Accuracy of virtual interocclusal records for partially edentulous patients

Statement of problem. Intraoral scans and virtual interocclusal records (VIRs) are widely used for contemporary prosthodontic treatment of patients with partial edentulism. The accuracy of VIRs in various clinical conditions is unclear. Purpose. The purpose of this in vitro study was to investigate whether the span and location of edentulous areas affect the accuracy of VIRs. Material and methods. Five sets of master stone casts were duplicated from a typodont model (Prosthetic Restoration Jaw Model; Nissin Dental) and then assigned into 5 study groups. Six pairs of interarch markers were placed on the master stone casts as reference points for measurements. The 5 study groups were group 1-Post: 1 posterior tooth missing; group 3-Post: 3 posterior teeth missing; group 6-Ant: 6 anterior teeth missing; group Bil-Post: bilateral posterior teeth missing; and group Dent: completely dentate arch. Master stone casts along with VIRs were scanned 10 times in each group by using an intraoral scanner (IOS) (Dental Wings Intraoral Scanner; Dental Wings Inc). Digital measurement of distances between the interarch markers was obtained on all digitally articulated casts and compared with the manual measurements (with electronic calipers with an accuracy of 0.02 mm). In addition, the differences (absolute values) between the digital and manual measurements were calculated at the edentulous locations for the groups 1-Post, 3-Post, 6-Ant, and Bil-Post and were compared with the corresponding interarch marker positions in the group Dent. Two-sample t tests were used for the statistical analysis (alpha=.05). Results. The overall differences (mean +/- standard deviation) between digital and manual measurements were group 1-Post: 0.10 +/- 0.19 mm, group 3-Post: 0.28 +/- 0.63 mm; group 6-Ant: 0.19 +/- 0.20 mm; group Bil-Post: 0.28 +/- 0.25 mm; and group Dent: 0.05 +/- 0.18 mm. Group Dent was the only group with no significant differences between digital and manual measurements at all 6 interarch marker positions and was used as the reference to analyze the measurements in the edentulous areas. No statistical difference was found (P=.237) at the group 1-Post's edentulous area when compared with the group Dent. In the group 3-Post, the edentulous areas showed statistically significant difference when compared with those of the group Dent (P=.002 and P=.003). In the group 6-Ant, the edentulous areas showed statistical differences when compared with those of the group Dent (P=.019 and P=.008). In the group Bil-Post, only 1 side of the edentulous areas showed statistical differences when compared with group Dent (P=.006 and P=.034). Conclusions. The span and location of edentulous areas impact the accuracy of VIRs. For a single missing posterior tooth, VIRs could achieve a high level of accuracy comparable with that of the dentate condition. Unilateral and bilateral extended edentulous spans with 3 or more missing posterior teeth and the extended edentulous span in the anterior region all affected the accuracy of VIRs.