3-DIMENSIONAL FINITE-ELEMENT ANALYSIS OF THE SHEAR BOND TEST

Objectives. The purpose of this study was to use finite element analys es to model the planar shear bond test and to evaluate the effects of modulus values, bonding agent thickness, and loading conditions on the stress distribution in the dentin adjacent to the bonding agent-denti n interface. Methods. All calculations were performed with the ANSYS f inite element program. The planar shear bond test was modeled as a cyl inder of resin-based composite bonded to a cylindrical dentin substrat e. The effects of material, geometry and loading variables were determ ined primarily by use of a three-dimensional structural element. Sever al runs were also made using an axisymmetric element with harmonic loa ding and a plane strain element to determine whether two-dimensional a nalyses yield valid results. Results. Stress calculations using three- dimensional finite element analyses confirmed the presence of large st ress concentration effects for all stress components at the bonding ag ent-dentin interface near the application of the load. The maximum ver tical shear stress generally occurs approximately 0.3 mm below the loa ding site and then decreases sharply in all directions. The stresses r each relatively uniform conditions within about 0.5 mm of the loading site and then increase again as the lower region of the interface is a pproached. Calculations using Various loading conditions indicated tha t a wire-loop method of loading leads to smaller stress concentration effects, but a shear bond strength determined by dividing a failure lo ad by the cross-sectional area grossly underestimates the true interfa cial bond strength. Significance. Most dental researchers are using te nsile and shear bond tests to predict the effects of process and mater ial variables on the clinical performance of bonding systems but no ev idence has yet shown that bond strength is relevant to clinical perfor mance. A critical factor in assessing the usefulness of bond tests is a thorough understanding of the stress states that cause failure in th e bond test and then to assess whether these stress states also exist in the clinical situation. Finite element analyses can help to answer this question but much additional work is needed to identify the failu re modes in service and to relate these failures to particular loading conditions. The present study represents only a first step in underst anding the stress states in the planar shear bond test.