|Year : 2020 | Volume
| Issue : 2 | Page : 99-106
Assessing the dimensional accuracy of the resultant casts made from monophase, one-step, two-step, and a novel two-step putty light body impression technique – An in vitro study
Harini K ShivaKumar1, Supriya Manvi2, Ulhas N Amasi3, Sounyala Rayannavar4
1 Department of Oral Maxillofacial Rehabilitation, KLE'S Institute of Dental Sciences, KAHER, Belgaum, Karnataka, India
2 Department of Prosthodontics, KLE'S Institute of Dental Sciences, Bengaluru, Karnataka, India
3 Department of Prosthodontics, Yashodha Dental Clinic, Bengaluru, Karnataka, India
4 Department of Prosthodontics, KLE'S Institute of Dental Sciences, KAHER, Belgaum, Karnataka, India
|Date of Submission||19-Dec-2019|
|Date of Decision||28-Jan-2020|
|Date of Acceptance||23-Mar-2020|
|Date of Web Publication||09-Jun-2020|
Dr. Harini K ShivaKumar
Department of Oral Maxillofacial Rehabilitation, Qassim Private Colleges, College of Dentistry Buraidah -51411
Source of Support: None, Conflict of Interest: None
Background: The clinical success of fixed prosthodontics and dental implants is dependent on the dimensional accuracy of the impression obtained. Although there are many studies on different impression materials and the accuracy of the dies, only a few studies on the techniques of impression making hence this study was taken to evaluate and compare the dimensional accuracy of casts made from four different impression techniques.
Aim: This study aims to assess the dimensional accuracy of the resultant casts made from a monophase, one-step, two-step, and novel two-step putty light body impression technique.
Settings and Design: An in vitro study.
Materials and Methods: A stainless steel model of two abutments with specific distance was fabricated. An impression of this model was made with four different impression techniques using a polyvinyl siloxane impression material using custom made trays. Ten impressions were made with each impression technique. Total 40 impressions made and casts poured with type IV gypsum, and accuracy of the casts measured using a traveling microscope. Three dimensions, i.e., diameter, height, and inter-abutment distance measurements were obtained.
Statistical Analysis: The statistical analysis was done using one-way ANOVA and Student Newman-Keuls test.
Results and Conclusion: The casts obtained from all four techniques had significant differences in dimensions as compared to that of the master model. The order for highest to lowest accuracy from, the stainless steel model was; monophase < one-step < two-step < two-step injection technique. The two-step and two-step injection techniques produced the most accurate cast, with the two-step injection technique performance being better than the two-step technique casts obtained.
Keywords: Acrylic resins, adhesives, elastomers, gypsum, polyethylene, polyvinyl, siloxanes, stainless steel, viscosity
|How to cite this article:|
ShivaKumar HK, Manvi S, Amasi UN, Rayannavar S. Assessing the dimensional accuracy of the resultant casts made from monophase, one-step, two-step, and a novel two-step putty light body impression technique – An in vitro study. Saudi J Oral Sci 2020;7:99-106
|How to cite this URL:|
ShivaKumar HK, Manvi S, Amasi UN, Rayannavar S. Assessing the dimensional accuracy of the resultant casts made from monophase, one-step, two-step, and a novel two-step putty light body impression technique – An in vitro study. Saudi J Oral Sci [serial online] 2020 [cited 2020 Sep 22];7:99-106. Available from: http://www.saudijos.org/text.asp?2020/7/2/99/286220
| Introduction|| |
The journey toward successful restoration begins with making accurate impressions. The overall goal of a dental impression is to produce an exact negative replica in three dimensions, of the hard and soft tissue of the oral cavity. High accuracy of dental impression is the mandatory first step  and an integral step in a complex process of fabricating a well-fitting indirect dental restoration. Various factors influence the choice of impression materials, the quality of the impression and the quality of the cast. Today, two of the most popular elastomers used in dental practice are the polyether and addition reaction silicone or vinyl polysiloxane. Today, it is proved that impression materials have advanced to such an extent that doubting the accuracy of impression material is out of the question, among all the impression materials polyvinyl siloxane is proved to be excellent with their unsurpassed accuracy and dimensional stability.
The factors that result in dimensional changes are temperature, humidity, and polymerization shrinkage. Various studies have been reported regarding the effect of humidity and temperature change on the dimensional stability of these two impression materials. The study was attempted to evaluate the effect of different temperatures, as reported in different regions of the Indian subcontinent, as well as the effect of different storage time on the dimensional stability of these impression materials.
Hence, the focus should be on the impression technique. A study was done with various impression techniques used for making an impression are: (1) putty wash single step, (2) putty wash twostep, (3) single mix, and (4) multiple mix techniques. In spite of the best available impression materials and advanced impression techniques, we still come across inaccuracy of fit of a dental prosthesis, which may be either due to the inaccuracy of impressions or dimensional changes of impression. Hence, this study is undertaken to compare the dimensional accuracy of three brands of Poly vinyl siloxane (PVS) impression materials and to evaluate the most accurate impression technique. Among the impression techniques, the double mix impression technique showed the better results compared with single mix impression technique.
Several techniques have been developed which can be categorized as monophase or dual-phase, monophase materials are used to perform in a single-step and dual-phase putty wash materials are used to perform the impression technique in one step and two-step. Hence, a novel two-step impression technique is performed using one more extra light body material which can enhance the dimensional accuracy of the first two materials.
The present study was done to evaluate the dimensional accuracy of casts made using different techniques, such as monophase, one step, two-step, and a novel two-step putty or light body impression techniques to fabricate the accurate prosthesis.
- To compare the dimensional accuracy of the resultant casts made from the monophase impression technique with the one-step impression technique
- To compare the dimensional accuracy of the resultant casts made from one-step impression technique with the two-step technique
- To compare the dimensional accuracy of the resultant casts made from two-step impression technique with the novel two-step putty light body impression technique
- To compare the dimensional accuracy of the resultant casts made from the novel two-step putty light body impression technique, with the monophase impression technique, one step impression technique, and two-step impression technique.
| Materials and Methods|| |
Fabrication of master model [Master model skecth-1]
A metallic master model simulating two identical full crowns tapered preparations with the dimensions of diameter-5.52 mm, height-6.99 mm, and inter-abutment distance-28.87 mm were fabricated. For measurement purpose, both the abutments were prepared with cross-grooves on the occlusal and proximal surfaces as reference points during fabrication. A depression was created in the center of a model on one side for the orientation of the tray. The finished model was mounted on a clear acrylic round block [Figure 1]. Measurements of height, diameter, and inter-abutments were done.
Custom tray fabrication
Self-cure Acrylic resin (DPI Cold Cure Acrylic Improved – Denture Base Polymer) custom trays [Figure 2] of uniform 3 mm thickness were prepared, with 2 mm and 4 mm of clearance between tray and master model for monophase and putty-light body impressions, respectively. To fabricate all the custom trays with identical spacer thickness, 2 and 4 mm of modeling wax was adapted over the model to provide space for impression materials and the impression was made using irreversible hydrocolloid with the help of stock tray and the cast was prepared. A uniform 3 mm thickness of wax was adapted over this spaced cast and a silicone putty mold was prepared and then the wax was eliminated. Then, the custom trays of identical thickness were fabricated with self-cure acrylic according to the guidelines.
Making of impressions
All impressions were made under controlled room temperature. The custom trays were coated with a layer of polyvinyl siloxane tray adhesive (3M ESPE) and were allowed to dry for a minimum of 15 min. The monophase impressions (Type 3 Lot no 090901) were made using an impression material that was dispensed with an automatic mixing syringe. The impressions were allowed to polymerize for 12 min. The one-step impressions were made with the putty (Type 0 Lot no 0912001737) and light body (Type 3 Lot no 100223) material simultaneously, where an estimated equal measurement of soft putty was taken and mixed with fingertips and the light body was dispensed with the automatic mixing syringe. In the two-step impression technique, the preliminary putty impression was made using polyethylene as spacer and light body was dispensed in the second step to complete the impression. A two-step novel technique was made with putty and light body materials simultaneously and allowed to polymerize on a model for 12 min, then on the coronal edge of each abutment, a hole was made through the polymerized material which coincides with one of the holes present in the custom tray [Figure 3]. Extra light body (Type 3 Lot no 091007) material was then added in the abutment space, an impression was reinserted onto the model, was allowed to polymerize for 12 min [Figure 4], [Figure 5], [Figure 6].
All impressions were made under controlled room temperature.
To reduce the number of factors that could have influenced the outcome, custom trays of identical thickness and spacer were used for all the impression techniques and same operator made all the impressions (considering the application of force).
Preparation of the working cast
All the impressions were stored for 1 h before pouring. Then Type IV gypsum (Kalabhai Karson Ltd.,) was mixed according to the manufacturer's directions (23 cc water and 100 gm powder). The dental stone was hand-mixed first for 10 s and then mixed mechanically under vacuum for 20 s, and then all the impressions were poured. The casts were allowed to sit at room temperature for 1 h before they are separated from an impression [Figure 7].
All the measurements were taken 48 h after the separation of casts from the impressions. Measurements of the casts and master model were done with the help of cross-reference grooves by using a traveling microscope. Three dimensions of model and casts were measured; the diameter of one abutment, the height of the same abutment and inter-abutment distance between the midpoint of each abutment. The master model was measured ten times and then each cast measurements were made. For each of the three dimensions on the stainless steel model, the measurements were made ten times, the coefficient of variability were calculated by dividing the standard deviations for each dimension on the stainless steel model by the corresponding mean values and multiplying them by 100. In the same way, the measurements on the stone casts for each dimension were repeated three times, and the corresponding mean values were considered as the statistical units. For each dimension, the difference between the mean values of the stone casts (MSC) and the mean values of the stainless steel model (MSSM), divided by the mean of the stainless steel model and multiplied by 100, were expressed as the percentage deviations from the stainless steel model for each test group, as follows.
Percentage deviation = ([MSC-MSSM]/MSSM) × 100.
Measurements of the casts and master model were done with the help of 3 cross reference grooves (as shown in schematic diagram) using travelling microscope. Three dimensions of model and casts were measured;
- The diameter of one abutment – mid horizontal cross reference groove is measured from one edge to the other edge on the coronal surface
- The height of the same abutment – vertical groove on proximal surface measured from tip of the abutment to base of the abutment
- Interabutment distance – measured between the midpoints of each abutments on the coronal surface. Moreover, all measurements were made by the same operator.
Mean and standard deviation [Table 1] and [Table 2] were calculated for the model and casts for each dimensions. All P values were obtained using the one-way ANOVA test and Student-Newman-Keuls multiple post hoc procedures.
|Table 2: Mean and standard deviation statistics summary of diameter, height and Inter-abutment distances among four techniques|
Click here to view
| Results|| |
In the present study, the P < 0.05 was obtained by one way ANOVA analysis [Table 3] showed significant differences in the dimensions of the diameter, height and inter-abutment distances of the resultant casts obtained from all the four techniques.
|Table 3: One-way ANOVA analysis for dimensions of stone casts according to impression technique (n=10)|
Click here to view
The pairwise comparison of four techniques was done using Student-Newman-Keuls tests [Tables 4.1 and 4.3] revealed that the P < 0.05 obtained for diameter and inter-abutment of the casts had significant differences. In [Table 4].2, the P = 0.31 obtained for the dimensions of the height had shown no statically significant difference between two-step and a novel two-step injection technique, but monophase and one-step had significant differences in the values (<0.05).
| Discussion|| |
The most commonly used materials in a fixed and removable partial denture are elastomeric impression materials. The addition silicones among all the elastomers are more widely used by the clinicians and are frequently called as polyvinyl siloxane. They have excellent physical properties and their accuracy is unsurpassed, they can record fine details as they have the best elastic recovery with no by product on polymerization and facilitate the pouring at the convenience of the operator and they also allow the opportunity to make a second pour. They are supplied in the number of viscosities, ranging from a very low for use with the syringe or wash material to medium, high and very high. They are supplied in an auto mix system which is convenient, provides a consistent mix and is cost-effective; Craig  reported that the number of bubbles incorporated in the mix is reduced with the auto mix system.
Several techniques have been suggested to improve the accuracy of polyvinyl siloxane impressions. Most commonly used are putty wash impression technique, putty wash one-step technique, and putty wash two-step technique. Polyethylene sheets are used as a spacer in the two-step putty wash impression technique, with these different techniques only the light body material should cover the entire preparation, but this cannot always be accomplished clinically. Impression with the light body material is made after putty material has polymerized and contracted so the contraction of the light body material results in a minimal dimensional change. Caputi andVarvara  reported that further improvement in dimensional accuracy may occur with the novel two-step putty light body technique in which polymerization of the putty and light body material is followed by the injection of extra light body material into the preparation. Hence, greater compensation for the contraction of the first two materials could enhance the dimensional accuracy of the impression.
In the present study, impressions were made of the master model using a custom acrylic resin tray. The use of a custom tray will minimize the potential cast distortion. An impression will be more accurate when the distance between the impression and the impressed area is minimal by reducing the amount of impression material used.,,,, To provide a uniform thickness of the material a 2 mm thickness of spacer was provided to monophase impression technique and 4 mm thickness for all putty light body impressions. Impression materials were mixed with the help of auto mix system to reduce the incorporation of bubbles and to obtain a more consistent mix as stated by Craig.
Results obtained in the present study support the rejection of the null hypothesis. For all groups, significant larger dimensions were observed when compared to the master model. This observation may also be explained by the expansion of stone material, the concept that a similar expansion rate is expected for all specimens would avoid any bias in the comparison of the accuracy of each impression technique.
To reduce the number of factors that could have influenced the outcome, custom trays of identical thickness and spacer were used for all the impression techniques and the same operator made all the impressions. Moreover, the same material was used for all the three putty light body techniques never the less there were noted difference in terms of accuracy among the different techniques.
The standard deviation of diameter [Graph 1], height [Graph 2], and inter abutment measurements [Graph 3] of the casts obtained from the monophase were 0.012, 0.006, and 0.017 respectively, the resultant P < 0.05, showed significantly greater in all dimensions as that of the model and also from the other three impression techniques. The use of monophase material also resulted in a significantly greater number of surface voids as compared to other materials used. Millar et al. also reported in his studies on surface defects that the risk of void formation is greater with monophase material. The monophase technique is the easiest to perform among all the techniques used in this study. However, it is worst in terms of dimensional accuracy. This could be attributed because of its high viscosity and reduced flow of the material.,
The standard deviation of diameter, height, and inter-abutment measurements of the casts obtained from one-step technique were 0.014, 0.003, and 0.009, respectively, the resultant P < 0.05, showed that the values were more significantly greater in all dimensions as compared to model. Among the techniques, it is slightly more accurate than a monophase but significantly less accurate than the other two techniques. However, Johnson and Craig  reported that there were no significant differences for addition silicones between techniques for measurements between preparations. Gordon et al. reported that inter abutment distances were greater for all dies using polysulfide, polyether, and addition silicone impression materials. The one step technique has the advantages of simplicity and reasonable economy; however, in this technique, the putty tends to wash off the prepared tooth which did not help in recording details to a satisfactory level.
In the present study, the standard deviation of diameter, height, and inter-abutment measurements of the casts obtained from two-step technique were 0.015, 0.002, and 0.004 respectively, the resultant P < 0.05, showed that the casts were more accurate than monophase and one step in terms of diameter and inter-abutment, but slightly less accurate from two-step injection technique. The height values showed were significantly greater from that of the model. Among the four techniques the P = 0.318, showed that it was not significantly much different from that of the two-step injection technique, but it was significantly more accurate than the monophase and one-step technique. Gordon et al. reported that a slight increase in vertical dimensions in his studies. Linket al., and Johnson and Craig, reported shorter vertical dimensions in their studies. Nissan et al. compared the one step and two-step impression techniques, with the polyethylene spacer and found no difference in the two techniques. Idris et al. also did the same study using a different method to create wash space and their conclusion was also same as Hung et al. This may be attributed to the fact that, the critical factor that influences the accuracy is the wash bulk, where it is difficult to control wash bulk with the polyethylene spacer.
The standard deviation of diameter, height, and inter-abutment measurements of the casts obtained from a novel two-step injection technique were, 0.019, 0.002, and 0.009 respectively, the resultant P < 0.05, showed that the casts were slightly less accurate than the master model, that they were greater in all dimensions. Among the other techniques, the values were significantly more accurate than the other three impression techniques. However, the height dimensions did not have significant differences in P = 0.318 when compared to two step impression technique. This may be attributed to the reduced bulk wash through the use of the extra light body material.
Furtherin vitro andin vivo studies are warranted to fully explore the relative merits of the two-step injection technique, in particular, regarding the formation of surface defects and performance in an oral environment that includes saliva.
The limitation of this study lies with differences in making impressionsin vivo compared to in vitro, which is moisture which is equivalent saliva and comes in contact with the impression material is absent in this study.
| Conclusion|| |
Within the limitations of the present study the following conclusions can be drawn:
- The dimensional accuracy of casts obtained from all the four groups was significantly different from that of the master model
- Significant differences in the dimensional accuracy of diameter inter-abutment distance were observed between all the four groups. The order of accuracy of the four groups was monophase < one-step < two-step < two-step injection
- Significant differences in the dimensional accuracy of height were observed between monophase and one-step technique, but not between two-step and two-step injection techniques.
Source of traveling microscope: Gogte Engineering College, Belgaum.
My sincere thanks to all the teaching staff of the Department of Physics, Gogte Engineering College, who helped me with the measurements for the study.
A word of thanks to Dr. Mamta Hebbal and Prof. Mr. Shivalingappa Javali, Statistician, for providing a scientific meaning to this study by way of their statistical analysis.
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Financial support and sponsorship
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], [Table 3], [Table 4]