New method for the in vitro evaluation of dental alloy bonding systems

Bonding systems are used in some fixed prosthetic devices with base alloys. However, different studies of the same dental alloy bonding agents, under similar circumstances, have yielded disparate results in bond strength testing.

This study compared directly 2 dental alloy bonding systems through a "duel" type of confrontation, which basically is a 2-way tensile force test.

Ninety Wiron 88 base alloy cylinders (diameter of 8 mm length 15 mm) were sandblasted on both sides with Al(2)0(3) powder (particle size 50 microm) during 10 seconds at an approximate distance of 5 mm, at an air pressure of 60 psi determined before sandblasting procedures. The surface of each cylinder was cleaned from Al(2)0(3) powder with a strong burst of oil-free air from a chairside air syringe. Thirty cylinders were randomly assigned to 1 of 3 groups for direct bond strength comparison: (1) Panavia 21 to Panavia EX, (2) Panavia 21 to Metabond, or (3) Panavia 21 to a combination of a resin bonding agent plus Panavia 21. Each group was composed of 10 specimens that used 3 cylinders for each specimen. Each side of the sample cylinder received the same quantity of cement and 1 cylinder at a time was bonded to it. Cylinder alignment was verified with a Boley gauge during luting procedures. The bonded 3-piece block was held together for 24 hours under a compressive force of 2 kg/cm(2) using a hydraulic press. Excess cement was removed with a brush, and the pertinent air sealant was applied to allow for autocuring of the cement. Specimens were later stored in water at room temperature for 48 hours before thermocycling procedures. Each specimen was thermocycled for 100 cycles with a 5-minute dwelling time in water at 4 degrees C and 60 degrees C. Specimens were subject to tensile force testing until debonding in 1 of the cylinders.

The opposing pull duel test (OPDT) showed that the Panavia EX failed (40. 3 MPa) 10 of 10 duels against Panavia 21, whereas Panavia 21 failed (49.7 MPa) 9 of 10 duels against Metabond, and Panavia 1 failed (50. 1 MPa) 10 of 10 duels against Photobond+Panavia 21. ANOVA revealed significant differences (P <.05) between PAN-EX group and MET and PHB+P21 groups. However, no significant differences were found between MET and PHB+P21 groups.

The opposing pull duel test was a valid method to directly compare bond strengths of 2 bonding systems to dental base alloys. There was a small dispersion of the values even though cement mixing and thickness variables were difficult to control. Duel tensile testing provides meaningful information on the superiority of one bonding system over another in this controlled environment.