The study will be conducted in the Conservative Dentistry Department, Faculty of Dentistry, Cairo University in conjunction with the Conservative Dentistry Department, Faculty of Dentistry, MSA University outpatient clinics. The predicted sample size was a total of 24. The sample size was increased by (20%) to account for possible dropouts during follow-up intervals to be total of (30) cases i.e. (15) for each group. Screening of patients that come to the Conservative Dentistry Department seeking dental care will continue until the target population is achieved. The patients will be subjected to examination and diagnosis. Once the patients that are potentially eligible for this study are identified, they will be contacted by the research operator who will explain the study and ascertain the patients' interest. If interested, more detailed evaluations and preparations, and schedule planning will be made. Then the patient will sign the informed consent to ensure the approval for all the prosecuted that will be done and his/her acceptance to participate in this trial. Randomization will be done using simple randomization by computerized sequence generation using www.random.org by generating numbers from 1:30 into two columns. Each participant will choose a random number from an opaque sealed envelope. When the participant chooses an envelope, it will be signed by the patient and the supervisor and the number on the envelope will be recorded in the patient chart to ensure that the patient is assigned to the randomized group. After anesthesia, prophylaxis was performed using a brush associated with pumice, mounted in a low-speed handpiece. The teeth will be cleaned from any plaque or debris. After shade selection, rubber dam isolation will be used to avoid any moisture contamination which might affect the clinical performance of the bond and restoration, and to provide favorable conditions for bond application, if any reason is found that contraindicate rubber dam usage the procedure will be done under the cotton roll and high suction insulation and the use of retraction cord if needed to avoid any moisture contamination. The class II preparations will be made with spherical diamond burs of appropriate size and removal of carious dentine will be performed with spherical carbide bur at low-speed hand-piece and hand instruments. The cavities were designed according to the principles of minimally invasive dentistry. The outline shape of the preparations will be limited to the removal of caries. No bevels were prepared. Minor finishing and polishing may be done to the teeth if needed to remove any sharp edges or friable/undermined enamel. PALFIQUE BOND (Palfique, Tokuyama, Japan) will be used with both types of resin composites to ensure standardization of the procedures. It is a one-component, one-coat application, self-etching, light-cured, dental adhesive system. By using the disposable applicator, the bond will be applied on the surface of the prepared cavity and then wait for 10 seconds or more. Then mild air is continuously applied to the surface for 5 seconds until the runny bond stays in the same position without any movement and light-cured for 10 seconds. Injectable Universal flowable resin composite (PALFIQUE® Universal Flow; Tokuyama, Tokyo, Japan) super-low flowability supplied in L-syringe with nozzle and dispensing Tips. "Super Low" has low flowability, non-slumping, non-running, and precision stacking properties. The layer dispensed will be 2 mm. in thickness and cured for 40 s. Conventional resin composite (ESTELITE® Alpha; Tokuyama, Tokyo, Japan). The composite was inserted using the incremental technique. Incremental filling techniques result in better light penetration and better polymerization of the composite resin, reduction of the cavity configuration factor, cuspal deflection, polymerization shrinkage stresses; and ensures that the resin adheres better to cavity walls. Each increment of 2 mm was cured for 40 s.

The restoration was performed for both groups using a pre-curved metallic sectional matrix, associated with a separating ring and a wooden wedge.

Following the removal of the matrix band, the proximal regions of the restorations were additionally polymerized buccally and lingually/palatally for 10 s.

Occlusal adjustments were made using articulating paper, and the quality of the interproximal contacts and cervical adaptation was checked by means of dental floss and interproximal radiographs. The restorations were finished with water-cooled fine and super-fine diamond burs. The polishing procedures of the occlusal surface were performed with abrasive rubber tips during the same appointment immediately after the restorative procedure for both groups. All participants will be instructed to follow oral hygiene measures to avoid plaque and bacterial accumulation which may negatively affect the clinical performance as fracture or loss of retention. The restoration will be evaluated for any fracture or loss of retention by using prob following Modified USPHS criteria.