Purpose: To assess the accuracy of three impression techniques for different span lengths of missing maxillary teeth.

Materials and methods: Three typodonts were divided into three groups simulating different span length zirconia bridges. Group S: 3-unit-posterior bridge, Group L: 4-unit-posterior bridge and Group A: 6-unit-anterior bridge. Reference standard tessellation language (STL) files were obtained by scanning the typodonts using the desktop scanner inEos X5. Each group was subdivided into three subgroups according to the impression technique used. Subgroup C: conventional PVS impression. Subgroup I: intraoral scanner (Primescan). Subgroup E: extraoral scanner (Medit t300). 15 impressions were taken per group, five per subgroup (n=5). All datasets were obtained in STL format and the conventional impressions were poured with type IV dental stone and digitized using the extraoral reference scanner. Accuracy of the different impression techniques were evaluated via a reverse engineering 3D software for deviation analysis.

Results: A statistically significant difference was found between the 3 different span lengths (P≤ 0.05). Primescan showed the lowest trueness values (39.2±1.82µm); (45.7±0.935µm); (77.8±1.73µm) followed by PVS (42.9±0.31µm); (53.8±3.75µm): (74.3±12.4µm) and Medit t300 (78.7±1.21µm); (80.3±1.04µm); (94.9±0.74µm). However, Medit t300 showed the lowest precision values (50.1±10.74µm); (59.64±7.0µm) and (64.39±3.55µm) followed by Primescan (66.8±9.27µm); (73.9±8.45µm) and (92.1±8.30µm) and PVS (78.3±5.38µm); (81.7±8.28µm) and (117.5±8.44µm) for the 3-unit-posterior, 4-unit-posterior and 6-unit-anterior bridges respectively.

Conclusion: Primescan showed the highest trueness, while Medit t300 showed the highest precision. Increasing the span length reduced the trueness and precision of the tested impression techniques; however, their values were within the acceptable clinical range.