Comparison of Retention and Seating of Implant-Supported Hard and Soft Metal Copings

Implant-supported restorations are generally used for the replacement of the lost teeth. Stability against masticatory forces and proper retention are critical for optimal durability of restorations. The aim of this experimental study was to compare the retention of cobalt-chromium (Co-Cr) copings made by different techniques.

Twenty-four solid abutment analogs were mounted and scanned with a desktop scanner. They were divided into two groups (n=12) and received metal copings fabricated by either soft or hard Co-Cr alloy. Soft Ceramill Sintron Co-Cr patterns were milled and sintered. Hard Co-Cr blocks were milled in a milling machine. The copings were sandblasted, polished, adjusted, and placed on the respective abutments. The frequency of adjustments was recorded for each abutment. The copings were cemented with zinc phosphate cement and underwent tensile test by a universal testing machine. The Mann-Whitney test and t-test were used to compare the two groups (α=0.05).

There was no significant difference in retention of copings between the experimental groups. The mean retentive force was 559.58±115.66 N and 557.13 ±130.48 N for the soft and hard metal groups, respectively (P=0.96). Considering the non-normal distribution of adjustment frequency data, the Mann-Whitney test showed that the frequency of adjustments was significantly higher in the hard metal group than the soft metal group (9.5 versus 0.1667; P<0.001).

Although hard metal copings required more adjustments, retention of soft and hard Co-Cr copings was not significantly different.