Artificial landmarks and areas’ accuracy gradient: a three-dimensional analysis of trueness and precision of IOS scans on the total edentulous maxilla

To assessing the areas’ accuracy gradient of the intraoral scanner (IOS) scans on a completely edentulous maxilla and the effectiveness of artificial landmarks. A completely edentulous maxillary typodont (MT) was scanned with an industrial metrological machine to obtain a reference scan in .stl format. Ten scans were made on MT with an IOS, subsequently superimposed to detect the areas’ accuracy gradient on MT scans. Artificial landmarks of 1-mm diameter were placed in the less accurate areas following two methods. In the first, flow-composite semispherical markers were used. In the second, circular markers were drawn with a dermographic pen. Three experimental groups were made (n=10): “No-Markers” for the control group (without markers), “Embossed-markers” for flow-composite markers, and “Flat-Markers” for ink-drawn ones. The scans were imported into a dedicated software, then trueness and precision were evaluated in µm. In addition to descriptive statistics (95% CI), the Games-Howell and Kruskal-Wallis tests were run to analyze the difference among groups (α=.05). Mean values for trueness were No-Markers=48.8 (39.2-58.3); Embossed-Markers=39.2 (37.5-40.8); Flat-Markers=60.5 (47.7-73.4), with statistically significant differences for Embossed-Markers/Flat-Markers (P=.011). Mean values for precision were No-Markers=46.7 (29.7-63.7); Embossed-Markers=41.4 (34.7-48); Flat-Markers=99.8 (69.3-130.3), with significant differences for Embossed-Markers/Flat-Markers (P=0.008) and No-Markers/Flat-Markers (P=0.005). The most inaccurate areas were tuberosities, palate, and ridges’ flattened areas. To increase the IOS scans accuracy on the completely edentulous maxilla, it is suggested to place embossed flow-composite markers specifically in the areas of greatest inaccuracy, but to avoid using flat markers.