Reported drawbacks of the LTD were enhanced

Reported drawbacks of the LTD were enhanced wear rates [11] with loss of small surface zirconia grains in the surrounding environment causing an increase in surface roughness and surface uplifts with both mechanical [12] and esthetic worsening [10]. Although hundreds of laboratory researches dealt with the effect of aging and its theoretically assumed mechanisms on the mechanical outcome and serviceability of the material [10] no studies to our knowledge have discussed the esthetic and color changes upon such phenomenon. The clear realization that the same microstructure that causes certain mechanical properties to manifest in zirconia is also responsible for its optical properties. Thus it\'s fair to conclude that aging related changes in the microstructure that leads to changes in the mechanical properties would also lead to optical changes. However through studying of the factors controlling LTD and its effects on the material microstructure and surface, esthetic outcome and sorafenib tosylate of the material with its variable products and processing techniques may to a great extent be affected.
Materials and methods Sixty translucent zirconia specimens were divided into four groups (n = 15) according to their thickness (Group A 0.5 mm, Group B 0.8 mm, Group C 1 mm and Group D 1.2 mm). Translucent zirconia specimens were obtained by cutting four InCoris TZI blocks (40 × 19 × 15 mm), using IsoMet 30HC precision cutting blade (Diameter 127 mm, thickness 0.76 mm) mounted on MICRACUT 150/201 precision cutter. The machine was adjusted using its built in micrometer to cut the InCoris TZI block under water coolant into slices of approximately 0.6 mm, 1 mm, 1.2 mm, and 1.5 mm thickness, 20% larger than the desired final size to compensate for sintering shrinkage caused during the sintering stage. The other dimensions of the slice were 19 mm length and 15 mm width. The thickness of each slice was checked with a digital caliper and minor corrections were done using Wetordry Sandpaper sheet of grit 400, 600, and 1200 in the presence of water to ensure flat surface and desired thicknesses. Prior to sintering the InCoris TZI slices were fully submerged in a plastic vessel containing A2 InCoris TZI Sirona coloring liquid allowing the slice disc to absorb the coloring solution for 5 min then the discs were removed from the plastic vessel using a pair of plastic tweezers. The recently colored slices were then placed on a glass slab for 2 h for drying. The InCoris TZI slices were placed on sintering boats filled with the sintering beads, at least 1 cm apart from each other, then sintered in Sirona inFire HTC speed with the pre-programmed InCoris TZI programs. The program was started to run automatically for 90 min and 1540 °C sintering temperature. After sintering, the thickness of each slice was checked with a digital caliper. The final thicknesses of the slices were 0.5 mm, 0.8 mm, 1.0 mm, and 1.2 mm. Polishing was carried out by low speed hand piece and an electric motor with a rate of 7000–10000 rpm under constant water coolant using polishing kit (K0262 Dialite ZR Intra-Oral Adjustment finishing and polishing system) and polishing paste ZI-Polish in the following sequence Green course grinder, Green medium polishing points for pre-polishing, Orange fine polishing points for high luster and finally (ZI-Polish) diamond polishing paste was applied with a special brush (Wheel Brush Rodeo) brain stem is double loaded with natural horse hair for best results of finalizing the surfaces. All the specimens were tested for degree of translucency using portable intraoral digital spectrophotometer (Vita EasyShade). Vita easy shade in “tooth single” mode was used to determine the values of CIELab coordinates from specimen placed on white and black background. Three measurements were taken for each specimen on white and black backgrounds and the average of each parameter (L*, a*and b*) was recorded. The values were used to calculate the translucency parameter (TP) according to the following formula: [13].where b is for black and w for white.