Retention of e.Max and Celtra Duo Copings With Resin Cement

Objectives: To evaluate the effect of light curing an adhesive on tooth structure prior to the use of a resin cement on the retention of e.max and Celtra Duo copings
Methods: 40 sound premolars were collected and prepared using a standard cutting machine (Lathe with water spray) to obtain a 22 degree taper and 4 mm of height. Preparations were scanned and crowns were designed with 2 handles used for debonding (Cerec 3). Crowns were milled from Celtra Duo LT A3 (n=20; G1 and G2) or e.Max CAD HT A3 (n=20; G3 and G4). Prior to bonding, crowns were etched with 5% HF for 20s, rinsed and ultrasonically cleaned. Silane was applied for 60s and dried and an experimental adhesive. applied For half of the specimens (G1 and G3), the adhesive was light cured for 20s with an LED curing light (output>100mW/cm2). Crowns were filled with an experimental dual cured resin cement and seated under a 2500g load for 6min. In G2 and G4, crowns were light cured 20s on occlusal, buccal and lingual surfaces. Specimens were thermocycled for 10,000 cycles ( 5-55⁰C, 15s dwell time). Crown retention force was measured using a universal testing machine and testing with a crosshead speed of 1mm/min. Crown retention strength (maximum load/area of preparation) was analyzed using 2-way ANOVA for factors ceramic material and curing mode (α=0.05)
Results: Strength values were (mean±SD): 7.59±3.09 (G1), 3.65±0.89 (G2), 5.28±1.89 (G3), and 4.07±1.77 (G4). Factors curing mode and the material*curing mode interaction were significant (p<.01). Curing the adhesive produced a statistically significant greater strength when using Celtra Duo crowns but not e.Max crowns
Conclusions: Light curing the adhesive under the resin cement when cementing Celtra Duo crowns produced significantly greater retention strength