attached to the prosthesis and initial retention forces as well as after artificial aging (50,000 chewing cycles, 15,000 insertion-removal cycles) were measured. Statistical analysis was performed using SPSS 20.0 (Mann-Whitney-U-test, p0.05). Results: The initial mean retention forces [IF] for ZC (12.23N) were significantly higher than the IF of T and K. But the IF of T (9.62N) were significantly higher (p0.001) than the IF of K (6.03N). After artificial aging T and K showed a significant decrease of retention forces (T:69.75%, K:47.27%; p0.001), but were not significantly different from each other (p=0.800). Whereas, the retention forces of ZC were not affected by aging (p=0.857). Conclusion: The retention forces of high-noble metal TC decreased significantly after aging, but were still within clinically acceptable function. Therefore, the design had an effect on the wear. Within the limitations of an in-vitro-study the clinical use of zirconia telescopic crowns with gold-friction pins can be recommended based on the continuous retention forces. Keywords: telescopic crowns, overdenture, retention forces, wear, CAD/CAM, zirconia