الفهرس 
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Abstract
The provisional restoration is a very important phase in fixed prosthesis treatment. It is used from the moment of tooth preparation to final restoration delivery time. The dental restorations success is determined mainly by four factors: biocompatibility, esthetics, fracture resistance and marginal fit.
Poor marginal adaptation may affect the restoration longevity as exposure of cement film to the oral environment leads to dissolution of cement. It also increases plaque accumulation which in turn increase the risk of secondary caries, micro leakage, pulpal inflammation and periodontal diseases causing restoration failure.
Marginal fit and fracture resistance can be influenced by several steps, starting from the impression phase to the final cementation phase. One of the most important factors that affect marginal fit and fracture resistance is fabrication technique.
There are many techniques used to make provisional restorations. First, manually technique was used, which can be done direct, indirect and indirect direct but with development of new materials and technology, there are new techniques can be used as CAD/CAM technique (computer aided design / computer aided manufacturing) and 3D printing technique to fulfill clinician and patient demands.
Conventional fabrication technique of provisional restorations was the most common technique, widely used and cheapest but it also has some limitation and drawbacks.
The CAD/CAM technique produce high quality prosthesis by using various materials, but it has some disadvantages as the high cost due to waste of material waste. The newly introduced technique (3D printing) is spreading fast and various resins are used. It’s cheaper and faster additive manufacturing technique.
This study was done to compare the marginal adaptation and fracture resistance of the provisional crowns fabricated by 3D printing, CAD/CAM and conventional manual techniques.
According to the sample size calculation, a total of twenty-one crowns were constructed which were divided into three equal groups, seven samples for each group according to the fabrication technique.
group (I): seven crowns fabricated by conventional manual technique.
group (II): seven crowns fabricated by CAD/CAM technique.
group (II): seven crowns fabricated by 3D printing technique.
Typodont model of maxillary 1st molar was prepared according to the following criteria: 2 mm occlusal reduction, 1.5 mm overall axial reductions. The prepared model was scanned using Dof freedom hd extraoral scanner. Duplication of master die into twenty-one epoxy resin dies through using silicone duplicating material and then divided into three equal group (n=7).
provisional crowns were designed. STL file was produced and sent to both milling machine and printer. The first group of provisional crowns were fabricated manually using an index of a previously constructed CAD/ CAM provisional crown charmtemp was mixed through the self-mixing gun and directly injected into the silicon index. The second group of provisional crowns were milled using a DGshape DWX-520 milling machine from PMMA CAD/CAM blank. The third group provisional crowns were printed using the Rapid shape 3D printer using Nextdent C&B PMMA resin material.
Marginal fit was measured by photographs using USB Digital microscope with a built-in camera (Omnimet image analysis software Buehler USA) connected with an IBM compatible personal computer using a fixed magnification of 50X. where Provisional crowns were placed on the die and fixed in place using special holding jig.
The provisional crowns were cemented on their corresponding epoxy resin dies using charmtemp NE zinic oxide non eugenol cement, avoiding the eugenol inhibition action of resin polymerization. Using cementation loading device to apply uniform load during setting of the cement under the crowns.
Finally, all crowns were subjected to fracture resistance test under a compressive load to the center to their long axis using computer controlled universal testing machine with a load cell of 5 newton (N) and at a crosshead speed 1mm/min. Data was recorded, tabulated and statistically analyzed.