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| ORIGINAL ARTICLE |
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| Year : 2022 | Volume
: 17
| Issue : 3 | Page : 699-704 |
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An in vitro digital comparative evaluation of the accuracy and dimensional stability of vinyl polyether silicone impression material with the conventionally used elastomeric materials scanned using a blue light scanner
Bhavna Mahesh Ahuja1, Pronob Kumar Sanyal1, Rakshith Guru2, Abhijeet Kore1
1 Department of Prosthodontics and Crown and Bridge, School of Dental Sciences, Krishna Institute of Medical Sciences Deemed To Be University, Karad, Maharashtra, India
2 Department of Prosthodontics and Crown and Bridge, ESIC Dental College, Gulbarga University, Gulbarga, Karnataka, India
| Date of Submission | 04-Aug-2020 |
| Date of Decision | 22-Nov-2020 |
| Date of Acceptance | 10-Dec-2020 |
| Date of Web Publication | 2-Nov-2022 |
Correspondence Address:
Dr. Bhavna Mahesh Ahuja
Department of Prosthodontics and Crown and Bridge, School of Dental Sciences, Krishna Institute of Medical Sciences Deemed to be University, Karad, Satara, Maharashtra
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/jdmimsu.jdmimsu_291_20
Background: The development of material science has allowed integrating qualities of polyether (PE) and Vinyl Polysiloxane (VPS) into a newer material Vinyl polyether silicone (VPES). There is limited literature available on this combination material. The aim was to evaluate and compare the accuracy and dimensional change of elastomeric impression materials with a three-dimensional (3D) approach. Materials and Methodology: Impressions were made of standard tooth model and custom trays using the three monophase impression materials, i.e., Group A–Vinyl polysiloxane (VPS), Group B-Polyether (PE), and Group C-Vinyl Polyether silicone (VPES). All the impressions were digitized and compared on eight predetermined points using a 3D compare software by the superimposition of computer-aided design files of impressions onto that of Standard tooth model. Three-dimensional comparison is repeated after storage of impressions for 1 week to re-evaluate the dimensional stability of the impression materials. Results: The average measurement of mean discrepancies of all the 8 points obtained on day 1 for VPS, PE, and VPES were 75.758 μm, 139.52 μm, and 49.24 μm, respectively, which helps in the determination of accuracy and after interval of 1 week 91.27 μm, 157.25 μm, and 89.76 μm, respectively, which helps to deduce that the linear dimensional change values for Group A, Group B, and Group C were 15.52 μm, 17.73 μm, and 40.52 μm, respectively. Conclusions: Average dimensional accuracy was highest of VPES followed by VPS and PE. Whereas VPS impression material shows the highest dimensional stability after prolonged storage of 1 week, followed by PE and then VPES impression material.
Keywords: Computer-aided design/computer-aided manufacturing, dimensional accuracy, elastomeric impression materials, linear dimensional stability, three-dimensional approach, vinyl polyether silicone
How to cite this article:
Ahuja BM, Sanyal PK, Guru R, Kore A. An in vitro digital comparative evaluation of the accuracy and dimensional stability of vinyl polyether silicone impression material with the conventionally used elastomeric materials scanned using a blue light scanner. J Datta Meghe Inst Med Sci Univ 2022;17:699-704 |
How to cite this URL:
Ahuja BM, Sanyal PK, Guru R, Kore A. An in vitro digital comparative evaluation of the accuracy and dimensional stability of vinyl polyether silicone impression material with the conventionally used elastomeric materials scanned using a blue light scanner. J Datta Meghe Inst Med Sci Univ [serial online] 2022 [cited 2023 Sep 25];17:699-704. Available from: https://journals.lww.com/dmms/pages/default.aspx/text.asp?2022/17/3/699/360203 |
| Introduction | |  |
In 2009, a Vinyl polyether silicone product (VPES) (EXA'lence; GC America) was commercially introduced. This material is available in a variety of consistencies and setting times. EXA'lence is composed of a combination of Vinyl polysiloxane (VPS) and Polyether (PE) and is promoted as a hydrophilic material. VPS and PE show excellent dimensional accuracy and dimensional stability under different test and storage conditions.[1],[2],[3],[4],[5],[6] EXA'lence is stated to be intrinsically hydrophilic with the optimal flow and high tear strength, resulting in a predictable performance under any clinical environment. It is not yet available for its use in Indian atmospheric conditions; hence, this study is selected to check the accuracy and dimensional stability of VPES (Exa'lence. GC America) as compared to conventionally used materials like VPS (Aquasil Ultra, Dentsply) and PE (Impregum soft, 3M) over a period of time to assess its efficiency in Indian conditions.
These days being the era of digitization, the use of optical scanners has reached new heights. In optical scanners, recent development is seen as blue light scanners, which are currently a boon to scanning technology in recording the impressions as it has fixed wavelength as compared to that of white light optical scanners. Jeon et al.[7] in his study concluded that, on the evaluation of the digitized abutment tooth impressions, the blue-light scanner exhibited greater repeatability than the white-light scanner; hence, the extra oral scanner used in this study was a blue light scanner to maximize the precision of recording impression scans.
The linear dimensional change of all the three impression materials was thus assessed using a three-dimensional (3D) approach.
| Materials and Methodology | | |
The present in vitro study was approved by the Institutional ethical committee (Protocol number– 0262/201/-2018). This study was conducted for the digital comparative evaluation of accuracy and dimensional stability of new elastomeric impression material with the conventional elastomeric impression materials [Table 1] on storage of impression for 1 week time interval. | Table 1: Impression materials with their company names used in this study
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Fabrication of standard reference model through computer-aided design/computer-aided manufacturing
Ivorine mandibular first molar was prepared using friction grip standard diamond points medium grit TF 13 (Mani, Prime Dental Products) to receive a circumferential shoulder as it is done in routine clinical practice. The width of the finish line from the optimally tapered axial wall to the cavosurface margin was 1 mm. The prepared tooth was scanned using Medit Identica Hybrid 3D Extraoral scanner (Blue light extraoral scanner). A virtual model was designed by 3D modeling using CAD software Zbrush (Pixologic developers) [Figure 1]a. In this 3D modeling of the standard reference model (SRM), base along with orientation grooves was designed (3 × 2 × 1.5), which aided in standardized positioning of the custom impression tray. This CAD design in stereolithography (SLA) format (standard tessellation language [.stl]) was then transferred to 3D Printer (Form 2, Formlabs) for the printing of SRM [Figure 1]b using SLA technology with 100% infill density. | Figure 1: (a) Virtual model was designed by 3D modelling using CAD software Zbrush having base along with orientation grooves (3 × 2 × 1.5) (b) Standard Reference model in standard hard resin material
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Fabrication of custom impression tray
Trays were designed in a way to have even space of 3 mm all around the tooth to obtain sufficient thickness of monophase impression material, projections corresponding to the orientation grooves in the base of the SRM to ensure accurate orientation and precise fit of the trays over the model during impression making [Figure 2]. This helped in precise and standardized fit of the Custom tray onto the model. CAD file was transferred for 3D printing to the machine (Aakriti 2.5 + 3D printer, Aarya Precision technology) using fused deposition method principle. The material used for the fabrication of the custom tray was acrylonitrile butadiene styrene with 50% infill density.
Impression making of standard reference model
For this in vitro study, 11 impressions were made with each of the three elastomeric impression materials individually, as shown in [Table 1]. Impression materials were manipulated according to the manufacturer's instructions. Care was taken to dispense the same amount of impression material in the recess made in the custom tray [Figure 3]. After loading the custom tray, it was placed on the SRM by proper orientation of projections of the custom tray into the corresponding grooves in the base of the model. Impression material was allowed to set for the specified time as per the manufacturer's instructions [Figure 4]. All the impressions of the three groups were washed to mimic the clinical situation and stored at room temperature. They were scanned after 1 day of impression making to simulate the time taken on average to send impressions to dental laboratories.
SRM was scanned using a blue light scanner (Medit Identica Hybrid). As this model was made up of standard hard resin in gray color, which provides the nonreflective surface, thus making it more favorable for the quick and accurate scan. The scanned data of this model were then edited to remove the base part of the model and was saved as a CAD file (.stl format) termed as CAD reference model CRM which was used in further study for digital comparison of the impression scans.
Scanning of impressions
Impressions were scanned on day 1 using Medit identica hybrid (Blue light non-contact extraoral surface scanner) without using any non-reflective spray. The scanned data of these impressions were saved and further used for comparison with the CRM file (.stl format) individually [Figure 5]. The excessive tray area was cropped in software leaving only the concerned impression area of the scan for further analysis. The impressions were stored at room temperature for 1 week time interval to check the dimensional stability of the elastomeric impression materials and were scanned afterward and again compared with the CRM file to check any change in dimensions using the superimposition of the scanned files of impressions over the CRM file.
Digital analysis of the scanned data
The software used for measurement in this in vitro study was CATIA-V5 R19. Initially, 3D scanned files were converted into the 3D model, which generally has. stl file format, which was then converted to model in CATIA software (Buffalo Grove, IL). The digitized impressions were assembled with the CRM in the assembly module in the software. The two surfaces were assembled such that there will be perfect contour matching with each other using the best fit alignment method manually. The surfaces were trimmed by using planes to cut into the section. The plane chosen was from the middle of the tooth to get a longitudinal section of the tooth mesiodistally. After sectioning, the discrepancies between the two superimposed surfaces were measured at eight selected points, which were evenly distributed in occlusal, middle, and cervical third areas of the tooth. Out of these 8 points, 4 points were near the finish line of the prepared tooth, which helped to measure the discrepancy in margin area in two planes, vertical and horizontal, respectively [Figure 6]. | Figure 6: (a) Schematic diagram of points for measurement. (b) Measurement of discrepancy
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The summary of the methodology is given in [Figure 7].
| Results | | |
A total of 33 impression samples were taken for this study, which were divided into 11 samples per group. The impressions were scanned using an extraoral scanner on day 1 and after an interval of 1 week. These scanned data of impressions were then used to check the dimensional accuracy of impression as compared to the CRM using CATIA V5. The values of the discrepancy between model and impression were recorded on day 1 and after the interval of 1 week. The linear dimensional change was calculated between the two readings to check the dimensional stability of the impression materials on storage of 1 week.
Three groups were compared for discrepancy value by analysis of variance followed by pairwise comparison by Tukeys' Post hoc test. Before and after comparison was done by Paired t-test. Simple/Multiple Bar charts; were used for data presentation. In the above tests, P ≤ 0.05 (P < 0.05) was taken to be statistically significant. The data were entered into Microsoft Excel 2010. All analyses were performed using the Statistical Package for the Social Sciences software version 20 (Altem Technologies (P) Limited).
Group A-The difference between mean discrepancy at day 1 and after 1 week at points 1, 2, 3, 4, 5, 6, and 7 among group A was found statistically insignificant with P nor equal to 0.5.
The difference between mean discrepancy at day 1 (42.64 ± 26.632) and after 1 week (145.45 ± 95.676) at point 8 among Group A was − 102.818, which was found statistically significant with P = 0.008 with confidence interval [CI] −171.931; −33.705.
Group B- The difference between mean discrepancy at day 1 and after 1 week at points 1, 2, 4, 6, 7, and 8 among Group B was found statistically insignificant with P not less than or equal to 0.5.
The difference between mean discrepancy at day 1 (91.55 ± 75.521) and after 1 week (182.18 ± 130.670) at point 3 among Group B was − 90.636, which was found statistically significant with P = 0.024 with CI − 166.866; −14.407.
The difference between mean discrepancy at day 1 (118.45 ± 68.925) and after 1 week (223.09 ± 157.379) at point 5 among Group B was-104.636, which was found statistically significant with P = 0.026 with CI − 194.128; −15.144.
Group C-The difference between mean discrepancy at day 1 and after 1 week at points 1, 4, 5 and 6 among Group C was found statistically insignificant with P not less than or equal to 0.5.
The difference between mean discrepancy at day 1and after 1 week at points 2, 3, 7, and 8 among Group C was statistically significant with P = 0.011, 0.016, 0.008, and 0.001 [Graph 1] and [Graph 2].
Linear dimensional change is calculated after calculating the discrepancies of all three impression materials after 1 week [Table 2]. | Table 2: Linear dimensional change between three impression groups on storage of 1 week
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| Discussion | | |
As EXA'lence has different composition from other elastomeric impression materials commonly used, it would be important to study its behavior under different test conditions. Previous studies available on EXA'lence material have shown the effect on surface detail reproduction, dimensional stability after prolonged storage in disinfectants by immersion in Glutaraldehyde, surface changes on disinfection by ozone, and cytotoxicity.[8],[9],[10],[11],[12] The previous studies on dimensional stability were done by using metal dies fabricated according to American Dental Association (ADA) specification 19,[8],[13] but there is the scarcity of literature on accuracy and dimensional stability of the VPES impression material using digital methods on a tooth model. The cuspal anatomy of the tooth with the highs and lows can complicate the general measures of accuracy and the dimensional changes of the recorded impressions. Hence, a tooth model was chosen for this study so as to gain close simulation with the clinical scenario.
The standard CRM that was used in this study for impression making was made up of standard hard grey resin material so as to provide a nonreflective surface for scanning under extraoral scanner, as the scanning of metal models which were commonly used in previous studies may require the use of the nonreflective sprays which ultimately leads to decreased precision of the impression recorded. Along with this, the extraoral scanner used in this study was a blue light scanner, which exhibited greater repeatability as compared to the white-light scanner, suggesting that blue-light scanning might be an important requisite for impression scanning.[14]
Literature has shown an average of approximately 10 μm error in impression scanning, which is considered to be within a reliable level. Thus, more of repeatability and reproducibility was observed in the results, with errors <10 μm. A blue light scanner uses a light source with a shorter wavelength, resulting in smaller scanning errors for the variables affecting the color and shape of the object being scanned.[15] Hence, it is a standardized error, which is the same for all the samples and the ideal model being scanned.
The average measurement of mean discrepancies of all the 8 points obtained on day 1 for Group A (VPS), Group B (PE), and Group C (VPES) was 75.758 μm, 139.52 μm, and 49.24 μm respectively, and after interval of 1 week 91.27 μm, 157.25 μm, and 89.76 μm respectively which helps to deduce that the average dimensional accuracy is highest of Group C (VPES) followed by Group A (VPS), followed by Group B (PE), which was in accordance with the earlier studies done by Stober et al.[16] where it was shown that vinyl siloxanether monophase impressions and vinyl siloxanether dual-viscosity impressions resulted in acceptable accuracy for clinical use with immersion disinfection, as results for vinyl siloxanether were comparable to representative PE and VPS materials groups. However, the findings of the study done by Schaefer et al.[17] differ from this study, as they concluded VPS had the highest accuracy, followed by VPES and PE.
To determine the dimensional stability of the impression materials, linear dimensional change was calculated between the average discrepancy measurements of day 1 and after an interval of 1 week. The linear dimensional change values for Group A (VPS), Group B (PE), and Group C (VPES) were 15.52 μm, 17.73 μm, and 40.52 μm, respectively. As dimensional stability of the impression materials will have an inverse relation with the linear dimensional change, hence highest dimensional stability was seen with Group A (VPS) as it has minimum dimensional change over storage period of 1 week (15.52 μm) followed by Group B (PE) which shows the dimensional change of 17.73 μm and then followed by Group C (VPES) (40.52 μm).This was in accordance with other studies where it was concluded that PVS showed superior dimensional stability compared to PE, and it has been suggested that impressions may be poured up to 4 weeks[15],[18] Whereas these findings were in contradiction to Nassar et al.[9] and Aslan and Ozkan[19] who checked the volumetric dimensional change of this new hybrid material with VPS and PE, he finally concluded that the highest volumetric dimensional change was seen in PE (−0.023 ± 0.002) group on day 1 followed by VPS (−0.009 ± 0.002) and VPES (−0.004 ± 0.001) respectively. The lowest volumetric dimensional change was observed in the VPES group on day 7 (−0.010 ± 0.0003) and the highest change was observed in the PE group on day 7 (−0.052 ± 0.0004). The probable reason for this could be because of the difference in atmospheric conditions as the impression was stored at room temperature, also the consistencies mentioned were different. Further investigation on different consistencies of VPES should help to reveal more in these atmospheric conditions.
PE showed limited linear dimensional change after storage for 1 week, this could be because of the high hydrophilic property of PE leading to absorption of water from the atmosphere during the storage period. This material shows greater stability over time when compared to other elastomeric impression materials, despite controversy regarding the time of pouring: Immediate or periods of up to 24 h[20],[21],[22] for 1 week[23],[24] or some even say 4 weeks.[5]
Limitations
Since the present study was performed in a laboratory, it was not possible to analyze the effect of factors such as saliva, blood, oral temperature, and special clinical conditions on the accuracy of impression techniques, which might have significant impacts on the obtained results. Errors in the best fit method are difficult to explain. There were highest discrepancies seen with PE group in the recording of the impression of standard CRM thus leading to minimal accuracy as compared to other two impression materials, which could be because of use of hand mix material as compared to use of cartridge system using auto mixing gun for dispensing the VPS and VPES impression materials.
Future perspectives
Different consistencies can be compared. Volumetric dimensional change can be assessed to check the dimensional stability of VPES impression material.
| Conclusions | | |
Within the limitations of this in vitro study, conclusions that were drawn are as follows:
- VPES impression material shows the highest dimensional accuracy, followed by Poly vinyl siloxane and PE. Hence, this new hybrid material gives comparable results as that of VPS and PE
- There is no statistically significant difference found in dimensional accuracy between polyvinyl siloxane and VPES impression materials, on day 1 or after a storage period of 1 week. Thus, both VPS and VPES can be used when precise impressions are needed to record fine details like finish lines in fixed restorations or for Implant Prosthesis
- VPES, due to its inherent property of hydrophilicity, makes it a better choice of impression material in cases where moisture control becomes difficult to achieve
- VPS impression material shows the highest dimensional stability, followed by PE and then VPES impression material. Hence when impressions are to be stored for a long time, VPS becomes the impression material of choice.
Acknowledgment
Dr. Shashank Bagaria, Manisha Bagaria, Dr. Minal Kumthekar, and Dr. Mamta Rohra for the immense support and help during the study and manuscript preparation.
Financial support and sponsorship
Nil.
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], [Figure 7]
[Table 1], [Table 2]
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