In Vitro Shear Bond Strength of Nobel Rondo Pressed Ceramics

Objective: The long-term survival of bonded ceramic restorations for posterior teeth is a clinical concern. This study aimed to evaluate the effect of bonding quality on the interface failure initiation loads of 2 all-ceramic materials with 2 resin cements.

Method: Nobel Rondo pressed ceramic zirconia (Group 1) and alumina (Group 2) were used to form disks 8mm in diameter by 4mm in thickness (n=80). The ceramic specimens were fabricated in a manner that simulated their clinical application. The ceramic specimens were fabricated using a wax pattern and attaching it to a wax spool, poured into a silicone ring and then transferred to a burnout furnace. The pressed porcelain discs were wet ground to ensure flat parallel surfaces. Each pressed ceramic material was further divided in two subgroups (n=20) that were determined by the type of resin cement used (Panavia(A) and Rely-X(B)). All luted specimens were thermo-cycled for 500 cycles between 5ºc and 55ºc with a 30-second dwell time prior to performing the shear bond strength test. The shear bond strengths of the specimens were determined using a universal testing machine at a cross-head speed of 0.5 mm/min., using a knife-edge shearing rod. The nominal bond strengths in Newton were determined by dividing the force at which bond failure occurred by the theoretical bonding area. An unpaired t-test was performed to determine the difference between groups.

Results: The characteristic fracture initiation loads ranged from 17.17 to 159.37 N. Group 1B (Zirconia and Rely-X) had the greatest mean observed load to fracture (109.37), which was significantly greater than all the other groups (P<.001).

Conclusions: These results suggest clinical use of the Nobel Rondo pressed zirconia and alumina with resin cements provide acceptable bond strengths.

Supported by NobelBiocare/University of Michigan Center for Excellence