In Vitro Crown Retention Tests Using Three RMGI Cements

Objectives: A luting agent that is easy to mix and deliver while providing high retentive forces is desirable and critical for final cementation and the long-term success of indirect restorations. To test three commercially available Resin Modified Glass Ionomer (RMGI) cements in vitro for retention. Methods: Freshly extracted human bicuspids were positioned in the center of Teflon cylinders and imbedded in self-curing resin, leaving the crown extruded. On a jeweler's lathe operating at 1000 rpm the teeth were machined with a diamond disc at low speed (250 rpm) under copious water-cooling. Total angle of convergence measured 32 + 1 degree; the occlusal table ±4 mm. Copings were waxed and cast in type III gold using routine laboratory techniques. 20 copings per group (n=20) were cemented with Group 1. Fuji  Plus (GC Int); Group 2. RelyX Luting Plus (3M/ESPE); Group 3. UltraCem RRGI Luting Cement (Ultradent Products Inc). The samples were stored in water at 37⁰ C for 24 hours before testing retention of the copings applying a tensile force in an Instron machine. The force at rupture was recorded in Kg/Force. Results: The average mean force at rupture and standard deviations were: Group 1. 31.32 ± 8.2; Group 2. 28.38 ± 8.6; Group 3. 37.48 ± 7.2. An ANOVA demonstrated a significant difference between Group 3 and Groups 1 and 2 (P<0.05). There was no statistically significant difference between Groups 1 and 2. Mixing of Fuji Plus required an activator/delivery gun and mechanical triturator while RelyX Luting Plus was mixed as a paste/paste. UltraCem RRGI Luting Cement comes in a self-contained mix/delivery system and requires no spatula, mixing pad or mechanical trituration. Conclusions: UltraCem RRGI Luting Cement demonstrated high retentive values while novel mixing and the delivery of the cement was easy and user-friendly.