The study aims to evaluate the clinical performance of Bulk-fill flowable resin-based composite versus submicron hybrid resin-based composite restoration in patients with posterior class I carious cavities.

Resin-based composites are now the preferred material for posterior tooth restoration Silva et al.,2023. To combat the polymerization shrinkage of resin-based composites, an incremental method for placing composite resin was created. Nevertheless, this method takes a lot of time and could cause air to become trapped between successive composite resin layers. Some structural and chemical modifications to the composite resin composition have been suggested in an attempt to lessen the undesirable consequences of the composites, such as the tension produced on the tooth or restoration interface Arbildo-Vega et al.,2020.

Newer resin formulations that combine small particles (0.1 μm-1.0 μm) and submicron particles (0.04 μm) with larger filler loading percentages are referred to as submicron hybrid composites. They exhibit enhanced polishability and gloss retention, as well as greater mechanical and physical properties Vishwanath et al.,2021.

Bulk-fill resin-based composites (BF-RBCs) were introduced to the dental market in the past decade to address challenges related to the incremental placement of conventional resin-based composites in posterior teeth. Originally, the term "bulk-fill" referred to resin composites that could be used in increments of 4-5mm, making them suitable for both full-body and base bulk-fill techniques. Current commercial bulk-fill resin-based composites (BF-RBCs) can be categorized based on their viscosity into flowable (low viscosity) and sculptable (high viscosity) types. In the past, flowable bulk-fill RBCs were known to have lower mechanical properties compared to high-viscosity RBCs. However, the addition of nanofillers in the latest generation of flowable BF-RBCs has improved their mechanical properties while preserving their low viscosity Gatica et al.,2023.

For the majority of commercially available flowable BF-RBCs, the manufacturer advises applying a top layer of conventional resin composite over the restoration. This makes it possible to partially offset its decreased flexural strength and prevent the restoration from wearing out too quickly Gatica et al.,2023. However according to the manufacturer's instructions for (Brilliant Bulk-Fill Flow, Coltene/Whaledent) it can be used for fillings in the posterior region even without an additional covering layer. It is composed of pre-polymerized fillers that include dental glass with nanosilica particles and silanized fillers to enhance bonding strength within the resin matrix, along with larger dental glass fillers to minimize polymerization shrinkage.

This project will be designed to test the null hypothesis that bulk-fill flowable resin-based composite will have the same clinical performance as the submicron hybrid resin-based composite in restoring class I carious cavities according to the Modified United State Public Health Service (USPHS) criteria.

Inclusion Criteria:

1. Co-operative patients approving to participate in the trial
2. Simple class I carious lesion scored based on the International Caries Detection and Assessment System (ICDAS) is code 2 or 3
3. Vital upper or lower molar
4. Presence of favorable occlusion.
5. Presence of opposing teeth.
6. Proper teeth aligment.

Exclusion Criteria:

1. Patients with poor oral hygiene
2. Bruxism or occlusion abnormalities.
3. Allergic reaction to the materials used.
4. Disabilities
5. Pregnancy
6. Heavy smoking
7. Xerostomia
8. Lack of Compliance
9. TMJ disorders
10. Unwillingness or inability to attend follow-ups.
11. Deep caries close to pulp.
12. Teeth with signs/symptoms of irreversible pulpitis or necrosis.
13. Endodontically treated teeth.
14. Extensive occlusal destruction
15. Periodontal affection