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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 5  |  Issue : 1  |  Page : 59-63

Dimensional accuracy and surface detail reproduction of hydrophilic polyvinylsiloxane impression material tested under dry and moist salivary conditions: An In vitro study


Department of Oral Medicine and Radiology, Saraswati-Dhanwantari Dental College and Hospital and Postgraduate Research Institute, Parbhani, Maharashtra, India

Date of Submission05-Jun-2020
Date of Acceptance27-Aug-2020
Date of Web Publication13-Mar-2021

Correspondence Address:
Dr. Abhishek Singh Nayyar
Department of Oral Medicine and Radiology, Saraswati-Dhanwantari Dental College and Hospital and Post-graduate Research Institute, Parbhani, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/bbrj.bbrj_86_20

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  Abstract 


Background: The dimensional accuracy and surface detail reproduction of impression materials play a major role in determining the extent to which indirectly produced prostheses and restorations have an acceptable fit. The purpose of the present study was to compare the dimensional accuracy and surface detail reproduction of hydrophilic polyvinylsiloxane (PVS) impression material tested under dry and moist salivary conditions. Methods: The study samples were assigned two groups based on the condition in which they were made. One group consisted of casts obtained from impressions made in dry condition (n = 12), while the other group consisted of casts obtained from impressions made in moist salivary conditions (n = 12). Impressions of the master model were made using hydrophilic PVS impression material by two-step putty-wash technique and working casts were obtained. Dimensional accuracy was measured by comparing the inter-abutment distance in each cast to the master model using a profile projector with an accuracy of 0.001 mm, while surface detail reproduction was evaluated using the American Dental Association specification No. 19 criteria of continuous replication of at least two of the three horizontal lines. Descriptive statistics such as mean and standard deviation were calculated for both the groups. Differences from the master model were analyzed by paired t–test, while one-way analysis of variance (ANOVA) was used for intergroup comparisons. P ≤ 0.05 was considered statistically significant. Results: One-way ANOVA revealed a highly significant difference in the dimensional accuracy of impressions made under moist conditions as against those which were made under dry condition (P < 0.001). The percentage change in dimension of 0.6% in Group A casts and 0.3% in Group B casts, also, showed a high clinical significance. Under dry condition, the impression material satisfactorily replicated the surface details in 100% of the cases, while under moist conditions, only 58% of the impressions were found to be satisfactory. Conclusion: The presence of moisture caused a significant adverse impact on the dimensional accuracy and surface detail reproduction of hydrophilic PVS impression material underlying the clinical significance of moisture control for successful impressions.

Keywords: Dimensional accuracy, dry and moist salivary conditions, hydrophilic polyvinylsiloxane impression material, surface detail reproduction


How to cite this article:
Nayyar AS. Dimensional accuracy and surface detail reproduction of hydrophilic polyvinylsiloxane impression material tested under dry and moist salivary conditions: An In vitro study. Biomed Biotechnol Res J 2021;5:59-63

How to cite this URL:
Nayyar AS. Dimensional accuracy and surface detail reproduction of hydrophilic polyvinylsiloxane impression material tested under dry and moist salivary conditions: An In vitro study. Biomed Biotechnol Res J [serial online] 2021 [cited 2021 May 12];5:59-63. Available from: https://www.bmbtrj.org/text.asp?2021/5/1/59/311101




  Introduction Top


A major limitation of polyvinylsiloxane (PVS) impression materials has been their hydrophobicity. To overcome PVS hydrophobicity, manufacturers incorporated surfactants (nonylphenoxy-polyethanol homologs) and marketed these materials as hydrophilic PVS. This was intended to facilitate the wetting of the moist oral tissues and tooth surfaces with the unset impression material and, thus, enhance the surface detail reproduction. However, impression materials with hydrophilic structures are also prone to moisture absorption and subsequently reduced dimensional accuracy.[1] The dimensional accuracy and surface detail reproduction of impression materials play a major role in determining the extent to which indirectly produced prostheses and restorations have an acceptable fit. Although there is a general acceptance that elastomeric impression materials are more accurate and precise than the hydrocolloids, there is a degree of uncertainty over the extent to which elastomers can be relied upon to produce acceptable impressions of the moist surfaces. Conventionally, this problem has been solved by suggesting the clinicians to thoroughly dry the area to be recorded.[2] Over the recent years, some silicone products have been modified to increase their hydrophilic nature and this has highly increased their ability to record surface details under moist conditions, although there has been some disagreement among the researchers as to the extent of this improvement. The research into the impression accuracy has relied heavily on in vitro studies rather than the clinical in-service evaluations wherein a plethora of factors become accountable to decrease the efficacy of the impression materials in registering the tissues, especially under moist conditions present inside the oral cavity as well as having acceptable dimensional changes hampering the successful recording of the impressions. The specification tests of the American Dental Association (ADA) (19) and the British Standards Institution (4269) are designed, though, to consider the individual properties. The main thrust of these tests is to ensure that impression materials meet the minimum requirements before marketing and to provide continuous quality control.[3] There are many types of stimulatory tests available nowadays; however, but their main drawback is that none of the tests provide an absolute simulation of the conditions actually present in the oral cavity. Nevertheless, these stimulatory tests can provide highly useful information.[4] When hydrophilic PVS impression materials were first used clinically in the presence of moisture in the form of water, saliva, crevicular fluid, and/or blood, decreased accuracy of the impression produced was reported implying failure of hydrophilic additives of PVS impression materials to wet the oral tissues under partial or complete moisture conditions.[5],[6] The purpose of the present study was to compare the dimensional accuracy and surface detail reproduction of the hydrophilic PVS impression material tested under dry and moist salivary conditions.


  Methods Top


The study samples were assigned two groups based on the condition in which they were made. One group consisted of casts obtained from impressions made in dry condition (n = 12), while the other group consisted of casts obtained from impressions made in moist salivary conditions (n = 12). Impressions of the master model were made using hydrophilic PVS impression material by two-step putty-wash technique and working casts were obtained. Dimensional accuracy was measured by comparing the inter-abutment distance in each cast to the master model using a profile projector with an accuracy of 0.001 mm, while surface detail reproduction was evaluated using the ADA specification No. 19 criteria of continuous replication of at least two of the three horizontal lines. The results obtained were subjected to the statistical analysis. The study protocol was approved by the Ethical Committee University of Department of Oral Medicine and Radiology, Saraswati-Dhanwantari Dental College and Hospital and Postgraduate Research Institute, Parbhani, Maharashtra, India

Methodology

The freshly extracted maxillary right second premolar and second molar teeth were obtained, cleaned, and disinfected. These teeth were positioned inversely in the frasaco rubber mold and a wax model was recovered. Maxillary right first molar was removed so as to simulate a clinical case of 3 unit fixed partial denture (FPD) and the model was processed to obtain the master model made up of heat cure acrylic resin. The premolar was prepared to receive a porcelain-fused-to-metal retainer, while the molar was prepared to receive an all-metal retainer for a 3 unit FPD. Three grooves in buccolingual direction and two grooves in mesiodistal direction (50 μm width) were placed on the occlusal surface so as to evaluate surface detail reproduction.

Group A impressions

In this group, impressions were made with hydrophilic PVS impression material by full-arch dentulous stock metal trays using a two-step putty reline technique under moist conditions. In the first step, a preliminary putty impression was made on the master model which was relieved with two layers of spacer wax (0.5 mm thickness). Four occlusal stops were made by removing wax on the nonfunctional cusps. Tray adhesive was applied onto the inner portion of the tray extending 2 mm onto the outer walls and allowed to dry for 15 min. Putty base and catalyst were hand mixed. The mix was loaded into a perforated metal stock tray. A total of 12 PVS putty custom trays were made. Before the wash, impression was made and a 100 μL quantity of saliva was applied to the prepared surface via a micropipette. The excess saliva was removed from the surface by a short, gentle blast of compressed air in the same way as a clinician would dry the prepared surface. Care was taken to ensure that the entire die was covered with a uniform layer of saliva, avoiding any excess. In the second step, a light-bodied impression material was also dispensed into the putty tray and it was re-seated over the master model accurately and was held in place for 10 min for the material to set. After the setting time, the air seal was broken with a light but firm pressure and the impression was recovered with a snap.

Group B impressions

In this group, 12 impressions were made in the dry condition in a similar manner as explained in Group A, the only difference being that before making second step wash impression, teeth were allowed to air dry and there was no application of saliva. Once the impressions were made, they were poured with dental stone.

The measurements of master model as well as Groups A and B casts were done in the Mechanical Department, B. I. E. T. College, Davangere, Karnataka. Dimensional accuracy was measured by comparing the inter-abutment distance in each cast to the master model using a profile projector with an accuracy of 0.001 mm, while surface detail reproduction was evaluated using the ADA specification No. 19 criteria of continuous replication of at least two of the three horizontal lines. The inter-abutment distance was measured from one pit to the other. For each cast, the inter-abutment distance was recorded three times by the same operator and the mean value was calculated. The measurements of the master model and the stone casts obtained with Groups A and B impressions were tabulated and statistically analyzed.

Statistical analysis done

Descriptive statistics such as mean and standard deviation were calculated for both the groups. Differences from the master model were analyzed by paired t-test, while one-way analysis of variance (ANOVA) was used for intergroup comparisons. P ≤ 0.05 was considered statistical significance.


  Results Top


The inter-abutment distance was significantly increased compared to the master model in both the groups (P < 0.001). It was observed that for Group A casts (obtained from impressions made under moist conditions), the mean inter-abutment distance was found to be 17.839 ± 0.0407 mm [Table 1], with the difference from the master model being 0.114 mm [Table 2] indicating an increase in the inter-abutment distance of up to 114 μm. In Group A casts, the percentage difference was found to be 0.6% and was found to be clinically as well as statistically significant [Table 3]. For Group B casts (obtained from impressions made under dry condition), the mean inter-abutment distance was found to be 17.771 ± 0.0458 mm [Table 1], with the difference from the master model being 0.046 mm [Table 2] indicating an increase in the inter-abutment distance of up to 46 μm. The percentage difference in Group B casts was found to be 0.3% and was, again, found to be clinically as well as statistically significant [Table 3]. The difference between the mean inter-abutment distances measured for Group A and Group B casts was found to be 0.068 mm, indicating an increase in the inter-abutment distance of up to 68 μm. One-way ANOVA revealed a highly significant difference between Groups A and B, indicating that the dimensional accuracy of impressions made under moist conditions was affected to a greater extent as compared to those made under dry conditions (P < 0.001). The percentage change in dimension of 0.6% in Group A casts and 0.3% in Group B casts, also, showed a high clinical significance [Table 3]. Under dry conditions, the impression material satisfactorily replicated the surface details in 100% of the cases, while under moist conditions, only 58% of the impressions were found to be satisfactory [Table 4].
Table 1: Mean inter-abutment distances for master models and casts obtained in dry and moist conditions

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Table 2: Mean increase in inter-abutment distances for casts obtained in dry and moist conditions using paired t-test

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Table 3: Mean percentage (%) increase in inter-abutment distances for casts obtained in dry and moist conditions using one-way analysis of variance

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Table 4: Total number of satisfactory and unsatisfactory impressions

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  Discussion Top


PVS impression materials have the ability to closely reproduce the surface details of the surfaces recorded as well as demonstrate a high degree of dimensional accuracy; however, they require an absolutely dry field for producing such an acceptable and highly accurate impression.[5],[6] The term hydrophilic, however, has been misinterpreted to imply that the impressions can be made under wet or moist conditions. Addition of certain nonionic surfactants renders PVSs hydrophilic making them easier to manipulate and register the impressions of moist surfaces with such dimensional accuracy.[7] Hydrophilic PVSs have exhibited comparable dimensional accuracy as with conventional PVSs when allowed to polymerize under dry conditions.[8],[9] In the present study, since all the procedures were standardized for both the groups, the difference in dimensional accuracy and stability among the test groups was assumed to be the effect of the presence of moisture and the procedure in general.

The results of the present study indicated that dimensional accuracy of hydrophilic PVS impression materials was adversely affected by the presence of moisture, and the increase in the mean inter-abutment distance for Group A of 114 μm was greater than the clinically acceptable range (0–90 μm). A similar increase of 46 μm in the inter-abutment distance seen in Group B was, though, found to be within the clinically acceptable range. In addition to dimensional accuracy, the present study, also, examined the surface detail reproduction of hydrophilic PVS impression materials wherein it could be seen that dry and moist conditions had a significant impact on surface detail reproduction of the material. Under dry conditions, the impression material satisfactorily replicated the surface details in 100% of the cases, while under moist conditions, only 58% of the impressions were found to be satisfactory.

The hydrophilic PVS impression material used in the present study did not always yield satisfactory impressions under moist conditions. To evaluate the surface detail reproduction of the impressions made under dry and moist conditions with the hydrophilic PVS impression materials, the impressions were evaluated according to the criteria proposed under ADA specification No. 19 with certain modifications in the master model and the procedure to make an impression to simulate clinical situations.[10],[11],[12],[13],[14],[15] ADA specification No. 19 states that an elastomeric impression material (light body) should have the ability of continuous replication of 1 of the 20 μm horizontal lines in at least 2 of the 3 specimens.[3] The use of saliva as a source of moisture in place of water was another modification used in the present study as compared to the previous studies.

Although the moist surface method used in the present study might appear more clinically relevant when compared to the oral cavity, there is moisture at the surface as well as within the bulk of the tissues. Water within the bulk of the tissues can diffuse to the surface during the recording of an impression, a limitation, which is actually the main constraint in getting the real clinical conditions being simulated while recording the impression in the in vitro study models.


  Conclusion Top


Within the limitations of the present study, it could be concluded that the presence of moisture carries a significant adverse impact on the dimensional accuracy and surface detail reproduction of the hydrophilic PVS impression materials, though impressions made under dry condition, also, showed a significant increase in the inter-abutment distance. Furthermore, the dimensional change for the material in the dry environment was within the ADA standards of maximal shrinkage value of 0.5%. Using the criteria similar to ADA specification No. 19 to test the surface detail reproduction of the PVS impression materials, the materials tested satisfactorily only under dry conditions, while the criteria could be met in only 58% of the cases under moist conditions. On the basis of the results of the present study, it could be concluded that moisture control remains an important factor for successful registration of the impression despite selecting the newer hydrophilic impression materials.

Acknowledgement

The authors would like to thank all the patients who contributed to the study without whom this study would not have been feasible.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Walker MP, Petrie CS, Haj-Ali R, Spencer P, Dumas C, Williams K. Moisture effect on polyether and polyvinylsiloxane dimensional accuracy and detail reproduction. J Prosthodont 2005;14:158-63.  Back to cited text no. 1
    
2.
McCabe JF, Carrick TE. Recording surface detail on moist surfaces with elastomeric impression materials. Eur J Prosthodont Restor Dent 2006;14:42-6.  Back to cited text no. 2
    
3.
Council on Dental Materials and Devices, ADA. Revised American Dental Association specification 19 for Non-aqueous, Elastomeric Dental Impression Materials. J Am Dent Assoc 1977;94:733-41.  Back to cited text no. 3
    
4.
Wassell RW, Abuasi HA. Laboratory assessment of impression accuracy by clinical simulation. J Dent 1992;20:108-14.  Back to cited text no. 4
    
5.
Petrie CS, Walker MP, O'mahony AM, Spencer P. Dimensional accuracy and surface detail reproduction of two hydrophilic vinyl polysiloxane impression materials tested under dry, moist, and wet conditions. J Prosthet Dent 2003;90:365-72.  Back to cited text no. 5
    
6.
Eames WB, Wallace SW, Suway NB, Rogers LB. Accuracy and dimensional stability of elastomeric impression materials. J Prosthet Dent 1979;42:159-62.  Back to cited text no. 6
    
7.
Johnson GH, Craig RG. Accuracy of addition silicones as a function of technique. J Prosthet Dent 1986;55:197-203.  Back to cited text no. 7
    
8.
Pratten DH, Craig RG. Wettability of a hydrophilic addition silicone impression material. J Prosthet Dent 1989;61:197-202.  Back to cited text no. 8
    
9.
Panichuttra R, Jones RM, Goodacre C, Munoz CA, Moore BK. Hydrophilic poly (vinyl siloxane) impression materials: Dimensional accuracy, wettability, and effect on gypsum hardness. Int J Prosthodont 1991;4:240-8.  Back to cited text no. 9
    
10.
Johnson GH, Craig RG. Accuracy of four types of rubber impression materials compared with time of pour and a repeat pour of models. J Prosthet Dent 1985;53:484-90.  Back to cited text no. 10
    
11.
Hansson O, Eklund J. Impressions for prosthodontic restorations reproducing narrow spaces and severe undercuts. Acta Odontol Scand 1988;46:199-206.  Back to cited text no. 11
    
12.
Gordon GE, Johnson GH, Drennon DG. The effect of tray selection on the accuracy of elastomeric impression materials. J Prosthet Dent 1990;63:12-5.  Back to cited text no. 12
    
13.
Wassell RW, Ibbetson RJ. The accuracy of polyvinyl siloxane impressions made with standard and reinforced stock trays. J Prosthet Dent 1991;65:748-57.  Back to cited text no. 13
    
14.
Schelb E, Cavazos E Jr., Troendle KB, Prihoda TJ. Surface detail reproduction of Type IV dental stones with selected polyvinyl siloxane impression materials. Quintessence Int 1991;22:51-5.  Back to cited text no. 14
    
15.
Thongthammachat S, Moore BK, Barco MT 2nd, Hovijitra S, Brown DT, Andres CJ. Dimensional accuracy of dental casts: Influence of tray material, impression material, and time. J Prosthodont 2002;11:98-108.  Back to cited text no. 15
    



 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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