Crown retention of Celtra Duo crowns

Objectives: To evaluate crown retention strength of Celtra Duo crowns following different bonding techniques.
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 e.max (n=10) or Celtra Duo (n=40). The e.max crowns were sintered, the Celtra Duo crowns were polished, and all crowns were etched with hydrofluoric acid. The reference e.max crowns were cemented with RelyX Ultimate cement and Scotchbond Universal adhesive. The Celtra Duo crowns and the tooth preparations received a coat of Prime and Bond Elect. The crowns were then cemented with an experimental resin cement and either light cured for 5,10, or 15 seconds or self-cured 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 (see table).
Conclusions: Additional light curing of the resin cement through the Celtra Duo crowns improved crown retention strength.