The transfer accuracy of digital and conventional full-arch impressions influenced by fixed orthodontic appliances: a reference aid–based in vitro study

Abstract

Objectives The aim of this in vitro study was to investigate the influence of fixed orthodontic appliances (FOAs) on the transfer accuracy of full-arch impressions by five intraoral scanners (IOSs): CS3600, Primescan, Trios 4, Medit i500, Emerald S, and one conventional alginate impression (CAI). Materials and methods To compare the data with the actual model situation, an established reference aid–based method was applied. A test model with human teeth was used and modified for each testing group, resulting in five different settings: natural teeth (group A), metal brackets without/with wire (groups B/C), ceramic brackets without/with wire (groups D/E). A total of 300 (n = 12 × 5 × 5) scan datasets of IOSs were analyzed using a 3D software (GOM Inspect) and 60 (n = 12 × 5) plaster casts of CAI were measured with a coordinate measurement machine. The deviations between the reference aid and the impressions were determined. Results For all groups with brackets (B to E), IOSs showed a higher transfer accuracy compared to CAI, even for long-span distances. However, some significant differences between the IOSs were observed (p < 0.05). Conclusions Within the limitations of this in vitro study, IOSs can be recommended for impressions with and without FOAs, even if CAI showed the smallest average deviations in settings without FOAs. Clinical relevance IOSs are widely used in orthodontics and the current study demonstrated that their use enables fast impression taking even in settings with fixed orthodontic appliances. In addition, for these settings, the transfer accuracy is higher than with conventional alginate impressions. Nevertheless, a re-investigation in a clinical setting should be performed to verify the current in vitro findings.

What to Prefer in Patients with Multibracket Appliances? Digital vs. Conventional Full-Arch Impressions—A Reference Aid-Based In Vivo Study

“…However, the accuracy of digital impression-taking with an IOS differs a lot when comparing dental arches with and without a bonded MBA. While two prior in vitro studies determined no clinically relevant effect of MBAs on the impression accuracy [14,15], more recent investigations described a distinct reduction in the transfer accuracy for full-arch impressions [16][17][18]. The effect, however, is still acceptable when compared to the data determined for CAIs [18].…”

“…Regarding the amount of time needed to obtain a full-arch impression, several studies have been published [11,13,[18][19][20]. While CAIs might demand the lowest amount of chairside time for the impression itself, the chairside time to remove and reinsert the archwire-which is recommended for improved impression quality and reduced patient discomfort-as well as the duration of the subsequent obligatory CPC process in the dental laboratory need to be considered.…”

“…While CAIs might demand the lowest amount of chairside time for the impression itself, the chairside time to remove and reinsert the archwire-which is recommended for improved impression quality and reduced patient discomfort-as well as the duration of the subsequent obligatory CPC process in the dental laboratory need to be considered. Therefore, CAIs have been shown to be less advantageous or equal (at best) compared to digital impressions [11,12,18,20]. Nevertheless, the presence of an MBA has been shown to increase the necessary amount of time needed for IOS in comparison to situations with natural teeth only [18,19].…”

“…Therefore, CAIs have been shown to be less advantageous or equal (at best) compared to digital impressions [11,12,18,20]. Nevertheless, the presence of an MBA has been shown to increase the necessary amount of time needed for IOS in comparison to situations with natural teeth only [18,19].…”

“…Therefore, in a previous in vitro study, the authors investigated the established reference-aid based methodology in different model settings, with and without MBA, using five IOSs for digital and one CAI for conventional impression-taking [18]. Even though the results of the laboratory study were promising, the data from a clinical setting might differ a lot from the in vitro data due to patient movement, soft tissue mobility, saliva flow, and anatomically-limited space for intraoral scanning tip or impression tray [26][27][28].…”