Tensile bond strengths of five luting agents to two CAD-CAM restorative materials and enamel

Statement of problem. CAD-CAM restorative materials arc popular because they have high esthetic value and short fabrication time. Unfortunately these materials are brittle and tend to fracture under heavy occlusal load. Purpose. The purpose of this in vitro study was to investigate the tensile bond strengths of 5 luting agents to 2 CAD-CAM restorative materials and enamel. Material and methods. One hundred truncated cones, with a 3-mm diameter bonding surface and 5-mm diameter base, were fabricated with Dicor MGC (n=50) or Cerec Vitablocs Mark II (n=50) with the Cercc system. Enamel surfaces of the crowns of 100 freshly extracted noncarious, anterior teeth, stored in 0.9% saline solution with 0.25% sodium azide (NaN3) as disinfectant, were prepared with sandpaper disks (320-grit size) on the Buehler Variable Speed Grinder-Polisher. The bonding surfaces of the Dicor MGC or Cercc Vitablocs Mark II truncated cones from each of the 2 tests systems were airborne particle abraded, chemically etched, and cemented on the prepared enamel surface of the tooth specimens with 5 luting agents: Vita Cerec Duo Cement, EnForce, Panavia 21, C&B Metabond, and Fuji Duct. All specimens were thermocycled 1000 times, in 5degrees C and 55degreesC water with a dwell time of 30 seconds in each temperature. Tensile force (MPa) was applied perpendicular to the bonding surfaces of the specimens with a universal testing machine until fracture. Fracture patterns were examined with a microscope at original magnification x 10. The differences in the tensile bond strengths were analyzed with the Tukey-Kramer test (alpha=.05). Results. The mean tensile bond strengths of Dicor MGC bonding to enamel with luting agents in descending order in MPa were EnForce (10.12 +/- 2.25), Panavia 21 (7.28 +/- 1.77), Cerec Duo (5.32 +/- 1.65), Fuji Duet (3.73 +/- 1.78), and C&B Metabond (3.11 +/- 1.11). EnForce had a significantly higher bond strength than C&B Metabond, Fuji Duet, Cerec Duo, and Panavia 21 (P=.05). The mean tensile bond strengths of Cerec Vitablocs Mark I I bonding to enamel with luting agents in descending order in MPa were as follow: Fuji Duet (11.51 +/- 2.79), EnForce (9.44 +/- 2.03), C&B Metabond (8.98 +/- 3.29), Cerec Duo (8.66 +/- 4.71), and Panavia 21 (5.10 +/- 2.49). Within this group, there was no significant difference between Fuji Duet and EnForce, but the bond strength of Fuji Duet was significantly higher than that of C&B Metabond, Panavia 21, and Cerec Duo (P=.05). The mean tensile strength of all the luting agents bonded to Cerec Vitablocs Mark II and enamel (8.74 MPa) was higher than Dicor MGC and enamel (5.91 MPa). Conclusion. In this in vitro study; within the Dicor MGC group, the mean bond strength of Panavia 21 with enamel was significantly higher than C&B Metabond, Panavia 21, Cerec Duo, and Fuji Duet. Within the Cercc Vitablocs Mark II group, the mean bond strength of Fuji Duet was significantly higher than C&B Metabond, Panavia 21, and Cerec Duo but was not significantly higher than EnForce.