The effect of veneering on the marginal fit of CAD/CAM-generated, copy-milled, and cast metal copings

Abstract

This in vitro study investigated the marginal fit of metal and zirconia copings before and after veneering on dies with shoulder/chamfer (s/c) finish lines. Using CAD/CAM, ten (n = 10) each s/c zirconia (NZ) copings and ten (n = 10) each s/c metal (MM) copings were generated. As controls, ten (n = 10) each s/c zirconia copings were copy-milled (ZZ) and ten (n = 10) each s/c metal copings were cast (CC). the vertical marginal discrepancy of the copings was measured at 20 predefined spots of the circular shoulder and chamfer finish lines in microns (mu m) before and after a first and a second veneering firing using a stereomicroscope at x40 magnification. Data were statistically analyzed, and the comparisons of CAD/CAM-milled (NZ, MM), copy-milled (ZZ), and cast (CC) copings before and after veneering were made at a significance level of p < 0.05. Gap width at s/c finish lines of ZZ was (91 +/- 11/100 +/- 28) and increased significantly (109 +/- 21/141 +/- 18) after the first firing (ZZ1). NZ showed significantly smaller gaps than ZZ (36 +/- 6/46 +/- 12) and (NZ1) after the first firing (61 +/- 16/71 +/- 29). Gap widths of CC groups (36 +/- 8/25 +/- 4) were not significantly different from NZ but were significantly lower after the (CC1) first veneering firing (40 +/- 8/42 +/- 7). MM copings showed gap values similar to NZ. Second firings did not significantly increase gaps in all groups except ZZ2 of chamfer finish line. Veneering increased the marginal gap width of copings. Within the limits of this in vitro study, aesthetic ceramic veneering of CAD/CAM-generated copings caused a statistically significant but tolerable loss of marginal fit precision.