الفهرس 
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Abstract
Aim: The objective of this study was to compare between the retention of the partial denture retained by conventional extra coronal attachments and that retained by resin bonded zirconia attachments.
Methodology: Two acrylic models representing Kennedy class I cases were fabricated with natural abutments teeth (first and second premolars) bilaterally. The control model abutments were prepared for full coverage crowns and conventional extra coronal attachments were fabricated by conventional casting of CAD/CAM designed wax pattern. The intervention model abutments were roughened lingually and distally and a rest seat was prepared on the distal side of each second premolar, the zirconia attachments were then milled from zirconia blocks using CAD/CAM technology. Metal framework partial dentures were then constructed for both models with nylon caps picked up. Universal testing machine was used to measure the force needed to separate the partial denture from the patrix of the attachment on each model.
Results: In the control model, there was statistically significant decrease in retention between 0 month and 3 months, and there was increase in retention between 3 months and 6 months that was not statistically significant. For the intervention model, there was statistically significant decrease in retention between 0 month and 3 months, and between 3 months and 6 months. Comparing the two groups together, there was statistically significant difference between them where the zirconia attachment offered higher degree of retention in all simulation time periods.
Conclusions: There was decrease in retention for both groups from zero to six months but finally both attachments offered acceptable degree of retention. The zirconia attachments provided higher degree of retention but with more accelerated rate of retention loss.