Abstract
INTRODUCTION: Wear of milling burs may affect the internal fit and surface roughness of the milled crown. AIM: To assess the wear of diamond and tungsten carbide (TC) burs from milling ceramic materials and the effect on internal fit and surface roughness. METHODS: Thirty crowns of each of the two materials were milled from the same standard preparation. Diamond burs were used for a feldspathic ceramic and TC burs for zirconia. Before and after the 10th, 20th and 30th milling, diamond particle loss was counted and cutting blade changes of the TC burs measured. Internal fit was measured using a silicone replica technique and surface roughness by 3D laser microscope. RESULTS: An average 26% loss of diamond particles occurred after 30 crowns, resulting in a 6% decrease in internal luting space and a 21% decrease in surface roughness. Wear of the TC burs resulted in a 13% decrease in the luting space, and a 16% increase in surface roughness. CONCLUSION: The wear of milling burs reduces the luting space, and the milling parameters must be adjusted to compensate for this. Surface roughness is affected by bur type: with diamond burs it decreased, and increased with TC burs.
Highlights
Wear of milling burs may affect the internal fit and surface roughness of the milled crown
Wear of the tungsten carbide (TC) burs resulted in a 13% decrease in the luting space, and a 16% increase in surface roughness
This would appear to be the first study to measure the wear of diamond burs in four quadrants and compare this with the internal fit and surface roughness, using two different materials
Summary
Wear of milling burs may affect the internal fit and surface roughness of the milled crown. A number of researchers have investigated the effect on the accuracy of the milled crowns and the loss of diamond particles from the bur after repeated machining up to 30 and sometimes 50 crowns using one diamond bur.[3,4] Yara and colleagues (2005)[3] found that a diamond bur could be used to fabricate up to 21 crowns when using two different milling systems using feldspathic ceramics of different Vickers hardness They showed that the crowns’ average surface roughness ranged from 1.1 to 2.1μm for the one system and from 0.8 to 1.6 μm for the other. They concluded that the Vickers Hardness of the ceramic blocks used influenced the diamond particle loss as well as the surface roughness.[3]
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