The clinical performance (using the modified Ryge criteria) and patient satisfaction ( using VAS questionnaire) of pressed BioHPP PEEK based posterior single crowns compared to zirconia based crowns are questionable as the peek is considered as a new material and need to be tested for future clinical application.

The study is held to evaluate the clinical performance (using the modified Ryge criteria) and patient satisfaction ( using VAS questionnaire) of pressed BioHPP PEEK based posterior single crowns compared to zirconia based crowns after one year follow-up. Patients requiring posterior single crowns are collected. After teeth preparation to receive single full coverage crowns, secondary impressions were taken. The patients were divided randomly into two groups ;one group will receive pressed BioHPP PEEK single crowns (the intervention) and the other group will receive veneered zirconia single crowns (the control). Fracture of restorations (1ry outcome) using modified Ryge criteria and the marginal adaptation (2ry outcome) using modified Ryge criteria and finally the patient satisfaction (3ry outcome) using a questionnaire, all outcomes will be evaluated every 2 months with total period of follow-up of one year.

Inclusion Criteria:

1. From 18-50 years old, be able to read and sign the informed consent document.

2. Have no active periodontal or pulpal diseases, have teeth with good restorations

3. Psychologically and physically able to withstand conventional dental procedures

4. Patients with teeth problems indicated for single posterior crowns:

   1. Badly decayed teeth
   2. Teeth restored with large filling restorations
   3. Endodontically treated teeth
   4. Malformed teeth
   5. Malposed teeth (Tilted, over-erupted, rotated, etc.)
   6. Spacing between posterior teeth

5. Able to return for follow-up examinations and evaluation

Exclusion Criteria:

1. Patient less than 18 or more than 50 years
2. Patient with active resistant periodontal diseases
3. Patients with poor oral hygiene and uncooperative patients
4. Pregnant women
5. Patients in the growth stage with partially erupted teeth
6. Psychiatric problems or unrealistic expectations
7. Lack of opposing dentition in the area of interest
8. Failed endodotically treated teeth; short or overextended, narrow, missed canal, ledge or perforated teeth (even if no clear symptoms for failure)

Double blinding (trial participants and outcome assessor)

• Dental colleague assessors who are blinded about the aim of the study and participant's allocation will be responsible for assessing the outcomes of this study.
• The level of intra- and inter-examiner reliability will be determined for each assessor by the performance of a calibration session prior to the start of the trial. A training exercise to the assessors with the main investigator will help to standardize measurement techniques and parameters. An interactive calibration session will enable the investigator to quantitate the measurement variability among and between assessors and enable the optimization of the measurement process. The main supervisor will solve any conflict that may arise between the assessors by repeating the assessing and giving the final opinion.