Evaluation of the effect of implant scan body materials, alignment, exposed heights, and inter-scan body distances on the accuracy of digital implant impressions

doi:10.21203/rs.3.rs-3331690/v1

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Evaluation of the effect of implant scan body materials, alignment, exposed heights, and inter-scan body distances on the accuracy of digital implant impressions

https://doi.org/10.21203/rs.3.rs-3331690/v1

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Background.

An accurate digital impression of the scan body is essential to replicate the actual implant position in the software program. However, studies analyzing the scanning accuracy using different scan body materials, angulations, exposures, and inter-scan body distances are scarce. The purpose of this in vitro study was to determine the effect of scan body materials, alignment, exposed heights, and inter-scan body distances on the accuracy of digital impressions.

Methods.

Two edentulous maxillary epoxy models were used in this study. The first model had 4 dummy implants (Dentium Superline; Dentium Co, Ltd). Two scan body materials, namely PEEK and titanium were tested together with the variable inter-scan body distances. The second model had 6 dummy implants; 3 with different angulations and 3 placed at different levels from the gingival margin. PEEK scan bodies were attached to all implants that were scanned by using a laboratory scanner. All standard tessellation language (STL) files were imported into a surface matching software program (GOM Inspect; GOM). Linear and angular deviation measurements were made. The Shapiro-Wilk test of normality was used. Comparison between the study was done using the appropriate test.

Results.

The linear and angular deviation values (µm) of the titanium group were higher than the PEEK group. Both linear and angular deviation values(µm) were significantly higher in the long inter-scan body distance group than the short one (P = .002). Regarding the effect of the angulation, the highest deviation values (µm) were recorded at the 30-degree angulation with no statistically significant difference between the 3 groups (P = .41). Regarding scan body exposed heights, the linear and angular deviation values (µm) were significantly increased (P < .001) as the supragingival exposed height of the scan body was reduced.

Conclusions.

PEEK scan body material, with a short inter-scan body distance and more exposed part of the scan body can enhance the accuracy of the digital impression. Scan body angulation did not significantly affect the accuracy of the digital impression although more deviation was reported with 30-degree angulation.

Digital impression

Scan body

Implant angulation

PEEK scan body

Implant alignment

Inter-scan body distance.

Accurate reproduction of the dental implant 3-dimensional (3D) position in relation to the surrounding structures is a crucial step in the construction of the implant prosthesis.^1–3Digital impression accuracy is influenced by the scan body material, with PEEK reporting the best results followed by titanium, then PEEK-titanium as the least accurate.^4–6

Partially visible scan bodies showed significantly higher deviations than fully visible ones and it was recommended to place longer scan bodies when scanning deep implants.^7,8 However, in other studies, no significant deviations were attributed to the subgingival implant depth.^9,10 Another study reported the opposite, as the largest deviations were reported when the scan body was fully exposed.¹¹

The accuracy of intraoral scanning might be affected by the inter-scan body distances.^12,13 It has been proposed that trueness tends to decrease as the distance between the implants increases. However, too short inter scan body distance may complicate intraoral scanning, therefore the position of the implants may be inaccurately transferred.¹⁴

Many studies compared the impact of implant angulation on the accuracy of scanning with conflicting results. Some studies reported better scan data accuracy in inclined implants than in parallel implants.^15,16 Other studies reported worse accuracy in inclined implants.^17,18

The purpose of the present study was to examine whether different scan body materials, inter-scan body distance, height of the exposed scan body, and implant angulations can affect the accuracy of scan body image matching. The null hypothesis was that no significant difference would be found between the studied groups.

Two edentulous maxillary epoxy resin models were used in the present study. To simulate the alveolar mucosa, the models were covered by a removable polyurethane layer (Epoxy maxillary model; Ramses Medical Products Factory) 2-mm in thickness.

In the first model: 4 internal connection dummy implants (Dentium Superline; Dentium Co, Ltd) Ø4.5×10-mm length were inserted at the right canine, right first premolar, left canine, and left first molar positions (Fig. 1). A dental surveyor (Ney surveyor; Dentsply Sirona) was used to ensure the parallel alignment of the implants placed.²¹

To evaluate the effect of different scan body materials, a PEEK scan body (Scanning jig; Dentium Co, Ltd) was tightened at 15 Ncm to the dummy implant placed at the right canine position. The model was scanned first without the gingival layer by using a laboratory scanner (inEos X5; Dentsply Sirona) and was saved as anSTL file. This file was used later on as a reference for comparison. The gingival layer was adapted, and a total of 19 scans were made by using the same laboratory scanner. The PEEK scan body was then removed, replaced by the titanium one, and the same procedure repeated (Fig. 2).

Sample size was estimated based on 95% confidence level to detect differences in linear absolute error (ΔASS) between titanium and peek scan bodies. Arcuri et al.⁶ reported mean ΔASS of titanium = 99.3 and 95% confidence interval (CI) = 0.08, 0.12, while mean ΔASS of PEEK = 54.7 and 95% CI = 0.03, 0.07. The calculated mean ± SD ΔASS difference = 44.6 ± 0.04 and 95% CI = 44.57, 44.63. The minimum sample size was calculated to be 17 per group, increased to 19 to make up for laboratory processing errors. The total sample size required = number of groups×number per group = 4×19 = 76.

To evaluate the effect of different inter-scan body distances on the accuracy of the digital impression, 2 PEEK scan bodies were tightened at 15 Ncm to the dummy implants placed at the right canine and first premolar positions. The distance between the 2 scan bodies was considered as the short inter-scan body distance (SID). Scanning was done first without the gingival layer and the STL file obtained was saved as a reference file for comparison. The gingival layer was then adapted, and a total of 19 model scans were made, and STL files obtained were exported. The scan bodies were then removed and tightened to implants placed at the left canine and first molar positions. The same procedure was then repeated considering the distance between the 2 scan bodies as the long inter-scan body distance (LID) (Fig. 3).

In the second model, 6 internal connection dummy implants (Dentium Superline; Dentium Co, Ltd) Ø4.5×10-mm length were used (Fig. 4). Three were inserted at the right side with different angulations by using the abutment angle determining device.¹⁹ A straight implant was inserted at the canine position, 15-degree distally tilted implant at the first premolar, and 30-degree distally tilted implant at the first molar position (Fig. 5). Three PEEK scan bodies were tightened to the dummy implants at 15 Ncm (Fig. 6). Scanning was done first without the gingival layer and the STL file obtained was saved as a reference file then the gingival layer was adapted, 19 model scans were done, and STL files were exported.

On the left side of the cast, 3 dummy implants were inserted at different depths as follows: 2-mm subgingival at the left canine position; 4-mm subgingival at the left first premolar and 6-mm subgingival at the left first molar position. The supragingival exposed height of the scan bodies were 10-mm, 8-mm, and 6-mm respectively. Scanning was done as mentioned before (Fig. 7). All scans in the present study were done by using the same laboratory scanner (inEos X5; Dentsply Sirona).

STL files were imported into a surface matching software program (GOM Inspect; GOM). The area-designated best fit image matching was performed for the test scans and the reference scans. A coordinate system was established and used throughout the entire inspection process to measure the 3D linear deviations and angular deviations (µm) of all scans. To calculate the distance and angular deviation, cylinders were fitted to each scan body in both test and reference models by using the computer software program, and a central axis was generated for each. For the distance deviation, a specific point from the axis was determined by the software in each model, and the resultant 3D distance between the 2 points was recorded to generate the 3D distance deviation (Fig. 8). For the angular deviation, the original axis from the reference model was considered to be at an angle of zero, and the resultant angle between the 2 axes was recorded to generate the angular deviation (Fig. 8).

Data were collected, tabulated, and statistically analysed with a statistical software program (IBM SPSS Statistics for Windows, v23.0; IBM Corp).²⁰ The Shapiro-Wilk test of normality was used. Scan body material and inter scan-body distance variables showed normal distribution. Means and standard deviations (SD) were calculated. Comparison between the study groups were done using independent samples t-test with calculation of mean difference and 95% confidence interval (CI). Scan body angulation and exposure variables showed non-normal distribution, so non-parametric analysis was adopted. Means, standard deviations (SD), medians and interquartile range (IQR) were calculated for all variables. Comparison between the groups was done using Kruskal Wallis test. Significance was set at P < .05.

The Mean values and standard deviations of linear and angular deviation values (µm) measured in the 2 study groups were presented in Table 1. Comparison between the 2 study groups was done by using independent samples t-test. Significance was set at P < .05. The linear deviation values (µm) were significantly higher in the titanium group (0.63 ± 0.05) than the PEEK group (0.23 ± 0.11). The angular deviation values were higher in the titanium group (1.22 ± 0.48) than the PEEK group (1.10 ± 0.35) with no statistically significant difference between the 2 groups (P = .53).

Table 1

Mean and standard deviations of linear and angular deviation values obtained from PEEK group and Titanium group.
	PEEK group	Titanium group	P
Linear deviation (µm) Mean ± standard deviation	0.23 ± 0.11	0.63 ± 0.05	P < .001*
Angular deviation (µm) Mean ± standard deviation	1.10 ± 0.35	1.22 ± 0.48	P = 0.53
*Statistically significant at P < .05

The linear and angular deviation values (µm) were significantly higher in the (LID) group (0.31 ± 0.04 and 1.00 ± 0.27, respectively) than the (SID) group (0.08 ± 0.06 and 0.49 ± 0.37, respectively) (P < .001 and P = .002, respectively) as presented in Table 2.

Table 2

Mean and standard deviations of linear and angular deviation values obtained from 2 inter-scan body distance groups.
	Short Inter-scan body distance (SID) group	Long Inter-scan body distance (LID) group	P
Linear deviation (µm) Mean ± standard deviation	0.08 ± 0.06	0.31 ± 0.04	P < .001*
Angular deviation (µm) Mean ± standard deviation	0.49 ± 0.37	1.00 ± 0.27	P = .002*
*Statistically significant at P < .05

Regarding the evaluation of the effect of the implant angulation and the scan body exposure variables on the accuracy of the digital scanning, comparison between the study groups in each variable were done using Kruskal Wallis. Significance was inferred at P < .05. The highest linear and angular deviation values (µm) were recorded at the 30-degree angulation group (1.24 ± 2.95 and 2.19 ± 1.44, respectively), followed by the 15-degree angulation group (1.52 ± 3.08 and 1.43 ± 0.59, respectively), and the least deviation values were reported in the 0-degree group (0.31 ± 0.04 and 1.00 ± 0.27, respectively) with no statistically significant difference between the 3 groups (P = .44 and P = .41, respectively) as presented in Table 3.

Table 3

Mean values and standard deviations of linear and angular deviation values obtained from 3 different implant angulation groups.
	30-degree group	15-degree group	0-degree group	P
Linear deviation (µm) Mean ± standard deviation	1.24 ± 2.95	1.52 ± 3.08	0.308 ± 0.04	P = .44
Angular deviation (µm) Mean ± standard deviation	2.19 ± 1.44	1.43 ± 0.59	1.00 ± 0.27	P = .41
Kruskal Wallis test

When different scan body exposure groups were compared, linear and angular deviation values (µm) were significant. The 6-mm exposed group showed the highest linear and angular deviation values (0.41 ± 0.13 and 7.55 ± 1.65, respectively), followed by 8-mm exposed group (0.11 ± 0.06 and 2.55 ± 1.03, respectively), while the 10-mm exposed group showed the lowest variation values (0.08 ± 0.06 and 0.49 ± 0.37, respectively) as presented in Table 4.

Table 4

Mean values and standard deviations of linear and angular deviation values obtained from 3 different scan body exposure height groups.
	6-mm exposed height group	8-mm exposed height group	10-mm exposed height group	P
Linear deviation (µm) Mean ± standard deviation	0.41 ± 0.13	0.11 ± 0.06	0.08 ± 0.06	P < .001*
Angular deviation (µm) Mean ± standard deviation	7.55 ± 1.65	2.55 ± 1.03	0.49 ± 0.37	P < .001*
*Statistically significant at P < .05

Accurate digital impression can guarantee accurate implant position reproduction and consequently a passively fitted implant prosthesis.^1,2 This study was designed to investigate different variables that may affect the accuracy of scan body image matching. The null hypothesis was partially rejected as the linear and angular deviation values showed no statistically significant difference between the study groups when the angulation variable was evaluated. Moreover, the titanium scan body deviation values were only significantly higher when the linear deviation values were compared to the PEEK group.

An extraoral laboratory optical scanner (inEos X5; Dentsply Sirona) was used in the present study to ensure standardization and precision of the scans produced.³ The superimposition of the test scans over the reference scans was obtained with the best fit method by using surface matching software program (GOM Inspect; GOM) allowing properly analyzed deviations of each implant from a linear and angular point of view.⁶

The accuracy of scanning different scan body materials was evaluated in the present study. PEEK showed higher accuracy on both linear and angular perspectives than titanium. The results are consistent with the results of a study performed by Arcuri et al.⁵ PEEK’s better performance might be credited to the optical properties of this material, enhancing the scanning accuracy by detecting more points over the surface compared to the reflective surface of the titanium metal scan body.

The results of the present study showed significantly higher deviation values when the LID was compared to the SID. A possible explanation is that during the stitching process of the 3D images obtained during scanning, errors may accumulate resulting in collective deviation in long-span scanning.^13,14

The effect of the supragingival height of the scan body exposed on the accuracy of the image matching in the software was evaluated in the present study. The results showed that the less the exposed height of the scan body, the more linear and angular deviation values have been reported. Those results are in accordance with 2 studies concluding that the more the amount of the scan body submerged in the gingiva, the less accurate was image superimposition of the scan body image in the software program.^7,8

The results of the present study showed that the implant angulation has no significant effect on the accuracy of the digital impression. However, 30-degree implant angulation showed the highest deviation results. Those results are consistent with some studies^17,18 and in contrary to a previous study concluding that more accurate definitive casts were produced when the implant divergence was great.¹⁵

Limitations of the present study include the in vitro design standardizing all the variables that is not possible in the clinical practice. An in vivo study should be conducted to verify the findings. Further research is needed to assess whether the linear and angular deviation findings of the present study might cause a clinical misfit of the implant prosthesis.

Based on the findings of this in vitro study, the following conclusions were drawn:

Scan body material significantly affects the accuracy of the digital implant impression with PEEK showing better results when compared to titanium.

The linear and angular deviation values were significantly increased by increasing the inter-scan body distance.

Implant angulation has no significant effect on the accuracy of the digital impression. However, 30-degree angulation produced the highest linear and angular deviation values.

The less the supragingival exposed height of the scan body, the less the accuracy of the digital implant impressions.

PEEK

Polyetheretherketone

STL

Standard Tessellation Language

3-D

3-Dimensional

SID

Short Inter-Scan Body Distance

LID

Long Inter-Scan Body Distance

Ethics approval and consent to participate:Not applicable.
Consent for publication: Not applicable.
Availability of data and materials: The raw data of the present study is available at: https://figshare.com/articles/dataset/Evaluation_of_the_effect_of_implant_scan_body_materials_alignment_exposed_heights_and_inter-scan_body_distances_on_the_accuracy_of_digital_implant_impressions_/24115989
Competing interests: The authors declared no competing of interests in this study.
Funding: Not applicable.
Acknowledgements:Not applicable.
Authors' contributions:

Mohamed Osama Badr: designed and conducted the research, collected data, interpreted the results, and wrote the paper draft.

Maryam Hamed Sabahy: helped in conducting the research, was involved in measurements and analysis and reviewed the paper.

Nayrouz Adel Metwally: was involved in planning the research, aided in interpreting the results, and writing the paper.

Mohamed Moataz Khamis: aided in research design, supervised the research, and was involved in critical revision of the paper.

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No competing interests reported.

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Evaluation of the effect of implant scan body materials, alignment, exposed heights, and inter-scan body distances on the accuracy of digital implant impressions

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Abstract

Background.

Methods.

Results.

Conclusions.

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BACKGROUND

METHODS

RESULTS

DISCUSSION

CONCLUSIONS

Abbreviations

Declarations

References

Additional Declarations

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