الفهرس 
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Abstract
to compare between retention of clasps made from PEEK and Cr-Co RPDs constructed by using CAD\CAM technology. Materials and methods: Ten patients were selected for this study with mandibular class III Kennedy classification with modification-1. The patients were randomly divided into two equal groups according to the material used for constructing the RPDs: group A delivered CAD-CAM polyetheretherketone (PEEK) RPDs and group B delivered CAD CAM designed and 3D printed resin pattern frameworks cast into Cr-Co RPDs. For each group, the force of retention was measured by digital forcemeter immediately, 3 months and six months after denture insertion. The retention loss was evaluated and compared between the two groups within all intervals of the study. Results: -The retention forces in group B (Cr-Co RPDs) were higher than that of group A (PEEK RPDs) engaging the same undercuts. Although the insignificant difference at T0, it was significant at T3 and T6 where in group A: T0=12.96N, T3=10.86 and T6=8.94N and in group B: T0=13.20, T3=12.6N and T6=12.11N.
- Both groups showing statically significant decrease in the retention force with time except between T3 and T6 in group B which was insignificant decrease.-The comparison between the loss of retention in the two groups, showed that group A was associated with significant higher retention loss than group B of along the study where in group A: T0-T6=4.02N and in group B: T0-T6=1.09N .Conclusions: Within the limitation of this study, it can be concluded that:(1) Although the difference in the retention force between PEEK and CR-CO clasps, this retention force is within the adequate required limits for retaining RPDs.(2)Cr-Co claps can be considered better than PEEK clasps engaging the same undercuts in regard to the maintaining of the retention force as long as possible..