Effects of Nano-Diamond-Coated Milling Bits on Cutting Dental Zirconia

Abstract

Hard alloy end mills are commonly employed for milling zirconia prostheses in dentistry. Nano-diamond-coated milling bits ensure high processing efficiency, accuracy, extended tool life, and reduced processing costs. This study aims at comparing various effects of cutting dental zirconia with nano-diamond-coated and ordinary milling bits. Two types of milling bits, one with nano-diamond coating and one without, were used to cut the dental zirconia green blanks (Ø98.5 mm, thickness: 25 mm) at three different speeds (1000, 1500, and 2000 rpm) in a dental milling machine. The unsintered and sintered zirconia surfaces were evaluated with glossmeter, optical profilometer for surface roughness, SEM, and EDX. The glossiness of the sintered zirconia block was statistically higher than that of the unsintered block (p < 0.05). For sintered zirconia, the nano-diamond-coated milling bit yielded a statistically (p < 0.05) higher glossiness in all spindle speeds than uncoated, save for the uncoated milling bit used at 1500 rpm. However, in terms of roughness, only sintering showed to be a statistically significant factor (p < 0.001) outweighing other two factors, and sintered zirconia always yielded lower surface roughness than the unsintered counterpart. Overall, the nano-diamond-coated milling bit can be operated at various speeds, resulting in a higher gloss on the sintered zirconia block, while an ordinary, uncoated milling bit can only achieve the same glossiness at a designated speed. The type of milling bits and the speeds have no significant effect on the surface roughness.