Effect of finish line designs on the dimensional accuracy of monolithic zirconia crowns fabricated with a material jetting technique.

STATEMENT OF PROBLEM

Finish line design is critical for the long-term stability of complete crown restorations. However, the optimal finish line design for monolithic crowns fabricated with material jetting (MJ), a type of printed zirconia, remains unknown.

PURPOSE

The purpose of this in vitro study was to evaluate the dimensional accuracy and marginal quality of monolithic zirconia complete crowns with various finish line designs fabricated through subtractive manufacturing (SM) or MJ.

MATERIAL AND METHODS

A standardized typodont right mandibular first molar was prepared with 5 different finish line designs: knife edge, 0.5-mm chamfer, 0.5-mm shoulder, 0.8-mm chamfer, and 0.8-mm shoulder. Complete crowns were designed with identical occlusal morphology and thickness. In total, 100 monolithic zirconia crowns were fabricated using SM and MJ (n=10 crowns for each finish line design and manufacturing method). Dimensional accuracy in the external, marginal, and intaglio regions was evaluated by using best-fit alignment with the design data. Marginal quality was assessed under a ×20 stereomicroscope. Differences among the test groups were analyzed by using MANOVA and post hoc least significant difference tests for accuracy data, and Scheirer-Ray-Hare test with Dunn post hoc test for margin quality data (α=.05).

RESULTS

Significant differences in accuracy were found for the external and marginal regions based on finish line design, and for external accuracy based on the manufacturing method (P<.05). The knife edge, 0.5-mm chamfer, and 0.5-mm shoulder designs demonstrated larger root mean square (RMS) deviations in the marginal region compared with the 0.8-mm chamfer and 0.8 mm-shoulder (P<.05). SM crowns exhibited the lowest external RMS value for the 0.8-mm chamfer (22.3 ±4.2 µm). No significant differences were observed in the intaglio region across the 5 margin designs (P>.05). MJ crowns exhibited lower external deviations and similar margin and intaglio RMS values compared with SM crowns (P>.05). Marginal quality was highest for the 0.8-mm chamfer and shoulder designs, while knife edge designs exhibited the most flaws, regardless of manufacturing method.

CONCLUSIONS

All 5 margin designs demonstrated reliable accuracy in monolithic zirconia crowns. However, crowns with 0.8-mm chamfer and 0.8-mm shoulder designs exhibited superior accuracy and marginal quality compared with knife edge, 0.5-mm chamfer, and 0.5-mm shoulder designs. MJ technology produced crowns showed higher external accuracy than SM.