الفهرس 
Statement of the problemOnly 14 pages are availabe for public view
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Abstract
The success of dental implants has changed treatment planning for patients with edentulous areas
dramatically. A critical determinant for placement of an implant is the height and width of bone
available in the edentate sites. The clinician also needs to evaluate the angulations of the ridge
before placing the implant. Ideally, implants should be placed parallel to each other and to
adjacent teeth.
Titanium is a metal, and suffers corrosion. Corrosion, the gradual degradation of materials by
electrochemical attack is a concern particularly when a metallic implant is placed in the hostile
electrolytic environment provided by the human body. The improvements in new ceramic materials made
it possible on 2000 to have the abutment part made of ceramic. This material was commonly known to
be more tissue friendly than titanium.
Conventional titanium abutments are widely used as the trans- gingival components of dental
implants. 1 In recent years, in order to achieve a final implant-supported prosthesis
indistinguishable from the adjacent natural teeth, zirconium abutments have been favored for their
aesthetic benefits, especially in the anterior zone. 2, 3 Zirconia has an excellent resistance to
corrosion, biocompatibility, and high levels of loading capacity.4
Dental implants have been used as a successful restoration treatment for tooth replacement over
the last few decades. Nevertheless, there is some controversy regarding the clinical procedures or
materials. The method for connecting the prosthesis to an implant is one of the most
important topics.5,6,7, 8
Cement-retained prostheses allow a passive fit, and have the advantage of simplicity in
fabrication, better esthetics and occlusion. In addition, reduced chair time is needed
compared to screw retained
prostheses. Therefore, cement-retained prostheses are more economical and effective.5 Such
advantages account for the recent increase in clinical use but clinicians often face difficulties
due to the inconvenient retrieval.6,9,10
Esthetic dentistry, driven by a high demand for esthetically appealing and naturally looking
restorations (especially all-ceramic restorations) has become a segment of dentistry which has
experienced tremendous improvements in recent years 11,12. The drawbacks of metal- ceramic
restorations have prompted the development of new all-ceramic systems that do not require metal,
yet have the high strength, precision fit,
superior esthetics and optical properties not seen in metal-ceramics systems13,14. Ivoclar Vivadent
patented lithium disilicate material, which exhibits superior esthetics and durability combined
with satisfactory physical properties to replicate natural tooth structure for aesthetically
pleasing and undetectable restorations. When fabricated to full-contour, the monolithic structure
is the most robust ceramic system tested to date 15.
Furthermore, due to a demand for posterior segment all-ceramic restorations, Yttrium Tetragonal
Zirconia Polycrystal(Y-TZP) based systems are a recent addition to the high-strength all ceramic
systems used for crowns and fixed partial dentures2. CAD/ CAM-produced, Y-TZP- based systems are
in considerable demand in esthetic and stress-bearing regions 16. The esthetic nature of zirconia,
coupled with its superior physical properties and biocompatibility have resulted in restorative
systems that meet the demands of today’s patients. All ceramic restorations benefit from
technologies that automate aspects of their fabrication 17. Automation implies less reliance on the
skill of the individual ceramist, as well as greater homogeneity and lower probability of defects
within the material itself .