Objectives: The aim of this study was to compare between clasp retention in metallic versus peek RPD frameworks constructed by using Purpose: The aim of this study was to assess the diagnostic accuracy of cone beam computed tomography (CBCT) in detection of simulated recurrent caries beneath composite restoration. Materials and Methods: In this study, a total of 60 proximal slots of class II cavities were prepared on 60 extracted human premolars and molars. Then, 30 teeth were randomly selected out of this sample and artificial carious lesions were created on these teeth by a round diamond bur no .2(study group). All cavities were restored by using composites resin and  radiographed with CBCT unit (Cranex 3D)  using 5x5mm field of view at three voxel sizes 0.85mm,0.125mm,0.200mm. Intra- and inter-observer agreements were calculated with Kappa statistics (κ). The area under the receiver operating characteristic (ROC) curve was used to evaluate the diagnostic accuracy. Results: The AUCs value for CBCT with voxel sizes 0.85mm,0.125mm, 0.200mm was 0.983 ,0.900,0.817, respectively. The kappa value for inter-observer agreement was 0.993,0.989,0.938 , respectively. Conclusion:  Diagnostic performance of CBCT was high in detecting the simulated small recurrent proximal caries under composite restoration,voxel  size 0.125mm can be used to detect caries lesions with adequate accuracy  and the least patient exposure dose.