Retention of CAD/CAM Copings Bonded with Resin and RMGI Cements

Objectives:
To measure retention of lithium disilicate and resin-ceramic hybrid copings bonded with resin and RMGI cements to tooth preparations.

Methods: 50 non-carious extracted mandibular premolars were center mounted in round holders with acrylic. The holders were mounted into a lathe attached to a high-speed handpiece. Standardized crown preparations with 22° axial convergence and 3mm height were milled. The crown preparations were then scanned with a Cerec 3 intraoral scanner and specially designed copings were milled from lithium disilicate (e.max, n=30) or resin-ceramic hybrid (Cerasmart, n=20) materials. The e.max crowns were sintered and etched. The crowns were then cemented according to manufacturer’s directions using the cements listed in the table below (resin cement: Multi-link Automix, Self-adhesive resin cement: G-CEM LinkAce, RMGI cement: FujiCEM 2). The crowns were allowed to self-cure under a 2kg weight. The crowns were stored in a moist bag for 24hours at 37°C, thermocycled for 10,000cycles from 5-55⁰C with a 30second dwell time. The specimens were placed in a custom fixture in a universal testing machine and loaded in tension at a crosshead speed of 0.5mm/min until debonding. The retention strength (MPa) at debonding was determined from the maximum recorded tensile force and surface area of the preparation. Data were compared with a 1-way ANOVA and Tukey analysis (alpha=0.05).
Results: Significant differences were found in the crown retention strength for the material/cements (p<.01). Groups with significant differences are labeled with different superscripts.
Conclusions:
The use of resin cements, is preferred for retention of resin ceramic coping materials. Resin cements, conventional and self-etching, as well as resin modified glass ionomer cements can be used for lithium disilicate coping material retention.