The aim of this study is to evaluate the antagonist enamel wear of two processing options of Celtra duo crowns (polished and glaze fired) restoring posterior teeth in comparison with sound enamel wear at baseline and 6 months

Adhesive dental ceramics have proven to guarantee optimal esthetic results alongside satisfactory mechanical properties. Due to these qualities, today they are considered the first-choice restorative materials both for minimal restorations and for the reconstruction of severely compromised teeth. Gold alloy reconstructions preferred in the past, especially for their optimal wear properties, have been progressively substituted by these new materials.

Loss of hard tooth substance is a natural process taking place during mastication. Also, Increased wear is a common reason of failure for restorations exposed to masticatory forces. Excessive wear may be responsible for numerous problems, such as hypersensitivity, loss of occlusal contact, defects of the periodontium, reduction of masticatory efficiency, tooth migration and wrong tooth relations, weakness of masticatory muscles, and changes in the vertical and horizontal jaw relations, which may cause functional and esthetic impairments.

An optimal restorative material should provide similar characteristics to natural dental tissues. The physiological wear of enamel and dentin should represent the reference for a reasonable wear pattern of restorative materials The manufacturers tend to improve the mechanical behavior of their products leads to the progressive offer of new ceramics for daily practice. Assessment of their wear behavior and comparison through detailed tests become necessary at this point.

comparing the wear of enamel opposing polished zirconia, polished lithium disilicate crowns opposing to natural tooth. Patients were recalled after 1year and impression were recorded with opposing arch and baseline and final cast were scanned and superimposed using 3 D scanner. They found that the mean of occlusal wear of the antagonistic enamel of polished zirconia was 42.0 μm, Enamel wear against natural antagonist (control group) 34.68 μm, whereas, for Enamel wear against polished lithium disilicate crowns (group 2) 40.06 μm Enamel wear against natural antagonist (control group) 35.09 μm.

studying the quality of CAD/CAM fabricated single tooth restorations (Ten zirconia restorations were compared to 12 metal ceramic and 10 lithium disilicate counterparts). They found that were no significant differences between the studied crown systems. No difference of the gingival response among the different crown systems. Eighty percent of zirconia crowns needed no occlusal adjustment; also it showed the least amount of marginal discrepancy.

Inclusion Criteria:

• Pt aged 21-60 years old, be able to read and sign the informed consent document.
• Psychologically and physically able to withstand conventional dental procedures.
• Patients needing posterior full coverage restorations
• Patients with sound natural antagonists.
• Have no active periodontal or pulpal diseases
• Able to attend punctually for preplanned visits and evaluation.

Exclusion Criteria:

• Patients with poor oral hygiene, high caries risk and uncooperative patients.
• Pregnant women.
• Psychiatric problems or unrealistic expectations.
• Lack of opposing dentition in the area of interest.
• Restored occlusal surface opposing the planned restoration.
• The presence of a removable or fixed orthodontic appliance.
• Patients with parafunctional habits.