This randomized clinical trial aims to evaluate the effect of different cavity designs on the clinical performance of 3D-printed resin composite partial-coverage restorations in vital molars with complex cavities over an 18-month follow-up period.

Despite these material advancements, growing evidence indicates that cavity preparation design exerts a greater influence on the clinical performance of indirect restorations than material selection alone. However, current evidence regarding preparation design is predominantly derived from in vitro studies and remains inadequately validated under clinical conditions, particularly in vital molars. Although recent randomized clinical trials have begun to address this gap, available data remain limited and largely confined to endodontically treated teeth. Therefore, a rigorously designed randomized clinical trial is warranted to evaluate the influence of different cavity preparation designs on the clinical performance of indirect restorations in vital molars.

Inclusion Criteria:

1. Adult patients aging 20-45 years.
2. Healthy males and females
3. Patients with good oral hygiene
4. Patients presenting with at least one eligible permanent molar requiring a partial-coverage restoration.
5. Patients willing and able to attend scheduled follow-up visits for 18 months.
6. Permanent maxillary or mandibular molars.
7. Vital teeth with a positive response to cold thermal testing.
8. Complex Large or severely compromised cavities resulting from primary or secondary caries (ICDAS 5 or 6) and/or replacement of large defective restorations with at least 2 missing cavity walls requiring overlay restorations
9. Well-formed and fully erupted in normal functional occlusion with natural antagonist and adjacent teeth.
10. Absence of any radiographic, periodontal or periapical changes.

Exclusion Criteria:

1. Participants with general/systemic illness.
2. Pregnant or lactating females.
3. Concomitant participation in another research study.
4. Inability or unwillingness to comply with study visits and procedures.
5. Heavy bruxism or other parafunctional habits
6. Known allergic reactions against any components of the used materials
7. Patients receiving orthodontic treatment.
8. Poor oral hygiene or high caries activity.
9. Non vital teeth.
10. Hypersensitive teeth.
11. Teeth with prior endodontic treatment.
12. Teeth with spontaneous pain or signs/symptoms of irreversible pulpitis.
13. Teeth with advanced periodontal disease or mobility.
14. Teeth with a history of direct or indirect pulp capping procedure.
15. Teeth with vertical root fractures or cracked tooth syndrome

Triple blinded