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Accuracy of optical scans and conventional silicone impressions compared

IWATE, Japan: Aiming to evaluate the accuracy of digital impressions for use in implant placement, researchers from Iwate Medical University in Japan have compared optical impression scans from an intra-oral scanner with conventional silicone impressions. The analysis showed that the distance error of the optical impressions was slightly greater that of the conventional method.

For many dental practitioners, digital technology has become vital in daily practice. Others, however, still rely on conventional methods used in the profession long before the introduction of digital alternatives. However, the question that arises in this connection is whether—apart from benefits such as being faster and often more convenient—digital methods are verifiably more accurate than traditional techniques.

Aiming to shed light on this issue, the Japanese researchers compared a virtual model created from a scan by an intra-oral scanner to a working cast fabricated based on a conventional silicone impression technique. The evaluation was limited to the use of optical impressions for implant placement. For this purpose, the researchers placed two implant abutments (Nobel Biocare), one 5 mm and one 7 mm in height, in a master model.

To evaluate the error of the intra-oral scanner, the master model was scanned ten times with the Lava Chairside Oral Scanner (Lava COS; 3M ESPE). To evaluate the error of conventional impressions, ten working casts were scanned with a computer numerical control coordinate measuring machine (Zeiss).

From comparison of the distance between two ball abutments that were connected to the implants, the researchers found that the trueness of distance error was 64.5 µm for the scanner and 22.5 µm for the working casts, making the conventional impression more accurate than the scanner.

For the 5 mm healing abutment, the mean angulation error of the Lava COS was greater than that of the working cast, indicating significant differences in trueness and precision, the researchers wrote. However, this was not observed for the 7 mm abutment.

As distance errors of the optical impression were slightly greater than that of the conventional impression, the researchers concluded that currently digital impressions are not equivalent replacements of conventional impressions for restorative procedures. However, they predicted that the development of information technology would most likely lead to improvement in the accuracy of optical impressions in the near future.

The study, titled “Examination of the position accuracy of implant abutments reproduced by intra-oral optical impression”, was published online on 5 October in the PLOS ONE journal.

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