الفهرس 
Evaluation Of The Marginal Accuracy And Internal Fit Of Metal Copings Fabricated By CAD/CAM Techniques Compared To Conventional Lost Wax Technique. (An in vitro study)
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Abstract
The aim of this study was to evaluate and compare the marginal gap and internal adaptation of metal copings produced by four techniques: 1. Conventional waxing technique (CW) 2. Milled metal technique (MM) 3. Milled wax technique (MW1) 4. Milled wax technique with margination (MW2) A master metal die was produced by taking an impression of a prepared acrylic Typodont first maxillary molar, which was poured in Duralay and cast from a base metal alloy. Forty stone dies were poured from forty poly-ether regular body impressions of the master metal die. These stone dies were randomly assigned to the four study groups (n=10) for each group. For the CAD/CAM groups the dies were scanned in the Shera Eco-Scan 7 series scanner and design was carried out according to predetermined parameters on the DWOS software, after designing the STL files where transferred to the milling station SheraEcomill 5X for production of the copings. The MM group was milled from Co-Cr blanks and after milling the copings were separated from the sprues and checked on their respective stone dies and master metal die. The CAD/CAM wax groups were then sprue, the MW2 group went through the process of margination before investment, the wax patterns were then invested and cast from Co-Cr alloy blanks. The produced metal copings were then de-vested, finished and evaluated on their stone dies and master metal die. For the (CW) group the wax patterns were produced by the conventional wax build up technique using blue inlay wax and P.K.Thomas wax droppers and then were cast in the conventional manner. The metal copings were then seated on the master metal die by the help of a spring loading device and the vertical marginal gap measurements were recorded by the direct view technique using a stereo-microscope, 10 measurements were taken ant each surface giving a total of 40 readings per sample