Objective: The aim of this scoping review was to analyze the available evidence on the preheating process and its effects on physicochemical properties of composite resins. Materials and Methods:A systematic search was performed in August 2021 using PubMed/Medline, Embase, Scopus, and ISI Web of Science databases and gray literature without language or date restriction. Inclusion criteria were in vitro studies that assessed the physicochemical properties and marginal adaptation of preheated composite. Exclusion criteria were studies with experimental composite, literature reviews, clinical studies. Data from selected studies were qualitatively analyzed.Results: In total, 104 studies were found from which 39 were included. The most used composite resin was Filtek Z350 XT (3 M/ESPE), preheated at 68 C in a Calset device (AdDent Inc., Danbury, CT, USA) for 5 or 15 min. Most studies showed decreased viscosity, increased conversion degree and microhardness of composite resins, and better marginal adaptation of direct and indirect restorations. Also, flexural strength was not affected, and data about bond strength were inconclusive due to heterogeneity among studies. Conclusion:The parameters used for preheating composite resins are heterogeneous. Preheating decreased viscosity, increased the conversion degree and microhardness of composite resins, and improved the marginal adaptation of direct and indirect restorations.Clinical Significance: The analysis of evidence showed a high heterogeneity among preheating protocols. Preheating may benefit the handling and physicochemical properties of composite resins.