Accuracy of PICN Restorations is Affected by Subtractive Manufacturing Machines

Objectives: Achieving high accuracy in digitally-manufactured dental restorations is essential to ensure long-term clinical success. The wear of diamond burs used for manufacturing is impacted by the properties of the machined materials but may vary among machines. This study aimed to examine the accuracy of polymer-infiltrated ceramic network (PICN) crowns produced by two subtractive manufacturing machines and investigate diamond bur deterioration with repeated use.
Methods: A full-contour maxillary second premolar crown was designed and subtractively manufactured using PICN materials (VITA Enamic). A total of 40 crowns were fabricated by two subtractive manufacturing machines – inLab MC X5 and PrograMill PM7 (n = 20/unit). Each crown specimen was scanned with a 3Shape E4 scanner. Accuracy (trueness and precision) was determined by superimposing scans with the digital design (reference model) in Geomagic Control X. The analysis was performed in six segments individually. Root mean square (RMS) values were statistically analyzed for inter- and intra-machine comparisons using Prism 10. Bur life percentages, shown in their corresponding CAM software, were also recorded during manufacturing.
Results: The intaglio surface of VITA Enamic crowns manufactured from PrograMill PM7 showed lower RMS values and deviation, indicating higher accuracy (18.3 ± 1.6 μm) but the inLab MC X5 unit resulted in higher trueness and precision of crown outer surfaces (17.1 ± 3.2 μm). Except for marginal and occlusal surfaces, there were statistically-significant differences between the two machines in the trueness of other manufactured crown regions (p<0.05). A lower rate of bur wear was observed in the PM7 machine but no significant influence on the manufacturing accuracy was found for either unit.
Conclusions: Different laboratory subtractive manufacturing machines produce inconsistently accurate PICN crowns with various bur deterioration rates. The differences between manufactured crowns and their original digital designs may impact long-term restorative performance and patient satisfaction.