|Year : 2021 | Volume
| Issue : 2 | Page : 100-106
Reliability of repour of varying thickness alginate impression following extended storage time intervals
Mohammed E Sayed1, Amit Porwal1, Ahlam Alhazmi2, Buthina Alaki3, Mahasin Alnemi4
1 Department of Prosthetic Dental Sciences, College of Dentistry, Jazan University, Jizan, Saudi Arabia
2 PG Prosthodontics Resident, Jeddah, Saudi Arabia
3 General Dentist, Private Clinic, Jazan, Saudi Arabia
4 General Dentist, Primary Health Care Center, Albhah, Saudi Arabia
|Date of Submission||26-Mar-2021|
|Date of Acceptance||20-Oct-2021|
|Date of Web Publication||12-Jan-2022|
College of Dentistry, Jazan University, Jazan
Source of Support: None, Conflict of Interest: None
Background: Obtaining multiple casts from an impression is desirable for the completion of numerous procedures for a patient. Recent literature on newly introduced extended-pour alginates reveals promising results for delayed pouring. However, literature on multiple pouring of impressions and the effects of impression thickness and storage time is not available. Subjects and Methods: Conventional and extended-pour alginates of various thicknesses (2, 4, and 6 mm) were evaluated for linear dimensional changes in both the intra-abutment and inter-abutment distances. Casts were poured twice with the time difference between the pours being 45 min; the storage time, however, was varied (15 min, 1 h, and 1, 3, and 7 days). The intra-abutment and inter-abutment measurements were compared with those of the standard metal die. Results: Compared with that of the metal die, the casts poured with 6 mm thickness of the impression material showed better accuracy between the first and the second pours and also revealed smaller statistical differences. Further, Cavex performed better than Major and GC brands. Conclusions: The dimensional stability of different alginate materials vary with thickness, storage time, and multiple pouring in both conventional and extended-pour alginates. Shorter storage time and greater thickness of the impression material are preferred when the same impression has to be poured twice. Clinical Significance: Alginate impressions can be poured twice, if made in adequate thickness and stored for short storage time, to generate additional set of accurate casts that aid in documentation, diagnostic and treatment procedures.
Keywords: Accuracy, alginate impression, extended pour, pouring, storage time, thickness
|How to cite this article:|
Sayed ME, Porwal A, Alhazmi A, Alaki B, Alnemi M. Reliability of repour of varying thickness alginate impression following extended storage time intervals. King Khalid Univ J Health Sci 2021;6:100-6
|How to cite this URL:|
Sayed ME, Porwal A, Alhazmi A, Alaki B, Alnemi M. Reliability of repour of varying thickness alginate impression following extended storage time intervals. King Khalid Univ J Health Sci [serial online] 2021 [cited 2022 Jun 26];6:100-6. Available from: https://www.kkujhs.org/text.asp?2021/6/2/100/335626
| Introduction|| |
The most commonly used impression material for obtaining an accurate diagnostic cast is alginate, which is an irreversible hydrocolloid impression material. With advancements in material research, various components and fillers are added to the impression material by manufacturers to regulate its physical characteristics and dimensional stability for extended periods; these additives are claimed to be dimensionally accurate and stable up to 168 h and pourable even after a long time.
The suggested time for pouring alginate impressions is 12 min, as the probability of the dimensions changing increases beyond that period. Hiraguchi et al. reported that for different brands of impression materials, different dimensional changes are observed even at 100% relative humidity.
This was practically not possible in the case where the impressions were sent to a laboratory and then poured after hours or even days. Now, however, with the availability of extended-pour materials, manufacturers claim pouring can be accomplished even after 5 days, and the casts obtained will be statistically accurate under specific storage conditions.
In the literature, various articles specify the storage time, accuracy of the casts obtained, and their effect on the dimensional stability of the impression materials.,, However, data related to the effects of the first and second pouring of the recently developed extended-pour materials with varying thicknesses and storage times, which is required to obtain standardized casts that can be utilized for the fabrication of various prostheses, is missing. In addition, general practitioners have found it increasingly difficult and time consuming to fabricate multiple impressions for diagnosis, mounting, and diagnostic wax-up fabrication, as well as for fabrication of provisional restorations.
The aim of this study was to evaluate the linear dimensional accuracy of stone models obtained using standardized molds fabricated from a new-generation extended-pour alginate impression material over 7 days for different thicknesses of the alginate material (2, 4, and 6 mm), storage times (15 min, 1 h, and 1, 3, and 7 days), and numbers of pours, as compared with conventional materials. The null hypotheses tested were that the linear dimensional accuracies of the stone models obtained are not affected by the first and the second pours, the type of alginate impression material, its thickness, or the storage time.
| Subjects and Methods|| |
This study was conducted in the Department of Prosthetic Dentistry, Jazan University College of Dentistry. Three brands of alginate impression materials, namely conventional (GC [Aroma Fine Plus, Tokyo, Japan]) and extended-pour alginates (Major [Algimajor, Major Prodotti Dentari, Moncalieri, Italy) and Cavex CA37 (Cavex Holland, RW Haarlem, Netherlands]) were selected to compare the effects of first and second pouring and alginate thickness on dimensional accuracy following storage over different time intervals. All the alginates were procured and stored in a cool and dry place. A standardized metallic die was prepared with two abutments. A standardized stainless steel model with two firmly attached abutment preparations that were tapered at 6° total was fabricated. It simulated a three-unit fixed partial denture situation, replacing a single tooth. Cross grooves were placed on the prepared abutments for making standardized measurements and for accurately assessing the changes [Figure 1].
Spacer thicknesses of 2, 4, and 6 mm were applied separately on the die, followed by mold fabrication and cast pouring. Light-cured acrylic trays were fabricated with a definitive stop on the standardized casts away from the area to be measured. Perforations 1 mm in diameter were made with spacing of 1 cm on the acrylic trays [Figure 2]. Room-temperature water was used to mix the alginate using an electric alginator. The water-to-powder ratio used was as recommended by each manufacturer. First pouring of the casts was carried out using type IV stone (Royal Rock Pink, Talladium Inc., Muirfield Ln. Valencia, CA) at time durations of 15 and 60 min and 24, 72, and 168 h; the casts were removed from the impressions after 45 min in each case and a second pour was performed. After the removal of the first casts, the impressions were rinsed with cold water, dried by shaking, and repoured. The samples that were to be poured at a later time were stored in 100% controlled humidity; each impression was wrapped in damp paper towels and stored in a sealed plastic bag that was kept in an airtight container.
|Figure 2: Photograph showing the prototype custom tray prepared for making alginate impressions on the metallic die|
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To control the setting expansion of the stone, the powder was accurately weighed on an electronic weighing machine, and water was dispensed using a graduated cup. The same batch type IV die stone was used to pour the impressions of all the different types of alginates. An automatic vacuum mixer (Mix-R, Dentalfarm, Torino, Italy) was used for mixing by following the manufacturer recommendations.
The dimensional accuracies of both the first and the second pour casts were compared with that of the master die. Ten casts were poured for each time interval and thickness for all alginate groups. The total number of impressions fabricated was 450 and the number of casts poured was 900 [Figure 3]. Universal alginate trays adhesive (Medicept, Medicept UK Ltd., UK) was used to ensure adhesion of the alginate to the tray and to avoid possible tearing or distortion during retrieval of the first pour. Any sample that revealed pouring defects or errors was discarded and new impressions were made. A stereomicroscope [Amscope SM-1tsz-144S-5M stereo zoom microscope with a 5 MP mounted digital camera; [Figure 4]] was used for making linear measurements on all the retrieved casts and the master model. Standardized photographs were taken for the stone casts and the master model using a millimeter ruler and a putty index, which served as a reference for the measurements. All the images were transferred to a computer, and the intra-abutment (vertical measurement) and inter-abutment (horizontal measurement) distances were measured, as described in [Figure 5], by a single-blinded expert investigator. All the measurements were performed 10 times on the steel model and then averaged for use as the reference. On the plaster model of each alginate, measurements were carried out three times and averaged for use as a statistical value. All the measurements were performed by a single investigator.
|Figure 3: Flowchart showing the group distribution and the sample collection method|
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|Figure 4: Photograph of the procedure done for measuring the distances on die with the help of stereomicroscope|
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The data were collected in Microsoft Excel and compared statistically using SPSS software SPSS 20 statistics software (SPSS Inc., Chicago, IL). T-test was used to evaluate the relevant variables within each group with statistical significance.
| Results|| |
The measurements of the metallic die as recorded by the stereomicroscope were 27.06 (inter-abutment) and 8.46 (intra-abutment) mm. These values were used as a reference for all the other models. Positive values indicate expansion of the alginate material, resulting in a larger cast, and vice versa.
[Table 1] shows the statistical differences between the first and the second pour casts in both the inter-abutment and intra-abutment dimensions for 2 mm thickness of alginate. The casts generated by GC after 15 min, 1 h, and 1 and 7 days showed significant differences in the inter-abutment measurements, and those corresponding to 1 h and 7 days revealed significant differences in the intra-abutment measurements on comparing the first and the second pour casts. In the case of Major, the casts corresponding to 15 min, 1 h, and 3 and 7 days showed significant differences in the inter-abutment measurements, and those corresponding to 1 h and 3 and 7 days exhibited significant differences in intra-abutment measurements. In the case of Cavex, the casts obtained after 15 min, 1 h, and 1 day showed significant differences in inter-abutment measurements, and those corresponding to 1 h and 3 days revealed significant differences in intra-abutment measurements.
|Table 1: Statistical difference of the brands between 1st pour and 2nd pour (2 mm) in horizontal and vertical dimensions|
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[Table 2] shows the statistical differences between the first and the second pour casts in both the inter-abutment and intra-abutment dimensions for 4 mm thickness of alginate. The casts generated by GC after 15 min and 1 day showed significant differences in the inter-abutment measurements, and those produced after 15 min and 1 and 7 days revealed significant differences in intra-abutment measurements on comparing the first and the second pour casts. In the case of Major, significant differences in the inter-abutment measurements were noticed for the casts prepared over 15 min, 1 h, and 3 days, and the cases fabricated over 15 min, 1 h, and 7 days exhibited significant differences in intra-abutment measurements. In the case of Cavex, the casts corresponding to 3 and 7 days showed significant differences in the inter-abutment measurements.
|Table 2: Statistical difference of the brands between 1st pour and 2nd pour (4 mm) in horizontal and vertical dimensions|
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[Table 3] shows the statistical differences between the first and the second pour casts in both the inter-abutment and intra-abutment dimensions for 6 mm thickness of alginate. The casts generated by GC over 7 days showed significant differences in the inter-abutment measurements, whereas those prepared in 15 min revealed significant differences in the intra-abutment measurements on comparing the first and the second pour casts. In the case of Major, significant differences in the inter-abutment measurements were observed for the casts prepared in 3 and 7 days, and significant differences in intra-abutment measurements were noticed for the casts produced after 15 min and 7 days. In the case of Cavex, the casts produced in 3 days showed significant differences in the inter-abutment measurements, whereas those generated after 1 and 7 days revealed significant differences in the intra-abutment measurements.
|Table 3: Statistical difference of the brands between 1st pour and 2nd pour (6 mm) in horizontal and vertical dimensions|
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| Discussion|| |
With the increased requirement of studies and working models for documentation of a case as well as for treatment planning and fabrication of temporary prostheses, a suitable material that can reproduce multiple casts with dimensional accuracy at low costs and minimal discomfort to the patient is desired., Various processes such as syneresis, imbibition, and shrinkage affect irreversible hydrocolloid material.,,, In the present study, three different brands were used for both conventional and extended pouring, and impressions were poured twice to investigate the behavior of these materials as the storage time changed; their behavior with changes in the space provided for the impression materials in both the vertical and horizontal dimensions were also examined. The results of this study show that all the materials behave differently in both the horizontal and vertical dimensions with changing thickness, storage time, and number of pouring.
The recommended space that should be provided for the alginate impression material is 5–7 mm and 4–5 mm. However, in this study, 2, 4, and 6 mm thicknesses were considered to observe the effect of increasing and decreasing thickness of the irreversible hydrocolloid material. Interpretation of our research data showed fewer statistically significant differences (P < 0.05) between the first and the second pours of the impressions in the horizontal and vertical dimensions when 6 mm of space was provided for the impression materials, suggesting that more space for the irreversible hydrocolloid should be provided when multiple casts are desired from the same impression.
It has been postulated in the literature that the latest brands of extended-pour alginates provide dimensional stability to the material and that impressions can be poured even after prolonged storage., This type of material can usually help practitioners in situations where they need to send their impressions to the laboratory, which can be located far away, for pouring the casts. In this study, two extended-pour alginates (Major and Cavex brands) were used and compared with the conventional alginate (GC brand). Cavex outperformed and showed the least number of significant differences between the first and the second pours in both inter-abutment and intra-abutment measurements.
Within 45 min first casts were removed and second casts were poured. This was carried out in accordance with the study of Haywood published in 1998, wherein it is mentioned that 45 min is the longest time that can be repeatedly tolerated without sacrificing accuracy and is ideal for realistically simulating the conditions of a dental clinic. Utmost care was taken to remove the first cast without any tearing or damage to the impression material. In case of any tear, new impressions were fabricated, and the old (damaged) ones were discarded. The impressions were stored according to the standardized protocol of wrapping each of them in damp paper towels and storing in sealed plastic bags, which were kept in an airtight container until the time of pouring.
The dimensional changes observed between different irreversible hydrocolloid impression materials vary and are dependent on multiple factors such as the constituents, storage time, and conditions, as well as the duration before pouring the impressions. According to the literature,, casts obtained from conventional alginates have slightly larger dimensions and should be poured as soon as possible for accuracy. On the other hand, extended-pour alginates usually produce smaller casts and should not be poured immediately. In this study, when the first and the second pours were compared for extended periods, the number of significant differences was similar for Cavex and GC at all storage times, while that of Major varied with different storage times.
In 2018, Choudhary et al. concluded that multiple casts can be produced from a single impression with acceptable accuracy, compared to the casts obtained with different impressions. In their study, only two durations were considered, that is, immediately and after 24 h. However, in the present study, five durations were considered (15 min, 1 h, 1 day, 3 days, and 7 days) to examine the behavior of the extended-pour alginates over a long period of time.
In the current study, the sample size considered for every group (n = 10) was very small; this is an area of focus for future research, and studies should be planned with a larger sample size to replicate practical clinical conditions and with standardization of various other factors to better understand the behavior of different irreversible hydrocolloid materials.
| Conclusions|| |
From the results of this study, we conclude the following:
- The dimensional stability of different alginate materials vary with thickness, storage time, and multiple pouring
- Casts produced from a thicker alginate (6 mm) reveal fewer differences between the first and the second pours in both inter-abutment and intra-abutment dimensions
- For extended periods, the casts produced from conventional alginate reveal similar statistically significant differences between the first and the second pours compared with those fabricated from extended-pour alginates.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3]