Comparison of Direct and Indirect Scanners in Digital Impression Systems: A Narrative Review

Introduction: Digital impression tools are an alternative to old impression materials and have developed significantly in recent years. These systems generally include two types of scanners: direct and indirect scanners. This article aimed to review and compare these two types of scanners. Description: Data were collected by reviewing a total of forty articles on dimensional accuracy, a combination of scans, and internal and marginal gaps for comparison of direct and indirect scanners. These articles were retrieved from PubMed and Scopus and published between 2010 and 2020 using the following keywords: intraoral scanner, lab scanner, marginal gap, internal gap, and accuracy rate. Results: Direct scanners had a lower amount of marginal and internal gaps, while indirect scanners had a lower deviation in more prepared teeth in the half and full arch due to the ability of stitching scans. Regarding the dimensional accuracy, the results of studies were inconsistent, but clinical studies pointed to the superiority of indirect scanners. The type of scanner suggested being selected depending on conditions such as the size of area, time, convenience of procedure, etc. The clinical results of both types of scanners were clinically acceptable.