In vitro comparison of the accuracy (trueness and precision) of six extraoral dental scanners with different scanning technologies

Statement of problem. The fabrication of prosthetic restorations using computer-aided design and computer-aided manufacturing (CAD-CAM) procedures depends on scanning surfaces. However, limited information is available regarding the effect of extraoral scanning systems on the accuracy of the fabrication process. Purpose. The purpose of this in vitro study was to evaluate and compare the accuracy (trueness and precision) and resolution of 6 CAD-CAM extraoral scanners by comparing features and scan technology. Material and methods. A master die was fabricated to simulate a dental preparation. The die was measured with a coordinate measuring machine (CMM) to obtain an accurate digital CAD reference model (CRM). The master die was then scanned 10 times with 3 structured light scanners, 2 laser scanners, and 1 contact scanner. The resulting laboratory scan data (LSD) were converted to a stereolithography (STL) format. The discrepancies between measurements were compared 3 dimensionally and at 3 selected areas of a virtual sagittal cut using CAD software. The Kruskal Wallis 1-way analysis of variance was first performed to compare scanners and then to group data according to scanner type. The Spearman rank correlation coefficient was used to test the association between resolution and all other variables (alpha=.05). Results. For all 6 scanners, the mean resolution value was 133.9 (SD 93.9) points/mm(2). The value for trueness was 38.8 (SD 6.2) mu m and for precision 45.5 (SD 4.8) mu m. Trueness values were 20.3 mu m (SD 32.7) at the axial surfaces, 46.6 mu m (SD 25.9) at the margin of the preparation, and 55.8 mu m (SD 29.3) at the center of the occlusal groove. The ZENO Scan was the most accurate and precise of the 6 scanners for most of the variables measured. Conclusions. The reliability of CAD-CAM scanners is not affected by a specific technology (light, laser, or contact) but by definite parameters. In addition, the entire scanning procedure is more accurate if the scanned surfaces are smooth and regular.