CAD/CAM-milled versus conventionally cast secondary crowns fabricated from high noble metal alloy: an in vitro study of retentive force

Aim: To investigate retentive forces (RFs) of CAD/CAM-milled and conventionally cast secondary crowns (SCs) after artificial aging in an in vitro study.
Materials and methods: Forty artificial premolars were manufactured and provided with 40 primary crowns (PCs) milled from a high noble metal alloy. SCs were fabricated from the same alloy. Ten SCs were produced with the help of a tactile scanning method (group A), 10 with the help of a photo-optical scan (spray; group B), 10 with the help of a photo-optical scan (acrylic dye; group C), and 10 using a conventional casting technique (group D). Cycles of separation were performed and RFs were measured at baseline and after 5,000 and 10,000 cycles. Surfaces were examined under a scanning electron microscope (SEM). Statistical analysis was conducted at a significance level of P ≤ 0.05.
Results: Group D showed the highest median RFs with respective interquartile ranges (IQRs) – baseline: 7.0(2.5) N; 5,000 cycles: 5.5(2.0) N; 10,000 cycles: 5.4(1.5) N compared with groups A, B, and C – baseline: 5.2(8.4)/3.4(11.3)/1.3(1.5) N; 5,000 cycles: 1.8(0.8)/2.1(1.7)/1.0(1.3) N; 10,000 cycles: 1.9(1.6)/2.4(2.5)/1.0(1.4) N, respectively. In contrast to groups A, B, and C, group D did not gain RF when RF values were compared after 5,000 and 10,000 cycles. The loss of RF between baseline (7.0 N) and after 10,000 cycles (5.4 N) was significant only for group D (P = 0.007), but not for groups A, B, and C.
Conclusion: Both CAD/CAM-milled and conventionally cast SCs from a high noble metal alloy can provide sufficient RF after 10,000 cycles of artificial aging. However, groups A, B, and C showed constantly lower RF values compared with group D.