FRACTURE-TOUGHNESS AND LOAD RELAXATION OF DENTIN BONDING RESIN SYSTEMS

Objectives. The fracture toughness (K-IC) and load relaxation of four dentin bonding resins were determined to characterize some of the mech anical properties of these materials after polymerization. Methods. A total of 40 single-edge notch bar specimens were fabricated, 10 each o f four commercially available brands, and subjected to three-point ben ding until fracture, as described in ASTM Standard E399-83 (1991a). Th e critical stress intensification factor, K-IC, was derived for each s pecimen and compared by analysis of variance and Scheffe's multiple co mparisons test (p < 0.01). To study the load relaxation characteristic s, five rectangular specimens (without notches) of each brand were sub jected to three-point loading until a predetermined limiting load valu e was reached. The test load was allowed to relax for 4 min, after whi ch the specimen was unloaded to the zero load condition, and the load was allowed to build up on its own accord for 3 min. Load relaxation v alues were measured from the chart, and the mean percent load drop was calculated. The load relaxation data were compared using analysis of variance and Scheffe's multiple comparisons test (p < 0.05). Results. The fracture toughness (K-IC) values of the four adhesive resins studi ed in this investigation ranged from 0.37 - 0.94 MPa.m(0.5) and were s tatistically different from each other (p<0.001). The load relaxation values were found to be greatest within the first 0.5 min, with the to tal load relaxation of the four bonding agents ranging from 16% - 30%. Two of the materials studied showed significantly different short-ter m load relaxation behavior than the other two resins (p < 0.05). Signi ficance. Bonding agents can be implicated as one of the factors that w eaken the interface between the dentin and the composite restorative m aterial. These materials are capable of a rapid short-term response, d emonstrating significant load relaxation in the first 0.5 min after lo ading.