الفهرس 
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Abstract
The study involved two routes in vitro and in vivo investigations conducted on partially edentulous mandibular arch representing Kennedy Class I classification (Bilateral free end saddle).
Two materials used in construction of extracoronal attachment retaining removable partial dentures were investigated; according to the material used they were classified into two groups:
• group (I): Casted Co-Cr Extracoronal attachment Retaining Removable Partial Denture.
• group (II): CAD/CAM milled Zirconia attachment Retaining Removable Partial Denture.
The in vitro part of the study was performed on 3D experimental model simulating symmetrical Kennedy Class I with the first premolars the last standing abutments for the evaluation of stresses induced in the supporting structure.
3D experimental model simulating symmetrical Kennedy Class I with the first premolars the last standing abutments, was designed to have a periodontal space about 0.25mm was created around root of the abutments simulating the periodontal membrane space. Also 2mm thickness mucosal space at ridges and 1mm mucosal space at edentulous ridges for mucosa simulation then the model was printed using 3D printing technology. After that a stent was fabricated for installation of a mucosa simulator material to the model at the predetermined space for it.
In both groups the last two abutments in each side was prepared to receive two crowns and an attachment which was CAD/CAM milled from Zirconia blanks, or cast co-cr according to the group, then a removable partial denture was conventionally constructed.
Strain gauge analysis was conducted using universal testing machine upon application of unilateral load in between second premolar and first molar distal to the abutments of the removable partial denture. Data was collected, tabulated and statistically analyzed.
The in vivo part of the study was evaluating dislodgment force, twelve patients were selected from the out-patient clinic of Prosthodontics Department, Faculty of Dentistry, Ain-Shams University. They were divided randomly and equally into two groups. The last standing two abutments at both sides of the arch in both groups were prepared to receive two crowns and an attachment, which was CAD/CAM milled from Zirconia blanks, or Co-Cr cast metal according to the group, then a removable partial denture was conventionally constructed. A digital force gauge device was used to measure the dislodgment force at the time of denture insertion.
The data were collected, tabulated and statistically analyzed, and the results within the limitations of this study, it can be concluded that
• CAD/CAM milled zirconia and Co-Cr cast metal attachments showed different distribution of forces as zirconia attachment transmits less stresses to the loaded and unloaded sides compared to metal attachment.
• CAD/CAM milled zirconia attachment retaining removable partial denture showed a higher measurement in dislodgment force compared to Co-Cr metal attachment at the initial insertion time.