الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 125 |  |  |
| | | from | 125 | | |
Abstract
Fifty rectangular samples (n=50) from Two Different CAD\CAM Materials. Vita Enamic CAD\CAM blocks, polymer infiltrated ceramics blocks (En) and IPS e.max CAD\CAM blocks, lithium disilicate glass ceramics blocks (E max). Samples were prepared into dimensions (14 x 2 x 1.5 mm). . A single notch was prepared in each sample. The notch width was less than or equal 0.3 mm ± 0.01mm. The tip of the single notch was located on the long surface of the sample at 0.24 to 0.48 mm from the bottom left corner
Samples were finished & polished according to manufacturer’s instructions. Vita Enamic samples were polished by Vita Enamic clinical 2 steps polishing kit, using the prepolishingVI-EC7m for standardized time of 60 seconds at a speed 8.000 rpm, followed by the high gloss polishing VI-EC6f for another 60 seconds following the protocol used by Flury et al (2010). The micromotor & handpiece were the same for the entire study. The procedure was performed by the same operator using light hand pressure as recommended by manufacturer.IPS e.max CAD samples were polished by polishing was done by the same operator with the Optrafine® pack (batch #NL1757, Ivoclar Vivadent SAS) (figure 0),. A manual dental piece was used without water spray: 15 seconds with a large drill (DC 83103040, Komet, Paris,France) at 30,000 rpm, 15 seconds with a dark-blue diamond polisher in cup shape at 7,000 rpm (polisher P), 15 seconds with a light-blue diamond finisher in cup shape at 7,000 rpm (finisher F), and 15 seconds with a small brush accompanied by polishing paste (Optrafie®HP, lot JL1606, Ivoclar Vivadent SAS) at 7,000 rpm (pol-LD). After samples were polished, they were washed by distilled water.
Samples were divided into two main groups, according to type of material , each group was composed of 25 specimens, Con= control group, Tc= subjected to thermocycling only, Tc/N stored in neutral media (Distilled Water pH7) + thermocycling, Tc/Alk stored in alkaline media (Sodium Bicarbonate pH 9) + thermocycling, Tc/Ac stored in acidic media (Coca Cola pH 2.2) + thermocycling. Thermocycling performed at 5-55oc for 10,000 cycles.
Samples were photographed using USB Digital microscope with a built-in camera (Scope Capture Digital Microscope, Guangdong, China) connected with personal computer using a fied magnification of 120X .The images were recorded with a resolution of 1280 × 1024 pixels per image. Digital microscope images were cropped to 350 x 400 pixels using Microsoft offie picture manager to standardize the area of roughness measurement. The cropped images were analyzed using WSxM software (Ver 5 develop 4.1, Nanotec, Electronica, and SL). Within the WSxM software, all limits, sizes, frames and measured parameters are expressed in pixels. Therefore, system calibration was done to convert the pixels into absolute real world units. Calibration was made by comparing an object of known size (a ruler) with a scale generated by the software. Subsequently, a 3D image of the surface profie of the specimens was created. Three 3D images were collected for each specimen, in the central area and in the sides at area of 1.0 µm × 1.0 µm. WSxM software was used to calculate average of heights (Ra) expressed in μm, which can be assumed as a reliable indices of surface roughness. Surface roughness (Ra) values were calculated from the following equation: Ra= 1/1 f(x) I dx. Smaller (Ra) values represent smoother surface and vice versa.
The specimen was immediately transferred to the universal testing machine (5848 Micro Tester; Instron, Norwood, MA, USA), putting the sample tip down in the test fixture. The specimen was tested in a 4-point bending test setup with a crosshead speed of 0.05 mm/min. The outer and inner span were 10 and 5 mm, respectively. After testing, all fractured specimens were processed for scanning electron microscopy (SEM; JSM-6610LV; JEOL, Tokyo, Japan) with common specimen processing, including fixation, dehydration, and gold sputter coating, to determine fracture location, crack propagation, and possible specimen imperfections. Finally, the exact dimensions of the fracture toughness notch were measured with a measuring optical microscope (400-NRC; Leitz, Wetzlar, Germany) at 250× magnification, after which KIc was calculated according to the equation (Wan et al. 2009)
Data presented as mean and standard deviation (SD). Kolmogorov–Smirnov test used for test of normality. Two-way ANOVA used to compare between groups and subgroup followed by pairwise comparison with Bonferroni correction (α=0.05).
Statistical analysis was performed with IBM® SPSS® (IBM Corp. Released 2017. IBM SPSS Statistics for Windows, Version 25.0. Armonk, NY: IBM Corp).
Descriptive statistics showed significant difference detected between the mean values of both type of ceramic. Vita Enamic surface roughness mean had significant higher value than IPS E.max CAD surface roughness mean. IPS e.max CAD fracture toughness mean had significant higher value than Vita Enamic fracture toughness mean.
Conclusions
Within the limitations of this in vitro study, the following conclusions were drawn:
1. Vita Enamic showed higher surface roughness than IPS e.max CAD after subjecting to aging.
2. IPS e.max CAD showed higher fracture toughness than Vita Enamic after subjecting to aging.
3. long standing strength of Vita Enami may be questionable as its fracture toughness was highly negatively affected after aging , specially in more aggressive oral environment.