Improved dental adhesives for bonding to the dentin of teeth have been introduced that may have the potential of bonding to bone. The properties of these materials have not been characterized. The purpose of this study was to measure the mechanical properties of three of these adhesive resins, Universal Bond II (UB2), Scotchbond II (SB2), and Tenure (Ten). These measurements were used to determine if the bond strengths approached the cohesive strengths of the materials and for finite element evaluation of polymerization shrinkage bond stress. Thin resin films (130 ± 5 μm) were cast and cured between microscope slides. The films (N=6) were tested using an Instron tensile test at 2.5 mm/min and a Rheometric Solids Analyzer (1 Hz) after 24 hours in air. The breaking strength and maximum strain of TEN, SB2, and UB2 were 19.0 ±2.8, 17.4 ± 3.7, 10.7 ± 1.0 MPa, and 8%, 6%, and 32%, respectively. The strength of UB2 was significantly different at P < 0.05. Rheometric analysis gave the dynamic (1 Hz) and static elastic modulus, tandmax, and Tg for TEN, SB2, and UB2 as follows: 1100, 1000, 600 MPa; 620, 530, 370 MPa; 0.20, 0.67, 0.21; and 75°C, 79°C, 84°C, respectively. The measurements were the first reported for properties of these materials.
The use of the measured mechanical properties in the finite element models to calculate the interfacial stress of bonded composite restoration demonstrated that the maximum shrinkage stresses were reduced below the bond strengths by using thick resin bonded films of 125 μm to allow stress relaxation. The finite element models indicated that variations in the maximum shrinkage stress and its location occurred depending on the curing conditions. These finite element analyses were the first models of curing shrinkage applied to dental bonding.