Effect of grinding and polishing on roughness and strength of zirconia
Available online 8 July 2017
Abstract
Statement of problem
The
clinical applications of high-translucency monolithic zirconia
restorations have increased. Chairside and laboratory adjustments of
these restorations are inevitable, which may lead to increased roughness
and reduced strength. The influence of grinding and polishing on
high-translucency zirconia has not been investigated.
Purpose
The
purpose of this in vitro study was to compare the roughness averages
(Ra) of ground and polished zirconia and investigate whether roughness
influenced strength after aging.
Material and methods
High-translucency
zirconia disks were milled, sintered, and glazed according to the
manufacturer’s recommendations. Specimens were randomized to 4 equal
groups. Group G received only grinding; groups GPB and GPK received
grinding and polishing with different polishing systems; and group C was
the (unground) control group. All specimens were subjected to
hydrothermal aging in an autoclave at 134°C at 200 kPa for 3 hours.
Roughness average was measured using a 3-dimensional (3D) optical
interferometer at baseline (Ra1), after grinding and polishing (Ra2),
and after aging (Ra3). A biaxial flexural strength test was performed at
a rate of 0.5 mm/min. Statistical analyses were performed using
commercial software (α=.05).
Results
Group G showed a significantly higher mean value of Ra3 (1.96 ±0.32 μm) than polished and glazed groups (P<.001),
which showed no statistically significant difference among them (GPB,
1.12 ±0.31 µm; GPK, 0.88 ±0.31 µm; C: 0.87 ±0.25 μm) (P>.05).
Compared with baseline, the roughness of groups G and GPB increased
significantly after surface treatments and after aging, whereas aging
did not significantly influence the roughness of groups GPK or C. Group G
showed the lowest mean value of biaxial flexural strength (879.01
±157.99 MPa), and the highest value was achieved by group C (962.40
±113.84 MPa); no statistically significant differences were found among
groups (P>.05). Additionally, no significant correlation was detected between the Ra and flexural strength of zirconia.
Conclusions
Grinding
increased the roughness of zirconia restorations, whereas proper
polishing resulted in smoothness comparable with glazed surfaces. The
results provide no evidence that grinding and polishing affect the
flexural strength of zirconia after aging.
Comments