Objective The objective of this study was to review the experimental staining procedures performed in in‐vitro studies for evaluating color stability of resin‐based composites used for direct restorations. Overview A review was performed with the purpose to identify in vitro procedures carried out to establish staining and color stability of resin‐based composites used for direct restorations. A literature search was performed on four online databases (PubMed, Scopus, Embase and Web of Science) for articles published from January 1st 2001 till March 20th 2021, using a combination of free words and Medical Subject Headings (MESH) terms: “Composite Resins” AND “Color Stability” OR “Staining.” Two reviewers screened titles and/or abstracts of 1728 unique studies. In total, 208 studies were selected for full‐text reading, from which 178 were included in the review. The assessed variables were specimen dimensions, shape, and surface finishing; time before immersion; staining media type, dwell time, temperature and renewal interval; type of composite; color and translucency assessment parameters and measuring system. One hundred and seventy‐eight articles analyzed color stability with staining liquids. Coffee was the most used staining medium (n = 102), followed by tea (n = 61), and red wine (n = 55). A disc‐shaped specimen was used in most studies (n = 170) with a 2 mm thickness (n = 116). Spectrophotometers were the most used color assessment devices (n = 154), followed by colorimeters (n = 17). Color differences were quantified with ΔE (n = 154), ΔE00 (n = 23). Acceptability and or perceptibility thresholds were also taken into consideration (n = 126). Conclusions The large variety of staining procedure suggests the need for standardization. Clinical Significance Aesthetic failure due to discoloration is a relevant clinical problem. Evaluating benefits and drawbacks of resin based composites artificial staining procedures will improve to predict materials clinical performances.

Background: This systematic review aims to evaluate the color stability of resin composite CAD/CAM blocks (CCB) when submitted to staining solutions. Methods: A systematic search was performed on different databases (Embase, Medline, Scopus, Web of Science). Search terms were: ‘polymer infiltrated’, ‘polymer-based’, ‘resin nanoceramic’, ‘resin ceramic’, ‘hybrid composite’, ‘hybrid ceramic’, ‘composite ceramic’, ‘resin infiltrated’, ‘CAD-CAM’, ‘CAD/CAM’, ‘color stability’, ‘staining’, ‘staining susceptibility’, ‘color change’, ‘color difference’. Inclusion criteria: in vitro articles published in the English language until 18 September 2022 without initial time restriction evaluating the color stability of CCB when submitted to staining solutions. Exclusion criteria: studies investigating color change induced by smoke or whitening treatments; studies not including a clinical evaluation of the results using the thresholds for color perceptibility and acceptability. Risk of bias assessment using the QUIN tool. Findings: Out of the 378 initially retrieved articles, 19 were included in this review. They investigated 17 different CCBs and different artificial staining by liquid protocols, including coffee, red wine, tea, and cola. CCBs exceeded clinical acceptability thresholds for color shift in 18 out of 19 studies, with a significantly higher color stability than conventional hybrid resin-based composites (RBCs), and a significantly lower color stability than ceramic materials. The identified differences in CCBs in color stability can be attributed to the material’s composition, but also to the heterogeneity of staining procedures. Interpretation and clinical implication: Clinicians should be aware that, although to a lower degree when compared to RBCs used in direct or indirect procedures, CCBs undergo color changes to a higher degree in comparison to ceramic materials.