Finish line distinctness and accuracy in 7 intraoral scanners versus conventional impression: an in vitro descriptive comparison

Abstract

BackgroundSeveral studies have evaluated accuracy of intraoral scanners (IOS), but data is lacking regarding variations between IOS systems in the depiction of the critical finish line and the finish line accuracy. The aim of this study was to analyze the level of finish line distinctness (FLD), and finish line accuracy (FLA), in 7 intraoral scanners (IOS) and one conventional impression (IMPR). Furthermore, to assess parameters of resolution, tessellation, topography, and color.MethodsA dental model with a crown preparation including supra and subgingival finish line was reference-scanned with an industrial scanner (ATOS), and scanned with seven IOS: 3M, CS3500 and CS3600, DWIO, Omnicam, Planscan and Trios. An IMPR was taken and poured, and the model was scanned with a laboratory scanner. The ATOS scan was cropped at finish line and best-fit aligned for 3D Compare Analysis (Geomagic). Accuracy was visualized, and descriptive analysis was performed.ResultsAll IOS, except Planscan, had comparable overall accuracy, however, FLD and FLA varied substantially. Trios presented the highest FLD, and with CS3600, the highest FLA. 3M, and DWIO had low overall FLD and low FLA in subgingival areas, whilst Planscan had overall low FLD and FLA, as well as lower general accuracy. IMPR presented high FLD, except in subgingival areas, and high FLA.Trios had the highest resolution by factor 1.6 to 3.1 among IOS, followed by IMPR, DWIO, Omnicam, CS3500, 3M, CS3600 and Planscan. Tessellation was found to be non-uniform except in 3M and DWIO. Topographic variation was found for 3M and Trios, with deviations below +/− 25 μm for Trios. Inclusion of color enhanced the identification of the finish line in Trios, Omnicam and CS3600, but not in Planscan.ConclusionsThere were sizeable variations between IOS with both higher and lower FLD and FLA than IMPR. High FLD was more related to high localized finish line resolution and non-uniform tessellation, than to high overall resolution. Topography variations were low. Color improved finish line identification in some IOS.It is imperative that clinicians critically evaluate the digital impression, being aware of varying technical limitations among IOS, in particular when challenging subgingival conditions apply.

A clinical comparison of digital and conventional impression techniques regarding finish line locations and impression time

“…In our study, the position of finish line had no significant effect on marginal gap. Nedelcu et al, evaluated the effect of finish line position on its accuracy. The results showed that all seven intraoral scanners tested in their study had lower accuracy wherever the finish line extended subgingivally.…”

“…Nedelcu et al, 46 repeating. Studies that compared digital and conventional techniques [28][29][30] confirmed the presence of a significant difference between the two methods, which is supported by our findings.…”

Influence of Tooth Preparation Design and Scan Angulations on the Accuracy of Two Intraoral Digital Scanners: An in Vitro Study Based on 3‐Dimensional Comparisons

“…However, often the conservative partial coverage design can be more complex in geometry, making it more difficult to scan when compared to the full coverage design 13 . Besides the presence or absence of adjacent teeth and preparation design, intraoral scanners play an important role in the accuracy of the impression and consequently the fit and marginal integrity of the definitive restoration 5,6,14‐17 . Some intraoral scanners use zinc oxide or titanium oxide powders in the scanning protocol.…”

“…Recent advancements in intraoral scanners and computer aided design and computer aided manufacturing (CAD/CAM) dentistry have facilitated the fabrication of restorations directly from an intraoral scan. [1][2][3] Although the trueness and precision of contemporary intraoral scanners have been reported, 4,[5][6][7] there is limited information in the literature on the influence, if any, of adjacent teeth or tooth preparation design on scan accuracy. Intraoral scanning can be limited by the mouth opening, size of scanning device, as well as adjacent oral structures.…”

“…13 Besides the presence or absence of adjacent teeth and preparation design, intraoral scanners play an important role in the accuracy of the impression and consequently the fit and marginal integrity of the definitive restoration. 5,6,[14][15][16][17] Some intraoral scanners use zinc oxide or titanium oxide powders in the scanning protocol. However, recent intraoral scanners usually do not require powder in their scanning protocol and seem to have comparable or better accuracy to that of the powdered protocol.…”