Comparison of conventional, photogrammetry, and intraoral scanning accuracy of complete-arch implant impression procedures evaluated with a coordinate measuring machine

Abstract

Statement of problem

Conventional implant impressions by using elastomeric impression material have been reported as a more reliable technique for a complete-arch implant record compared with intraoral scanner procedures. Photogrammetry technology may provide a reliable alternative to digital scanning or a conventional impression; however, its accuracy remains unclear.

Purpose

The purpose of this in vitro study was to measure and compare the implant abutment replica positions of the definitive cast with the implant abutment replica positions obtained by the conventional technique, photogrammetry, and 2 intraoral scanners.

Material and methods

An edentulous maxillary cast with 6 implant abutment replicas (RC analog for screw-retained abutment straight) was prepared. Three impression techniques were performed: the conventional impression technique (CNV group) by using a custom tray elastomeric impression procedure after splinting the impression copings at room temperature (23°C), photogrammetry (PG group) technology (Icam4D), digital scans by using 2 different IOSs following the manufacturer′s recommended scanning protocol, namely IOS-1 (iTero Element) and IOS-2 (TRIOS 3) groups (n=10). A coordinate measuring machine (CMM Contura G2 10/16/06 RDS) was used to measure the implant abutment replica positions of the definitive casts and to compare the linear discrepancies at the x-, y-, and z-axes and the angular distortion of each implant abutment replica position by using a computer aided-design software program (Geomagic) and the best fit technique. The 3D linear gap discrepancy was calculated. Measurements were repeated 3 times. The Shapiro-Wilk test revealed that the data were not normally distributed; therefore, the Kruskal-Wallis test was used to analyze the data, followed by pairwise Mann-Whitney U tests (α=.05).

Results

Significant y-axis linear and XY and YZ angular discrepancies were found among the CNV, PG, IOS-1, and IOS-2 groups (P<.05). The PG group obtained a significantly higher distortion on the y-axis and 3D gap compared with all the remaining groups (P=.004). The 3D discrepancy of the CNV group was 11.7 μm, of the IOS-1 group was 18.4 μm, of the IOS-2 was 21.1 μm, and of the PG group was 77.6 μm. In all groups, the interquartile range was higher than the median errors from the discrepancies measured from the definitive cast, indicating that the relative precision was low.

Conclusions

The conventional technique reported the lowest 3D discrepancy for the implant abutment position translation capabilities of all the implant techniques evaluated. The intraoral scanners tested provided no significant differences in linear distortion compared with the conventional method. However, the photogrammetry system tested provided the least accurate values, with the highest 3D discrepancy for the implant abutment positions among all the groups.