Korean J Orthod.  2016 Jan;46(1):3-12. 10.4041/kjod.2016.46.1.3.

A comparison of the precision of three-dimensional images acquired by 2 digital intraoral scanners: effects of tooth irregularity and scanning direction

• Anh JW
• Park JM
• Chun YS
• Kim M
• Kim M

• KMID: 2152892
• DOI: http://doi.org/10.4041/kjod.2016.46.1.3

Abstract

OBJECTIVE
The purpose of this study was to compare the precision of three-dimensional (3D) images acquired using iTero(R) (Align Technology Inc., San Jose, CA, USA) and Trios(R) (3Shape Dental Systems, Copenhagen, Denmark) digital intraoral scanners, and to evaluate the effects of the severity of tooth irregularities and scanning sequence on precision.
METHODS
Dental arch models were fabricated with differing degrees of tooth irregularity and divided into 2 groups based on scanning sequence. To assess their precision, images were superimposed and an optimized superimposition algorithm was employed to measure any 3D deviation. The t-test, paired t-test, and one-way ANOVA were performed (p < 0.05) for statistical analysis.
RESULTS
The iTero(R) and Trios(R) systems showed no statistically significant difference in precision among models with differing degrees of tooth irregularity. However, there were statistically significant differences in the precision of the 2 scanners when the starting points of scanning were different. The iTero(R) scanner (mean deviation, 29.84 +/- 12.08 microm) proved to be less precise than the Trios(R) scanner (22.17 +/- 4.47 microm).
CONCLUSIONS
The precision of 3D images differed according to the degree of tooth irregularity, scanning sequence, and scanner type. However, from a clinical standpoint, both scanners were highly accurate regardless of the degree of tooth irregularity.

Keyword

Three-dimensional scanner; Digital models; Dental cast analysis; Three-dimensional diagnosis and treatment planning

MeSH Terms

Dental Arch
Imaging, Three-Dimensional*
Tooth*

Figure

• 

  Figure 1 Dental arch models according to the severity of tooth irregularity expressed as arch length discrepancy (ALD). C1, Ideal arch dentition (ALD, 0 mm); C2, mildly crowded dentition (ALD, 3 mm); C3, moderately crowded dentition (ALD, 7 mm); C4, severely crowded dentition (ALD, 10 mm). Fiducials with a diameter of 1.5 mm were attached at 5 locations on the model base located 4 mm below the dentogingival junction. Two posterior fiducials were located below the mesiobuccal cusp of the first molars and 1 anterior ball marker was located below the contact point between the central incisors. Two canine fiducials were located directly below the cusp tips of the right and left canine teeth.

• 

  Figure 2 Scanning sequences and reference faces for model division and the model sections. A, The Group Right sequence on the iTero®. The right molars were scanned first in the order of the occlusal side ①, buccal side ②, and palatal side ③; subsequently, the left molars were scanned in the same fashion in the order of ④, ⑤, and ⑥. Both scanned images were merged and connected at the anterior area. The scanning sequence for Group Left first scanned the left molars in reverse. B, The sequence for Group Right on the Trios®. Scanning started from the occlusal side of the right molars and proceeded toward the left occlusal side ①, continued along the buccal side in the reverse direction ②, and lastly, from the palatal side of the right molars, proceeding toward the palatal side of the left molars ③. The scanning sequence for Group Left first scanned the left side in reverse. C, The reference faces for model division and the model sections. Face 1 is a plane passing through the posterior fiducials on both sides, Face 2 is a plane passing through the anterior ball marker and perpendicular to Face 1, and Faces 3 and 4 are planes passing the fiducials in the canine region and the intersection point of Faces 1 and 2.The scanned images were divided into 6 sections: RM, right molar; RP, right premolar; RA, right anterior; LM, left molar; LP, left premolar; LA, left anterior.

• 

  Figure 3 A color presentation of the deviations between surfaces from the iTero® scanner. The color map was set to range from 0 µm to +200 µm. For the models in upper box A (C1Right, C2Right, C3Right, and C4Right), scanning started in the right molar region and then continued on the left side; in lower box B (C1Left, C2Left, C3Left, and C4Left), scanning started in the left molar region and then continued on the right side.C1, Ideal arch dentition; C2, mildly crowded dentition; C3, moderately crowded dentition; C4, severely crowded dentition.

• 

  Figure 4 A color presentation of the deviations between surfaces from the Trios® scanner. The color map was set to range from 0 µm to +200 µm. For the models in upper box A (C1Right, C2Right, C3Right, and C4Right), scanning started on the occlusal side of the right molar and continued toward the left side; in lower box B (C1Left, C2Left, C3Left, and C4Left), scanning started on the occlusal side of the left molar and continued toward the right side.C1, Ideal arch dentition; C2, mildly crowded dentition; C3, moderately crowded dentition; C4, severely crowded dentition.

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