aim of study is to evaluate esthetic and biomechanical outcome of maxillary anterior single-tooth zirconia implant supported PEKK crowns compared to lithium disilicate crowns on PEKK abutments .

High performance polymers may be a valid alternative to other conventional materials for abutments and crowns over zirconia implants because of their cushioning effect and elastic modulus (5.1GPa), which absorb occlusal forces and avoid overload of the underlying bone from the direct transmission of biting impacts ; which could optimize and preserve osseointegration with time. Zirconia implants with high performance polymers restorations can be considered a good alternative for replacing natural teeth.

For many years lithium disilicate has been the esthetics standard used in Veneers ,Inlays , onlays, occlusal veneers, partial crowns,minimally invasive crowns and Implant superstructures due to its natural-looking tooth colouring and excellent light-optical properties.

Due to the promising esthetics of high performance polymers as it can be veneered with different veneering materials it would successfully restore esthetics.

Inclusion Criteria:

• Age >18 years
• No active intraoral or systemic disease
• No pregnancy or lactation
• controlled periodontal conditions
• Adequate bone volume to place an implant
• Occlusal function with a natural tooth

Exclusion Criteria:

1. Current pregnancy.
2. Psychiatric disorders.
3. Smokers
4. Poor motivation.
5. Several occlusal parafunction.
6. Persistent intraoral infections.
7. Severe mucosal disease.
8. Active periodontitis.
9. Poor oral hygiene.
10. Lack of occluding dentition at implant rehabilitation level