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12 Dental Tribune Middle East & Africa Edition | September-October 2014clinical Contact mail: cynthiakassis@yahoo.com Contact Information < Page 10 Fig 5. CAD-CAM milling machine Fig 6. Milling machine that the average Chipping Factor (CF) of the CEREC cop- ings was: 2.8% for the 0° bevel angle, 3.5% for the 30° bevel angle and 10% for the 60° bevel angle. For the EVEREST cop- ings the average CF was: 0.6% for the 0° bevel angle, 3.2% for the 30° bevel angle and 2.0% for the 60° bevel angle. Univar- iate Analysis of Variance and multiple comparisons showed that there was a statistically significant difference in the quality of margins between the two systems for the 0° and 60° bevel finishing line.30 Mjör and Al have evaluated CAD/CAM restorations and found that they have a margin- al fit as good as or superior to that of traditional impressions. A further benefit found with CAD/CAM restorations has been the reduced incidence of secondary caries (the leading cause of direct restoration fail- ure with both amalgam and composite materials), attrib- uted to the high accuracy of the approximal fit and the ability to ascertain that this is accurate prior to completion of the resto- ration and cementation.31 Another study evaluated the ac- curacy of marginal and inter- nal fit between the all-ceramic crownsmanufacturedbyacon- ventional double-layer comput- er-aided design/computer-aid- ed manufacturing (CAD/CAM) system and a single-layer sys- tem. Ten standardized crowns were fabricated from each of these two systems: convention- al double-layer CAD/CAM sys- tem (Procera) and a single-lay- er system (Cerec 3D). Marginal discrepancies of Procera cop- ings were significantly smaller than those of Procera crowns and Cerec 3D crowns (p 0.05). On internal gaps, Cerec 3D crowns showed significantly larger internal gaps than Pro- cera copings and crowns (p < 0.05). Within the limitations of this study, the single-layer sys- tem demonstrated acceptable marginal and internal fit.32 On the other hand, depending on the preparation design, ei- ther an adhesive or a non-adhe- sive luting cement can be used with these materials. CAD/CAM restorative materi- als can be cemented with ei- ther traditional luting cements such as zinc phosphate, poly- carboxylate cement, glass iono- mers, or resin-modified glass ionomers. Materials that can be sealed with these include zir- conia, lithium disilicate, alu- mina, and resin nano-ceramics .33,34 Concerning the resin adhesive cements, they offer superior es- thetics and low viscosity. They chemically bond to the restoration surface and the tooth surface, either providing all of the retention or, for reten- tive preparations, improved re- tentivestrength.Theyalsohave greater compressive strength.35 Meanwhile zirconia fixed par- tial dentures showed good to sufficient marginal integrity in combination with Panavia/ ED, Compolute/EBS and RelyX Unicem.36 When evaluating the initial and the artificially aged push-out bond strength (PBS) between ceramic and dentin produced by one of five resin cements, there was a significant effect of resin cement (p<0.0001): RelyX Unicem showed sig- nificantly higher PBS than the other cements. Syntac/Vario- link II showed significantly higher PBS than SmartCEM2 (p<0.001). No significant dif- ferences were found between SpeedCEM, SmartCem2, and iCEM. The predominant fail- ure mode was adhesive failure of cements at the dentin inter- face except for RelyX Unicem which in most cases showed cohesive failure in ceramic.37 Conclusion Digital impressions tend to re- duce repeat visits and retreat- ment while increasing treat- ment effectiveness. Patients will benefit from more comfort and a much more pleasant ex- perience in the dentist’s chair.38 The quality of adaptation of CAD/CAM-generated restora- tions is an area of current in- terest. Studies demonstrate the clinically acceptable durabil- ity of CAD/CAM restorations for color matching, interfacial staining, secondary caries, anatomic contour, marginal adaptation, surface texture, and postoperative sensitiv- ity.39,40,41,42,43 Adhesive cementation seems to be the key for the long-term clinical success of CAD/CAM inlays and onlays.44 References 1. WittnebenJG, Weber HP:A Systematic review of the clini- cal performance of CAD/CAM single-tooth restorations.Int J Prosthodontics 2009; vol 22,5: 466-471 Full list of references is avail- able from the publisher. Your practice is our inspiration.™ Herculite® XRV Ultra™ Kerr, making history again