Bond strength enhancement for additively manufactured zirconia: Micro-retentive design approach.

Purpose: To investigate the effect of digitally designed micro-retention features on the bond strength of additively manufactured (AM) zirconia copings.

Materials and methods: Sixty titanium base abutments (NobelParallel, NobelBiocare), pretreated with 50 µm alumina particles were divided into four groups (n = 15 per group); one group with subtractively manufactured zirconia copings (SM), and three test groups comprising one group with AM zirconia copings without any intaglio surface modification (AM-N), and two groups with digitally designed inverted pyramid-shaped micro-textures incorporated to the intaglio surface of the AM zirconia copings with two sizes: Ra 120 µm (AM-120) and Ra 240 µm (AM-240). All copings were bonded to the abutments using a conventional resin cement (Multilink Hybrid). Pull-off tensile strength was measured with a universal testing machine (Instron), and statistical analysis was performed using analysis of variance and post-hoc test.

Results: Mean tensile strength values were 574.5 N for the SM group and 450.7 N, 990.8 N, 1097 N, for AM-N, AM-120, and AM-240, respectively. No statistically significant difference was found between the SM and AM-N groups (p > 0.05) or between the AM-120 and AM-240 groups (p > 0.05). However, the AM-120 and AM-240 groups demonstrated significantly higher tensile strength compared to the SM and AM-N groups (p < 0.001).

Conclusion: Provision of inverted micro-textured pyramidal shapes provided a simulation of etched surfaces to the intaglio surface of AM zirconia copings and significantly enhanced their retention strength to Ti-base abutments compared to subtractive and non-textured AM zirconia.