Internal Adaptation of Cusp-weakened Class I Preparations Restored with Bulk-fill, Bi-layered, and Incremental Restorative Techniques: A Micro-CT Analysis

Objective: The aim was to evaluate the internal adaptation of composite restorations in cusp -weakened Class I preparations restored by incremental, bi-layered, and bulk-fill techniques using a microcomputed tomography analysis (micro-CT). Methods: Sixty sound extracted human third molars were prepared with standardized cusp -weakened Class I cavity preparations and divided into six groups (n=10). Two groups were restored using an incremental oblique technique with a nanofilled (Filtek Supreme XT, 3M Oral Care, St Paul, MN, USA) and a nanohybrid composite (GrandioSO, VOCO, Cuxhaven, Germany). The other two groups were restored using a bi-layered technique with a bulk-fill flowable composite base (Filtek Bulk Fill Flowable, 3M Oral Care; X-tra Base bulk-fill flowable, VOCO) covered with the conventional composite of the same type. In the remaining groups, teeth were restored with a single-increment technique using bulk-fill full -body composites (Filtek Bulk Fill Posterior, 3M Oral Care; Admira Fusion, VOCO). All teeth were subjected to thermocycling (20,000 cycles, 5 degrees C and 55 degrees C) and mechanical loading (250,000 cycles, 2.5 Hz, 50 N) before analysis of internal adaptation by micro-CT. One-way analysis of variance (ANOVA) and the Games-Howell test were used to analyze the percentage and volume of internal gaps (p<0.05). Results: There was found to be significantly higher internal adaptation for the nanofilled composite used incrementally or associated with a flowable base compared with the nanohybrid composite used incrementally (p=0.002). Conclusions: Bulk-fill and bi-layered techniques performed similarly in terms of internal adaptation for both types of composites. The incremental technique with the nanofilled composite demonstrated a higher internal adaptation than with the nanohybrid composite.