Accuracy evaluation of digital impressions on horizontal finish line designs

Aim In the last years, intraoral scanners (IOSs) have gained success in prosthodontics. This study aimed to evaluate the accuracy of digital impressions performed with two different intraoral scanners on subgingival chamfer and shoulder prepared teeth considering all the abutment surface and the marginal level. Material and Methods Two upper arch models were produced with elements #16 and #21 receiving a chamfer and a shoulder preparation design. Each model was scanned 10 times with two IOSs: Medit i700 (Medit Corp, Seongbukgu, South Korea) and TRIOS 3 (3Shape, Copenhagen, Denmark). The trueness on the prepared abutments was measured using Geomagic Control X, by superimposition between the scans performed with the IOSs and the scans performed with a laboratory scanner (Aadva Lab Scan, GC Corporation, Tokyo, Japan), and expressed as RMS deviation values and as a color-coded map. Precision was measured by superimposing the scans of the IOSs showing the highest trueness with the other IOSs' scans. The trueness considering the preparation margin alone was measured as well. Results The IOSs under study demonstrated a high accuracy, with comparable trueness on the prepared abutments and statistically significant differences in precision. Medit i700 demonstrated the highest precision. At the marginal level, statistically significant differences in trueness were observed between the two IOSs with an overall low accuracy. Conclusions Medit i700 and TRIOS 3 provided an acceptable in vitro accuracy in the scanning of abutments with horizontal subgingival preparations, both on incisors and molars. However, none of the scanners used provided an acceptable accuracy when only the margin was evaluated. This suggests an incorrect margin reproduction with a possible alteration in the adaptation of the prosthesis.