Mohamed El-KhodarySaad El-Din¹, Ashraf Anwar Gebreel², MostafaSaadSwedan^{3 1} Professor of Prosthodontics, Faculty of Dentistry, Mansoura University, Egypt. ² Assistant professor of Prosthodontics, Faculty of Dentistry, Mansoura University, Egypt. ³. Demonstrator, Prosthodontics, Faculty of Dentistry, Mansoura University, Egypt. Abstract: Objectives: The thermoplastic material partial denture is more comfortable and seems to be highly aesthetic as it has the same color as the abutment. The flexible framework removable partial dentures can replace any number of teeth in a dental arch, similar to the cast metal removable partial dentures. The aim of this study was to evaluate radiographically the effect of distal extension removable partial denture either constructed from thermoplastics or vitallium materials on bone height change of abutment teeth. Methods: Total number of ten healthy patients was selected and grouped into two groups. Group I received mandibular bilateral distal extension partial dentures constructed from vitallium and group II received mandibular bilateral distal extension removable partial dentures constructed from thermoplastic material. For every patient constructed conventional maxillary complete denture then radiographic evaluation was done at insertion of dentures and after six months from insertion. Results: For both groups, there was no significant difference in bone loss between mesial and distal aspects. There was a statistically significant difference in bone loss between group I (Metallic RPD) and group II (Thermoplastic RPD) for mesial and distal aspects of the abutment. Group I (Metallic RPD) recorded a significant higher bone loss at mesial and distal aspects of the abutment teeth than group II (Thermoplastic RPD). Conclusions: Thermoplastic mandibular distal extension removable partial denture material was superior to vitallium material regarding the preservation of abutment alveolar bone. Keywords:Distal extension removable partial dentures, vitallium, radiographic evaluation.