For years, the ceramo-metal restoration has been the gold standard in crown and bridge procedures .They have been used for many years and studied extensively. Studies have demonstrated a 94% success rate over a 10-year period and good long-term clinical reliability. Although chipping of veneering porcelain is a possible complication, fracture of the metal framework is uncommon . They require sufficient tooth reduction to allow space for at least 0.3 mm of metal coping and 0.7 mm of veneering porcelain, and a minimum facial reduction of 1.2 mm according to Hobo and Shillingburg. When comparing ceramo-metallic crowns to zirconia crowns, several points are noteworthy. Laboratory testing has determined that the fracture strength of a ceramo-metallic crown using 1.5 mm reduction is similar to zirconia crowns with only 1 mm of reduction5. Some manufacturers have even suggested a 0.6 mm minimum reduction for posterior zircona crowns. Which has led some dentists to prescribe all-zirconia restorations to preserve tooth structure6 Zirconia became popular in dentistry because of the material's excellent mechanical properties which include high strength, fracture toughness and biocompatibility.New monolithic CAD/CAM restorative materials are designed to improve the optical and mechanical properties of the avoid veneering failure .To increase translucency and aesthetics of full-contour zirconia ,some modifications ,such as sintering temperature ,fabrication processes and addition of colouring liquids have been applied. These modifications may affect the mechanical and autocatalytic surface-transformation ((low-temperature degradation (LTD)) properties of zirconia.) The primary etiologic factor of gingival inflammation is a plaque, and by inadequate crown shape its accumulation can be facilitated . A single crown can cause inflammation of the periodontal tissue, if the hygienic principles have not been observed during its production. If the finish line of the artificial crown disrupts the biologic width and is placed in the connective tissue attachment area, the inflammation may occur. Even with increased hygiene, the gingival inflammation can occur, if the crown preparation margin is located deeply subgingivally Taking care of the periodontal tissue health the precision of the preparation margin, tightness of proximal contacts, conformity of the tooth crown anatomic shape, occlusal morphology and surface smoothness must be checked . The contact of the crown and the tooth must be tight and uniform .

While choosing material for crown production it must be taken into account that the bacterial adhesive capacity of the prosthetic material is affected by the surface roughness .asperities, free energy of the surface and composition of materials (it is the lowest for ceramic, but the highest for acrylates).Early-colonizing bacteria play a pivotal role for the subsequent adhesion of cariogenic microorganisms such as Streptococcus mutans and periodontal pathogens such as Tannerella forsythensis, Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, which may induce gingival and periodontal inflammation Periodontal diagnosis generally requires measurement of periodontal tissue destruction (e.g., probing pocket depth \[PPD\] and clinical attachment level \[CAL\]) and gingival inflammation (e.g., bleeding on probing \[BOP\] and gingival index \[GI\]). Although the techniques used are straightforward and noninvasive. These parameters are static and thus reflect disease history and not present disease activity .Therefore, it is necessary to develop diagnostic tests that can identify active periodontal sites, predict future disease progression, and assess response to periodontal treatment. Periodontopathic bacteria increase the risk of periodontitis, and immune responses against bacterial products and subsequent secretion of proinflammatory cytokines are crucial in periodontal tissue destruction .Interleukin-1β (IL-1β) is an important mediator of inflammatory response and is involved in cell proliferation, differentiation, and apoptosis, and in the pathophysiology of periodontitis.