|Year : 2022 | Volume
| Issue : 2 | Page : 114-120
Role of scan body material and shape on the accuracy of complete arch implant digitalization
Raadhikka Karthhik1, Bharath Raj1, BV Karthikeyan2
1 Department of Prosthodontics, V.S. Dental College and Hospital, Bengaluru, Karnataka, India
2 Department of Periodontics, Krishnadevaraya College of Dental Sciences, Bengaluru, Karnataka, India
|Date of Submission||13-Sep-2021|
|Date of Decision||14-Nov-2021|
|Date of Acceptance||12-Feb-2022|
|Date of Web Publication||01-Jul-2022|
#13, 6th C Cross, Sairam Layout, Attur, Yelahanka, Bengaluru - 560 064, Karnataka
Source of Support: None, Conflict of Interest: None
Purpose: The aim of the study was to evaluate how the intraoral scan body (SB) material and shape affects the scanning accuracy and scan time in completely edentulous situations since it is not well understood.
Methodology: Two SB systems were evaluated: SB-1 group (Polyetheretherketone (PEEK)/Flag shaped, Biohorizon, USA), and SB-2 group (Titanium/cylindrical shape, Bioline, GmbH). On completely edentulous mandibular model with 4 dental implants (TMR 4.6, Biohorizon, USA) with scan bodies were positioned in the first molar and canine. The model was scanned using a calibrated laboratory scanner (D2000; 3Shape) to generate a master reference model (MRM). Ten consecutive digital impressions Standard Tessellation Language file were made of the model using an intraoral scanner (Trios, 3Shape A/S) for both the test groups. The test scans were superimposed over the MRM using a best-fit algorithm, and then, the distance deviation and angular deviation of the scan bodies were calculated. Scan time was also recorded. Mann–Whitney U-test was used to statistical analysis. P > 0.05 considered statistically significant.
Results: Statistically significant differences were found between the SB material and shape on the linear measurement, angular deviation, and scan time (P < 0.05). The SB-1 group achieved higher accuracy overall and also exhibited noticeably lower scan time.
Conclusion: The quality of digital intraoral impressions seems to be influenced by both the geometry and material of the SB. For clinical practice, the PEEK material seems clinically beneficial for decision-making.
Keywords: Body, Polyetheretherketone intraoral digital optical scanning, shape and size, titanium intraoral digital optical scanning digital impression complete-arch
|How to cite this article:|
Karthhik R, Raj B, Karthikeyan B V. Role of scan body material and shape on the accuracy of complete arch implant digitalization. J Oral Res Rev 2022;14:114-20
|How to cite this URL:|
Karthhik R, Raj B, Karthikeyan B V. Role of scan body material and shape on the accuracy of complete arch implant digitalization. J Oral Res Rev [serial online] 2022 [cited 2022 Aug 15];14:114-20. Available from: https://www.jorr.org/text.asp?2022/14/2/114/349712
| Introduction|| |
Dental implants are reliable and well-documented method of replacement of missing teeth. The precision of intraoral impressions is one of the most important factors to achieve a perfect fit. Conventional impressions are associated with transfer problems and to minimize sources of error, intraoral digital optical scanning (IOS) has been introduced which enable a computer-based determination of the actual implant position using data obtained from digital intraoral scanners. Conventional implant impression methods have disadvantages of being inaccurate; to overcome the pitfalls, digital impressions are in use in the current day. They have features like ease of use and being more accurate than older techniques.
The accuracy of the optical transfer is defined by its precision and trueness. The precision expresses how close repeated scans are to each other. Deviation of virtual model from actual dimension of object is denoted by trueness. Both are important considerations in the digital implant dentistry workflow and should be optimized by not only the scanning devices but also the scan bodies themselves.
While the overall quality of the digitized data depends heavily on the specific IOS system there are other important factors that can play a role in the overall accuracy of the implant impressions are intaroral scan bodies (ISB). At present, the ISBs are manufactured as monolithic components or by a combination of different materials, as titanium alloy, polyetheretherketone (PEEK), aluminum alloy, and various resins. ISB design is composed by two main units: the scan region and the base. The surface characteristics of the scan region material like shape, design and type of material may influence the optical digital detection in terms of number of points acquired by the IOS while base material may affect the fit and wear resistance during the screwing onto the implant., The geometry of scan bodies varies from a spherical design to a cylindrical design with diverse intermediate forms. The height of commercially available scan bodies ranges from 3 to 17 mm.,
Due to the influence of saliva, which creates reflective surfaces, it is challenging to scan shiny, rough or translucent surfaces when compared to dull, smooth and opaque surfaces which can be scanned with more ease.,,]10] Scanning of partially edentulous condition is relatively easier and more accurate as there are reference points. However, in completely edentulous region scanning is very challenging as there are no fixed reference points.
To date, very few studies have evaluated and is unclear on the accuracy of an impression obtained using a digital intraoral scanner with scan bodies in completely edentulous condition as they differ in their design features and type of material the order in which the quadrants surfaces should be scanned.,, Thus, the purpose of this in vitro study is to measure and compare for the first time the linear and angular discrepancies of the scan bodies positions obtained by using two different scan body (SB) geometries and material when performing a digital scan for complete-arch implant impression. The results of this study may be important in identifying differences in the accuracy and scan time of various scan bodies in digital impression techniques, and help the clinician determine if any specific SB designs are beneficial in a completely edentulous situation.
| Methodology|| |
An edentulous mandibular polymethylmethacrylate model with 4 internal hexagonal connection implant analogs (4.6 mm × 12 mm, BioHorizons, Birmingham AL, USA) was positioned at the sites of in the first molar and canine region of the model and secured with acrylic resin (Pattern Resin; GC America). The distance between the 2 middle implants was approximately 25 mm and approximately 17 mm from the middle implant to posterior implant.
The model embedded with analogs of two different intraoral SB systems: SB-1 (BioHorizons, Birmingham AL, USA) and SB-2 group (Bioline Dental GmbH and Co, Wermeuchen, Germany) [Figure 1]. Without the removable gingival part was scanned. It was done by means of an calibrated structured laboratory reference scanner (D2000; 3Shape) with a precision of 5μmand exported to open-format standard tessellation language (STL) files to serve as the master reference model (MRM) [Figure 2].
|Figure 1: Implant scan bodies system used. (a) SB-1 group (PEEK/Flag shaped, Biohorizon, USA). (b) SB-2 group (titanium/cylindrical shape, bioline, GmbH). SB: Scan body, PEEK: Polyetheretherketone|
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Intraoral scan procedure
A prosthodontist (B.R.) and (B.V.K) with 5 years of experience using IOSs recorded different digital scans of the mandibular completely edentulous model with two different intraoral SB systems. A third operator (R.K) secured the SB onto the implant analog. SB-1 was hand tightened, a torque of 10 Ncm was applied with the system-specific ratchet, and SB-2 was snap fitted until stable on each implant replica on the mandibular edentulous model. Later, proper ISB seating over the analog was visually checked by magnifying loupes (Heine, Herrsching, Germany). All the digital scans were performed in a room the ceiling light comprised of 54-W fluorescent tubes registering 4500 lumens and 3500 K white spectrum color temperature. The luminosity at the Model was 800 lux measured by using a light meter (LX1330B Light Meter; Dr. Meter Digital Illuminance).
Scan body-1 specimens
Each model with the positioned scan bodies was scanned ten times with a laser scanner Trios3, 3Shape A/S, Copenhagen, Denmark) with the software version 184.108.40.206. The scanner works on principle of confocal microscopy laser technology and it is powder free. Scanning was done without removing or changing the SB positions, between the scanning cycles. The scan strategy recommended by the producer was followed, starting from the ISB occlusal-palatal surfaces with an approximate 45° wand inclination and a wave movement in the anterior area to avoid image splitting. Further, buccal aspect and other left out areas were scanned. All scans scan was considered complete once the SB surfaces were captured entirely and no major holes in were present. A STL file was created. The same procedure was repeated until 10 STL files were obtained for the SB-1 group. Scan time was also recorded.
Scan body-2 specimens
For SB-2, the digital scan was obtained using the same IOS, and the same scanning protocol as performed on SB-1 group. An SB-2 file was created. The same procedure was repeated until 10 STL files were obtained for the SB-2 group with the scan time recorded.
The workflow of the study is presented in [Figure 2].
Data processing and accuracy assessment
The surfaces of the consecutive models of SB-1 and SB-2 were placed in the same coordinate system of MRM. With the implemented best-fit algorithms searching for the shortest distance of corresponding points of two surfaces, the models were registered [Figure 3]. The applied mean-square-distance-metric ensured a median alignment of the virtual models. The MRM served as reference, and the following ten models of each SB-1 and SB-2 were each registered onto the first models. The surface of the scan bodies was blinded during the registration process to guarantee that only the unchanged structures were used for registration. The scan bodies used for each measurement were labeled 1 through 4 and the same labels were used for every inspection [Figure 4].
|Figure 3: Surface registration map after best fit alignment between the master reference file and one of the test standard tessellation language SB-1 and files SB-2 group. SB: Scan body|
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|Figure 4: STL file of master reference model (a) SB-1 group (b) SB-2 group, STL files of test scans (c) SB-1 group (d) SB-2 group. Scan bodies used are labeled 1 through 4 and same was used for measurements. SB: Scan body, STL: Standard tessellation language|
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The three-dimensional (3D) position of scan bodies on the MRM was calculated and used as a reference to calculate the SB discrepancies within different STL files of scan bodies of study groups. The data for each SB were condensed to the center point of the scan bodies in the x- (buccolingual), y-(mesiodistal), and z-(apicocoronal) axis. 3D linear Euclidean distance (dXYZ) directions of the center point displacement were calculated in micrometers (mm). Thus, these three axes each represent the deviation in one spatial dimension. The Euclidian distance, on the other hand, describes the deviation in 3D space, which was calculated as a vector calculation of the 3D offset.
To determine the angular deviation, cylinders were fit to each SB using the same computer software program and a central axis was generated for each. The nominal axis from the MRM was considered to be at an angle of zero, and the resultant 3D angle between the MRM and test model was recorded, and then averaged, to generate the angular deviation among the two scan bodies.
| Results|| |
In this in vitro study, influence of SB on scanning accuracy was investigated by measuring the linear (mm) and angular (degrees) discrepancies between the scan bodies. Further, scan time (min) for completely edentulous situation is determined. The Shapiro–Wilk test revealed that the data were not normally distributed. The mean and standard deviations were recorded. These values were compared between SB-1 and SB-2 using Mann–Whitney U-test for pairwise comparison. The level of significance was set to P < 0.05. Statistical analysis was conducted with SPSS 22 (SPSS Inc., Chicago, IL, USA). Linear (x-, y-, and z-axis), angular (degrees), and 3D discrepancies are presented in [Table 1] and [Table 2]. The boxplots of linear, angular discrepancies, and scan time are presented in [Figure 5] and [Figure 6].
|Table 1: Descriptive analysis Linear (X-, Y-, Z-axis and), angular(s) deviations and scan time of scan body-1 with scan body-2|
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|Table 2: Mann–Whitney U results comparing the effects of scan body-1 and scan body-2 on linear deviation, angular deviation and scan time|
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|Figure 5: Boxplot of linear (x-, y-, z-axis) SB-scan body; SB-1 group (PEEK/Flag shaped, Biohorizon, USA) and SB-2 group (titanium/cylindrical shape, bioline, GmbH). SB: Scan body, PEEK: Polyetheretherketone|
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|Figure 6: (a) Boxplot of dXYZ deviations (mm) (b), angular deviations (degrees). (c) Boxplot of scan time (min). SB-scan body; SB-1 group [PEEK/flag shaped, Biohorizon, USA] and SB-2 group (Titanium/cylindrical shape, Bioline, GmbH). SB: Scan body, PEEK: Polyetheretherketone|
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Comparison of linear and angular measurements
The test revealed significant differences in the linear x-, y-, and z-axis distortion between the SB-1 and SB-2 groups (P < 0.05). The most accurate SB positions were obtained on the Y-axis. In the present paper, absolute linear deviations at the 25%–75% quantiles (Q1, Q3) were below 1.6 mm on the Y-axis, 23 mm on the X-axis, and 28 mm on the Z-axis. The extreme values recorded were 1.34 mm and 22.32, 31.34 and 3.54 mm, 35.02 and 40.86 mm, respectively. In terms of 3D linear deviation (dXYZ), a significant difference of 58.33 and 100.26 mm was noted, respectively (P = 0.0001). Such data suggested a variation in linear accuracy of the IOS for complete-arch implant impression in vitro, however, the extreme deviations up to 139.44 mm were far below the 150 mm implants-prosthesis misfit limit value widely considered in the literature to avoid long-term clinical complications.
For angular measurements, the mean angle between the scan bodies showed SB-2 group (0.89°), a significantly higher angular discrepancy than the SB-1 group (0.89°) (P < 0.0001). In the present paper, the accepted angular discrepancy is within the acceptable range. Such data suggested that the reported SB-1 angular deviations may not affect negatively the overall implants-prosthesis fit particularly in case of screw retained complete-arch restoration.
Comparison of scan time
With regard to scan time, a statistically significant difference in the means of the scan time between the two tested scan bodies (P = 0.0004). The mean scan times were significantly less for the SB-1 group (2.31 min) than for the SB-2 (2.95 min).
| Discussion|| |
Commercially available implant scan bodies from different manufacturers are highly variable in their characteristic material and surface topography, which could influence the accuracy of implant positioning. Till date, to the best of our knowledge, the influence of ISB material, shape and scan time over the IOS impression accuracy is very scarce in the literature. Hence, in this in vitro study, evaluated the influence of ISB material (PEEK and titanium), shape (different geometry) and time on the accuracy of digital complete-arch implant impression.
In the present study, following standardization protocol were attempted in designing the study to prevent the error in registration and measurements of scan bodies and its possible influence on scan accuracy. (1) Scan bodies were seated on each implant replica of the model, as per the manufacturer recommendations (PEEK-snap fitted: titanium hand tightened with calibrated driver). (2) Scan bodies were not disconnected until the test and reference scan were completed to minimize the damage to the scan bodies and eliminate possibility repeated positional error. (3) The intraoral scanner 3 shape (Trios3, 3Shape A/S, Copenhagen, Denmark) showing a very high precision in recording up to 5 μ was used to produce standard STL files of test groups. (4) MRM, was scanned with Dental lab scanner D250 (Trios3, 3Shape A/S, Copenhagen, Denmark) without distortion as it works on continuous image acquisition technique with laser planes projected on the whole model for model reconstruction. Few studies have used CMM to produce MRM which allows the recording of precise 3D measurement but has shown reduced accuracy in measuring freeform surfaces because of the size and shape of the touch spherical probe tip., (5) The “best-fit algorithm” was applied for the superimposition of images as this methodology allows to calculate the point-to-point distance between the surface of the test and reference scans with high precision. (6) Scan bodies used in the study were of similar size and mounted on the same implant analog as it can cause positional error and can affect the extent of information optically recorded.
However, the material and geometries of scan bodies differed significantly among the study groups evaluated. The quality of a digitized surface reconstruction, and any subsequent measurements, is generally accepted to be shape-dependent, whereas the type of material affects the number of points acquired., Dull, smooth and opaque surfaces are more easily scanned than shiny, rough or translucent ones., Scan bodies of SB-1 group has snap fitting connection, having an overall cylindrical shape with unique top surface (flag shaped consisting of two semi-circular holes and occlusal notch) for easy identification from the occlusal view. It is made of the PEEK material which is a high strength thermoplastic material and having a dimension of 4.5 mm platform with 8 mm in height. On the other handscan bodies of, SB-2 group were cylindrical with relatively flat and a partially angled upper part, internal hex of diameter of 4.6 mm, a height of 8 mm and were produced with a 0.01 mm tolerance. It is completely made of titanium alloy material which has the advantage to resists distortion due to repeated use with sterilization. The surface of the scan region was sandblasted to reduce surface reflection during the scanning procedures. Further it is the most commonly available design that could be readily reverse engineered to simulate scan bodies.
ISB material (Pk & T) (P < 0.0001) and shape (flag shaped and cylindrical) (P = 0.0009) significantly influenced the scanning accuracy of complete edentoulous-arch implant impression, considering both linear and angular deviations from the reference scan. Further, significant difference in scan time was detected (P = 0.1892). SB-1 group had more detailed optical scanning and this might be due to (1) The major segment of the scan bodies was presented with more characteristics on the surface, making it easy to be identified from various directions and improve the surface recognition performed by the CAD software. (2) The use of PEEK materials might have reduced the problem of light reflectance that can occur in the metal alloy and would have promoted optimum scanning properties, resulting in a more detailed optical scanning., On contrary, the less precise accuracy of scan bodies position in SB-2 group could be a result of potentially compromised optical properties of the ISB material (1) Reflective titanium surface would have reduced the number of points recorded by an IOS. (2) Less surface distinguishing shape (cylindrical with flat side) would have induced less asymmentry in shape which is required to index the ISB on CAD software.
Different research protocols which have been followed in previous studies makes the comparison between studies on implant digital scan accuracy in completely edentulous situation difficult within this study. This result is similar to the results of the previous studies that reported the accuracy of the SB design and material on the accuracy of digital impressions.,,,, In in a recent systematic review, it was concluded that the materials of a SB could impact scanning accuracy. A recent study reported better scanning accuracy of PEEK scan bodies in comparison with titanium scan bodies. In an in vitro study, Mizumoto et al. indicated that the accuracy of digital impressions was affected by SB geometry. A shorter and simpler designed SB might perform better in terms of both scanning time and scanning accuracy. Vandeweghe et al. analyzed complete-arch implant impression accuracy of different scan bodies using four IOS and found to have a significant effect on the accuracy. Only one study has specifically investigated the relationship between the effect of SB geometry and shape on scan accuracy and found significant differences in the 3D positioning and angular deviation between two commercially available ISBs.
The displacement of the SB may adversely affect the final implant-supported prostheses if there was a deviation of more than 100 μm in the scanning accuracy., Jemt argued that there should be a gap of <150 μm between a prosthesis and an abutment To obtain the passive fit of implant-supported prostheses, it is essential to reduce errors less than 100 μm in the impression process using the SB. For complete arch implant impressions, however, higher amounts of inaccuracies have been shown, ranging in distance deviations of 47–226 μm. The current study demonstrated results within this range. In the present study scanning inaccuracy was <91.29 mm for SB1 and 139.34 mm for SB2 group.
Although the results of this in vitro study are very promising, there are few limitations. (1) The main limitation of the present study is in vitro nature of study, scanning in the mouth may doubles the error compared to scanning a model due to the different environment. (2) Results reported in our study are inherent to the specific IOS device and the corresponding scan bodies. (3) Limited number of different SB designs were tested. (4) Scan bodies were never splinted for extraoral or intraoral scanning which could have improved scanning accuracy. (5) This study did not investigate the prosthetic misfit when the implant-supported prostheses were produced when using the completely digital workflow. (6) Only one scanning protocol was adopted and the possible influence of different scanning strategies and the operator effect were not analyzed.
As the geometry and materials of the scan bodies itself may influence scanning accuracy in completely edentulous conditions, more evidence is needed to clarify this. The scan bodies should be designed with more characteristic reference points than most of the commercially available cylindrical scan bodies. Further development of the scanning devices, scanning protocols, imaging techniques and influence of the distance between implant scan bodies is necessary to enhance the precision of optical acquisition of implant scan bodies.
| Conclusion|| |
Within the limitations of this study, it can be concluded that the implant SB material and shape significantly influenced the scanning accuracy of complete-arch digital impression. PEEK ISBs with unique geometry showed the highest accuracy on both linear and angular perspective with less scan time, followed by titanium with simple cylindrical shape. Nevertheless, this study could help in making a decision about scan bodies material and geometry in daily practice by recommendations made in the conclusions.
Kempegowda Institute of Medical Sciences, Institutional ethical Committe (registered under CDSCO vide file no. ECR/307/KRIS/Inst/Kar/2013).
Financial support and sponsorship
It is a fully self-funded study.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2]