Objectives: The current brittle-regime grinding applied during the CAD/CAM milling and handpiece grinding is detrimental to the strength of ceramics due to the formation of microfractures. This work presents a safer yet efficient alternative known as ‘ductile-regime grinding’. The hypothesis is that dental ceramics will transition from brittle- to ductile-regime grinding, and applying ductile-regime grinding parameters, namely, threshold load and grit size, will significantly diminish strength loss while maintaining removal efficiency.

Material and Methods: Disc-shaped samples of a lithium disilicate glass-ceramic (IPS e.max CAD), Feldspathic ceramic (Mark II), polycrystalline zirconia with different yttria concentrations (3Y-TZP and 5Y-PSZ) were tested. Micro-scratch tests with a single diamond indenter were conducted under controlled scratching loads. Additionally, grinding using conventional lapping technology was performed by controlling grinding grit sizes. The strength of scratched and ground samples under each tested condition was measured using a flexural strength test. Surface and subsurface damage were analyzed using Scanning electron microscopy (SEM) and Focused Ion Beam (FIB-SEM). The removal rate and surface roughness of ground samples were also measured. Statistical analysis was performed using one-way and two-way ANOVA. Results with p < 0.05 were considered significant.

Results: SEM surface analysis of scratch tracks on tested ceramics revealed ductile and brittle removal modes under single-particle sliding. Strength degradation and subsurface damage observations validated the threshold loads and grit size of ductile grinding for IPS e.max CAD, Mark II, and 5Y-PSZ. Scratching and grinding at the subthreshold region preserved the strength of tested ceramics. 3Y-TZP showed high tolerance to damage with no drop in strength compared to the other three ceramics. Ductile grinding resulted in a comparable removal rate, less surface roughness, and maintained strength compared to brittle grinding.

Conclusions: Establishing the threshold load and grit size for ductile grinding lays the groundwork for future research on implementing ductile-regime grinding protocols to achieve damage-free ceramics restorations.