PURPOSE: To investigate the impact of diamond rotary instrument grit size and rotational speed on cutting efficiency through lithium disilicate and zirconia ceramic materials. MATERIAL AND METHODS: A rectangular-shaped specimen of 12.5 × 14.5 mm and 2 mm thickness of forty lithium disilicate (IPS Emax
Ivoclar) and forty 4 mol% yttria zirconia (Katana STML
Noritake) was milled and sintered according to the manufacturer's instructions. Two diamond rotary instruments (X-tra coarse, 230 µm grit size, and fine, 46 µm grit size
Komet USA) were used to cut into the ceramic materials at 200 000 and 50 000 revolutions per minute (RPM) under a continuous water cooling rate of 50 mL/min (n = 10/grit/speed). Handpiece movement was controlled, torque was maintained at 3.4 Ncm, and pressure was maintained at 2 N using a load sensor. The efficiency of each rotary instrument was calculated. Scanning electron microscope images were made of each rotary instrument to visualize wear and deterioration. Data were analyzed statistically (α = 0.05). RESULTS: Ceramic material cutting efficiency differed amongst diamond rotary instruments (P<
.002). A coarse diamond rotary instrument at 200 000 RPM cut both ceramics efficiently (P <
.002)for zirconia and lithium disilicate specimens
cutting efficiency was .064 and .107 mm/sec, respectively. Only coarse diamond rotary instruments can cut 10 mm in 10 minutes. High speed led to more efficient cutting regardless of ceramic material or rotary instrument grit (P<
.002). Scanning electron images show higher wear and degradation in both grit diamond rotary instruments at 200,000 RPM than at 50,000 RPM. CONCLUSIONS: Coarse-grit diamond rotary instruments cut zirconia and lithium disilicate ceramics more efficiently than fine-grit ones. High-speed 200 000 RPM cuts ceramics more efficiently than 50 000 RPM at a lower speed.