Fracture Resistance of 3-Unit Zirconia Fixed Dental Prostheses Differing in Wall Thickness Fabricated by Either 3D-Printing or Milling.

BACKGROUND

To evaluate the fracture resistance of 3D-printed 3-unit fixed dental prostheses (FDPs) made from tetragonal zirconia polycrystal (3Y-TZP).

METHODS

Based on a maxillary typodont model with a missing first molar and neighboring teeth with full crown preparations, FDPs differing in wall thickness (d = 0.6 mm / d = 0.8 mm / d = 1.0 mm) were designed. For all test groups, 12 samples were fabricated from 3Y-TZP by either 3D-printing or milling. For 3D-printing, pontic designs were modified by basal slots to enable regular firing times. After luting on CoCr dies, samples underwent artificial aging. Loads tilted by 30° were applied on the mesio-buccal cusp of the pontic, and fracture resistance F was assessed. Welch ANOVA and Dunnett-T3 tests were used for statistical evaluation.

RESULTS

Significant differences in F were identified (Welch ANOVA, < 0.001). For milled FDPs, fracture originated from connector areas, and F increased with increasing wall thickness (d = 0.6 mm: 1536 ± 131 N, d = 0.8 mm: 2226 ± 145 N, d = 1.0 mm: 2686 ± 127 N, significant differences but for the comparison d = 0.8 mm vs. d = 1.0 mm). For 3D-printed FDPs, the loaded cusp fractured, and F did not change with FDP wall thicknesses ( > 0.779, F = 1110 ± 26 N for all PZ FDPs). Milled FDPs showed significantly higher F when compared to 3D-printed FDPs with identical wall thickness.

CONCLUSIONS

Although 3D-printed zirconia FDPs still show lower fracture resistance values than their milled counterparts, all tested FDP configurations clearly exceed the clinical reference thresholds and can therefore be recommended for clinical use.