Microgrinding of lithium metasilicate/disilicate glass-ceramics.

Lithium metasilicate and disilicate glass-ceramics (LMGC and LDGC) are attractive dental materials but poor surface quality produced in current milling/grinding is a technical bottleneck. This paper reports on the microgrinding characteristics and mechanisms of LMGC and LDGC using micro-pencil diamond tools at different conditions. Surface quality was assessed using 3D laser confocal microscopy in terms of comprehensive roughness parameters. A combination of brittle and localized ductile removal mixture and brittle fracture was featured on the microground LMCG and LDGC surfaces identified through microscopic examination. The generation of brittle and localized ductile areas significantly depended on the diamond grit size and the depth of cut, resulting in different surface asperities. Better surface quality was achieved with reduced diamond grit size and depth of cut. The nanoscale maximum grit cutting depth in microginding achieved the best average and maximum roughness values of 0.241 ± 0.009 μm and 4.380 ± 0.861 μm for LMGC with approximately 80% and 60% reductions in comparison with dental CAD/CAM milling, respectively. Microgrinding of LDGC also achieved the best average and maximum roughness values of 0.168 ± 0.013 μm and 3.693 ± 0.467 μm with more than 90% improvement compared with simulated conventional grinding, simplifying the manufacturing procedure for LDGC restorations. Microgrinding also produced the kurtosis and skewness for both materials comparable to human teeth. More diamond tool wear occurred in microgrinding of high-strength LDGC than low-strength LMGC. Although microgrinding of multiphase LMCG and LDGC in ductile regime can be challenging due to microstructural diversity, the technique can advance current CAD/CAM milling/grinding for high-quality shaping of high-strength ceramic restorations. [Display omitted] • The microgrinding mechanisms of lithium metasilicate/disilicate glass-ceramics (LMGC and LDGC) were elucidated. • A combination of brittle and localized ductile removal mixture and brittle fracture was dominant in microgrinding of multi-phase ceramics. • Microstructures, mechanical properties and microgrinding conditions remarkably influenced removal mechanisms and quality. • Microgrinding of LMGC and LDGC achieved huge reductions in roughness and comparable kurtosis and skewness to human teeth. • Microgrinding may advance dental CAD/CAM milling techniques and simplify the prodcution of high-strength ceramic restorations. [ABSTRACT FROM AUTHOR]