| Summary: | This study investigates the impact of wet milling and submerged milling on the surface
roughness of milled lithium disilicate glass ceramic with sequential milling and before
and after crystallization process. Submerged milling is gaining traction for its potential to
dissipate heat, reduce friction, remove debris more efficiently, increase milling tool
longevity, and ensure accurate and efficient milling of final products. A total of 24 Hass
Amber® Mill lithium disilicate blocks were divided into 2 groups according to different
milling methods: wet milling group (n = 12) and submerged milling group (n = 12). The
milling process was performed using a 5-axis CRAFT 5X milling machine. The milled
surfaces of the lithium disilicate glass ceramic were evaluated for surface roughness (Ra)
using a 3D optical non-contact surface profilometer and observed through Scanning
Electron Microscopy (SEM), both before and after the crystallization process. The
diamond-coated milling burs (GC 25, GC 20, GC 10) were initially observed under SEM
and at 1st, 6th, and 12th milling. Overall comparisons between the surface roughness of
lithium disilicate discs of the two groups were done using Paired T-test. Comparisons
between the surface roughness of the disc before and after crystallization were done using
Paired T-test. The comparison of surface roughness intragroup was done using one-way
ANOVA. Significance was set at p value < 0.05. Results indicated that the mean surface
roughness of lithium disilicate discs milled with submerged milling technique was
significantly lower than that of wet milled discs, both before (p < 0.001, t = 7.093) and
after crystallization (p < 0.001, t = 6.020). Within each milling group, Ra reduced after
crystallization, with significant differences pre- and post-crystallization (wet: p < 0.001, t = 3.344; submerged: p < 0.001, t = 4.683). One-way ANOVA results showed that there
was no significant difference in surface roughness between discs in the same group (p >
0.05 for all groups), suggesting that the 12-cycle milling sequence did not significantly
affect the surface roughness. SEM analysis showed loss of abrasive particles on milling
bur in both wet and submerged milling groups. This study concludes that submerged
milling is more effective in reducing surface roughness compared to wet milling and that
crystallization plays a crucial role in further reducing the surface roughness of lithium
disilicate glass ceramics. Also, using sequential milling tool usage up to the 12th mill did
not affect the surface roughness of milled lithium disilicate.
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