A New Method of Evaluation of Fracture Patterns Following Microtensile Bond Strength Testing Using Polarized Light Microscopy

Purpose: This work describes a new method using polarized light microscopy to determine the failure modes of fractured beams following microtensile bond strength testing. The outcomes were validated using SEM and EDX elemental analysis. Materials and Methods: Resin adhesives and resin composites bonded to caries-free dentin samples as well as disks of adhesive and composite were observed with reflected polarized light microscopy (PLM) to obtain standard images. A set of beams fractured in the microtensile bond test were observed with PLM and compared with the standard images to determine failure mode through PLM color matching with the standard dentin, adhesive, or composite images. Samples were analyzed by EDX under SEM and compared with the PLM outcomes. Results: Reflected PLM images showed that the fractured surfaces covered with resin-based materials (adhesives or composite) appeared pink in color, in contrast to dentin surfaces, which appeared yellow. EDX mapping together with SEM observation confirmed the results obtained by PLM. Conclusion: The results of EDX mapping and SEM observation showed that the use of polarized light microscopy is a simple, viable method for differentiation between the resin-covered dentin surfaces for determining fracture pattern analysis after bond testing. Keywords: polarized light microscope, microtensile bond strength, fracture patterns, EDX