Fatigue behavior of dental resin composites: Flexural fatigue in vitro versus 6 years in vivo

OBJECTIVES: To evaluate fatigue behavior of direct resin composite restorations (Tetric Ceram vs. Grandio) in vitro and in vivo over an observation period of 6 years. METHODS: For the in vitro part, Young's moduli (YM) were calculated and both initial (FS: flexural strength) and fatigue flexural strength (FFL: flexural fatigue limit) were evaluated in a four-point bending setup (n = 15) in distilled water at 37°C. For the in vivo part, 30 patients received 68 direct resin composite restorations of the same materials (Grandio bonded with Solobond M; Tetric Ceram bonded with Syntac). Patients revealed a minimum of two different class II restorations in different quadrants. Epoxy replicas of restored teeth were analyzed under a scanning electron microscope (SEM) at 30× magnification for fatigue characteristics, and 11 selected restorations per group were assessed for marginal fatigue characteristics at 200×. RESULTS: In vitro, YM was 15.7 GPa (Grandio) and 8.7 GPa (Tetric Ceram; p < 0.05), FS was 115.0 MPa (Grandio) versus 101.5 MPa (Tetric Ceram; p > 0.05), and FFL was 63.0 MPa (Grandio) versus 44.3 MPa (Tetric Ceram; p < 0.05). In vivo, no significant difference in fatigue behavior (cracks, chippings) was evaluated for the different materials under investigation. However, marginal breakdown was more pronounced under the SEM for Tetric Ceram (7.9% vs. 4.8% for Grandio; p < 0.05), but without being clinically relevant. SEM analysis exhibited distinct wear patterns after 6 years with no significant differences among materials as well. SIGNIFICANCES: Despite higher in vitro values for YM, FS, and FFL for Grandio, clinical outcome for both resin composite materials over 6 years of clinical service was similar. Higher FFLs in vitro seem to be related to less marginal composite fractures in vivo but without any influence on clinical outcome until the 6 years recall.