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.