الفهرس 
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Abstract
This in vitro study was carried out To compare between telescopic crown and extra coronal attachment as direct retainers for RPD restoring Kennedy class I distal extension cases. Two identical partially edentulous models of lower Kennedy class I were used upon which two metal skeletons were constructed. The components of the three metal skeletons were the same except the direct retainer which was, extra coronal attachment for the first model and telescopic crown for the second one.
Strain induced distal to the principle abutment and second molar area of the ridge were measured using strain gauge analysis method .the selected areas on the model were prepared to receive flexible electro conductive wire cemented by suitable adhesive to measure the strain induced in the selected areas.
Static vertical tissue-ward load of 10 kg (100N) was applied at second premolar area and second molar area on the saddle area, unilaterally and bilaterally and the stresses induced on the abutment the teeth and second molar area of the residual ridge were recorded in each simulation.
The strain values were calculated at apical regions of all root surfaces of the abutment teeth and area corresponding second molar on the residual ridge. The data were collected and tabulated to compare between the two different retainers tested in this study.