Exploring Retention Force Behavior in Various Digital Double Crown Systems Through in Vitro Studies

Objectives: Digital dentistry has the potential to enhance the accuracy and efficiency of daily dental practice. Utilizing digital methods for producing telescopic crowns, including primary and secondary crowns, enables precise control of the primary crown's degree and eliminates common production errors found in conventional dentistry. Therefore, our study aims to investigate the retention behavior of various telescope crown systems manufactured through digital methods.
Methods: Using exocad dental CAD software, four groups of primary and secondary crowns were designed after scanning a standard dental model with a desktop scanner (E4 Dental Scanner; 3 shape, Copenhagen, Denmark). These groups consisted of zirconia-SLM (Selective Laser Melting) titanium, SLM Ti-SLM Ti, SLM Co-Cr-SLM Co-Cr, and SLM Co-Cr-SLM Ti, with each group containing three samples. A preload of 50N was applied to each test specimen. The degree of primary crown convergence was set at 4 and 6 degree for each different material system. Ten tests were conducted for each set, and retention was measured using an Instron universal testing system (LLYOD instrument LR 5K, Segensworth, UK).
Results: The choice of materials significantly influenced initial retention (P<0.05). The Ti-Ti 6 degree group exhibited the lowest retention (28.11N), while the Co-Cr 6 degree group demonstrated the highest retention (174.62N). The setting of the convergence angle had a significant impact on retention, particularly between the Ti-Ti group and the CoCr-CoCr group (P<0.001).
Conclusions: The digital fabrication of double crowns is influenced by various materials and the convergence angles of inner crowns