The aim of this clinical study was to compare the clinical performance of CAD/CAM endochrone and fibre-reinforced composite restorations in root canal treated teeth with excessive loss.

Restoration of endodontically treated teeth is one of the significant challenges encountered in dentistry. The restoration of these teeth is often confronted with a series of complex factors. Following endodontic treatment, the coronal structure of the tooth may have been significantly weakened or lost. This condition makes it difficult to properly place restorative materials and restore the tooth's durability. Additionally, the weakness or loss of coronal structure after root canal treatment makes it difficult for these teeth to perform their normal functions and withstand chewing forces. Consequently, the restoration of endodontically treated teeth is a process that requires careful planning by dentists, selection of appropriate materials, and implementation of suitable techniques.

Endocrown restorations and fiber-reinforced composites (e.g., EverX Flow) are commonly used options in the restoration of such teeth. Endocrown restorations help support the tooth by covering a significant portion of the coronal structure.

GC Cerasmart 270 (GC Corporation, Tokyo, Japan) is a resin nanoceramic structure containing approximately 71% (by weight) of nanoceramic particles bonded to a resin matrix. Restorations designed digitally can be milled from a milling device for use in the production of restorations. With its enhanced strength and wear resistance, smooth restorations can be produced, limiting both aesthetic appearance and wear of opposing teeth.

Fiber-reinforced composites contain glass fibers to increase durability, thereby reducing the fragility of teeth after root canal treatment and aiding in preventing cracks. EverX Flow is a flowable composite reinforced with short fibers indicated for dentin replacement (along with a traditional composite as the enamel layer) in direct restorations and core build-ups. Due to its short fibers, EverX Flow efficiently strengthens restorations and demonstrates high fracture resistance.

In each patient, one or more endodontically treated teeth will be randomly assigned to be restored using either GC Cerasmart 270 blocks or EverX Flow (combined with GC Achord). GC Cem One Resin Cement will be used for adhesive procedures in the endocrown group, while GC G-Premio Bond will be used in the fiber composite group. Restoration procedures will be performed by a single operator. Restorations will be evaluated by two calibrated evaluators according to modified USPHS criteria at baseline and at 6 and 12 months. Data will be statistically analyzed using chi-square Cochrane and McNemar tests (p <0.05).

Inclusion Criteria:

• Healthy individuals without any systemic disease
• Those between the ages of 18-65
• Individuals who brush their teeth twice a day
• Patients with at least 1 root canal treatment, loss of one or more tubercles and loss of at least 1 tooth wall in their posterior teeth after intraoral examination
• Tooth margins at gingival or supramarginal level
• Patients whose periodontal and endodontic treatments have been successfully completed and who do not show any subjective symptoms
• Voluntary individuals who agree to participate in the study and sign the informed consent form will be included in the study.
• Patients will be informed about the study, read the informed consent form and agree to be included in the study.
• Ability to apply rubber cover

Exclusion Criteria:

• Individuals with uncontrolled systemic diseases
• Individuals with mental retardation who cannot co-operate
• Individuals with advanced periodontal disease
• Individuals using removable partial dentures
• Toothache, inadequate endodontic treatment or signs of periapical lesions on clinical examination or radiographic examination
• Vital teeth
• Individuals with bruxism
• Individuals with malocclusion
• Teeth with severe loss of material that requires extraction of the relevant tooth
• Patients read the informed consent form following the information about the study and did not agree to be included in the study