New research suggests using scan aids has both pros and cons

Anisha Hall Hoppe, Dental Tribune International

Mon. 13. November 2023

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FREIBURG, Germany: The use of intra-oral scanners for full-arch digitisation of edentulous arches with multiple implants has not been recommended, owing to significant errors. A study by researchers in Freiburg and Berlin in Germany compared the accuracy of intra-oral scans for multiple implants with and without the use of a scan aid. The goal was to understand the potential improvements the scan aid could provide in the context of edentulous arch scans, assessing parameters such as linear deviation, precision and software recognition of scan bodies. The findings highlight the role of scan aids in improving registration of scan bodies and reducing linear deviation in intra-oral scans.

Having less distinct anatomical surface morphology, the edentulous jaw makes it difficult to stitch intra-oral scan images accurately to form a complete virtual model, and the intra-oral environment can introduce additional inaccuracies. Efforts to overcome these issues have included devices that create an optical bridge or increase the scannable surface, aiming to minimise stitching errors, but require additional time-consuming steps that add complexity to the process. Nonetheless, these devices have been shown to improve scanning accuracy.

A prior study introduced an optical bridge for universal use that can be adjusted chairside and is easy to handle. It tested three different designs and materials for trueness, precision and clinical applicability. The most user-friendly and accurate scan aid had an irregular design and a grey colour. The aim of the current study was to evaluate the accuracy of this universal 3D-printed scan aid in vivo.

The study used a case-control format, scanning implants in the edentulous jaw with and without the universal scan aid. Twenty-two participants with an edentulous arch and at least three implants were selected. The patients had received CAMLOG Screw-Line, SICace (SIC invent) or Straumann Standard Plus implants, and system-specific scan bodies were used. Two types of intra-oral scanners, the CS 3600 from Carestream Dental (CS) and TRIOS 3 from 3Shape (TR), were employed. The scans were capped at 9 minutes, because it has been found that repeated scanning does not increase accuracy in areas with minimal surface morphology.

Failure to register the scan body during scanning was reported for 25% of Straumann, 20% of Camlog and 8% of SIC scan bodies. For the CS scanner, 83% of scan bodies were successfully scanned with the scan aid and 70% without, compared with 96% and 86%, respectively, for the TR scanner.

The scan aid statistically significantly minimised the total mean linear deviation when using the CS scanner. However, for the TR scanner, there was no difference.

As for precision, statistically significant differences were found between the two scanners when the scan aid was not used. The scan aid decreased precision significantly for the TR scanner. Other parameters showed increased variability, particularly regarding precision within each group of scan bodies, suggesting that the scan aid’s usefulness might be influenced by the specific scanning technology used.

For instance, the CS scanner uses active triangulation, which may be more prone to errors in edentulous arch scans and could benefit more from the scan aid than the TR scanner, which uses confocal microscopy. The use of the scan aid also improved the software’s recognition of scan bodies for both scanners.

The authors cautioned about the interpretation of accuracy regarding the results, owing to inherent errors in extra-oral reference models and potential deviations related to scan body height. They concluded that, while the scan aid can significantly improve linear deviation with the CS scanner and enhance software recognition of scan bodies, it may also lead to increased variability in precision.

The study, titled “Enhancing intraoral scanner accuracy using scan aid for multiple implants in the edentulous arch: An in vivo study”, was published in the August 2023 issue of Clinical Oral Implants Research.