Variatied Placement Procedures of Composite Resins on Dentin Bond Strengths

Objectives: To compare the bond strengths of various bonding agents used in dental schools and to assess whether the variation in placement of composite resin affects bond strength.

Methods: Prime and Bond NT and PQ1 bonding agents were used in two different samples to bond composite Z250.  Similar amount of pressure were utilized to test the effects bonding. Extracted molars were mounted in acrylic resin and sectioned with a diamond saw above the CEJ, perpendicular to the long axis of the tooth for dentin bonding. After testing the two bonding agents, the Instron was used to measure the manual pressures of the bonding agent.  It was found that light pressure (1MPa) and high pressure (3MPa) were satisfactory for testing.  The varying pressures were used with TPH³ composite and Prime and Bond NT.  The incremental placement technique was used for both groups as two layers of composite were used for each (0.5mm followed by 1.5mm).  Composite TPH³ cylinders were formed 2mm high in an Ultradent bonding mold. The cylinders were bonded to the cut dentin with 20 sec of visible light cure. The Bonds matured in 37^oC water for 24 hours. An Instron machine applied a shear force parallel to the bond interface. The bonds were tested at crosshead speed of 0.02”/minute until failure. Strengths were measured in Mega Pascal (MPa).

Results: When comparing the bond strength of PQ1 to Prime and Bond NT, no significant differences were noted after 24hrs. 

Conclusions: After evaluating the bond strengths of composites placed using a low pressure placement technique versus a high pressure placement technique, no significant differences were noted.  Further tests will be done to elucidate the optimal reference values for material placement.