Abstract
The continuous need for simplified, minimally invasive restorative procedures with a high precision has led to the advancement of highly filled flowable resin-based materials. These materials present excellent initial outcomes in various clinical applications, including the injection molding technique. Given that several clinical reports present signs of wear and staining, this systematic review aims to investigate the mechanical and optical properties of highly filled flowable composite resins. A comprehensive literature research was conducted to identify relevant studies from the PubMed, the Cochrane Library, and Scopus databases. Data extraction and screening was performed by two independent evaluators. Both in vitro studies and clinical trials were included. A total of thirty-one studies were included in this review. A total of 27 in vitro studies investigated highly filled flowable composite resins independently, or in comparison with conventional composite resins, traditional flowable composites, bulk-fill flowable composites, glass ionomer cements, and compomers. Additionally, four randomized controlled clinical trials (RCTs) compared highly filled flowable composite resins with their conventional counterparts. Highly filled flowable composite resins exhibit adequate optical properties. Despite their significant improvements, their mechanical properties remain inferior to those of medium-viscosity composite resins. These materials demonstrate a favorable initial performance in the injection molding technique. Based on a limited number of RCTs, these materials demonstrate an adequate performance in class I and II restorations; however these findings should be interpreted with caution. The reported drawbacks in laboratory studies may contraindicate their clinical application in extensive cavities, load-bearing areas, and in cases of excessive tooth wear and parafunctional activity. A careful clinical case selection is strongly recommended.