الفهرس 
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Abstract
Objectives: Radiographically evaluate crestal alveolar bone height change of abutment teeth and distal extension ridge by using three different resilient design options. Materials and Methods: Fifteen male patients were selected for this study with maxillary complete edentulous arch against mandibular distal extension ridges posterior to first premolar teeth. The patients were divided into three equal groups according to resilient material introduce into the denture where the mandibular distal extension removable partial denture (RPD) designed with Flexible base, Resilient layer and Occlusal reactive for group A, B and C respectively. After processing the complete maxillary acrylic resin denture and mandibular resilient (RPD), adjusting of occlusion was carried out. The abutment teeth alveolar bone height changes and distal extension ridge were evaluated radiographically immediately after insertion, after 6 and 12 months of denture insertion. Corel Draw 8 was used to evaluate alveolar bone height change of the abutment teeth and Posterior Area Index was used to evaluate the bone height change of mandibular distal extension ridge. Results: 1- For all flexible design RPD, The resorption of the abutment crestal alveolar bone and distal extension ridge were found statistically insignificant during the first interval period (six months) of study. Reverse observation was found during the second interval and follow-up period of the study. 2- Flexible denture base RPD was significantly increased abutment and distal extension ridge resorption compared to either resilient layer or occlusal reactive RPD during the second interval period and total follow - up period. 3- There is no significant difference in the supporting alveolar bone resorption was found when comparing the resilient layer RPD and occlusal reactive RPD along interval period of the study. Conclusion: 1- from tissue preservation point of view, Resilient layer and Occlusal reactive RPD were superior to flexible denture base regarding abutment teeth and distal extension ridge resorption. 2- Resilient layer and Occlusal reactive RPD flexible design were the first choice of prosthetic treatment when resilient material introduced through the denture. Recommendations: Flexible denture base RPD should be considered as a temporary denture base for short interval period, not more than 6 months, as acetal resin flexible denture base may be deformed greatly with long time wear of the denture. Deformation of flexible base needs a further investigation.