American Journal of Orthodontics & Dentofacial OrthopedicsVolume 144, Issue 3 , Pages 471-478, September 2013
Introduction
Digital impression devices are used
alternatively to conventional impression techniques and materials. The
aims of this study were to evaluate the precision of digital intraoral
scanning under clinical conditions (iTero; Align Technologies, San Jose,
Calif) and to compare it with the precision of extraoral digitization.
Methods
One
patient received 10 full-arch intraoral scans with the iTero and
conventional impressions with a polyether impression material (Impregum
Penta; 3M ESPE, Seefeld, Germany). Stone cast models manufactured from
the impressions were digitized 10 times with an extraoral scanner
(D250; 3Shape, Copenhagen, Denmark) and 10 times with the iTero. Virtual
models provided by each method were roughly aligned, and the model
edges were trimmed with cutting planes to create common borders
(Rapidform XOR; Inus Technologies, Seoul, Korea). A second model
alignment was then performed along the closest distances of the surfaces
(Artec Studio software; Artec Group, Luxembourg, Luxembourg). To assess
precision, deviations between corresponding models were compared.
Repeated intraoral scanning was evaluated in group 1, repeated extraoral
model scanning with the iTero was assessed in group 2, and repeated
model scanning with the D250 was assessed in group 3. Deviations between
models were measured and expressed as maximums, means, medians, and
root mean square errors for quantitative analysis. Color-coded displays
of the deviations allowed qualitative visualization of the deviations.
Results
The
greatest deviations and therefore the lowest precision were in group 1,
with mean deviations of 50 μm, median deviations of 37 μm, and root
mean square errors of 73 μm. Group 2 showed a higher precision, with
mean deviations of 25 μm, median deviations of 18 μm, and root mean
square errors of 51 μm. Scanning with the D250 had the highest
precision, with mean deviations of 10 μm, median deviations of 5 μm, and
root mean square errors of 20 μm. Intraoral and extraoral scanning with
the iTero resulted in deviations at the facial surfaces of the anterior
teeth and the buccal molar surfaces.
Conclusions
Scanning
with the iTero is less accurate than scanning with the D250. Intraoral
scanning with the iTero is less accurate than model scanning with the
iTero, suggesting that the intraoral conditions (saliva, limited
spacing) contribute to the inaccuracy of a scan. For treatment planning
and manufacturing of tooth-supported appliances, virtual models created
with the iTero can be used. An extended scanning protocol could improve
the scanning results in some regions.
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