Ductile-Brittle Transition Behaviour of Lithium Metasilicate/Disilicate Glass-Ceramics in Diamond Grinding

Abstract

Lithium metasilicate/disilicate glass-ceramics (LMGC/LDGC) are attractive composite materials for all-ceramic dental restorations due to their promising strength and biocompatibility. However, their strong mechanical properties make it hard to machine with current dental chairside CAD/CAM-milling. The root cause is the unclarity of their mechanical behaviour under dynamic abrasive machining. This paper conducted single-diamond scratching experiments on LMGC and LDGC to extract the actual diamond grain-material contact in grinding to understand their ductile-brittle transition behaviour. Scanning electronic microscopy (SEM) observation was performed to identify the fully-ductile, ductile-brittle and fully-brittle regimes of the two studied materials. 3D laser confocal microscopy (LCM) was used to measure the critical cutting depths for these regimes. The critical cutting depths for fully-ductile and fully-brittle regimes are 89 nm and 133 nm for LMGC, and 209 nm and 428 nm for LDGC, respectively. These results provide an in-depth understanding of ductile-brittle transition behaviour of LMGC/LDGC under abrasive machining and a guidance for dental technicians to choose proper machining conditions for high-quality LDGC restorations.