Effects of Glass Fiber Layering on the Flexural Strength of Microfill and Hybrid Composites

ABSTRACT Statement of the Problem: In stress‐bearing cavities, low fracture resistance adversely affects the longevity of the dental resin composite restorations. Purpose: The aim of this in vitro study was to investigate the effect of glass fiber layering on the flexural strength of microfill and hybrid composites. Materials and Methods: Flexural test specimens (N = 75) were prepared according to International Organization for Standardization (ISO) 4049 specifications (25 × 2 × 2 mm) by using a standard metallic mold. Materials used and groups were as follows (N = 15): group 1: hybrid composite (Clearfil APX, Kuraray Co.Ltd, Osaka, Japan); group 2: microfill composite (Clearfil ST, Kuraray Co.Ltd.); group 3: hybrid + microfill composite; group 4: woven glass fiber (EverstickNet, StickTech Ltd, Turku, Finland) + hybrid composite; group 5: woven glass fiber + microfill composite. The specimens were stored in distilled water at 37°C for 7 days. Afterward, they were loaded to fracture (1 mm/min) by using a universal testing machine (AG‐50 kNG Shimadzu Co., Kyoto, Japan). Flexural strengths were expressed as maximum flexural load per cross‐sectional area of the specimen. The results were statistically analyzed with Kruskall–Wallis and Mann–Whitney U tests (p