In vivo deviation of residual ridge between digital and conventional impressions in the partially edentulous maxilla: a pilot study

Purpose This in vivo study aims to investigate the deviation of the residual ridge between digital and conventional impressions in the partially edentulous maxilla. Methods Forty-four patients (22 female, 22 male; 64.8 ± 6.6 years) with partially edentulous maxillae were included in the study. Digital impressions were obtained using an intraoral scanner (TRIOS 3, 3Shape). Conventional impressions were taken with a selective pressure impression technique using the custom tray and a silicone rubber impression material. These impressions were poured with type 4 gypsum. Models were scanned using a desktop scanner (DS-EX Pro C, Shining 3D Dental). The dimensional differences between the digital and conventional impression scans were calculated and defined as the total deviation by the Geomagic Control X software. The vertical displacement at the incisive papilla, mesial, center, and distal points of each residual ridge were measured between the digital and conventional impression scans and defined as the deviations at Point P, Point M, Point C, and Point D, respectively. The residual ridges were divided into distal extension and non-distal extension. Results The total deviation and deviation at Point P between the two scans was 0.0 08 mm and 0.0 69 mm, respectively. The total deviation and deviation at Point P exhibit ed no significant difference among patients. For the residual ridge of non-distal extension, the deviations showed no significant difference at Point M, Point C, or Point D (0.032 mm, 0.044 mm, and 0.034 mm, respectively). For the distal extension, the deviations at Point D and Point C (0.136 mm and 0.082 mm, respectively) were significantly greater than that at Point M (0.027 mm) and significantly greater than the deviations at Point D and Point C for non-distal extension (0.034 mm and 0.044 mm, respectively). The deviations of distal extension increased with the number of missing teeth. Conclusion The location of the residual ridge had significant effect on its deviation between digital and conventional impressions. This study provides the reference value for the conversion from digital anatomic impressions to digital pressure impressions.