The aim of this study will be to evaluate the clinical performance of polyethylene fiber reinforced resin composite restorations versus bulk fill resin composite restorations in endodontically treated teeth.

Statement of the problem:

Restoration of non-vital teeth is always challenging for dentists. Without placing the coronal restoration, root canal treatments are not considered complete. Appropriate treatment plan selection should be based on remaining tooth structure, cavity wall thickness, tooth position in the arch, and load applied to the tooth. Previously, endodontically treated teeth (ETT) were reconstructed automatically with post, core, and full crown. But this treatment plan had many risks like root perforation, sacrificing a considerable amount of sound tooth structure, and tooth fracture.Several techniques and materials have been developed for the restoration of endodontically treated teeth including complete cast coverage, composite resins and amalgam and indirect restorations covering cusps. Resin-based materials provide rigidity and increase the fracture resistance of non-vital teeth by rein-forcing unsupported tissues. Advanced adhesive systems with improved physical properties are more aesthetic and support remaining tooth structures better than amalgam. In order to reduce polymerization shrinkage stresses, flowable resins with low elastic modulus have been suggested as a stress-absorbing layer under composite restorations. On the other hand, the use of flowable resin does not increase fracture resistance, and this layer results in contraction stresses.

Rational:

In fact, the primary aims of "biomimetic dentistry" are to be as minimally invasive as possible, and to substitute the missing hard dental tissues with restorative materials closely resembling the natural tissues regarding their mechanical features and properties.

Leno weaved Ultra-high-molecular-weight polyethylene (LWUHMWPE) fibers are plasma treated fibers. LWUHMWPE fiber reinforcement Ribbond systems (Ribbond THM, Ribbond Inc, Seattle, WA, USA) have been introduced in the attempt to increase composite resin toughness, thus increasing both durability and damage tolerance. These bondable reinforcement fibers can be closely adapted to the residual tooth structure without requiring additional preparation. The high modulus of elasticity and low flexural modulus of polyethylene fiber have a modifying effect on the interfacial stresses developed along the cavity walls.

According to a systematic review published in 2021 that was done to evaluate various in vitro studies, it was confirmed that the effect of the Ultra-high-molecular weight polyethylene fibers is increasing the fracture resistance and making more favorable fractures in endodontically treated teeth. However, there is no enough clinical data regarding this point, so this proposal is introduced.

Inclusion Criteria:

Participant:

1. Patients ages 18 to 55 years.
2. Patients with endodontically treated teeth.
3. Patients with good general health.
4. Patients with good recall availability.

Teeth:

1. Successfully endotreated molar teeth.
2. Endodontically treated teeth (ETT) with at least two remaining walls.
3. ETT without apical or periapical pathosis.
4. ETT with healthy peridontium.

Exclusion Criteria:

Participant;

1. Patients who are allergic to product ingredient.
2. Patients who need indirect restorations.
3. Patients with poor oral hygiene.
4. Patients with history of bruxism and parafunctional habits.

Teeth:

1. Teeth with noncarious cervical lesions.
2. ETT with more than two remaining walls.
3. Presence of apical or periapical pathosis.
4. Teeth with advanced periodontal diseases. -