In vitro accuracy of digital and conventional impressions in the partially edentulous maxilla

Abstract

Objectives: This in vitro study compared the dimensional accuracy of conventional impressions (CI) with that of digital impressions (DI) in a partially edentulous maxilla. DIs were made by two intraoral scanners, Omnicam (OC) and Primescan (PS).

Materials and methods: CI and both intraoral scanners were used to take 30 impressions of two identical reference models. CIs were poured with type 4 gypsum and the saw-cut models were digitized. The reference models simulated a maxilla with six prepared teeth that accommodated a cross-arch fixed partial denture. Center points of five precision balls and center points at the margin level of each prepared tooth were used to detect changes in dimensions and tooth axis between the reference model and the scans.

Results: For DI, the largest deviations (176 µm for OC and 122 µm for PS) occurred over the cross-arch. For CI, the largest deviation (118 µm) occurred over the anterior segment. For shorter distances up to a quadrant, DI was superior to CI. For longer scan distances, DI was comparable (2 sextant and anterior segment) or inferior (cross-arch) to CI. Vertical and tooth axis deviations were significantly smaller for CI than for DI (p < 0.001).

Conclusions: The impression method affected the impression accuracy of a partially edentulous maxilla with prepared teeth. DI is recommended for scans up to a quadrant. Larger scan volumes are not yet suitable for fabricating a fixed partial denture because of the high scatter of accuracy values.

Clinical relevance: In contrast to conventional impressions, digital impressions lead to comparable or better results concerning scans up to a quadrant. Consequently, for larger scan volumes, several smaller scans should be performed or, if restoration-related not possible, it is recommended to take conventional impressions.

Keywords: Complete arch; Conventional impression; Digital impression; Intraoral scan; Partially edentulous.

Fig. 1

Reference models. Center points of prepared teeth (RM = right molar. RC = right canine. RI = right incisor. LI = left incisor. LC = left canine. LM = left molar) are marked with a square. Center points of each precision ball (P₁–P₅) are marked with a circle. a For conventional impression. b For digital impression

Fig. 2

Schematic diagram of generating the reference data set

Fig. 3

Total distance deviations pooled for clinical category for conventional impression (CI) and intraoral scanners (OC, Omnicam. PS, Primescan). a Signed distance deviations. b Absolute distance deviations

Fig. 4

Total and vertical distance deviations for conventional impression (CI) and intraoral scanners (OC, Omnicam. PS, Primescan) displayed for 50% and 90% quantile values

Fig. 5

Tooth axis for conventional impression (CI) and intraoral scanners (OC, Omnicam. PS, Primescan) displayed for 50% and 90% quantiles

Fig. 6

Horizontal deviations (with an enlargement factor of 50) of center points of prepared teeth (RM = right molar. RC = right canine. RI = right incisor. LI = left incisor. LC = left canine. LM = left molar) for conventional impression (CI) and intraoral scanners (OC = Omnicam. PS = Primescan). Circular lines (zero line (grey dashed line) with center RM and radius defined by reference distance to RC, RI, LI, LC, or LM state point deviations in the scans for which no distance deviations occur. a Conventional impression. b Digital impression