الفهرس 
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Abstract
Eighteen male patients had maxillary edentulous ridges opposing bilateral mandibular distal extension ridges with only the six anterior teeth remaining were selected for this study. The remaining teeth were periodontally compromised, and the grade of their mobility was not more than grade II mobility. According to the design concept of mandibular bilateral distal extension RPD, the patients were randomly divided into three equal groups which were: Group (I) where the patients received NC RPD concept, Group (II) where the patients received stable base precision attachment removable partial denture (PA RPD) concept, and Group (III) where the patients received stress broken design RPD concept. To evaluate what type of RPD concept would beneficially or adversely affect the supporting alveolar bone and abutment teeth, three parameters were used in this study for evaluation, which were mandibular residual alveolar ridge resorption, abutment mobility, and abutment alveolar bone resorption. Residual alveolar bone changes were evaluated using panoramic radiographic with standardized exposure and x ray film processing .The panoramic x ray films were scanned, and the scanned films were traced using computerized Corel draw program. Alveolar bone height measurements were done vertically along bisected planes with alveolar crest height. Abutment supporting alveolar bone changes was detected using periapical radiographs with long paralleling technique. The periapical xray film position was held in its accurate position during frequent exposure using film holder with occlusal imprints. Abutment mobility was measured using microperiodontometer according to Muhlemann technique .For NC RPD, and stable base precision attachment RPD, the measurement of abutment mobility was made after removal of ceramometallic fixed splint. The measurement of the mandibular residual ridge resorption, abutment mobility, and abutment alveolar bone resorption, was performed after first six months, second six months, and one year from RPD insertion. Within the limitations of this study including research time and patient samples, the following conclusions could be approached: 1): Stable base precision attachments RPD, and NC RPD had less damaging stresses to residual ridges and abutments than stress broken RPD concept in terms of their influence on alveolar bone resorption, and abutment alveolar bone resorption. 2) When we use the stable base precision attachment RPD, it showed the least residual ridge resorption compared with the other designs. 3) The stress broken RPD was not biologically accepted design regarding residual alveolar ridge resorption, and abutment alveolar ridge resorption. 4) This study awarrened against the close association between prosthesis fitness and supporting tissue changes, and the importance of frequent recall for prosthesis adjustment