Aim: To evaluate retention of Casted versus Milled Cobalt-chromium (Co-Cr) removable partial denture (RPD) framework in mandibular Kennedy class I.
Material & methods: A mandibular Kennedy class I educational model was scanned after distal rest seats preparation in first premolars bilaterally to produce standard tessellation language (STL) file. The latter was 3D-Printed to produce a 3D-printed resin cast. In the area of the second premolar bilaterally two implants were inserted, Multi-unit abutments were screwed to the implant, surveyed crowns were screwed to the abutments, and an STL file of the cast was obtained. Twelve Cobalt-Chromium (Co-Cr) RPD frameworks were then constructed and divided into two equal groups based on fabrication technique: casting (casted group) and milling (mill group). Evaluation of retention was done at different cycles starting from insertion (T0) to 4320 cycles (T4) simulating three years of function using a Universal testing machine.
Results: Mill group showed significantly higher initial (T0) retention compared to Casted group. Moreover, the highest loss of retention percentage (29%) was observed at the first interval (T0-T1) after simulating one month of function in Mill group. On the other hand, Casted group showed the highest loss of retention percentage (42%) at third interval (T2-T3) after simulating one year of function. After simulating three years of function, Mill group showed significantly higher retention values than Casted group.
Conclusion: Mill group showed significantly higher initial (T0) retention compared to Casted group. After simulating three years of function, Mill group showed significantly higher retention values than Casted group.