Efficiency of Diamond Rotary Instruments in Cutting Through Zirconia and Lithium Disilicate Restorations

To investigate the impact of diamond rotary instrument grit size and rotational speed on cutting efficiency through lithium disilicate and zirconia ceramic materials.

Rectangularshaped specimens measuring 12.5 × 14.5 mm and 2 mm thick-40 lithium disilicate (IPS e.max, Ivoclar) and 40 4 mol% yttria zirconia (Katana STML, Noritake)-were 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/minute (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 microscopy (SEM) images were made of each rotary instrument to visualize wear and deterioration. Data were analyzed statistically (α = .05).

Ceramic material cutting efficiency differed among diamond rotary instruments (P < .001). A coarse diamond rotary instrument at 200,000 RPM cut both ceramics efficiently (P < .001) for zirconia and lithium disilicate specimens; cutting efficiency was 0.064 and 0.107 mm/second, 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 < .001). SEM images show higher wear and degradation at 200,000 RPM than at 50,000 RPM for both grit diamond rotary instruments.

Coarse-grit diamond rotary instruments cut zirconia and lithium disilicate ceramics more efficiently than fine-grit ones. High-speed cutting at 200,000 RPM cuts ceramics more efficiently than a lower speed at 50,000 RPM.