الفهرس 
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Abstract
Technical advances in hardware, software and materials provide
dentists with new and improved options for indirect restorative materials.
CAD/CAM technologies offer more options to dentists and technicians
for fabricating dental restorations. Lava™ Ultimate CAD/CAM Restoration
is a “new to the world” CAD/CAM product utilizing 3M‟s revolutionary
nanoceramic technology.
Because of different compositions and manufacturing techniques, dental
ceramics vary in their physical and mechanical properties. One important
property is the strength of the materials, and specially the flexural strength,
because of the brittle nature of ceramics. Therefore, the aim of this study was to
evaluate the biaxial flexure strength of lava ultimate which is composed of resin
nano ceramic to that of IPS e-max press and VitaVM7and also to compare
surface roughness as well as color stability of the three restorative materials.
The material used in this study was: Lava™ Ultimate CAD/CAM
Restorative [Resin Nano Ceramic (RNC)], IPS e.max® Press (lithiumdiscilicate)
and VITA VM7.
Ninety disc specimens were prepared and divided according to the
material used into three groups thirty disc each (n=30). Each group is subdivided
into 3 sub-groups (n=10) for each test.
Lava ultimate samples construction was performed by using DWX
dental milling machines.
Summary
76
For IPS E-Max Press samples construction; the cylindrical split copper
mold was used to allow the fabrication of wax discs with the intended
dimension (12 mm diameter and 2 mm thickness).
For fabrication of VM7 ceramic discs; the specimens were made
directly into the mold that can be sectioned and then assembled again, where
the condensation of the VM7 powder and liquid were directly condensed into
the specimen hole in the split copper mold after placement of vita akzent
glaze as a separating medium.
The biaxial flexure strength (BFS) test has been used for the
determination of fracture characteristics of brittle materials. Ten discs from
each group were tested using a universal testing machine. The BFS was
calculated in accordance with equation:
Confocal Laser Scanning Microscopy (LSM) was used to measure the
surface roughness.
Using VITA Easyshade compact the baseline colour measurements
were measured before the immersion in staining solutions (tea). Initial color
values were used as a baseline of color change evaluation. All measurements
were made on white background in order to eliminate background light.
Specimens were immersed in tea for a period of 4 weeks Specimens were
washed thoroughly and dried then subjected to color measurement by CIE
L*a*b*. The Color difference ΔE between the color coordinates was obtained
through Hunter equation:
Δ Eab*= [(ΔL*) 2+ (Δa*) 2+ (Δb*) 2]½
Summary
77
The mean value of biaxial flexure strength test of lava ultimate
specimens was 197.05±19.62 MPa while that of E-max press specimens was
215.3±37.97 MPa and that of VM7 specimens was 44.5±11.83 MPa.
On comparing the mean in the three groups the difference was
statistically significant where the ANOVA test was 132.956 and the p-value
was 0.0001.
On applying the post hoc test between groups it was found that there was
no significant difference between Lava Ultimate group and E-max press, while
there was a highly significant increase in Lava Ultimate than VM7, also there
was a significant increase in E-max press group than the VM7.
The mean value of the surface roughness test of Lava Ultimate
specimens was 0.899±0.289 um while that of E-max press specimens was
0.845±0.292 um and that of VM7 specimens was 2.826±0.867 um.
On comparing the means in the three groups the difference were
statistically significant where ANOVA test was 41.439 with p-value 0.000.
On applying the post hoc test between groups it was found that there
was no significant difference between Lava ultimate and E-max press, while
there was a significant increase in SR in VM7 group more than Lava ultimate
and E-max press groups.
The mean values of the ΔE of Lava Ultimate specimens was
5.873±0.923 while that of E-max press specimens was 3.358±0.742 and that
of VM7 specimens was 1.95±1.104.
On comparing the means in the three groups the difference were
statistically significant where ANOVA test was 45.082 with p-value 0.0001.
Summary
78
On applying the post hoc test between groups it was found that there
was a significant increase in ΔE in Lava Ultimate than E-max press. Also,
there was a significant decrease in ΔE in VM7 group more than Lava
Ultimate and E-max press groups.
from our study we concluded that the biaxial flexure strength test of the
IPS e max press and the Lava Ultimate showed significantly higher values
than VM7. IPS Emax press showed higher values than Lava Ultimate but with
no significant difference
The surface roughness of both Lava Ultimate and Emax press was
significantly lower values than VM7 group (i.e. VM7 is the roughest material).
Lava Ultimate had the least color stability due to its composite matrix although
it could be repolished every now and then. VM7 was the most color stable so it
could be used as veneers although it is the weakest ceramic in the study