Retention of Cast Chrome-Cobalt Versus Milled Chrome-Cobalt Telescopic Retainer for an Implant Supported Overdenture: An in Vitro Study

Aim: The objective of this study was to compare the retention of frameworks using milled versus cast cobalt chromium alloys for implant supported mandibular overdentures using a universal testing machine. Methodology: An epoxy resin model of edentulous mandible was constructed and prepared to receive four implants in the intra-foraminal region of the model. Four pre-milled titanium abutments were screwed to them which were considered to be the primary coping. The secondary copings were either Group C (cast cobalt chromium frameworks) or Group M (milled cobalt chromium frameworks). Retention was measured at baseline, after subjected to chewing cycles of 12,500 cycles and then after subjected to chewing cycles of 37,500 using the chewing simulator. Results: Both the cast and the milled groups showed a statistically significant decrease in retention when subjected to different cycles. Group C showed a higher non-significant change in retention from baseline to 12500 cycles. While Group M showed a higher non-significant change in retention from 12500 cycles to 37500 cycles and from baseline to 37500 cycles. Conclusion: The retention of the milled frameworks is higher than the cast frameworks up to an equivalent period of 1 month, after which the retention of both frameworks became equivalent.