A Randomized clinical trial to evaluate the clinical Performance of Posterior Restorations of Bulk Fill Resin Composite without Preheating Versus Repeated Preheating for One, Five and Ten times .The null hypothesis of this study is that there is no significant difference in clinical performance of the restoration during restoring posterior teeth when using bulk-fill without preheating and after repeated preheating for one , five and ten times in restoration of posterior teeth.

Dental resin composites are widely used for adhesive restorative procedures nowadays due to the significant improvement in their physical and mechanical properties. However, volumetric shrinkage is still an inherent drawback of the polymerization of the resin matrix .

Preheating improves adaptation, polymerization shrinkage and degree of conversion without affect mechanical properties of resin composite restorations.

In clinical situation, composite resin syringe is repeatedly used for restoration of several cavities and if preheating is applied, this syringe will undergo several heating cycles so repeated preheating effect on composite resin should be tested.

Follow up Period will be 1 year , Evaluation will be done at 3,6,9 and 12 months .

Inclusion Criteria:

• a)Inclusion Criteria of participants

  1. Patient age between (18-60) years old.

  2. Patient is capable of informed consent. 3-Patients with a high level of oral hygiene.

     b)Inclusion Criteria of teeth:

  1. vital teeth
  2. Carious molar teeth.

Exclusion Criteria:

• a)Exclusion criteria of participants

  1. Participants with general systematic illness.

  2. Experience with allergic reactions against any component of used materials.

  3. Concomitant participation in another research study.

  4. Patients receiving Orthodontic treatment.

  5. Pregnant or lactating females.

  6. patient with heavy Bruxism habits.

     b)Exclusion criteria of the teeth

  1. The tooth to be filled is an abutment tooth for a removable prosthesis.
  2. The tooth to be filled is periodontally involved (grade 2 or grade 3 mobile).
  3. Endodontically treated tooth.
  4. tooth with previous restoration
  5. Exposed tooth.