Deep‐layer integrity in bulk restorations: Effects of placement technique on fiber‐ and particulate‐reinforced bulk‐fill composites properties

Abstract

This study investigated the influence of bulk‐fill versus incremental placement techniques on the mechanical properties of the bottom layer of fiber‐ and particulate‐reinforced bulk‐fill resin composites following long‐term water storage. Five materials were evaluated: a conventional composite, a high‐viscosity bulk‐fill, a fiber‐reinforced flowable bulk‐fill, and two particulate‐reinforced flowable bulk‐fills. Specimens were prepared using a custom mold to simulate clinically relevant placement techniques, either incremental or bulk‐fill techniques. Specimens stored in distilled water for either 24 h or 30 d. The incremental technique produced similar flexural strength between top and bottom layers, whereas the bulk‐fill technique showed higher top‐layer strength, except for the fiber‐reinforced composite, which maintained comparable performance across layers and conditions. Long‐term storage reduced differences among bulk‐fill materials. Hardness was generally higher in packable composites, with the fiber‐reinforced material outperforming other flowable types. Extended water storage only reduced the hardness of the conventional composite. The fiber‐reinforced bulk‐fill composite exhibited stable and superior mechanical performance under all conditions, whereas particulate packable composites remained the strongest overall. Incremental placement improved deep‐layer properties in particulate bulk‐fill composites.