In-vitro studies do not represent the actual masticatory environment and cannot simulate the intricate chewing pattern. Hence, there is a need for an in vivo study evaluating the wear potential of the newly introduced strength - color gradient multilayered zirconia IPS e.max ZirCAD Prime (5Y-TZP/3Y-TZP) and compare it to Lithium Disilicate IPS e.max CAD which has proven to have favorable wear patterns.

• There will be no difference in wear caused by monolithic Zirconia (5Y-TZP/3Y-TZP) IPS E-max ZirCad Prime and Lithium Disilicate IPS e.max CAD to the antagonist.
• There will be no difference in the wear of the new monolithic zirconia IPS e.max ZirCAD Prime and lithium disilicate IPS e.max CAD.

Inclusion Criteria:

• All subjects are required to:

  1- Be aged 21-50 years old, be able to read and sign the informed consent document. 2- Psychologically and physically able to withstand conventional dental procedures.

  3- Patients with mutilated posterior teeth indicated for full coverage restorations.

  4- Patients with sound natural antagonists. 5- Able to attend punctually for preplanned visits and evaluation. 6- Have no active periodontal or pulpal diseases.

  7- There should be no apparent loss or wear in opposing enamel.

Exclusion Criteria:

1. Patient with active resistant periodontal diseases.
2. Patients with parafunctional habits and bruxism.
3. Patients with poor oral hygiene, high caries risk and uncooperative patients. 3- Pregnant women.
4. Patients in the growth stage with partially erupted teeth. 5- Psychiatric problems or unrealistic expectations.

6- Lack of opposing dentition in the area of interest. 7- Restored occlusal surface opposing the planned restoration. 8- The presence of a removable or fixed orthodontic appliance.