Dimensional accuracy of microcomputed tomography-scanned half-arch impressions.

Statement Of Problem: Accuracy in impression making may be enhanced by digitizing the physical impression directly and thereby be unhampered by errors introduced by gypsum casts.

Purpose: The purpose of this in vitro study was to compare the dimensional accuracy of microcomputed tomography (micro-CT) scans of impressions with that of optical scans of impressions and gypsum casts.

Material And Methods: A titanium maxillary cast with 3 metrology-grade ruby spheres in place of 3 teeth was used as a reference. Sphere 1 (S1) to sphere 2 (S2) distance (S1-S2) was 25.036 mm, and sphere 1 (S1) to sphere 3 (S3) distance (S1-S3) was 41.846 mm. Half-arch impressions were made of the titanium cast using polyvinyl siloxane impression material with a 1-step 2-phase technique. The polyvinyl siloxane impressions were then micro-CT scanned and optically scanned, and the resulting stone casts were also optically scanned. Scans from the 3 groups-CT scanning of impressions (CT), optical scanning of impressions (OP), and optical scanning of stone casts (SC)-were used to measure the distances between the 3 ruby spheres and were compared with the reference titanium model. The Wilcoxon signed-rank test for matched pairs was used to compare the groups (α=.01).

Results: For the distance of 25.036 mm, S1-S2 distance, CT scans of impressions (CT) showed an error of 20 ±20 μm, whereas optical scans of stone casts (SC) showed an error of 0 ±20 μm. At a distance of 41.846 mm, S1-S3 distance, CT showed an error of 0 ±40 μm, whereas SC showed an error of -40 ±40 μm. The difference in error between measurements at both distances was statistically significant (P<.01). The group of optical scans of impressions (OP) had to be excluded because of missing data and deformed features on the scan.

Conclusions: Although optically scanned stone models are more dimensionally accurate than micro-CT scanned impressions at a 25.036-mm distance, at a distance of 41.846 mm, micro-CT scanned impressions showed less error than optically scanned stone models. Micro-CT scanning of half-arch impressions is a viable method of digitizing a physical impression of dental structures and capturing data about the patient's oral structures. A digital image obtained by micro-CT scanning is more accurate than that obtained by optical scans of stone casts for long-span restorations.