In-vitro accuracy of full arch scans with a systematic review of nine different scanning patterns

doi:10.21203/rs.3.rs-4882279/v1

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Research Article

In-vitro accuracy of full arch scans with a systematic review of nine different scanning patterns

https://doi.org/10.21203/rs.3.rs-4882279/v1

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Objective

Evaluation of the accuracy of direct digitization of maxillary scans depending on the scanning strategy.

Materials and Method

A maxillary model with a metal bar fixed between the second molars as a reference structure was digitized using the CEREC Primescan AC scanner (N = 225 scans). Nine scanning strategies were selected (n = 25 scans per strategy), differing in scan area segmentation (F = full jaw, H = half jaw, S = sextant) and scan movement pattern (L = linear, Z = zig-zag, C = combined). Accuracy was assessed by evaluating linear differences in the X, Y, and Z axes and angular deviations (α axial, α coronal, α total) compared to a reference dataset. Differences in accuracy were analyzed using Kruskal-Wallis and Mann-Whitney U tests. Precision was analyzed by the standard deviation of linear and angular aberrations (ISO 5725-1) (p < 0.05).

Results

Strategy F_L showed significantly higher trueness and precision than F_Z for VE (p = 0.009), V_E(y) (p = 0.010), α_overall (p = 0.004), and α_axial (p = 0.002). Strategy F_C demonstrated significantly better trueness than F_Z for VE (p = 0.007), αoverall (p = 0.010), and αcoronal (p = 0.013). For scan segmentation, F_L showed better accuracy for V_E(y) (p = 0.001) and α_axial (p < 0.001) than H_L. Strategy H_L showed better trueness for V_E(z) than F_L and S_L (p = 0.001, p = 0.002). The scanning patterns F_L, F_C, and H_L exhibited the best performance for trueness and precision.

Conclusions

Scanning motion and segmentation significantly impact the accuracy and precision of full-arch scans.

Clinical relevance:

The scanning strategy is decisive for improving clinical workflow and accuracy of full-arch scans.

Full-arch digitization

Scanning strategies

Accuracy

Intraoral scanner

The digital workflow in dentistry has recently been transformed by the influence of computer-aided design (CAD) and computer-aided manufacturing (CAM) in almost all areas of clinical applications, e.g. orthodontics and prosthodontics. Nowadays, modern digital technologies in the field of dentistry offer a higher level of efficiency and quality in diagnostics, for clinical monitoring and therapy planning or for restoration fabrication. In addition, the standardization of the workflow eliminates inaccuracies contingent on conventional impression taking and model fabrication. Moreover, the documentation by means of direct digitization leads to more objective treatment as decisions are based on the acquired diagnosis data [1, 2].

The complete digital workflow without the process of a conventional impression involves three coordinated steps: data acquisition, data processing, and fabrication of the restoration [3]. The accuracy of the scan – hence the data acquisition – has a decisive role in this first step of the digital workflow, as the further steps based on this process. The use of intraoral scanners is convincing for scans up to a quadrant, with equivalent or even superior accuracy of the resulting dental model data [4]. However, new, innovative prosthetic concepts require the creation of full arch data for comprehensive diagnostics and full arch rehabilitation [4, 5]. Scanning a complete jaw continues to be a challenge [6, 7] as a larger scan distance is associated with an accumulation of scanning errors or merging errors and therefore, a resulting higher deviation, especially for full arch scans [21].

As there is currently also no clear guideline for analyzing the accuracy of entire jaw datasets, two methods are described in the literature. One option is an analysis using the best-fit algorithm to superimpose test and reference data for further calculation of metric deviations [4, 8, 9]. However, limitations such as unrecognized misalignments caused by the software algorithm must be considered. In contrast, the second method of metrical analysis of real geometric values of reference objects fixed on the analysis model or on the patients arch in-vivo avoids overlapping errors in the data sets [6, 10–13].

Besides, the accuracy of intraoral scans can be influenced by several factors. In this context the scanning system and its calibration [14], experience of the operator [15] as well as the scanning strategy [16, 17] have been proven to influence the resulting model data accuracy. Several studies have shown that accuracy improves with a more complex, non-linear scanning strategy [17–19], while others still recommend the use of manufacturer’s suggested strategy [20]. It is assumed that the number of errors might raise with scan path length and the superimposition of a strictly linear data acquisition [21]. To date, no clear statement can still be given whether a separation of the scan path or a variation of the scanning movement has a significant effect on the accuracy, e.g. trueness and precision. For this reason, this study was conducted by systematical combination of different motion patterns and scan segmentation to investigate the possible influence on scan trueness and precision. Therefore, two hypotheses were investigated in our study:

1. The movement pattern has no influence on the trueness and precision of the full-a scan.

2. The arch segmentation of the scan path has no influence on the trueness and precision of the whole-jaw scan.

A maxillary full-arch model made of polyurethane (AlphaDie MF, LOT 2012008441; Schütz Dental GmbH, Rosbach, Germany) with a homogeneous, matt surface was used as analysis model to conduct the study. A metal bar was inserted in the area of the second molars and used as a reference structure (GARANT, DIN 875-00-g; Hoffmann Group, Munich, Germany).

Acquisition of the reference dataset of the bar

The reference measurement of the metal bar was carried out with a coordination measuring device (CMM: Mitutoyo Crysta Apex C 574; Createch Medical Mendaro, Spain; software: MCOSMOS Mitutoyo Software; Mitutoyo, Neuss, Germany) before it was fixed on the analysis model. This measurement was performed at a temperature of 20°C with a maximum permissible error of (MPEe) of the CMM of 1.9 µm + (3*L/1000). Subsequently, the STL dataset generated by the CMM was imported into the analysis software (Geomagic Control 2015; version: 2015.3.1.0, 64-bit, Geomagic, Morrisville, MC, US). The calculated reference length of the metal bar was 55.066 mm.

Scanning of the upper jaw model

The CEREC Primescan AC (software version 2015.3.1.0, Dentsply Sirona, Bensheim, Germany) was used for all scans (n = 25/strategy). Nine different scanning strategies were developed for direct digitization, combining the segmentation of the scan area (F = full jaw, H = half jaw, and S = Sextant) and three different scan movement patterns (_L = linear, _Z = zig-zag, and _C = combined) as shown in Fig. 1. During the scan, it was ensured that a maximum of 20 mm of the bar ends were captured by the scanner to avoid connection of the complete bar in the virtual dataset.

An experienced operator [K.S.] performed all scans using the extraoral data acquisition mode of the CEREC Primescan AC. Each scan was obtained under the same conditions with constant ambient light settings. At the beginning of each scan, the CEREC Primescan AC scanning device was calibrated using the “Calibration Set Primescan” according to manufacturer’s guidelines. A maximum of two scans were performed successively with a following break of 30 minutes, so that any influence by heating of the scanning device could be excluded.

Data analysis and calculation of the parameters (linear parameters/angular parameters)

Each scan dataset (N = 225, n = 25 per group) was exported as an STL dataset from the respective scan software of the CEREC Primescan AC and imported into the analysis software (Geomagic Control 2015). The data was virtually adjusted in a three-dimensional coordinate system, that included XZ-, XY-, and YZ-axes as the coronal, transversal and sagittal planes (Fig. 2). Using the "Contact Feature" mode of the analysis software, anterior surfaces (AP 1 and AP 2), posterior surfaces (PP 1 and PP 2), and vestibular surfaces (VP 1 and VP 2) were constructed at each bar end (Fig. 2).

By the intersection of the planes further vectors and points were defined: the intersection lines of the anterior and posterior surfaces resulted in the horizontal vectors $\:\stackrel{⃑}{V}$1 (AP1 and PP1) and $\:\stackrel{⃑}{V}$2 (AP2 and PP2). The points P1 and P2 were determined as the intersections of $\:\stackrel{⃑}{V}$1 and VP1 or $\:\stackrel{⃑}{V}$2 and VP2, respectively (Fig. 3). For the metric analysis of the torsion in all three dimensions, the vestibular surface of the second quadrant (VP2) was parallel shifted by the calculated reference length of the metal bar (L = 55.066 mm) in the direction of the first quadrant to construct the surface VP2'. The surface VP2' with the vector $\:\stackrel{⃑}{V}$2 resulted in the constructed point P2'. To calculate the metric values of the torsion in the X-, Y- and Z- axes, the vectorial error $\:{\stackrel{⃑}{V}}_{E}$ between P2' and P1 was then analyzed using the calculation formula below (x, y, and z are the coordinates of the X-, Y-, and Z-axes):

$$\:{\stackrel{⃑}{V}}_{E}=\left(\begin{array}{cc}{x}_{p1}-&\:{x}_{p2}\\\:{y}_{p1}-&\:{y}_{p2}\\\:{z}_{p1}-&\:{z}_{p2}\end{array}\right)$$

To determine the angular deviations of the upper bar edges, α_overall was first calculated as follows: $\:\alpha\:$_overall = $\:\alpha\:$cos = $\:\frac{{X}_{V1}*{X}_{V2}+{Y}_{V2}*{Y}_{V2}+{Z}_{V1}*{Z}_{V2}}{\sqrt{{{X}_{V1}}^{2}+{{Y}_{V1}}^{2}+{{Z}_{V1}}^{2}}\:*\:\sqrt{{{X}_{V2}}^{2}+{{Y}_{V2}}^{2}+{{Z}_{V2}}^{2}}}\:*\:\frac{180}{\pi\:}$

In addition, the differentiated projection of α_overall on the coronal and horizontal planes gives further information about the direction of the angular torsion of the bar. It was calculated using the following equations (x, y, and z are the coordinates of the X-, Y-, and Z-axes):

$$\:\alpha\:\text{c}\text{o}\text{r}\text{o}\text{n}\text{a}\text{l}\:=\:\alpha\:\text{c}\text{o}\text{s}\:=\:\frac{{X}_{V1}*{X}_{V2}+{Y}_{V2}*{Y}_{V2}}{\sqrt{{{X}_{V1}}^{2}+{{Y}_{V1}}^{2}}\:*\:\sqrt{{{X}_{V2}}^{2}+{{Y}_{V2}}^{2}}}\:*\:\frac{180}{\pi\:}$$

$$\:\alpha\:\text{a}\text{x}\text{i}\text{a}\text{l}\:=\:\alpha\:\text{c}\text{o}\text{s}\:=\frac{{X}_{V1}*{X}_{V2}+{Z}_{V1}*{Z}_{V2}}{\sqrt{{X}^{2}+{{Z}_{V1}}^{2}}\:*\:\sqrt{{{X}_{V2}}^{2}+{{Z}_{V2}}^{2}}}\:*\:\frac{180}{\pi\:}$$

Statistical analysis

Statistical data analysis was performed using SPSS statistics software (version 26.0.0.0, IBM, Armonk, NY, USA). The significance level was set at 5% (p < 0.05). The Kolmogorov Smirnov and Shapiro-Wilk test was performed to assess the normal distribution.

To determine differences in the trueness between the scanning strategies (segmentation and movement), Kruskal-Wallis and the Mann-Whitney-U test with Bonferroni correction (p < 0.017) were used. For the analysis of precision (according to ISO 5725-1) the standard deviation was used.

The deviations are expressed as standard deviation, median, minimum and maximum in Table 1 and Table 2 including the 95% confidence interval for each parameter. The boxplots of all tested strategies are displayed in Fig. 4 and Fig. 5.

Table 1

Descriptive statistics of linear deviations with mean values (M), standard deviation (SD), median (MD) and 95% confidence interval (CI) of CEREC Primescan AC
		ΔL (µm)	VE (µm)	VE(x) (µm)	VE(y) (µm)	VE(z) (µm)
Strategie FL	M	-64.94	171.53	-67.92	-34.46	121.22
	SD	58.84	59.41	59.03	60.58	75.32
	MIN	-169.07	49.77	-173.24	-126.79	(-59.77)
	MED	-61.67 ^A/1/a	181.65 ^A.C/1/a	-65.13 ^A/1/a	-44.12^A/1/a	127.89^A/1/a
	MAX	60.95	288.59	60.24	78.16	272.12
	95% CI	-89.24/-40.65	147.00/196.05	-92.28/-43.56	-59.46/-9.45	90.13/152.32
Strategie FZ	M	-66.59	301.86*	-50.30	41.59*	148.29
	SD	92.73	215.91	95.53	256.96	184.96
	MIN	-261.60	52.45	-262.30	-642.98	-360.63
	MED	-59.09^A/1/a	242.12^B/1/a	-61.57 ^A/1/a	47.96^B/1/a	159.20^A.B/1/a
	MAX	152.92	945.63	243.22	940.55	539.82
	95% CI	-104.87/-28.31	212.74/390.99	-89.73/-10.86	-64.47/147.66	71.94/224.64
Strategie FC	M	-76.23	205.54*	-74.59	19.34*	127.60
	SD	67.11	143.63	73.25	149.18	117.78
	MIN	-258.54	44.94	-266.69	-133.18	-125.56
	MED	-92.44^A/1/a	164.93^A/1/a	-93.13^A/1/a	-24.96^A/1.2/a	123.22^A/1/a
	MAX	74.67	803.07	78.61	601.37	460.59
	95% CI	-103.94/-48.53	146.25/264.83	-104.83/-44.35	-42.24/80.92	78.98/176.22
Strategie HL	M	-63.45	175.91*	-61.31	-53.01*	26.16
	SD	73.98	88.16	80.35	132.94	91.23
	MIN	-208.70	43.61	-209.81	-439.21	-141.91
	MED	-65.38 ^A/1/a	151.6 ^C.A/1/a	-65.42 ^A/1/a	-26.40 ^A.B/1/a	21.67^B/1/a
	MAX	97.88	443.0	96.66	137.00	225.42
	95% CI	-93.99/-32.90	139.52/212.31	-94.48/-28.14	-107.89/1.86	-11.51/63.82
Strategie HZ	M	-86.05*	322.01*	-89.07*	115.89*	77.71*
	SD	132.44	313.47	132.91	283.71	282.10
	MIN	-448.36	33.68	-446.19	-204.45	-1037.96
	MED	-60.13^A/1/a	177.74^A/1/a	-62.45 ^A/1/a	6.53^A/1/a	112.88^A/1/a
	MAX	155.07	1123.22	154.87	923.66	474.73
	95% CI	-140.72/-31.37	192.61/451.41	-143.93/-34.30	-1.23/232.99	-38.74/194.15
Strategie HC	M	-86.66	238.95	-77.72	10.97	43.48*
	SD	67.27	142.08	88.11	208.04	142.25
	MIN	-233.82	50.79	-234.56	-553.95	-442.04
	MED	-79.58^A/1/a	215.08^A/1/a	-82.15 ^A/1/a	-3.16 ^A/1/a	62.36 ^A/1/a
	MAX	35.21	575.84	131.88	432.82	223.60
	95% CI	-114.43/-58.88	180.30/297.61	-114.09/-41.34	-74.90/96.84	-15.24/102.21
Strategie SL	M	-49.94	182.13*	-50.10	68.91*	12.97
	SD	46.27	116.81	46.27	163.53	107.61
	MIN	-134.28	44.50	-135.1	-313.18	-185.56
	MED	-41.74^A/1/a	164.63^A/1/a	-42.44 ^A/1/a	68.7^A/2/a	2.77^A/2/a
	MAX	33.76	524.96	33.41	484.95	186.92
	95% CI	-69.04/-30.82	133.91/230.36	-69.20/-31.00	1.42/136.41	-31.45/57.39
Strategie SZ	M	-79.20	303.54*	-81.18*	147.89*	153.65
	SD	96.24	237.87	99.16	241.0	174.42
	MIN	-304.23	45.93	-334.15	-157.98	-145.63
	MED	-84.30 ^A/1/a	192.89 ^A/1/a	-86.04 ^A/1/a	56.16^A/1/a	130.41^B/1/a
	MAX	70.98	1016.27	71.23	827.17	541.89
	95% CI	-118.94/-39.46	205.35/401.74	-122.11/-40.24	48.42/247.36	81.65/225.64
Strategie SC	M	-85.08	216.37*	-83.54	41.15	45.81*
	SD	61.04	120.51	67.58	141.54	165.74
	MIN	-236.11	75.88	-235.46	-263.70	-436.34
	MED	-84.32 ^A/1/a	210.34^A/1/a	-85.03 ^A/1/a	34.34^A/1/a	31.84 ^A.B/1/a
	MAX	16.72	584.13	102.13	279.91	522.57
	95% CI	-110.28/-59.87	166.62/266.12	-111.44/-55.64	-17.28/99.57	-22.61/114.23

Table 2 Descriptive statistics of angle measurements with mean values (M), standard deviation (SD), median (MD) and 95 % confidence interval (CI) of CEREC Primescan AC
	Angular measurements overall (°)					Angular measurements coronal (°)					Angular measurements horizontal (°)
Strategy	SD	M	MED	MIN/MAX	95% CI	SD	M	MED	MIN/MAX	95% CI	SD	M	MED	MIN/MAX	95% CI
FL	0.12	0.21	0.21^A/1/a	0.00/0.57	0.15/0.27	0.13	0.17*	0.14^A.B/1/a	0.00/0.56	0.11/0.23	0.06	0.09	0.08^A/1/a	0.00/0.21	0.05/0.12
FZ	0.50	0.48*	0.36^B/1/a	0.09/2.00	0.26/0.69	0.35	0.33`	0.25^B/1/a	0.04/1.43	0.18/0.48	0.38	0.32‘	1.40^B/1/a	0.17/1.4	0.15/0.48
FC	0.32	0.32*	0.23^A/1/a	0.05/1.59	0.17/0.45	0.15	0.21*	0.18^A/1/a	0.03/0.65	0.14/0.27	0.32	0.19*	0.12^A/1.2/a	0.01/1.58	0.04/0.33
HL	0.19	0.29*	0.26^A/1/a	0.08/0.78	0.20/0.37	0.12	0.15	0.14^A/1/a	0.01/0.4	0.10/0.21	0.18	0.22*	0.17^A/2/a	0.05/0.72	0.14/0.30
HZ	0.21	0.31*	0.27^A/1/a	0.08/1.01	0.21/0.40	0.14	0.18*	0.14^A/1/a	0.01/0.47	0.11/0.24	0.21	0.22‘	0.17^A/1/a	0.02/0.91	0.12/0.31
HC	0.17	0.29	0.27^A/1/a	0.06/0.77	0.20/0.36	0.16	0.20	0.17^A/1/a	0.00/0.65	0.13/0.27	0.13	0.17‘	0.12^A/1/a	0.02/0.51	0.11/0.23
SL	0.14	0.23*	0.22^A/1/a	0.06/0.69	0.16/0.30	0.10	0.15	0.16^A/1/a	0.00/0.31	0.11/0.20	0.15	0.14*	0.09^A.B/1/a	0.00/0.68	0.07/0.20
SZ	0.36	0.46*	0.33^A/1/a	0.07/1.32	0.17/0.66	0.19	0.30	0.32^A/1/a	0.01/0.67	0.22/0.38	0.35	0.30‘	0.14^A/1/a	0.01/1.22	0.15/0.45
SC	0.58	0.42*	0.25^A/1/a	0.08/2.66	0.17/0.67	0.33	0.26*	0.21^A/1/a	0.01/1.56	0.12/0.41	0.49	0.31‘	0.16^A/1/a	0.04/2.16	0.10/0.52

Shapiro-Wilk test resulted in 1 out of 9 normally distributed group for the linear parameter, for the angular parameters 9 out of 9 were not normally distributed. For the trueness, statistically significant differences between the nine different strategies were found.

Influence of movement pattern

For parameters V_E (p = 0.008), V_E(y) (p = 0.023), $\:\alpha\:$_overall (p = 0.006) and $\:\alpha\:$_axial (p = 0.033), strategy F_L results in significantly higher trueness than strategy F_Z. For V_E (p = 0.008), $\:\alpha\:$_overall (p = 0.006) and $\:\alpha\:$_coronal (p = 0.005) strategy F_C shows significantly better trueness than strategy F_Z. Considering V_E(z), strategy F_C resulted in better trueness than F_L and H_L than H_Z (p < 0.001 to p = 0.011).

For parameters V_E and V_E(y) the angular parameters $\:\alpha\:$_overall, $\:\alpha\:$_coronal, $\:\alpha\:$_axial, the significantly better trueness agrees with a better precision. Strategy F_L indicates a better precision compared to F_C for $\:{\stackrel{⃑}{\text{V}}}_{\text{E}}\left(\text{z}\right)$.

Influence of scan segmentation

For parameters V_E(y) (p = 0.005) and $\:\alpha\:$_axial (p = 0.002), strategy F_L showed significantly higher trueness than H_L. For V_E(z) (p = 0.001) strategy H_L resulted in significantly better trueness than F_L and S_L.

Considering parameters V_E(y) and $\:\alpha\:$_axial, strategy F_L resulted in better precision than strategy H_L. For parameter V_E(z) strategy H_L showed better precision than strategy S_L.

The analyses of the study showed that there were significant differences between the applied strategies. Therefore, the hypotheses that there will be no significant differences between the applied movement pattern (1) and scan segmentation (2) must be rejected.

The influence of the scanning strategy on the accuracy has been demonstrated several times in literature [16, 18, 22]. For better comparability, three different motion patterns were systematically combined with three possible segmentations of the upper jaw in the present study. Thus, in addition to previously published strategies, new strategies developed and investigated. For the scanner CEREC Primescan AC, two movement patterns were proved to be preferable over a third variation. Strategies with linear movements was found to be advantageous. It was assumed that the constant movement would result in fewer interruptions during image acquisition [17]. Müller et al. [18] recommended scanning according to the manufacturer's specified scanning protocol, that means strategy F_L in case of CEREC Primescan AC. Better accuracy through a strategy with combined linear and rotating movements was found by Passos et al. [17].

For the present investigation no differences regarding the X-axis could be determined between the different scanning strategies. Regarding the deviations in the Y- and Z-axes, the strategies F_C and F_L showed a significant better accuracy than strategy F_Z. The same results applied the angular parameters α_overall, α_coronal, and α_axial investigated. These results were supported by a simultaneously better precision.

A reason for the lower trueness results by use of zig-zag movements could be the lack of occlusal orientation structure, which lead to greater errors due to inaccurate image overlap. In addition, the changing motion shapes for the zig-zag movements may be a disadvantage due to the frequent change of the focal plane of the optical acquisition unit. This assumption is also consistent with findings from existing literature [17].

The trueness and precision for VE (y) and α_axial of strategy F_L was better compared to strategy H_L. Strategy F_L is consistent with the manufacturer's recommendation, but also the strategy with the longest scan path distance in one turn. There is the assumption that a lower number of rotations of the handpiece might lead to less interference in the data acquisition [17]. Compared to Y-axis, it is conceivable that the error in the anterior-posterior direction accumulates due to the larger scan section. As a clinical consequence, deviations of the α_axial angle may lead to a misfit of the restoration due to a shift in the direction of the Y-axis.

In contrast, Waldecker et al. [21] found that linear aberrations increase with path length. By dividing the jaw into three, instead of two sections, the accumulated error within one dental arch should be reduced. However, this thesis can only partially be confirmed in the present investigation.

For the parameter V_E(z), the strategy H_L showed higher accuracy than the strategies F_L and S_L. Similar results were shown in a study conducted with the Omnicam (Dentsply Sirona, Bensheim, Germany) as strategy H_L also showed the best results in this context [19]. However, since Omnicam and CEREC Primescan AC use entirely different cameras, this comparison can only be confirmed by performing the tests with the same scanner model.

In the present study, accuracy was determined according to ISO 5725-1 by the parameters trueness and precision [23]. According to this definition, precision describes the conformity of the data sets. Trueness is defined as the deviation of a data set from a prior specified reference. For a better comparison to current literature, a method was used developed by Güth et al. [10, 11] that avoids the superimposition errors within the data sets by counting only the bar as a reference object in the sense of a real geometry. The decisive benefit is that the vector and angular inaccuracies can be determined in relation to the X-, Y-, and Z- axes and thus, a more precise statement can be made about the subsequent intraoral fit of the restoration. A successful in vivo application of this method has also been confirmed [11].

However, like every scientific work, the present work is subject to several limitations. according to the guideline published in 2021 by Mehl et al. [24], the standard deviation of trueness can only be used to evaluate precision if the results are normally distributed. For this reason, the statements on precision made in this study have only limited validity. When using intraoral scanners clinically, patient-specific aspects such as movements, reflections of saliva, handling of soft tissues, and lack of space should always be considered [22]. Besides, for a more patient-like configuration, it would make sense to fix the reference object in the plane of the row of teeth to be in the same focal plane.

Furthermore, it should be noted that only the initial section of the digital workflow is investigated in this study. The accuracy of the fabricated prosthesis depends, among other things, on the number of interfaces, the design of the fabrication file, and the milling process [25].

Another point is that the scans in our study were performed on a maxillary model including only one experienced operator. According to Kuhr et al. [26], the scanning of the maxillary model results in the advantage of a larger surface area in the palatal region, which can be used as an orientation structure. Due to the anatomical shape of the model with physiologically shaped teeth, the study design is like a clinical setup.

Overall, the findings of the current investigations suggest that linear and combined movements in combination with full jaw or half jaw segmentation (strategies F_L, F_C, and H_L) are advantageous for the CEREC Primescan AC regarding trueness and precision. In order to develop a clinical guideline, further clinical studies with the implementation of the above-mentioned scanning strategies and other manufacturers′ models of intraoral scanners have to be conducted.

For the CEREC Primescan AC the scanning pattern F_L, F_C, and H_L exhibited the best performance for trueness and precision. Overall, the findings of the current investigations suggest that linear and combined movements in combination with full jaw or half jaw segmentation (strategies F_L, F_C, and H_L) are advantageous for the CEREC Primescan AC regarding trueness and precision.

Within the limitations of this study, it can be concluded that:

1. the combination of full arch with the linear or combined movement pattern (strategies F_L and F_C) resulted in better trueness and precision for most measured parameters compared to the zig-zag movement (F_Z) for CEREC Primescan AC.
2. the linear motion pattern in combination with full-arch or half-jaw segmentation (strategies F_L, H_L) showed significantly better trueness compared to sextant segmentation (S_L) for linear measurement parameters for CEREC Primescan AC.

Thus, scanning movement and scan segmentation have a significant influence in trueness and precision of full-arch scans. However, for clear recommendations of ideal scan paths for the clinical practice, further studies should be carried out.

Ethics approval: This article does not contain any studies with human participants or animals performed by any of the authors.

Conflict of interest : The authors declare that they have no conflict of interest.

Funding: No funding was received for conducting this study.

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No competing interests reported.

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In-vitro accuracy of full arch scans with a systematic review of nine different scanning patterns

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Abstract

Objective

Materials and Method

Results

Conclusions

Clinical relevance:

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Introduction

Material and Methods

Acquisition of the reference dataset of the bar

Scanning of the upper jaw model

Data analysis and calculation of the parameters (linear parameters/angular parameters)

Statistical analysis

Results

Influence of movement pattern

Influence of scan segmentation

Discussion

Conclusions

Declarations

References

Additional Declarations

Status:

Version 1