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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 12  |  Issue : 1  |  Page : 7-15

To evaluate the effect of storage temperature on the linear dimensional accuracy of delayed and repeat pours of two addition silicone impression materials


1 Jaipur Dental Hospital, Abohar, Punjab, India
2 Department of Dental and Maxillofacial, Bahrain Defence Force Royal Medical Service, Military Hospital, Riffa, Bahrain, Bahrain
3 College of Dentistry, Prince Sattam Bin Abdul Aziz University, Al-Kharj, Saudi Arabia
4 Dr. Khatri Dental Clinic and Implant Centre, Bikaner, Rajasthan, India
5 Department of Community and Preventive Dentistry, Guru Govind Singh Dental College, Burhanpur, Madhya Pradesh, India

Date of Submission03-May-2019
Date of Decision24-Aug-2019
Date of Acceptance27-Sep-2019
Date of Web Publication27-Jan-2020

Correspondence Address:
Manish Sen Kinra
Jaipur Dental Hospital, Abohar, Punjab
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/IJDS.IJDS_47_19

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  Abstract 


Background: Addition silicone elastomers are the most commonly used impression materials for making final impression for fixed partial dentures, implants, and removable partial dentures. The dimensional stability and accuracy of addition silicone impression material is influenced by the storage time, temperature, and repeat pour. Aim and Objectives: The aims and objectives of this study were to evaluate the accuracy of two different types of addition silicone elastomeric impression materials, stored at different temperatures; to evaluate the accuracy of two different types of addition silicone elastomeric impression materials after delayed and repeated pour; and to compare the linear dimensions of two different types of addition silicone elastomeric impression materials with a control die. Materials and Methods: A machined standard steel master die and a metal custom impression tray were made for making a final impression of machined standard steel master die. The final impression was made by using two different brands of addition silicone impression materials (Aquasil™ Ultra Impression material, Dentsply/Caulk, Milford, DE, USA, and 3M™ ESPE™). Double-step putty light-body impression technique was used for making the final impression. In this manner, a total of eighty impressions were made, and they were divided into two groups namely Group I and Group II. To study the effect of delayed pours and storage temperature, the two groups were further divided into four subgroups, with ten impressions each. All the ten impressions of each subgroup were stored in an acrylizer at 40°C, −10°C for 24 h, −2°C for 48 h, and 0°C for 1 week inside a refrigerator in sealed plastic bags before being poured with type IV dental stone. To study the effect of repeat pours on the accuracy of stone casts, all the ten impressions of each subgroup were immediately re-poured with type IV die stone after the removal of the first set of casts. Thus, again a fresh set of eighty casts were obtained having forty casts to each group. Results: When the impressions were stored in the acrylizer at 40°C, −10°C for 24 h, −2°C for 48 h, and 0°C for 1 week, the addition silicone impression materials did not show any significant change when compared to the control samples. Conclusion: Both the types of addition silicone elastomeric impression materials maintained their accuracy after delayed pours and repeat pours. Storing impressions under different conditions caused no adverse effect upon the accuracy of both types of addition silicone elastomeric impression materials. There was no significant change in the dimensions of stone casts obtained from both impression materials as compared to the dimensions of the master die. Even though if the addition silicone impression material is delayed, i.e. poured up to 1 week, repeat poured, and exposed from − 10°C to 40°C, the linear dimensional accuracy will not be adversely affected.

Keywords: Addition silicone impression material, custom impression tray, delayed pour, dimensional stability, double-step impression technique, light body, linear dimensional accuracy, putty, repeat pour, spacer, temperature


How to cite this article:
Kinra MS, Alghatam HM, Al Bin Al AA, Sharanesha RB, Khatri PK, Sharma A. To evaluate the effect of storage temperature on the linear dimensional accuracy of delayed and repeat pours of two addition silicone impression materials. Indian J Dent Sci 2020;12:7-15

How to cite this URL:
Kinra MS, Alghatam HM, Al Bin Al AA, Sharanesha RB, Khatri PK, Sharma A. To evaluate the effect of storage temperature on the linear dimensional accuracy of delayed and repeat pours of two addition silicone impression materials. Indian J Dent Sci [serial online] 2020 [cited 2020 Mar 28];12:7-15. Available from: http://www.ijds.in/text.asp?2020/12/1/7/276886




  Introduction Top


The dimensional stability and accuracy of elastomeric impression materials such as polyvinyl siloxane is well established;[1],[2] therefore, many dentists delay pouring of the impression and commonly send the unpoured impression to a remote dental laboratory. Nevertheless, the effect of extreme changes in temperatures that could occur during the routine transportation of impression is unknown.[3]

This, in turn, may affect the accuracy of a final prosthesis or temporary prosthesis obtained from them. Various studies have been done in the past regarding delay pour, repeat pour, and the effect of temperature[4] on addition silicone impression materials. However, in none of the studies, all the above three factors were present. Even though the addition silicone impression material is delayed poured up to 1 week, repeat poured, and exposed from − 10°C to 40°C, the linear dimension al accuracy was never adversely affected. Thus, the present study was conducted to create a new philosophy on the effect of storage temperatures on the linear dimensional accuracy of delayed and repeat pours of two brands of addition silicone impression materials.


  Materials and Methods Top


Fabrication of the master die

A machined standard steel master die of size 32 mm × 27 mm was fabricated with four identical posts at the Industrial Training Institute, Sundernagar, Himachal Pradesh, India [Figure 1]. Each post had a uniform taper of 6° simulating four tapered complete crown abutments. The master die was firmly attached to the platform so as to immobilize it during the final impression making. Reference cross grooves were prepared on the abutment's occlusal surfaces. Four reference points, i.e. A, B, C, and D, were marked on the center point of each cross groove. A custom-made spacer (Dentsply India Pvt. Ltd, indiranagar Bengaluru, Karnataka, India) with a uniform thickness of 2 mm was fabricated on each post with the help of a vacuum press machine (Bio Star, India) to provide uniform space for light-body impression material (Aquasil ™ Ultra Impression material, Dentsply Caulk, Milford, DE, USA) while making the final impressions.
Figure 1: Master die

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Fabrication of metal custom impression tray

A specially prepared metal custom impression tray having a uniform space of approximately 5 mm for the addition silicone impression material was fabricated for making the final impressions [Figure 2]. A flat base was used for precise positioning of the metal custom impression tray during impression making. Reference lines were made on one surface of the metal custom impression tray and on die platform for a similar placement of the metal custom impression tray every time the impression was made.
Figure 2: Metal custom impression tray

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Impression of the master die

All the impressions of the master die were made in a metal custom impression tray at room temperature using double-step impression technique. The master die was stabilized on a flat base. A thin even coat of a tray adhesive (Aquasil, Caulk, Milford, DE, USA/Dentsply India) was applied to the metal custom impression tray and allowed to dry according to the manufacturer's recommendations.

A vacuum-forming plastic spacer (Dentsply India) of 2 mm was placed over each post on the master die, and the preliminary heavy body putty impression (Aquasil Ultra Impression material, Caulk, Milford, DE, USA/Dentsply) was made with the metal custom impression tray. The plastic spacers (Dentsply India) were removed before making a final impression to make uniform space of 2 mm for light body. Then, the light bodied polyvinyl siloxane impression material (Aquasil Ultra Impression material, Caulk, Milford, DE, USA/Dentsply) was mixed using an automix dispensing cartridge at room temperature, and the impression of the master die was made as recommended by the manufacturer. The tray was seated gently over the master model while maintaining finger pressure until the material was set. To compensate for polymerization at room temperature, the impressions were allowed to set for twice the manufacturer's recommended setting time (4 min) as indicated in the ADA specification number 19 for laboratory testing.

After the impression material was set, the impression was removed from the die with a straight pull. Impressions with air entrapment or without details were discarded. The impressions were disinfected using a disinfectant spray (Zeta 7 solution Zhermack S. P. A, BadiaPolesine Italy). The impressions were poured immediately with Type IV dental stone (Kalrock Kalabai, Mumbai, Maharashtra, India). In this manner, a total of eighty impressions were obtained using two different brands of polyvinyl siloxane impression material (Aquasil Ultra Impression material, Dentsply/Caulk, Milford, D and 3M ESPE). On the basis of the brands used, the impressions were divided into two groups, namely Group I (Aquasil Ultra Impression material, Dentsply/Caulk, Milford, D) and Group II (3M ESPE). Each group had forty impressions of each brand. Each group was further divided according to the different storage time and storage temperatures intervals, for delayed and repeat pour, into four subgroups having ten samples each.

Delayed pours

To study the effect of storage temperature and delayed pours on the accuracy of the stone casts, all the ten impressions of each subgroup were stored at 40°C for 90 min in an acrylizer (Bison, Intensive industries, New Delhi, India), −10°C for 24 h, −2°C for 48 h, and 0°C for 1 week inside a refrigerator (LG, GL-528 YSX 4/2010, LG Electronic, Saket, New Delhi, India Pvt Ltd) in sealed plastic bags before being poured with Type IV dental stone (Kalrock Kalabai, Mumbai, Maharashtra, India).

Hence, for each subgroup, ten stone casts were obtained by pouring the impressions with Type IV dental stone (Kalrock Kalabai, Mumbai, Maharashtra, India) after storing in the abovementioned storage time and temperature. In this manner, for each group, a total of forty stone casts were obtained. As previously mentioned, from the two groups of impression materials, eighty stone casts were retrieved. The groups and subgroups for delayed pours are summarized in [Table 1].
Table 1: Various groups and subgroups based on materials and time intervals for delayed pour and repeat pour

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Repeated pours

To study the effect of repeat pours on the accuracy of the stone casts, all the ten impressions of each subgroup were immediately re-poured with Type IV dental stone (Kalrock Kalabai, Mumbai, Maharashtra, India) after the removal of the first set of casts. Thus, again, a fresh set of eighty casts were obtained, with forty casts belonging to each group. The groups and subgroups for repeat pours are summarized in [Table 1].

Pouring of the impressions

The impressions were poured with Type IV dental stone (Kal Rock Kalabai, Mumbai, India). The stone casts were removed from the impressions after 60 min to ensure complete setting of the stone. The casts obtained were numbered and stored at room temperature.

Measurements

A traveling microscope (Parco India, Janakpuri, New Delhi, Delhi, India) was utilized for the measurements of the master die and the obtained stone casts [Figure 3]. The master die was placed on the table, and distance between the reference points was measured by a traveling microscope capable of measuring up to 0.001 mm. The distance between the following reference points, i.e. A-B, B-C, C-D, and D-A, was measured [Table 2]. For each measurement, three readings were recorded, and the mean was calculated. A similar measurement was recorded on the stone casts obtained from each subgroup of delayed and repeat pours. Each stone cast measurement was also repeated three times, and the mean for all distance measurements was calculated. The A-B, B-C, C-D, and D-A dimensions on the obtained stone casts were compared with the respective dimensions of the master die. The data thus obtained were subjected to statistical analysis using a paired t-test and an unpaired t-test as shown in [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11], [Table 12], [Table 13], [Table 14].
Figure 3: Traveling microscope

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Table 2: Various dimensions of the master die

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Table 3: Measurement of stone casts at reference points A-B in Group I compared with control at different intervals using paired t-test

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Table 4: Measurement of stone casts at reference points A-B in Group II compared with control at different intervals using paired t-test

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Table 5: Comparison of stone cast measurement at reference points A-B between Group I and Group II at different intervals using unpaired t-test

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Table 6: Measurement of stone casts at reference points B-C in Group I compared with control at different intervals using paired t-test

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Table 7: Measurement of stone casts at reference points B-C in Group II compared with control at different intervals using paired t-test

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Table 8: Comparison of stone cast measurement at reference points B-C between Group I and Group II at different intervals using unpaired t-test

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Table 9: Measurement of stone casts at reference points C-D in Group I compared with control at different intervals using paired t-test

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Table 10: Measurement of stone casts at reference points C - D in Group II compared with control versus different intervals using paired t-test

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Table 11: Comparison of stone cast measurement at reference points C-D between Group I and Group II at different intervals using unpaired t-test

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Table 12: Measurement of stone casts at reference points D-A in Group I compared with control at different intervals using paired t-test

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Table 13: Measurement of stone casts at reference points D-A in Group II compared with control at different intervals using paired t-test

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Table 14: Comparison of stone cast measurement at reference points D-A between Group I and Group II at different intervals using unpaired t-test

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  Results Top


In this study, a total of 160 samples were prepared from two different brands of addition silicone impression materials (Aquasil Ultra Impression material, Dentsply/Caulk, Milford, DE and 3M ESPE) and one brand of Type IV dental stone (Kal Rock Kalabai, Mumbai, India). These samples were evaluated for linear dimensional accuracy after exposing them at a prescribed temperature, and they were also delayed poured at time intervals of 90 min at 40°C in an acrylizer, 24 h at − 10°C, 48 h at −2°C, and 0°C for 1 week in a refrigerator and repeated pouring of casts was also done.

The unpaired t-test and paired t-test analyses state that this little decrease and increase in the dimensions of stone casts at reference points A, B, C, and D after delayed and repeat pouring at time intervals of 90 min at 40°C, 24 h at −10°C, 48 h at −2°C, and 0°C at 1 week did not show statistically significant difference for both Group I and Group II addition silicone impression materials. This implied that delayed pour, repeat pour, and storing impression at the abovementioned temperatures up to 1 week did not significantly affect the linear dimensional accuracy of the obtained casts.

Measurements on the master die

The mean of three measurements was taken from each of the linear distance between the reference points (A-B, B-C, C-D, and D-A) on the master die [Table 2].


  Discussion Top


Among the various advantages of addition silicone impression materials,[5],[6],[7],[8],[9] the most important is the ability to provide delayed and repeat pours.[10] Custom impression tray[11],[12] should be rigid, should be dimensionally stable, and should allow a uniform layer of impression material to be displaced along the borders.

Two-millimeter thickness of rubber base material provides accurate impression higher than thicknesses of 4 mm and 6 mm because of lesser polymerization shrinkage.[13] The uniform amount of impression material in the custom impression tray minimizes the polymerization shrinkage of the impression material and improves the accuracy of the cast.[5],[14],[15]

Shillingburg et al.[16] reported the technique of making acrylic resin custom impression tray and stated that it can be utilized with addition polyvinyl siloxane impression material which gives more accurate result due to a uniform thickness of 2–3 mm of the impression material.

Addition silicone materials do not produce any by-product during polymerization and have better and improved properties than condensation silicones.[9] As most of the time a prosthesis is fabricated employing an indirect approach and an impression has to be sent to a remote laboratory, this causes delayed pouring[17],[18],[19] of the impression and exposure of the impression to a wide range of temperatures from −10°C to 60°C. The delayed pouring of the impression and exposure to wide range of temperatures should not result in any change in die accuracy.

For various laboratory procedures,[20] duplicate casts are required to be used as working or refractory casts so that the master cast remains unaltered. For this purpose, repeat pours[21],[22] are required. Repeat pour means the retrieval of an extra cast from the same impression. These repeat pours are required if cast obtained from the first pour is not satisfactory. Repeat pours are also advantageous when more than one working casts are required.

The delayed pours and repeat pours can affect the dimensions of the impressions due to continuing polymerization of the addition silicone impression material.[23] Storing the impression at a wide range of temperatures can also affect the dimensional stability of the impression. Distortion of the impression materials may also occur during the retrieval of stone casts when multiple casts are poured from the same impression.[15] The time interval, exposure of impression to a wide range of temperatures, and repeat pour from the same impression are of clinical interest.

Research gaps were identified in the proposed field of investigation; thus, further research was needed to find whether the linear dimensional accuracy of addition silicone impression material will be affected or not when addition silicone impression is delay poured for 1 week, repeat poured, and stored at different temperatures (−10°C to 40°C). Hence, the present study was carried out to evaluate the effect of storage temperature on the linear dimensional accuracy of delayed and repeated pours of two brands of addition silicone impression materials. The scope of this study is not only limited to the fixed prosthodontics but it can be also used for inlays, onlays, implant-supported fixed partial dentures, cast partial dentures, implant-supported maxillofacial prosthesis, and implant-supported removable prosthesis.

In this study, a stainless steel master die was fabricated having four posts on it with uniform taper of 6°[16] on each post. The die was fabricated similar to that of the master die used by Luebke et al.[24] These posts represent four prepared abutments which had four reference points namely A, B, C, and D on the occlusal surfaces to analyze the effect of storage temperature, delayed pour, and repeat pours. A flat base was made for repeatedly positioning the metal custom impression tray in the same position. Reference lines were made on the surface of the metal custom impression tray and on metal flat platform. This was done so that when repeatedly impressions were made, every time, the same position of custom impression tray is achieved.

All the impressions were made with double-step putty wash impression technique.[24],[25],[26] The same technique was used by Johnson and Craig[14] for making final impression using addition silicone impression material, and they reported that impressions made with this technique were most accurate as compared with other techniques.[5],[23],[24],[27]

The final impression of the standardized stainless steel master die was made using a stainless steel custom impression tray.[5],[12] For making the final impression, a stainless steel custom impression tray was used instead of stock impression tray because various authors have stated that custom impression tray provides more accurate impression than stock impression tray.[16] Tray adhesive was applied on the metal custom impression tray and was allowed to dry as per manufacturer's instructions. This helps in achieving good adhesion between the custom impression tray and addition silicone impression material and also helps in achieving accurate impression.[5]

Double-step impression technique was used for making the final impression because this provides accurate impression by recording all details in light-body addition silicone impression material.[16] Due to this reason, various authors[7],[13] have stated that 2 mm of relief is needed in double step impression technique for light-body addition silicone impression material.

In the first step of impression making, a vacuum-forming plastic spacer of 2 mm was placed over each post on the master die. After making initial impression, the plastic spacer was removed, which resulted in uniform space of 2 mm for light-body addition silicone impression material.

An automixing gun was used for making impression as various authors[16] have stated that it provides homogeneously mixed material and also reduces air bubbles in the impression material as compared to manual mixed materials. The polymerized impressions were removed from the die with a straight pull instead of continuous force because continuous force or jerky force can distort the final impression. For pouring final impression, type IV dental stone was used. This was selected because it has high strength and low expansion and is frequently used in dental laboratories for pouring final impression. The prepared impressions were placed in sealed plastic bags in the refrigerator so that the impressions did not get contaminated. The obtained impressions were stored at 40°C for 90 min in an acrylizer, −10°C for 24 h, −2°C for 48 h, and 0°C for 1 week inside the refrigerator in sealed plastic bags before being poured with type IV die stone.

The repeat pouring of the impressions was done at the time of retrieval of the first cast after 60 min to ensure the complete setting of the die stone of the first pour. These time intervals were the same as described by Luebke et al.[24] in a similar type of study. To determine linear dimensional changes, the dimensions of the master die between the reference points A-B, B-C, C-D, and D-A were measured with the help of a traveling microscope capable of measuring up to 0.001 mm. The same instrument was used by Johnson and Craig[14] in a similar type of study. It is clear from the observations of [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11], [Table 12], [Table 13], [Table 14], which depict the dimensions on stone casts of Group I and Group II compared with master die between the reference points A-B, B-C, C-D, and D-A, that there were no significant changes in these dimensions even after storing the impressions and delayed pouring of impressions at all time intervals. Similarly, no significant changes in these dimensions were observed after the repeat pours at all time intervals.

As evident from the results of the abovementioned tables, there is a tendency toward a slight increase in all the dimensions after the storage of the impressions at a different temperature, delayed pour, and repeat pour as compared to the master die, but no specific pattern was observed. However, this change was statistically insignificant. According to the ADA specification number 19 for elastomeric impression materials, dimensional changes should not be more than 0.50%. The results of the present study were also within this limit. The results of this study are also in agreement with those of various authors[3],[24],[25],[26],[27],[28],[29],[30],[31],[32],[33],[34],[35],[36] that storage temperature has no clinically significant effect upon the dimensional accuracy of addition silicone impression materials. This study is also in agreement with the studies of various authors[2],[4],[10],[13],[14],[15],[16],[17],[21],[22],[23],[27],[28],[30],[31],[32],[33],[34],[35],[36],[37],[38],[39],[40],[41],[42],[43],[44],[45],[46],[47],[48],[49],[50],[51] that delayed pour has no clinically significant effect upon the dimensional accuracy of addition silicone impression materials. The present study is in agreement with the studies of various authors[1],[2],[6],[7],[15],[16],[23],[24],[32],[42],[50] that repeat pour has no clinically significant effect on the dimensional accuracy of addition silicone impression materials.


  Conclusion Top


Thus, it was concluded from the present study that even though addition silicone impression material is delayed poured up to 1 week, repeat poured, and exposed from −10°C to 40°C, linear dimensional accuracy will not be adversely effected.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

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