This study is conducted to evaluate the clinical performance of indirect overlay restorations with different cavity preparation designs in endodontically treated molars over two years.

First Validation of endodontic treatment using a periapical radiograph and proper history taking.

{I}• Cavity Preparation Procedures for Comparator Group:

• Removal of any remnants of temporary filling and excess gutta percha to the level of root canal orifice.
• Removal of all undermined enamel.
• Then 1.5 to 2 mm cusp reduction will be performed for the buccal and lingual walls.
• The occlusal box will be of 2.5 mm width, 2 mm depth cavity walls and will be flared to produce a 6 degree of divergence.
• The cavity will have internal rounded angles, finished enamel with sharp non-beveled margins and smooth well-defined walls.
• Immediate Dentin Sealing and Cavity Optimization: Immediate dentin sealing will be performed through the use of a universal adhesive followed by the injection of injectable flowable resin composite. Blocking of undercuts using injectable flowable resin composite and margin elevation if required.
• The final retentive design will include occlusal clearance of 2 mm with occlusal box cavity of depth 2 mm with all margins in enamel occlusally and all dentin surfaces will be covered.

{II}• Cavity Preparation Procedures for Intervention Group:

• Removal of any remnants of temporary filling and excess gutta percha to the level of root canal orifice.

• No additional removal of the tooth structure will be performed at this step.

• Cavity optimization will be performed first.

• Blocking of undercuts using injectable flowable resin composite and margin elevation if required.

• The occlusal cavity will be restored during cavity optimization with injectable resin composite to reduce the areas of dentin exposure and preserve the remaining tooth structure.

• The dentin substitute resin composite will establish the biobase.

• An anatomical non retentive preparation design will be performed to show continuous inclined plane preparation with 2 mm cuspal reduction, concave chamfer margins, and 1 to 1.5 mm thick butt-joint preparation in the interproximal portion.

• The final cavity design will include occlusal clearance of 2 mm with total cusp coverage, with biomimetic features (anatomical, non-retentive design) with no occlusal box cavity.

  • The CAD/CAM partial coverage overlay restoration will be designed, then milled using SHOFU Hard hybrid ceramic blocks for both groups following its design.
  • Cementation for both groups:

• Selective etching of the enamel margins of the cavity will be made using 37% phosphoric acid.

• Application of Universal Adhesive according to manufacturer's instructions and cured.

• Regarding the milled indirect overlay restorations; surface roughening with Dura-Green Stones SHOFU will be performed, followed by the application of a suitable priming agent, then the injection of resin cement in the fitting surface, and finally the restoration will be cemented.

• Restoration will be placed onto the prepared cavities allowing for excess resin cement to emerge which will then be tac-cured for 5 second using a standard intensity light cure allowing for slight hardening of the excess resin cement.

• Removal of excess cement using a sharp explorer, excavator or a c-blade along with the use of interdental flossing to ensure elimination of interdental excess resin cement material.

• Completing the remaining curing cycle after excess removal to the full curing time.

Inclusion Criteria:

Patient Related Criteria:

• Adult patients (age: 20-60 years) of both genders.
• Healthy patients (not suffering of any systematic or chronic diseases).
• Able to tolerate the necessary restorative procedures.
• Willing to sign the informed ethical consent.
• Accepts the follow-up period.

Tooth Related Criteria:

• Proper endodontically treated teeth.
• First and second permanent molars.
• Absence of any peri-apical lesions.
• Absence of any periodontal disease involvement.
• Large access cavities with one or two missing walls.
• Patients with proper oral hygiene.
• Presence of opposing tooth.

Exclusion Criteria:

• Patient related:
• Patients younger than 20 or older than 60 years old.
• Pregnant females.
• Patients with any systemic or chronic diseases.
• Patients not accepting the follow-up period.
• Patients not willing to sign the informed ethical consent.
• Patients with known allergies to latex and/or resinous material.

Tooth related

• Endodontically treated anterior, premolar and third molar teeth.
• Hopelessly carious/destructed teeth necessitating extraction.
• Mobile teeth, indicating periodontal disease or trauma.
• External or internal resorption.
• Poor endodontic treatment.
• Periapical lesion present.
• Cervical carious lesions involved.