الفهرس 
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Abstract
This study was conducted to evaluate clinically and radiographically the supporting structures around main abutments in maxillary distal extension cases restored by two different materials. The clinical parameters were: pocket depth, gingival index, caries experience, retention of the prosthesis and patient satisfaction, while the radiographic parameters were bone height and bone density. The evaluation period was one year follow up period.
The 24 male patients were selected from those attending the out-patient clinic, Removable Prosthodontics Department, Faculty of Dentistry, Minia University to participate in this study. The basic requirement for selection was bilateral distal maxillary free end saddle starting from premolar teeth. The patients were carefully selected and thoroughly examined in an attempt to reduce human variables and eliminate any factor that might adversely affect the results of this study. Patients having systemic conditions that might affect the results or heavy smokers were excluded.
Patients were rehabilitated by combined tooth and mucosa supported maxillary removable partial dentures. Patients participating in this study were randomly divided into two equal groups.
group 1: patients received maxillary partial dentures with metallic cobalt-chromium frameworks and cobalt- chromium clasps.
group 2: The patients received maxillary partial dentures with thermoplastic frameworks and acetal resin clasps
Standard clinical and laboratory techniques were followed for partial denture construction for all patients according to the material used. The clinical parameters as well as the radiographic were examined for every patient at denture delivery, and after 3, 6, 9 and 12 months of denture insertion.
The patients responded to most of the statements of OHIP questionnaire with high satisfaction for the treatment. Patients of thermoplastic group strongly agreed the treatment more than metallic group patients .
The bone height and density around abutment teeth decreased with time for both groups , but group I was highly significant than the second group regarding bone density but not the bone height changes at the different follow up periods.
For clinical parameters there was Increase in pocket depth and gingival index measurements for both groups. The values for the thermoplastic group was significantly higher than that for the metallic group at the different follow-up intervals
For retention of the prosthesis; The results of this study showed that retentive force mean values were significantly lower in Thermoplastic group in comparison with metallic group at denture insertion and at all follow up intervals
For caries experience, in this study, the removable partial denture itself appeared to slightly affect caries status; as only one abutment of each group, showed caries 12 months after follow up
Clinical implications: Since there were lesser reductions in bone height around acetal resin clasp abutments, it could be used successfully to retain partial dentures. However, meticulous oral hygiene and proper insertion and removal of partial denture with acetal resin clasps are required to decrease gingival inflammation and crevicular fluid amount.
Conclusion and Recommendations
Within the limitations of this study, it may be conclude that:
• Thermoformed removable partial dentures were superior to cobalt-chromium RPDs in terms of bone height loss around the abutment but not in terms of, bone dentistry, periodontal pocket depth or gingival index.
• The patients were more satisfied by thermoformed resin RPD than the metallic RPD despite their lower retention values. In their response to the questionnaire, the patients did not complain from retention with thermoformed RPDs.
• Acetal resin provides less retention compared to chrome cobalt. So, further study has to be done regarding various thicknesses and designs of clasps and framework for its successful dental application.
• Acetal resin may be used as a framework material suitable for removable partial dentures with flexible, esthetic clasps that is highly accepted by patients. However, meticulous oral hygiene and proper insertion and removal of partial denture with acetal resin clasps are required to decrease gingival inflammation..