Retention force of removable partial dentures with different double crowns

Objectives The aim of the study was to compare the retentive behaviors of double crowns with different designs and material compositions before and after artificial aging. Materials and methods Six pairs of double crowns were fabricated: telescopic crowns 0 degrees made of high-noble metal (group A) or non-precious metal (group B), telescopic zirconia copings with secondary crowns made of electroplated gold 2 degrees (group C), crowns with friction pins 2 degrees made of non-precious metal (group D) or zirconia (group E), and conical crowns 6 degrees made of high-noble metal (group F). Retention forces were assessed before and after artificial aging, and after axial and non-axial loading. Results Initially, specimens in group D (13.9 N), B (12.5 N), and E (12.2 N) exhibited the highest retention forces. Retention forces in groups A (9.6 N), C (7.4 N), and F (6.0 N) were statistically significantly lower than those of the other groups (p < 0.05). After artificial aging, double crowns with additional retention elements exhibited the highest retention forces. The largest retention force losses were evident in groups A (70%), B (64%), C (39%), and F (47%). Conclusions Double crowns with different designs and made of different materials exhibited different retention forces and different long-term retentive behavior. The highest retention force losses were evident in double crowns with more extended surface contact, such as telescopic crowns.