Comparison of photogrammetric imaging, intraoral scanning and conventional impression accuracy of full-arch dental implant rehabilitation: an in vitro study

Abstract

Background

To compare the accuracy of photogrammetric imaging, intraoral scanning and conventional impression technique in full-arch dental implant rehabilitation.

Methods

A resin edentulous mandibular model with six parallel implants was fabricated as master model. And three impression groups were performed: conventional splinted open tray impression technique (CON, n = 10); intraoral scanning technique with 3 Shape scanner (IOS, n = 10; TRIOS3, 3 Shape); digital photogrammetry impression technique with two different photogrammetric system namely PG-1 (Icam4D) and PG-2 (PIC) groups (n = 10). The reference values of master model and test values of CON group were digitized with a laboratory reference scanner, and for all groups the STL files were exported for analyzation. The differences in trueness and precision among the three groups were analyzed using reverse engineering software, focusing on three-dimensional (3D) linearity, angularity, and root mean square (RMS) deviations.

Results

For trueness, median deviations (μm) for CON, IOS, PG-1, and PG-2 were 66.05, 78.58, 25.23, and 28.15, with angle deviations of 0.35°, 0.52°, 0.12°, and 0.14°, and RMS deviations (μm) of 40.50, 91.75, 10.87, and 13.35, respectively. Significant differences in X, Y-axis, 3D linearity, angularity, and RMS deviations among groups (p < 0.01). For precision, linear deviations (μm) were 39.32, 45.33, 15.80, and 17.78, with angle deviations of 0.24°, 0.38°, 0.10°, and 0.13°, and RMS deviations (μm) of 36.55, 82.8, 3.7, and 4.6, respectively. Significant differences in X, Y-axis, 3D linearity, XZ-plane, and RMS deviations among groups (p < 0.05).

Conclusions

The Icam4D and PIC photogrammetric impression systems exhibited the highest levels of accuracy, followed by conventional impression techniques, whereas intraoral scanning techniques demonstrated the least accuracy.

Introduction

Implant-supported complete-arch prostheses have emerged as the predominant treatment modality for fully-edentulous patients, owing to their superior retention, stability and long-term success. The achievement of a passive fit is paramount for ensuring the long-term success of full arch implant restorations. Conversely, poor adaptation can lead to biological and mechanical complications, potentially culminating in implant failure [1, 2]. The precise replication of the implants or abutments position to the cast, as obtained through different impression procedures, is necessary to achieve passive fit of restorations [3].

Conventional splinted open-tray impression technique, recognized for their reliable accuracy, was considered as the gold standard impression technique for full arch implant restorations during the past decades, and has been widely accepted in clinical practice [4]. However, the conventional impression technique is relatively complicated, time-consuming, and often causes discomforts to patients [5].

With the development of digital technology, Intraoral scanning has become increasingly prevalent in dental implant impressions [6–8]. Compared with the conventional impression technique, the intraoral scanning techniques demonstrate significant advantages in efficiency, patient preference, and model storage [9–12]. Nevertheless, specific investigations have highlighted the limited accuracy when employed in full-arch, multi-implant impression scenarios [6, 7, 13]. The size of the edentulous area negatively affects the accuracy, as the lack of natural reference objects compromises the quality of stitching of the images [14, 15].

Photogrammetry is another digital method that utilizes reference points in photographs to create digital impressions without direct contact with the objects being measured [16]. In recent years, the extraoral scanner based on photogrammetry technology has been applied in full-arch implant rehabilitation. This technique not only overcomes the limitations of traditional impression technology, and also enhances operational efficiency and improves patient comfort [17–21]. Using this technology, only the position of the implant is located, while the recording of soft tissue surface or bite is completed through intraoral scanners or traditional modeling techniques [18]. Although some studies have reported the reliability of photogrammetry, there is still a lack of sufficient evidence to support its accuracy in full arch implant restorations.

Trueness and precision are well-described standardized measures to evaluate the accuracy of digital and conventional impressions. While trueness represents the test group compared with the true reference, precision describes the repeatability of a procedure. This study compared trueness and precision of the coordinates for six implants in a completely edentulous arch (with parallel implant screw-retained abutment). These measurements were obtained using conventional splinted open-tray impression, Intraoral scanning, and two distinct photogrammetry impression techniques, respectively. The reference measurements were determined by a laboratory scanner. The null hypotheses posited that there would be no significant differences in the overall linear, angular, and root mean square (RMS) deviations of implant abutment positions among the three impression techniques, as well as no significant differences between the two photogrammetry impression techniques.

Material and methods

Master model

A mandibular acrylic model featuring a soft tissue replica was fabricated. Six dental implants (RC 4.1 * 10 mm; Institute Straumann AG) were placed parallelly at the sites of lateral incisor, the first premolar, and the first molar bilaterally. Additionally the screw-retained abutment (RC 4.6 mm for screw-retained abutment straight; Institute Straumann AG) with a gingival height of 2.5 mm was connected to the implants. The inter-implant distances were approximately 20 mm, 13 mm, and 15 mm, respectively (Fig. 1).

Fig. 1.

Complete-arch master cast with six implant abutments

Reference scan

Six original abutment-level scan bodies (CARES Mono Scanbody, D4.6 mm PEEK/TAN, Straumann) were connected to the abutment on the master model and hand-tightened to approximately 10 Ncm. The reference scan was obtained using a laboratory scanner (D2000, 3Shape) with a reported precision of 5 μm. An open-format standard tessellation language (STL) file was exported as the reference scan.

Test scan

Three impression groups were performed from the master model: Group I (CON) utilized a conventional splinted open-tray impression; Group II (IOS) employed an intraoral scanning; and Group III (PG) involved two subgroups using different photogrammetry systems, PG- 1 employing Icam4D and PG- 2 utilizing PIC.

For Group CON, a custom tray was fabricated using light-cured resin and coated with a thin layer of tray adhesive. Abutment-level impression copings were connected to the abutments on the master model, and splinted with autopolymerized acrylic resin (Pattern Resin; GC). The splinted bars were then cut and rejoined with the same material to minimize polymerization shrinkage. Polyvinyl siloxane impression material (Silagum putty/light; DMG) was used to create impressions and artificial gums were fabricated. The stone casts were poured with low expansion type IV gypsum. Scan bodies that used for reference scan were screwed on the abutment analogs and hand-tightened to approximately 10 Ncm. After that, the laboratory reference scanner was applied to digitize the stone casts. These procedures were repeated ten times under the same conditions.

For Group IOS, the abutment-level scan bodies that used for reference scan were connected to the abutments on the master cast and hand-tightened to approximately 10 Ncm according to the manufacturer's recommendations. Scanning was performed under identical environmental conditions using a pre-calibrated IOS (TRIOS 3, 3Shape A/S; software version 1.7.3.1), with ambient light set at 1003 lx and no interference from external light sources. The scanning strategy was starting from the occlusal surface of the right molar area, continuing to the contralateral molar area, subsequently rotated to the buccal surface at a 45-degree angle and went back right molar area. Then the lingual surface was captured as the tip went from right molar to left at a 45-degree angle. Each scanning range reached 1 cm distal to the scan body at the first molar position. These procedures were repeated ten times, and ten STL files were obtained.

For Group PG, special optical markers and a photogrammetry system were prepared. For PG- 1, the scan bodies (IcamBody;Imetric4D Imaging Sàrl) were positioned and hand-tightened on each implant abutment according to the manufacturer's instructions, ensuring that the viewfinder captured both sides of each scanner simultaneously. The Icam4D photogrammetry system (Imetric4D Imaging Sàrl) digitized the master implant cast by moving at a uniform speed from left side to right. Ten digital records were obtained, and ten STL files were generated. For PG- 2, the scan bodies (PIC Transfer; PIC Dental) were connected and hand-tightened as the manufacturer’s recommendations. The photogrammetry camera (PIC Camera; PIC Dental) was positioned 15 to 30 cm away from the master cast, maintaining a maximum angle of 45 degrees to accurately capture the implant abutment positions. These procedures were repeated ten times under the same conditions. Subsequently, scan bodies of PG- 1 and PG- 2 were converted to the scan bodies utilized in CON and IOS groups, which were selected from the library. The corresponding STL files were exported for accuracy analysis.

The experimental flow is shown in Fig. 2.

Fig. 2.

The flow chart of the experiment

Data analysis

All the STL files were imported into dental CAD software (exocad DentalCAD; exocad), where the scanned data was converted into a unified SB format using a digital library, while also removing interference from other parts of the model (Fig. 3a,b). Subsequently, the updated STL files were imported into a specific software program (Geomagic Control X; 3D systems) for accuracy assessment. A coordinate system was created on the reference data. The central point of the bottom plane of scan body A was set as the origin (0, 0, 0), and the central axis of scan body A was defined as the z-axis. The central point of scan body F was located on the YZ plane (Fig. 3c,d). The coordinates (x, y, z) of the central points and the orientation of the central axes were calculated of each scan body(Fig. 3d,e).

Fig. 3.

a The reference scan obtained with laboratory scanner. b Convert the scan bodies of PG- 1 group to unified scan body. c Marking of scanning body. d Obtain the bottom midpoint coordinate value. e Obtain the coordinate value of the central axis direction. f Colorimetric map showing the RMS deviation reference and PG- 2 group

Trueness was assessed by comparing the test data with the reference data. The linear discrepancy was evaluated by comparing the central point of each scan body and the sum of them in the test data with the corresponding point in the reference data, represented by Δx, Δy, and Δz. The discrepancy was calculated the overall deviation of the six scan bodies using the formula $\mathrm{\Delta }D=\sqrt[2]{\mathrm{\Delta }x2+\mathrm{\Delta }y2+\mathrm{\Delta }z2}$. Angular discrepancy was evaluated by the angle between the central axis of each scan body in the test data with the corresponding axis in the reference data. RMS values were obtained by “best-fit algorithm” and 3D comparison, and the outcomes of 3D comparison were presented in the Colorimetric maps (Fig. 3f).

Precision was evaluated as follows:To assess linear and angular discrepancy, each of the test data was aligned with the reference data in the coordinate system. Pairwise comparisons were carried out within the test group. To assess RMS discrepancy, the test data were aligned to each other within the group using ‘best-fit’ algorithm, and pairwise 3D comparisons were carried out. Totally, 45 comparisons were made within the group.

Statistical analysis was performed with a specific software program (IBM SPSS Statistics, v25.0 for Windows; IBM Corp). The Shapiro–Wilk test revealed that the data were not normally distributed. Therefore, the Kruskal–Wallis test was used to analyze the data and multiple comparisons using the Dunn – Bonferroni test, the results were described by the median and interquartile (α = 0.05).

Results

The linear, angular and RMS discrepancies observed in the CON, IOS and PG groups are presented in Tables 1, 2, 3.

Table 1.

Descriptive statistics for linear discrepancies (μm)

		Trueness				Precision
		CON	IOS	PG- 1	PG- 2	CON	IOS	PG- 1	PG- 2
X axis	Median	32.79 b	41.6a	12.59 c	15.53 c	21.03b	27.91 a	10.03 c	12.21 c
	Q25,Q75	24.30,36.24	36.37,47.4	9.83,14.13	12.16,17.42	17.54,28.41	22.85,30.58	9.06,11.05	11.69,13.23
Y axis	Median	42.28 b	49.93 a	13.56 c	17.35 c	19.45b	29.76 a	7.15 c	9.03 c
	Q25,Q75	38.68,45.17	42.75,56.28	9.26,15.50	15.68,20.19	14.67,28.78	14.67,42.87	6.53,7.97	8.06,9.98
Z axis	Median	13.54 a	16.65 a	7.91 b	9.18 b	11.56 b	15.83 a	6.41 c	7.18 c
	Q25,Q75	11.94,16.65	14.85,19.32	6.25,10.57	7.65,13.57	10.04,16.21	13.35,19.51	5.85,7.06	4.94,8.80
3D discrepancy	Median	66.05 b	77.58 a	25.23 c	28.15c	39.32 b	45.33 a	15.80 c	17.78 c
	Q25,Q75	59.81,70.65	75.38,83.66	22.14,28.86	25.36,31.56	29.11,50.16	36.21,59.94	14.03,16.65	16.65,19.14

CON conventional impression, IOS intraoral scanner, PG- 1 Icam4D photogrammetry, PG- 2 PIC photogrammetry;

^a,b,c different letters indicate the presence of significant difference between groups using post hoc tests (p < 0.05)

Table 2.

Descriptive statistics for angulation discrepancies (°)

		Trueness				Precision
		CON	IOS	PG- 1	PG- 2	CON	IOS	PG- 1	PG- 2
XZ angle	Median	0.17b	0.51 a	0.08c	0.09 c	0.13 b	0.30 a	0.04 c	0.07 c
	Q25,Q75	0.14,0.20	0.49,0.54	0.07,0.09	0.08,0.10	0.10,0.21	0.21,0.41	0.03,0.05	0.05,0.08
YZ angle	Median	0.26b	0.36 a	0.06c	0.08 c	0.17 a	0.16a	0.03 b	0.09 b
	Q25,Q75	0.17,0.36	0.33,0.40	0.04,0.08	0.06,0.09	0.10,0.22	0.14,0.26	0.02,0.04	0.06,0.12
angular discrepancies	Median	0.35 b	0.52 a	0.12 c	0.14c	0.24 b	0.38 a	0.10 c	0.13c
	Q25,Q75	0.26,0.45	0.49,0.54	0.11,0.14	0.12,0.15	0.18,0.29	0.29,0.48	0.08,0.13	0.10,0.15

CON conventional impression, IOS intraoral scanner, PG- 1 Icam4D photogrammetry, PG- 2 PIC photogrammetry

^a,b,c different letters indicate the presence of significant difference between groups using post hoc tests (p < 0.05)

Table 3.

Descriptive statistics for RMS discrepancies (μm)

	Trueness				Precision
	CON	IOS	PG- 1	PG- 2	CON	IOS	PG- 1	PG- 2
Median	40.50 b	91.75 a	10.87c	13.35c	36.55b	82.8 a	3.7 c	4.6 c
Q25,Q75	35.36,45.95	83.72,96.97	9.2,12.9	9.17,15.1	26.5,46.4	73.24,91.80	2.4,3.4	3.8,5.25

CON conventional impression, IOS intraoral scanner, PG- 1 Icam4D photogrammetry, PG- 2 PIC photogrammetry

^a,b,c different letters indicate the presence of significant difference between groups using post hoc tests (p < 0.05)

In the comparison of linear accuracy, the median, 25% quartile and 75% quartile (Q25, Q75) of trueness and precision for the deviations of X, Y and Z- axes and 3D discrepancy of groups CON, IOS, PG- 1 and PG- 2 are shown in Table 1, respectively. Groups PG- 1 and PG- 2 exhibited similar levels of accuracy (p > 0.05) and demonstrated higher accuracy than both group IOS (p < 0.001) and group CON (p < 0.05), while group CON was more accurate than group IOS (p < 0.05). The accuracy of Z-axis was similar for groups CON and IOS. Boxplots illustrating the 3D Discrepancy of CON, IOS, PG- 1 and PG- 2 are displayed in Fig. 4a,b.

Fig. 4.

Boxplots for accuracy of CON, IOS and PG- 1 and PG- 2 groups. a linear discrepancies in 3D deviation for trueness. b linear discrepancies in 3D deviation for precision. c angular discrepancies for trueness. d angular discrepancies for precision. T: trueness; P: precision; CON, conventional impression; IOS, intraoral scanner; PG- 1, Icam4D photogrammetry; PG- 2, PIC photogrammetry (^**p < 0.01; ^****p < 0.001; ns: no significance, p > 0.05)

Regarding angulation accuracy, a comparative analysis revealed that group PG- 1and PG- 2 exhibited higher accuracy than group IOS and CON in overall angular accuracy (p < 0.05) (Table 2, Fig. 4c,d). No statistical difference was observed in the precision of the YZ plane between groups CON and IOS.

In the comparison of RMS 3D deviation, it was found that the accuracy of group PG- 1and PG- 2 was significantly superior to that of groups IOS and CON (Table 3). The IOS group presented a significantly higher distortion in the RMS value compared with all other groups (p < 0.001).

Discussion

This study compared the accuracy of three impression techniques on an edentulous jaw model with six implants: conventional, intraoral scanning, and two types of photogrammetry. The null hypotheses were partially rejected, as significant differences were found among the three test groups. However, no significant differences were found between the two photogrammetry impression techniques. In this study, the photogrammetry imaging groups exhibited the smallest 3D discrepancy in terms of trueness and precision, followed by the conventional impression technique, with intraoral scanning showing the largest discrepancy. It is generally accepted that in achieving passive fit for full-arch implant-supported prostheses, a tolerance of less than 150 microns is acceptable [1]. There are many factors that can lead to deviations in the positioning of the prosthesis, including impression taking, model processing, digital design, digital milling, and prosthetic techniques. Among these, impression taking is the first and most critical step [3]. In this study, several key parameters of impression accuracy were analyzed, and all measured deviations were found to be well below the 150-micron threshold, indicating that the three impression techniques evaluated have the potential to meet the stringent clinical requirements for passive fit of prostheses. However, it should be noted that the present study focused primarily only on the impression process, which was only the first step leading to the aforementioned deviations, and did not involve the fabrication and verification of the prosthesis framework. Further clinical studies are essential to essential to comprehensively verify the availability and accuracy of these impression techniques in clinical application.

To the best of our knowledge, this is the first in vitro study that aimed to investigate and compare the accuracy of two photogrammetric systems for complete-arch implant impression. The result indicated that the accuracy of both photogrammetry techniques is superior to conventional impression and intraoral scanning techniques. The PIC stereo camera and ICam4D devices are based on the same concept of using IR sensors and stereo vision to record the 3D coordinates of implants. The PG technique replicates the position of the scan bodies by capturing intraoral images of the scan bodies with specific reference points. Compared to intraoral scanning, this approach avoids the process of series of image superimposition, thereby ensuring superior accuracy [17–19].

Most in vitro studies have reported higher accuracy for photogrammetry impression techniques than other methods, which is consistent with the findings of this study [20–22]. In vitro study has also shown that the deviation of photogrammetry technique can be as low as 2 μm [20]. However, contradicting results and conclusions have been reported by individual studies [23, 24]. Revilla-Leon et al.'s in vitro study demonstrated that the precision of photogrammetry was 308 μm and 273.6 μm on the X and Y axes for linear discrepancies, respectively, with a 3D discrepancy of 77.6 μm [23]. Upon evaluating the accuracy of each implant abutment position, it was found that photogrammetry techniques exhibited varying three-dimensional deviations among the six implant abutments positions [24]. These discrepancies could be attributed to differences in reference files and measurement methods utilized in the study designs. In previous studies [23, 24], the reference files were obtained using a coordinate measuring machine (CMM), whereas in the present study, laboratory scanners were employed. Compared with laboratory scanners, CMM demonstrate superior accuracy and repeatability; however, the spherical probe size and shape of the CMM machine limit its ability to detect complex and undercut areas, which may lead to inaccuracies in the reference data [25]. In the present study, a higher accuracy was observed on the z-axis compared with the x and y-axes, which was consistent with the previous study [23, 24, 26]. However, direct results comparisons are difficult due to variations in photogrammetry scan body designs, post-processing procedures and software programs.

Photogrammetry techniques offer a convenient alternative to conventional and intraoral scanning impression methods, allowing patient's unrestricted movement during the procedure. It was reported that the presence of blood, saliva does not compromise the accuracy [27, 28]. However, the photogrammetry system only records the position information of the implant abutments in the patient's oral cavity. During clinical application, additional processes are required to gather soft tissue information obtained by conventional impression techniques or intraoral scanning techniques, which are then fitted to match the data obtained by photogrammetric techniques [28]. Thus, there is still possibility of further increase in deviations during the fitting process. Despite this limitation, the majority of in-vivo studies indicated that the accuracy of photogrammetric impressions was superior to or comparable with other impression techniques [17, 29–31]. A recent in vivo study [32] evaluating photogrammetry techniques indicated that after capturing target points on the first scan bodies, the camera of photogrammetry system continues to capture optical targets on the next scan body, recording the relationship between these adjacent scan bodies. This process potentially introduces cumulative errors throughout the scanning procedure. Furthermore, since the camera is positioned extraorally, interference from perioral tissues likely results in fewer target points being captured in the posterior regions of the mouth, which may lead to reduced accuracy of distal implants. These challenges arise during the clinical application of photogrammetric impressions technique in vivo and could impact its overall accuracy. Such negative factors are difficult to fully replicate in vitro. Consequently, whether photogrammetry techniques can serve as a reliable alternative to conventional complete-arch implant impression or intraoral scanning procedures still requires further clinical research support.

The process of conventional impression is complex and involves multiple steps, including impression coping connection, tray selection, mixing impression materials, tray placement, material solidification, tray removal, and plaster model processing. During this process, various errors leading to discrepancies may occur and accumulate, such as distortion of resin, shrinkage of impression material, and plaster model expansion. The issue is particularly pronounced in edentulous cases due to the increased impression range and more implants [4, 5]. Currently, the conventional impression technology is widely used in the dental implant prostheses impression, and most studies supported the use of open tray splint and sectioning-reconnection techniques to optimize the accuracy [4, 5, 33]. Splinting can provide stabilization of transfer copings against torque from tightening and reduce position deviations of copings components, sectioning-reconnection can compensate for impression material polymerization shrinkage [5]. Therefore, this study employed the open tray splint impression technique. The findings of this study demonstrated that the accuracy (trueness ± precision) of the conventional impression was 66.03 ± 39.32 μm in linear deviation, 0.33 ± 0.24° in angular deviation and 40.50 ± 36.55 μm in RMS deviation, consistent with other studies reporting values such as 45.65 ± 59.60 µm in linear deviation [34], 0.40 ± 0.33°in angular deviation, and 35 ± 26 µm in RMS [35]. In most in vivo studies, the conventional impression method serves as a positive control, facilitating comparisons between conventional and digital techniques. Results from two in vivo studies indicate mean linear deviation values ranging from 2–185 µm when comparing conventional and intraoral scanning impressions [36, 37]. Additionally, one in vivo study reported a characteristic value of 70 µm for the photogrammetry group [19].

The intraoral scanning group reported the lowest accuracy in this study, which may be attributed to its structure and working principle. Intraoral scanning produces 3D images by stitching together a series of images [30]. Inherent errors occur and accumulate during the stitching process, leading to cumulative deviation in long-span scanning. The absence of stable and distinctive reference points for image alignment in edentulous jaws exacerbates these inaccuracies, especially when the distance between implants is considerable [38–40]. It has been proposed that the application of auxiliary structures in IOS has shown potential to enhance the accuracy of complete arch scans. These structures can provide additional landmarks or stabilize the scanning process, thereby improving the trueness and precision of the digital impressions [15, 34, 41]. However, there is still lack of clinical studies to verify its effectiveness in vivo. Flügge and colleagues reported decreased accuracy of intraoral scanning with increasing inter-implant distance [42]. Clinical study documented that intraoral scanning values range from 21.30 μm to 815.60 μm, leading researchers to conclude that the accuracy of intraoral scanning is influenced by both the number of implants and the distance between them [30, 31]. Another process that these conventional and intraoral scanning groups have to undergo is the transformation of the STL file to the digital working cast through the “Best Fit” alignment with the implant library in CAD design software. The effect of this step is proportional to the number of scan bodies [43]. Another key factor influencing the accuracy of IOS is the scan pattern. In this study, we initiated the scanning from the occlusal perspective. Subsequently, the buccal and lingual surfaces were captured at 45 degrees. Our previous study indicated that the aforementioned scan pattern exhibited superior scanning accuracy for TRIOS3 scanner in vitro [44]. For clinical application, however, scanning initiated from a 45° angle relative to the palatal surface and then buccal surface may achieve higher accuracy [45, 46].

In this study, parallel implants were used on the master model. However, non-parallel implants or anatomical variations could significantly impact the outcomes. In traditional impression techniques, as the inter-implant angle increases, the stress between the impression coping and the implants or abutments rises during tray removal, which leads to a certain degree of deformation of the impression materials [47]. In contrast, IOS can circumvent this problem, as some studies have shown that inter-implant angle has no significant effect on intraoral scan accuracy [48]. Gimenez-Gonzalez et al. found that neither parallel nor 30° inter-implant angles had a significant effect on the accuracy of intraoral scanning [49]. Interestingly, for photogrammetry, significantly higher scanning accuracy of PG with non-parallel scan bodies in comparison with parallel scan bodies were reported [50]. A possible explanation was that certain angle between the scan bodies facilitates the recognition of PG. Overall, the effect of implant angle on impression accuracy remains uncertain, and more clinical studies are needed for further exploration.

A Limitation of this study is that the in vitro experiments could not completely imitate the patient's oral condition. Therefore, this study cannot evaluate the effects of factors such as oral saliva, gingival crevicular fluid, humid environment, mucosal mobility, and patient mouth opening that may be present during actual clinical procedures on impression accuracy. Another limitation of this studies is that only the situation of parallel implant placement is assessed. However, non-parallel implant placement is not uncommon in the clinical practice due to anatomical constraints or surgical considerations. Further studies are needed to systematically assessed the impact of inter-implant angle on the accuracy of these impression techniques.

Conclusions

Based on the findings of this in vitro study, we concluded that the accuracy of the Icam 4D and PIC photogrammetry impression techniques is comparable. The photogrammetric method demonstrated greater accuracy than both the conventional impression method and the intraoral impression technique.

Authors’ contributions

Study concept and test design: Z. Li, B. Huang, Z.Chen. Experiment, data collection, assessment, processing and statistical analysis: K.Abuduwaili, R.Huang. Figure generation, data visualization, and images: K.Abuduwaili, J.Song, Y.Liu. Writing and editing of the full text: all authors. Project administration and management: Z. Li, B. Huang.

Funding

Special Foundation for Science and Technology Innovation of Guangdong Province(87000–52910003).

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.