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| Year : 2014 | Volume
: 25
| Issue : 2 | Page : 184-187 |
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| A comparative evaluation of tray spacer thickness and repeat pour on the accuracy of monophasic polyvinyl siloxane impression material: In vitro study |
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Sandeep Kumar1, Deepti Yadav2, Reena Yadav3, Aman Arora4
1 Department of Prosthodontics, Jan Nayak Ch. Devi Lal Dental College, Sirsa, India
2 Department of Orthodontics, Inderprastha Dental College, Sahibabad, Uttar Pradesh, India
3 Dental Department, B.K Hospital, Faridabad, India
4 Department of Prosthodontics, DAV Dental College, Yamunanagar, Haryana, India
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| Date of Submission | 31-Dec-2012 |
| Date of Decision | 10-Jun-2013 |
| Date of Acceptance | 27-Jan-2014 |
| Date of Web Publication | 4-Jul-2014 |
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 Abstract | | |
Purpose: This study was aimed to determine the effect of various tray spacer thickness and subsequent repeated pours on the accuracy and dimensional stability of the impression made from monophasic polyvinyl siloxane material.
Materials and Methods: Custom trays with different spacer thickness (2, 4 and 6 mm) were used for making an impression of a master model simulating 3 unit fixed partial denture with monophasic polyvinyl siloxane material. These impressions were poured with die stone and repoured. Distance between the reference points were measured and subjected to statistical analysis.
Result: Casts obtained from 1 st , 2 nd and 3 rd pour of the impression in 2, 4 and 6 mm spacer thickness tray have similar dimensional accuracy amongst each other and with the master model except in molar diameter and inter-abutment distances of cast obtained from 6 mm spacer thickness tray.
Conclusion: The vertical distance of stone dies were decreased, whereas horizontal distance increased as the thickness of impression material is increased. There were statistically non-significant changes occurring among the repeated pours in 2, 4 and 6 mm spacer thickness.
Clinical Implication: 2 and 4 mm spacer thickness are acceptable for making an impression for three unit fixed partial denture with monophasic polyvinyl siloxane material and it was not affected by two subsequent (1 st and 2 nd ) repeated pours. Keywords: Monophasic polyvinyl siloxane, repeat pour, tray space
How to cite this article:
Kumar S, Yadav D, Yadav R, Arora A. A comparative evaluation of tray spacer thickness and repeat pour on the accuracy of monophasic polyvinyl siloxane impression material: In vitro study. Indian J Dent Res 2014;25:184-7 |
How to cite this URL:
Kumar S, Yadav D, Yadav R, Arora A. A comparative evaluation of tray spacer thickness and repeat pour on the accuracy of monophasic polyvinyl siloxane impression material: In vitro study. Indian J Dent Res [serial online] 2014 [cited 2022 May 23];25:184-7. Available from: https://www.ijdr.in/text.asp?2014/25/2/184/135916 |
Polyvinyl siloxane impression materials have become the impression material of choice in many clinical situations. They possess excellent physical properties and handling characteristics. These materials are somewhat technique sensitive and are best used in conjunction with an acrylic resin custom tray. [1]
Tray selection also affects the accuracy of impression material. Custom trays of acrylic resin and thermoplastic material were similar regarding die accuracy and produced clinically acceptable casts. The stock tray produced casts with greater dimensional change due to variable thickness of the impression material in the stock trays which leads to more and uneven polymerization shrinkage, resulting in dimensional changes and inaccuracies in the cast. [2]
Monophasic impression materials were introduced for use as both tray and syringe materials. The basis for this use is the shear thinning or pseudoplastic property of material where the apparent viscosity of material is decreased as the shear rate is increased. Thus, monophasic impression material can possess sufficient viscosity to avoid excessive flow if loaded into an impression tray, yet it can also exhibit an apparent lower viscosity suitable for intrasulcular impressions, when it is expressed through an impression syringe tip. [3]
Accuracy of impressions with repeated pours is of interest clinically because duplicate models are sometimes desired. The dimensions of a model from a repeat pour can be affected by continuing polymerization of the impression material and by distortion of the impression during removal of the previous model. [4]
This study was determined the effect of various tray spacer thickness and subsequent repeated pours on the accuracy and dimensional stability of the impression made from monophasic polyvinyl siloxane material.
| Materials and methods | |  |
The master model consisted of a dentate mandibular arch of an acrylic resin typodont (Columbia Dentoform Corp., Long Island City, USA) with missing right mandibular 1 st molar. Second premolar and 2 nd molar were prepared as abutments to receive porcelain-fused-to-metal prosthesis [Figure 1]. Three sharply defined notches were placed on the finish line of each prepared tooth as reference points. Distance measured between reference points [Figure 2] were as:
- Distance a-b and d-e, which represented the 2 nd premolar and 2 nd molar diameter respectively
- Distance a-c and d-f, which represented the 2 nd premolar and 2 nd molar vertical height respectively
- Distance c-f which represented inter-abutment dimension between 2 nd premolar and 2 nd molar.
Monophasic polyvinyl siloxane impression material used for making impressions of the master model. Ten impressions were made with 2, 4 and 6 mm spacer thickness tray [Figure 3] and casts were obtained in die stone class IV (Ultrarock, Kalabhai Karson Pvt. Ltd., India). These casts were grouped as follows:
Group A: Casts obtained from the impression with 2mm spacer thickness tray
Group B: Casts obtained from the impression with 4mm spacer thickness tray
Group C: Casts obtained from the impression with 6mm spacer thickness tray.
With each impression (in 2, 4 and 6 mm spacer thickness tray) 3 casts were obtained by repeat pouring of the impression and these were sub-grouped as follows:
Subgroup 1: Casts obtained from 1 st pour from the impression (in 2 mm, 4 mm and 6 mm spacer thickness tray)
Subgroup 2: Casts obtained from 2 nd pour (1 st repeat pour) from the same impression (in 2, 4 and 6 mm spacer thickness tray)
Subgroup 3: Casts obtained from 3 rd pour (2 nd repeat pour) from the same impression (in 2, 4 and 6 mm spacer thickness tray).
Distance between the reference points on the master model and all ninety casts [Figure 4] obtained from different impressions and after repeated pours was measured with the help of a Coordinate Measuring Machine (CMM, Lloyd, Germany) [Figure 5] with accuracy of 0.0001 mm. The data of each measured dimension (bucco-lingual, occlusal-cervical and inter-abutment) were compared and statistically analyzed by one way analysis of variance test [Table 1] and [Table 2]. When a statistically significant difference was detected, Scheffe test (post hoc test) was applied to determine the significance (at P < 0.05) of statistical difference between the means of various distances. | Table 1: Intragroup comparison at various distances of Group A, B and C by one way ANOVA test
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 | Table 2: Intergroup comparison at various distances of subgroup 1, 2 and 3 by one way ANOVA test
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| Observations and results | | |
On the basis of statistical analysis following results were drawn [Figure 6] and [Figure 7]:
- 1 st , 2 nd and 3 rd pour of the impression in Group A, B and C casts have similar dimensional accuracy amongst each other and with the master model except in d-e and c-f distances of Group C casts
- All the three pours (1 st , 2 nd and 3 rd pour casts) in Group A and Group B casts have similar dimensional accuracy amongst each other and with the master model
- All the three pours (1 st , 2 nd and 3 rd pour casts) in Group C casts have similar dimensional accuracy amongst each other but when compared with the master model it showed a statistically significant difference in d-e and c-f distances.
 | Figure 6: Intragroup comparison of various distances between the master model and stone dies of Group A, B and C
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 | Figure 7: Intergroup comparison of various distances between the master model and stone dies of Subgroup 1, 2 and 3
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| Discussion | | |
Accuracy and dimensional stability of impression materials have been the goals of researchers and clinicians. The factors affecting dimensional changes are thickness of impression material around the tooth or required area, the time period for which the material is allowed to set in the mouth and length of time between making of impression and pouring. [5] In this study, monophasic polyvinyl siloxane is used with one step, single mix impression technique. This technique depends on the pseudoplastic/shear thinning/thixotropic property of the material which is controlled by the shape, size and types of filler content (e.g. cristobalite, diatomaceous earth, fumed silica). [6]
This study results showed that the vertical distance (a-c and d-f) decreased, whereas horizontal distance (a-b, d-e and c-f) of the stone dies increased. These changes occurred because during polymerization, the impression material contracted toward the tray wall, making stone dies wider in horizontal aspect (only in the B-L distance) and shorter in vertical aspect. When the thickness of impression material is increased (from 2 to 4 and 6 mm), it results in more contraction of material toward the tray walls leading to maximum contraction in 6 mm spaced custom tray. The changes which occurred in dimension of molar (height and diameter) were more when compared with the premolar. It might be due to the presence of larger cervical undercut in the molar region which leads to more incorporation of impression material and hence, greater volumetric contraction of material occurred toward the tray walls.
These results are in agreement to Johnson and Craig [7] and Gordon et al . [2] According to these authors, the addition silicone material produced dies that were larger in diameter, shorter in length and slightly larger in the inter-abutment distance. Hence, they concluded that custom trays produced dies that were more accurate when compared with those produced by stock trays. For elastomeric impression material, Philips [8] recommended a maximum 2 mm tray space, Reisbick and Matyas [9] suggested 2-4 mm tray space while Asgar [10] recommended 3-4 mm tray space is required for obtaining accurate impression.
The results of the present study are not in agreement with the Tjan et al. [11] who concluded that on increasing the tray space, the inter-preparation dimensions appeared to be significantly reduced and it presented a minor problem for a fixed partial denture when cast in one piece as it can be resolved by sectioning the fixed partial denture and resoldering it.
Accuracy of impressions with repeated pours is of interest clinically, because duplicate models are sometimes desired, when unacceptable cast with voids and finish line distortion is obtained from the impression and if cast fractures during removal from impression or during shipping to the laboratory. Accuracy of casts obtained from repeated pours can be affected due to viscoelastic property of impression material, as it prevents complete elastic recovery of the impression. [12]
The present study showed that there were statistically non-significant changes occurring among the repeated pours in 2, 4 and 6 mm spaced custom trays. Hence, when multiple pours are desired, the monophasic impression material should be used.
These results are in agreement with the Morgano et al., [13] Johnson and Craig [4] and Lacy et al. [14] According to these authors, medium body of addition silicone demonstrated greater accuracy and were unaffected by the repeat pour and delay in pouring the impression, so they concluded that the polyvinyl siloxane is the material of choice when multiple pours are desired.
The limitations of the present study is that Ivorine Teeth (Columbia Dentoform Corp., Long Island City, USA) were used instead of natural teeth as the affinity of the material to the artificial teeth was different than the natural teeth, the difference between room and mouth temperature and surface moisture, which affect the detail reproduction of the impression material was not simulated in this study. Hence, further investigations and in vivo study are needed to take care of these limitations.
| Conclusion | | |
- The vertical distance (height) of the stone dies decreased, whereas horizontal distance (diameter and inter-abutment distance) increased as the thickness of spacer in impression tray is increased (from 2 to 4 and 6 mm)
- The vertical distance (height) and horizontal distances (diameter and inter-abutment distance) of the stone dies remains same among the repeated pours (1 st and 2 nd ) in 2, 4 and 6 mm spacer thickness tray.
| Acknowledgments | | |
I would like to acknowledge with sincere gratitude, the effort put into this manuscript by Prof. (Dr.) Aman Arora M.D.S.
| References | | |
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| 11. | Tjan AH, Nemetz H, Nguyen LT, Contino R. Effect of tray space on the accuracy of monophasic polyvinylsiloxane impressions. J Prosthet Dent 1992;68:19-28.
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| 12. | de Araujo PA, Jorgensen KD, Finger W. Viscoelastic properties of setting elastomeric impression materials. J Prosthet Dent 1985;54:633-6.
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| 13. | Morgano SM, Milot P, Ducharme P, Rose L. Ability of various impression materials to produce duplicate dies from successive impressions. J Prosthet Dent 1995;73:333-40.
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| 14. | Lacy AM, Fukui H, Bellman T, Jendresen MD. Time-dependent accuracy of elastomer impression materials. Part II: Polyether, polysulfides, and polyvinylsiloxane. J Prosthet Dent 1981;45:329-33.
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Correspondence Address:
Sandeep Kumar
Department of Prosthodontics, Jan Nayak Ch. Devi Lal Dental College, Sirsa
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0970-9290.135916
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2] |
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