الفهرس 
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Abstract
The dental profession constantly strives to improve the strength, longevity, and esthetics with all
restorations.
Restoration of teeth after endodontic treatment is becoming an integral part of the restorative
practice in dentistry and retaining them throughout life remains a challenge. Endodontically
treated teeth are weaker and tend to have a lower lifetime prognosis so they require special
considerations for the final restoration. Multiple studies have shown that endodontically treated
teeth benefit from the placement of crowns.
Although the metal-ceramic system is still widely used to fabricate crowns and is considered as the
standard treatment in dentistry, aesthetic concerns have stimulated the development of new dental
ceramic systems. The ongoing search for ceramic materials with mechanical properties suitable for
use in high-load areas has resulted in the development of new ceramics with high strength which
created wonderful opportunities for the fabrication of lifelike crowns that provide reliable,
long-term results. At present, ceramics are the materials of choice for crowns due to their
superior aesthetic and biocompatibility features.
The performance of the all-ceramic crown system is complex because the crown- cement system should
be considered a single structure comprising layers of materials with different mechanical
properties.
The importance of precise marginal adaptation and the subsequent implications of marginal
discrepancies, including microleakage, caries and periodontal inflammation, have been emphasized in
many studies. In addition to marginal fit, internal fit and accuracy play a significant role in the
longevity of a full-coverage restoration as well. Several definitions for marginal deficiencies
have been proposed, such as internal gap, marginal gap, horizontal marginal discrepancy,
over-extended margin, seating discrepancy and others.
The internal fit (IF) is a clinically relevant topic and can affect the strength of a crown cement
system. The IF should be uniform to avoid compromising either the retention or the resistance of
the crown and should also provide an appropriate luting space. Dental cements are used to maintain
the position of the restoration for long periods; however, some factors seem to influence the
seat during the cementation procedure, such as the height and