Acoustic emission analysis of fiber-reinforced composite in flexural testing

Objectives. The aim of this study was to examine the emission of acoustic signals from six commercially available fiber-reinforced composites (FRC) used in the frameworks of fixed partial dentures in material bending. Methods. FRC test specimens were made of six commercially available fiber products of polyethylene or glass and five light-curing resins. FRC test specimens were polymerized with a hand light-curing unit or with a light-curing oven. The flexural test for determination of ultimate flexural strength of test specimens (n=6) was based on the ISO 10477 standard after the specimens were stored in air or in water for two weeks. The acoustic emission (AE) signals were monitored during three-point loading test of the test specimens using a test with increasing loading levels until the specimens fractured. Results. Generally, stress level required for the AE activity initiation ranged from 107 MPa (Ribbond) to 579 MPa (everStick). The ultimate flexural strength of FRC specimens were higher, ranging from 132 to 764 MPa, being highest with everStick and Vectris FRC, and lowest with Ribbond FRC. ANOVA showed a statistically significant difference between the initiation of AE activity and the ultimate flexural strength according to the brand (p<0.001), storing conditions (p<0.001) and polymerization procedure (p<0.001). AE activity and ultimate flexural strength correlated significantly (p<0.010,r=0.887). Significance. The result of this study suggested that AE activity in FRC specimens started at a 19–32% lower stress level than occurred at final fracture.