الفهرس 
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Abstract
Metal-ceramic restorations are still commonly used in dentistry. Metal-ceramic bonding could be considered as a crucial issue for efficacious dental restorations. This study compared the bond strength of porcelain to cobalt-chromium metal alloy substructure fabricated by three different techniques.
In This in vitro study, we have three groups each of fourteen (n=14) according to the technique of fabrication; group I: selective laser sintering technique (additive technique), group II: CAD/CAM milling technique (subtractive technique), group III (control): lost wax technique.
For standardizations of all specimens, the same design was used for the fabrication of the three groups; castable resin patterns were milled using the same STL file used for the other two groups for the conventional casting group fabrication, instead of the traditional wax patterns constructed manually to standardize the metal bar design in all the test specimens. A thin layer of wash opaque porcelain, a layer of opaque porcelain, and a layer of body porcelain were fused to the central rectangular area of the metal bar using a special mold 3 mm width, 8 mm length and a thickness of 1.1 mm (in compliance with ISO Standard 9693).
The metal-ceramic bond strength was measured by the three-point bending test using a universal testing machine. Specimens were placed in the bending apparatus (20 mm distance between the supports) with the ceramic positioned opposite to the applied force until debonding took place.
The results showed the highest bond strength values associated with laser sintering group with Mean ± SD of 232.8 ± 35.4. The results of CAD/CAM group showed moderate bond strength values with Mean ± SD of 117.6 ± 12.8. The results of lost wax casting group showed lowest bond strength values with Mean ± SD of 93.1 ± 12.9
When comparing the means and SD of the results of the 3 groups there was a high statistical difference between them (lost wax casting,CAD/ CAM,laser sintering) P-value <0.05 and this means that laser sintering group withstand greater forces at the bonding test more than the other 2 groups until failure occurred.
There was high statistical significant difference found between Laser Sintering, CAD/CAM and lost wax casting.
Lost wax casting group has the lowest significant difference in relation to laser sintering group and CAD/ CAM group, and there was no significant difference between lost wax casting group and CAD /CAM group.