Effect of repeated milling tool use in a dental CAD/CAM system on the marginal and internal fit of zirconia crowns

초록

Purpose: This study aimed to analyze and compare the marginal and internal fit of zirconia crowns fabricated using three types of milling tools with different durations of use (0, 50, and >100 hours). Methods: Zirconia crowns were designed using computer-aided design software, and the design files were extracted. Zirconia blocks (Luxen, Dentalmax) were milled using a five-axis milling machine (DWX-52D, Roland). Crowns were fabricated using unused milling tools, tools used for 50 clinical hours, and tools used for >100 clinical hours (n=12). The morphology of the milling tools was examined using a scanning electron microscope (VEGA, TESCAN). The marginal and internal fit of the fabricated zirconia crowns was evaluated using a D2000 scanner (3Shape) via the scanning method. Differences in fit among the crowns fabricated with tools of various usage durations were analyzed using one-way analysis of variance, with post-hoc analysis conducted through Tukey’s honest significant difference test (α=0.05). Results: Significant differences in zirconia crown fit were observed among the three tooluse groups (p<0.001). Milling tools used for >100 hours produced crowns with significantly lower marginal fit (p<0.05). Similarly, reproducibility in the 100-hour group was significantly reduced (p<0.05). Conclusion: Repeated clinical use of milling tools over extended periods may adversely affect the marginal fit and reproducibility of zirconia crowns.

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