The purpose of this study will be to evaluate the clinical performance of CAD-CAM onlay restorations fabricated using rubber dam scanning techniques up to 12 months and laboratory investigation of their marginal fit.

A total of 54 molars will be prepared for CAD-CAM onlay restorations. The preparations will be divided into three groups according to the technique of scanning. Group I: 18 preparations will be scanned without rubber dam using standard technique, group II: 18 preparations will be scanned under rubber dam isolation using cut technique, and group III: 18 preparations will be scanned under rubber dam isolation using lock technique. Final restorations will be milled, checked and cemented, then will be evaluated using the modified FDI criteria at baseline, three months, six months, and one year.

Thirty resin dies will be 3D printed after scanning of a first molar tooth prepared for onlay. The dies will be scanned after they fit in a typodont and grouped with the same technique (n=10 per group). The digital scans will be superimposed using a 3D best-fit alignment method and 3D deviation will be calculated for each group itself and to the other groups. The marginal fit of the restorations produced will be checked using two methods: Triple scan and measuring the cement thickness after cementation and sectioning of the samples.

All data will be collected, and statistically analyzed using suitable tests.

Inclusion Criteria:

1. Healthy adult patients (18-45 years old).
2. Patients in need of class II (OM or OD) caries in molar teeth with initial, moderate or extensive stage according to the staging of caries lesions in The International Caries Detection and Assessment system (ICDASTM codes 2 to 6) (32,33).
3. Presence of proximal caries in digital x-ray with score 2 to 4 according to the ICDAS/ICCMS™ radiographic scoring system(32,33).
4. Vital teeth with absence of clinical signs and symptoms of periapical pathology.
5. Patient Ability to tolerate Rubber Dam applications.
6. Patients who will agree to attend regular check-ups.

Exclusion Criteria:

1. Bad oral hygiene (Grade 3)(34).
2. Non- vital teeth or endodontically treated teeth.
3. Severe Periodontal problems (pockets ≥6mm).
4. Patients with para-functional habits (e.g., Bruxism, attrition, wear facets)