Objectives: The aim of this study was to evaluate the effect of two different treatment modalities on the supporting structure of pier abutment in free end saddle case.Materials and methods: Twenty patients were selected with completely dentulous lower arch (or partially restored with suitable restoration), and Kennedy class I modification 2 upper arch with bilateral pier abutment on each side of the arch, Cases were divided into two equal groups. For the first group, the patients received upper partial denture with metallic cobalt-chromium framework and conventional metal RPI clasps engaging the pier abutments. For the second group, the patients received upper partial denture with metallic cobalt-chromium framework and fexible versacryl clasps engage the pier abutments. The supporting structures of the removable partial dentures were clinically and radiographically evaluated, probing depth, bone density and bone height were the evaluated parameters. After baseline recording following denture insertion, subsequent measurement were obtained at regular follow up appointments 6, 12, 18 months. Probing depth measurements were obtained at three points around each pier abutment in the two groups and the mean values of the reading were calculated for each abutment. Radiographic evaluation was performed using the Digora system. Acrylic template was constructed for each patient. The linear measurement system supplied by the software of the Digora machine was used for recording changes in bone density and bone height mesial and distal to the abutments.Results: Results obtained showed greatest increase in the probing depth for the group I followed by group II which showed the least changes. It seemed that versacryl clasp retainer was more tissue friendly than metal clasp. Statistical analysis revealed insignificant differences between the two groups in pocket depth measurement. Statistical analysis of bone density and bone height changes around the pier abutments showed significant difference between the two groups. The greatest decrease in bone density and bone height was recorded for group I followed by group II. These results implies that versacryl material either absorbed the stress and transmitted least amount to the abutment or transmitted it more favorably than the rigid metal clasp. The first group showed highly significant reduction in bone height and bone density after the first follow up period, the second group showed less reduction in bone height and increase in the bone density measurement in the last follow up period, These could be discussed due to that the versacryl material transmitted force within physiological limit of the supporting structure and hence initiating bone remodeling process.versacryl material transmitted force within physiological limit of the supporting structure and hence initiating bone remodeling process.Conclusion: Using removable partial dentures caused some changes in the periodontal structure of the abutment teeth.1.These changes are accepted clinically and the success of removable partial denture depends on maintaining a high standard of oral hygiene with frequent removal of plaque to maintain the health of gingiva and abutment teeth.2.Conventional metal RPI clasp and flexible versacryl clasp are both clinically and biologically successful as retainers for removable partial dentures.3.Flexible versacryl clasp is superior to Cobalt-chromium clasp regarding bone height and bone density measurements.