- Email: [email protected]
Effect of storage time on mechanical properties of extended-pour irreversible hydrocolloid impression materials
RESEARCH AND EDUCATION
Effect of storage time on mechanical properties of extendedpour irreversible hydrocolloid impression materials Volkan Sahin, DDS, PhD,a Hossein Jodati, MSc,b and Zafer Evis, MSc, PhDc
ABSTRACT Statement of problem. Recent commercial extended-pour irreversible hydrocolloid impression materials (EPIHIMs) claim to maintain dimensional stability up to 120 hours. However, data regarding their mechanical properties and performance after 120 hours of storage are lacking. Purpose. The purpose of this in vitro study was to test the elastic recovery, strain in compression, and tear strength properties of 5 commercially available EPIHIMs, immediately after preparation and after 120 hours of storage under specific storage conditions. Material and methods. A total of 150 specimens were prepared in accordance with the ISO 21563:2013 standard from 5 commercially available EPIHIMs (Blueprint Xcreme, Kromopan, Alginmax, Hydrogum 5, and Alginelle). The specimens were subjected to elastic recovery, strain in compression, and tear strength tests immediately after specimen preparation (n=5) and after 120 hours of storage inside clear plastic zipper bags held at 23 C (n=5). Data were analyzed with a multivariate analysis of variance (MANOVA) test for brand and duration parameters. Normality of data was analyzed with the Shapiro-Wilk test. The Duncan test or Games-Howell test was used for multiple comparisons (a=.05). Results. Elastic recovery and strain in compression values of the EPIHIMs tested were affected by brand and duration parameters (P<.001). Tear strength values of the EPIHIMs tested were affected by brand (P<.001); however, they were not affected by duration (P>.05). Data distribution was normal except for Alginmax in terms of the elastic recovery values and Blueprint Xcreme in terms of the strain in compression values (P<.05). Significant interactions were present between brand and duration for the strain in compression and tear strength values of the EPIHIMs tested (P<.05). Statistically significant difference was not found among mean elastic recovery values of the tested EPIHIM brands (P<.001). Moreover, a statistically significant increase was present in elastic recovery values of the tested EPIHIMs after 120 hours of storage (P<.001). Statistically significant difference was not found among mean strain in compression values of the tested EPIHIM brands tested immediately after preparation (P>.05). However, 120 hours of storage led both to a statistically significant decrease in mean strain in compression values of the tested EPIHIMs (P<.001) except for Alginelle (P>.05) and a statistically significant difference among mean strain in compression values of the tested EPIHIM brands (P<.001). Storage time did not influence mean tear strength values of the EPIHIMs tested (P>.05). However, statistically significant differences were present among mean tear strength values of the tested EPIHIM brands tested immediately after preparation (P<.001) and after 120 hours of storage (P<.001). Conclusions. Despite variations in elastic recovery, strain in compression, and tear strength properties of the EPIHIMs tested, all the materials fulfilled the requirements to comply with the ISO 21563:2013 standard even after 120 hours of storage. (J Prosthet Dent 2019;-:---)
Irreversible hydrocolloid impression materials (IHIMs) are made in 2 phases: sol and gel. In the sol phase, IHIM powder is mixed with water and forms liquid or semiliquid. Later in the gel phase, semisolid, gel-like material
is formed through a chemical reaction,1 where soluble sodium alginate reacts with calcium sulfate and produces insoluble calcium alginate gel. Meanwhile, the rate of production of calcium alginate is regulated by presence
This study was financially supported by Türkiye Bilimsel ve Teknolojik Aras¸tırma Kurumu (The Scientific and Technological Research Council of Turkey) with the project #215M056. a Professor, Department of Prosthodontics, Faculty of Dentistry, Kırıkkale University, Kırıkkale, Turkey. b Doctoral student, Biomedical Engineering Department, Middle East Technical University, Ankara, Turkey. c Professor, Engineering Sciences Department and Biomedical Engineering Department, Middle East Technical University, Ankara, Turkey.
THE JOURNAL OF PROSTHETIC DENTISTRY
1
2
Volume
Clinical Implications Decrease in mean strain in compression values of the irreversible hydrocolloid impression materials after 120 hours of storage might require additional attention during removal of the gypsum cast because decreased strain in compression values led to impressions with increased stiffness.
and amount of a third soluble salt, such as sodium phosphate.2 However, alginates are composed of guluronic acid and mannuronic acid monomers, and only the guluronic acid monomers are believed to participate in intermolecular cross-linking with divalent cations to form hydrogels. The composition (mannuronic acid and guluronic acid monomer ratio), sequence of the monomers, guluronic acid block length, and molecular weight are factors that affect the physical properties of alginate and its resultant hydrogels.3 Hydrogels derived from alginates with higher guluronic acid monomer content have higher stiffness.3 The ISO 21563:2013 standard4 refers to hydrocolloid impression materials, and IHIMs are required to provide adequate elastic recovery, strain in compression, and tear strength values to comply with this standard. The elastic recovery test determines the ability of the IHIMs to recover from deformation with a minimum admissible value of 95%.4 The strain in compression test is used to determine the required flexibility to allow the removal of the impression from the mouth without injury to the oral tissues and the appropriate stiffness of the impressions to withstand deforming forces. Strain in compression value in a range of 5% to 20% is acceptable as stated in the ISO 21563:2013 standard.4 Dental impressions might tear during impression removal from the mouth or cast removal from the impression.5 Defects in the impression influence precision of the casts.6 Therefore, imposed tensile stresses must be endured by IHIMs to prevent rupture.7 Tear strength acts as an indicator for the stability of these impressions, and having high tear strength at the time of removal is necessary to make accurate gypsum casts. Conventional IHIMs usually need to be poured within 12 minutes after removal of the impression from the mouth; otherwise unacceptable distortion occurs.8,9 Recently introduced extended-pour irreversible hydrocolloid impression materials (EPIHIMs) were developed to postpone pouring impressions so they can be sent to a dental laboratory. The manufacturers claim these materials maintain their dimensional stability up to 120 hours.10,11 The purpose of this in vitro study was to test elastic recovery, strain in compression, and tear strength THE JOURNAL OF PROSTHETIC DENTISTRY
-
Issue
-
Table 1. Extended-pour irreversible hydrocolloid impression materials tested
Manufacturer
Lot #
Recommended Powder-to-Water Ratio
Blueprint Xcreme
Dentsply Sirona
1511228928
25 mL/17 mL
Kromopan
Lascod S.p.A
Alginmax
Major Prodotti Dentari S.p.A.
Hydrogum 5
Zhermack S.p.A.
Alginelle
Lascod S.p.A
Brand Name
0166291163.207
9 g/20 mL
16117
9.5 g/20 mL
260391
7 g/15 mL
0164320149.207
9 g/20 mL
properties of 5 commercially available EPIHIMs immediately after preparation and after 120 hours of storage under specific storage conditions. The null hypothesis was that storage time would have no influence on the elastic recovery, strain in compression, or tear strength properties of the EPIHIMs tested. MATERIAL AND METHODS A total of 150 specimens were prepared in accordance with the ISO 21563:2013 standard4 from 5 commercially available EPIHIMs (Blueprint Xcreme, Kromopan, Alginmax, Hydrogum 5, and Alginelle). Manufacturer information, lot numbers, and water-to-powder ratios used during specimen preparation are provided in Table 1. Specimen preparation and test procedures were carried out under ambient laboratory conditions of 23 ±2 C and 50 ±10% relative humidity in accordance with the ISO 21563:2013 standard.4 Ten specimens were produced from each EPIHIM for each test procedure. The specimens were divided into 2 groups (n=5); the first group provided the base line measurements, which were tested instantly after specimen preparation, and those in the second group (n=5) were individually stored inside clear plastic zipper bags held at 23 C for an additional 120 hours after fabrication. Sample size was based on the ISO 21563:2013 standard4 as the standard requires preparation of either 3 or 5 specimens for each test procedure, so 5 specimens prepared for each EPIHIM brand were used in each test for the duration of the storage tested. A 2piece split mold with a fixation ring was used for preparation of specimens for the elastic recovery and strain in compression tests, where the specimens (Fig. 1) have a cylindrical shape with a diameter of 12.50 mm and height of 20.00 mm (Fig. 2). A polymeric tear test mold (Fig. 3) was used to prepare specimens with a length of 102.00 mm, width of 19.00 mm, and a thickness of 4.00 mm for the tear strength test (Fig. 4). Specimen-forming molds were conditioned in a laboratory oven (Protherm PLF 130/18; Alser Teknik) at 35 ±2 C for at least 15 minutes before the specimen-forming step. EPIHIM powder was mixed with deionized water (23 C) by using a mixer unit (AM100; Shanghai Foshion Medical Instrument Co Ltd) Sahin et al
-
2019
3
Figure 1. Specimen-forming split mold with fixation ring used for preparation of specimens subjected to elastic recovery and strain in compression tests. A, Disassembled. B, Assembled.
Figure 2. Elastic recovery test specimens of Blueprint Xcreme EPIHIM.
Figure 4. Tear strength test specimens of Blueprint Xcreme EPIHIM.
Figure 3. Polymeric tear test specimen forming plate for tear strength test specimens.
for 15 seconds. After removal of the mold from the oven, the mold cavity was slightly overfilled with the EPIHIM, and the specimen-containing mold was transferred to a hot water bath held at 35 ±2 C. For the elastic recovery test, the specimen was aligned with the dial indicator spindle, deformed 4.0 ±0.1 mm, and released within 5 seconds. The elastic recovery (K) for each specimen was to the nearest 0.1% calculated 2 from the equation K = 100− 100 h1h−h 0
Sahin et al
, where h0 is the
initial length of the specimen (20.00 mm), h1 is the length recorded by the dial indicator 10 seconds after the indicator spindle contacted the top of the specimen before deformation, and h2 is the length recorded by the dial indicator 40 seconds after deformation. For the strain in compression test, the specimen was axially aligned with the center of the loading shaft foot. The strain in compression (E) for each specimen was calculated to the nearest 0.1% from the equation E= 100
h1 −h2 h0
, where E is the percentage of strain in
compression, h0 is the height of the split mold, h1 is the dial indicator reading 30 seconds after application of the initial load of 1.2 ±0.1 N, and h2 is the dial indicator reading at 30 seconds after application of the total load of 12.2 ±0.1 N. For the tear strength test, a dial indicator (2112-101F; Insize Inc) was used to measure the thickness of the specimen at a point centered on and just inside the apex of the 90-degree angle edge. The specimen was loaded in tension until rupture with a crosshead speed of 500 mm/ min within 90 seconds after removal of the mold THE JOURNAL OF PROSTHETIC DENTISTRY
4
Volume
Table 2. Multivariate analysis of variance (brand, storage) of elastic recovery, strain in compression, and tear strength tests F
P .001
69.05
<.001
Brand×duration
1.12
.361
Kromopan
94.69 ±0.69
Brand
9.56
<.001
Alginmax
144.35
<.001
Hydrogum5
Brand Duration
Strain in compression
Duration Brand×duration Tear strength
6.21
.001
55.51
<.001
Duration
0.98
.329
Brand×duration
4.01
.008
Brand
Brand
Statistic
df
P
Blueprint Xcreme
0.88
10
.135
Kromopan
0.90
10
.238
Alginmax
0.73
10
.002*
Hydrogum 5
0.88
10
.113
Strain in compression
Alginelle
0.85
10
.063
Blueprint Xcreme
0.83
10
.030*
Kromopan
0.88
10
.139
Tear strength
Alginmax
0.92
10
.327
Hydrogum 5
0.86
10
.077
Alginelle
0.92
10
.341
Blueprint Xcreme
0.91
10
.278
Kromopan
0.93
10
.492
Alginmax
0.92
10
.392
Hydrogum 5
0.86
10
.068
Alginelle
0.92
10
.335
*P<.05 indicates significant difference.
containing the specimen from the water bath. The force required to achieve rupture was recorded. The tear strength Ts, for each specimen was calculated to the nearest 0.01 N/mm from the equation Ts = Fd, where F is the maximum force (N) applied to cause rupture of the specimen and d is the specimen thickness (mm). The same test procedure was applied for the specimens in the second group, which were stored inside clear plastic zipper bags held at 23 C for an additional 120 hours. Data were analyzed with a multivariate analysis of variance (MANOVA) test for brand and duration parameters by using a statistical software (SPSS v. 15.0; SPSS Inc). Normality of data was analyzed with the Shapiro-Wilk test. The Duncan test or Games-Howell test was used for multiple comparisons (a=.05). RESULTS Elastic recovery and strain in compression values of the EPIHIMs tested were affected by brand and duration parameters (P<.001). Tear strength values of the EPIHIMs tested were affected by brand (P<.001); however, they were not affected by duration (P>.05). Significant THE JOURNAL OF PROSTHETIC DENTISTRY
Baseline
Blueprint Xcreme
Alginelle
120 h of Storage
95.56 ±0.40A
b
97.45 ±0.26B
a
b
97.41 ±0.52B
a
93.41 ±2.56A
b
96.18 ±0.30Ba
95.62 ±0.30A
b
97.31 ±0.24B
a
b
96.56 ±0.53B
a
95.09 ±0.12
A
A
Different superscript uppercase letters indicate statistically significant differences among brands. Different subscript lowercase letters indicate statistically significant differences among storage durations.
Elastic Recovery (%)
Table 3. Shapiro-Wilk test results for normality of data Elastic recovery
-
Elastic Recovery (%) Brand
P<.05 indicates significant difference.
Effect
Issue
Table 4. Mean values, standard deviations, and multiple comparison results of elastic recovery test
6.00
Effect Elastic recovery
-
100 90 80 70 60 50 40 30 20 10 0 Blueprint Xcreme
Kromopan Alginmax Hydrogum5 Alginelle
Brand Baseline
120 hours of storage
Figure 5. Interaction plot for elastic recovery test.
interactions were present between brand and duration for the strain in compression and tear strength values of the EPIHIMs tested (P <.05) (Table 2). Data distribution was normal except for Alginmax in terms of the elastic recovery values and Blueprint Xcreme in terms of the strain in compression values (P<.05) (Table 3). Multiple comparisons were performed by using the GamesHowell test for the elastic recovery and tear strength properties because the Levene test indicated significant differences for these properties (P<.001). Multiple comparisons were carried out by using the Duncan test for the strain in compression property because the Levene test did not indicate a significant difference for this property (P>.05). A statistically significant difference was not found among the mean elastic recovery values of the tested EPIHIM brands (P<.001), but a statistically significant increase was found in the elastic recovery values of the tested EPIHIMs after 120 hours of storage (P<.001) (Table 4). Statistically significant interaction was not found between the brand and duration parameters for this test (P>.05) (Fig. 5). A statistically significant difference was not found among the mean strain in compression values of the tested EPIHIM brands tested immediately after preparation (P>.05). However, 120 hours of storage led to a statistically significant decrease in the mean strain in Sahin et al
2019
5
Table 5. Mean values, standard deviations, and multiple comparison results of strain in compression recovery test Strain in Compression (%) Brand Blueprint Xcreme
Baseline
120 h of Storage
14.49 ±1.08A
a
8.81 ±0.43D
a
11.53 ±0.63C 12.12
A
b
Kromopan
15.03 ±1.40
Alginmax
16.33 ±1.25A
a
Hydrogum5
14.55 ±1.85A
a
9.02 ±0.39D
b
a
13.12 ±1.09B
a
Alginelle
14.23 ±1.84
A
b ±0.70BCb
Different superscript uppercase letters indicate statistically significant differences among brands. Different subscript lowercase letters indicate statistically significant differences among storage durations.
Strain in Compression (%)
-
100 90 80 70 60 50 40 30 20 10 0 Blueprint Xcreme
Kromopan Alginmax Hydrogum5 Alginelle
Brand Table 6. Mean values, standard deviations, and multiple comparison results of tear strength test
Baseline
Figure 6. Interaction plot for strain in compression test.
Tear Strength (N/mm) Baseline
120 h of Storage
Blueprint Xcreme
1.14 ±0.19A
a
1.03 ±0.17F
a
Kromopan
0.91 ±0.06B
a
0.84 ±0.06G
a
Alginmax
0.70 ±0.08C
a
0.89 ±0.07FGa
Hydrogum5
1.09 ±0.05A
a
1.18 ±0.12E
a
Alginelle
0.53 ±0.02D
a
0.57 ±0.04H
a
Different superscript uppercase letters indicate statistically significant differences among brands. Different subscript lowercase letters indicate statistically significant differences among storage durations.
compression values of the tested EPIHIMs (P<.001), except for Alginelle (P>.05), to a statistically significant difference among the mean strain in compression values of the tested EPIHIM brands (P<.001) (Table 5), and to a statistically significant interaction between brand and duration parameters for this test (P<.001) (Fig. 6). Alginelle maintained its strain in compression value even after 120 hours of storage (baseline: 14.23 ±1.84%, after 120 hours: 13.12 ±1.09%, P>.05). Mean strain in compression values of the Kromopan and Alginmax decreased (Kromopan: baseline: 15.03 ±1.40%, after 120 hours: 11.53 ±0.63%, P<.05, Alginmax: baseline: 16.33 ±1.25%, after 120 hours: 12.12 ±0.70%, P<.05). The highest decrease in the mean strain in compression values of all the tested EPIHIMs was observed for Hydrogum 5 and Blueprint Xcreme materials (Hydrogum 5: baseline: 14.55 ±1.85%, after 120 hours: 9.02 ±0.39%, P<.05, Blueprint Xcreme: baseline: 14.49 ±1.08%, after 120 hours: 8.81 ±0.43%, P<.05). Storage time did not influence the mean tear strength values of the EPIHIMs tested (P>.05). However, statistically significant differences were found among the mean tear strength values of the EPIHIM brands tested immediately after preparation (P<.001) and after 120 hours of storage (P<.001) (Table 6). At baseline measurements, Blueprint Xcreme and Hydrogum 5 had the highest mean tear strength values (1.14 ±0.19 N/mm, 1.09 ±0.05 N/mm), followed by Kromopan (0.91 ±0.06 N/mm) and Alginmax (0.70 ±0.08 N/mm), whereas Alginelle had the lowest mean tear strength values (0.53 ±0.02 N/mm). Hydrogum 5 had the highest mean tear Sahin et al
Tear Strength (N/mm)
Brand
120 hours of storage
1.2 1 0.8 0.6 0.4 0.2 0 Blueprint Xcreme
Kromopan Alginmax Hydrogum5 Alginelle
Brand Baseline
120 hours of storage
Figure 7. Interaction plot for tear strength test.
strength value after 120 hours of storage (1.18 ±0.12 N/mm), followed by Blueprint Xcreme (1.03 ±0.17 N/mm), Alginmax, and Kromopan (0.89 ±0.07 N/mm, 0.84 ±0.06 N/mm), whereas Alginelle had the lowest mean tear strength values (0.57 ±0.04 N/mm). Variations in the mean tear strength values of the EPIHIMs subjected to prolonged storage time led to a statistically significant interaction between brand and duration parameters for this test (P<.001) (Fig. 7). DISCUSSION This in vitro study investigated the elastic recovery, strain in compression, and tear strength properties of 5 commercially available EPIHIMs immediately after preparation and after 120 hours of storage under specific storage conditions. The null hypothesis was accepted for the tear strength property because storage time had no influence on this property. However, the null hypothesis was rejected for the elastic recovery and strain in compression properties because 120 hours of storage led to a statistically significant increase in mean elastic recovery values of all the tested EPIHIMs and a decrease in THE JOURNAL OF PROSTHETIC DENTISTRY
6
the mean strain in compression values of the tested EPIHIMs except Alginelle. The EPIHIMs tested in the present study were chosen from available materials that the manufacturers claimed to be dimensionally stable up to 120 hours in controlled storage conditions. The ISO 21563:2013 standard4 refers to hydrocolloid impression materials, and the tests mentioned refer to conventional IHIMs. Therefore, the tests applicable to IHIMs simulate clinical conditions, where the impressions removed from the mouth undergo the testing procedures immediately. However, testing procedures for the EPIHIMs have not yet been specified. In this study, modified test procedures were applied to determine the elastic recovery, strain in compression, and tear strengths of EPIHIMs after prolonged storage. Any alteration in strain in compression and tear strength of EPIHIMs after prolonged storage might result in damaging gypsum casts during removal. The results of the present in vitro study indicated that prolonged storage led to an increase in the mean elastic recovery values of all the EPIHIMs tested, which indicates prolonged storage improved recovery capabilities of these impression materials. This increase may be because prolonged storage time enabled progress of the gelation reaction of the EPIHIMs tested, where the additional gelation reaction provided the increased mean elastic recovery values. Prolonged storage led to a statistically significant decrease in mean strain in compression values of the tested EPIHIMS, except for Alginelle. This decrease may also be related to the fact that prolonged storage time enabled progress of the gelation reaction of the EPIHIMs tested, where the additional gelation reaction provided more guluronic acid monomers to interact with calcium cations to form hydrogels with increased stiffness. The difference in behavior of the Alginelle material may be because the alginate component had lower guluronic acid monomers. Although the decreased strain in compression values of the EPIHIMs are still in the acceptable 5% to 20% range as stated in the ISO 21563:2013 standard,4 care during removal of the gypsum cast is recommended because decreased strain in compression values lead to impressions with increased stiffness. The effect of EPIHIM brand on mechanical properties such as tear strength is possibly dependent on the materials’ chemical composition, especially the composition of the alginate component, and needs further investigation. As there was an increase in the elastic
THE JOURNAL OF PROSTHETIC DENTISTRY
Volume
-
Issue
-
recovery and decrease in the strain in compression properties of the tested EPIHIMs, setting new standards applicable to this specific impression material type should be considered. Limitations of this in vitro study included that the procedure used for determining tear strength values of EPIHIMs excluded a measurement of the thickness of the specimen at the moment of tearing. This value is not required to calculate tear strength in the ISO 21563: 2013 standard.4 CONCLUSIONS Based on the findings of this in vitro study, the following conclusion was drawn: 1. Despite variations in elastic recovery, strain in compression, and tear strength properties of the EPIHIMs tested, all the materials complied with the requirements of the ISO 21563:2013 standard, even after 120 hours of storage. REFERENCES 1. Fu S, Thacker A, Sperger DM, Boni RL, Buckner IS, Velankar S, et al. Relevance of rheological properties of sodium alginate in solution to calcium alginate gel properties. AAPS PharmSciTech 2011;12:453-60. 2. Anusavice KJ, Shen C, Rawls HR. Phillips’ science of dental materials. 12th ed. St. Louis: Elsevier Saunders; 2013. p. 171-7. 3. Lee KY, Mooney DJ. Alginate: properties and biomedical applications. Prog Polym Sci 2012;37:106-26. 4. International Organization for Standardization. ISO 21563: 2013. Dentistryhydrocolloid impression materials. Geneva: International Organization for Standardization; 2013. Available at: http://www.iso.org/iso/home.html. 5. Phoenix RD, Cagna DR, DeFreest CF. Stewart’s clinical removable partial prosthodontics. 4th ed. Hanover Park: Quintessence; 2008. p. 271-7. 6. Lee EA. Impression material selection in contemporary fixed prosthodontics: technique, rationale, and indications. Compend Contin Educ Dent 2005;26: 780, 2-4, 6-9. 7. Vrijhoef M, Battistuzzi P. Tear energy of impression materials. J Dent 1986;14: 175-7. 8. Donovan TE, Chee WW. A review of contemporary impression materials and techniques. Dent Clin North Am 2004;48:445-70. 9. Miller MW. Syneresis in alginate impression materials. Br Dent J 1975;139: 425-30. 10. Jamani KD. The effect of pouring time and storage condition on the accuracy of irreversible hydrocolloid impressions. Saudi Dent J 2002;14:126-30. 11. Walker MP, Burckhard J, Mitts DA, Williams KB. Dimensional change over time of extended-storage alginate impression materials. Angle Orthod 2010;80:1110-5. Corresponding author: Dr Volkan Sahin Department of Prosthodontics, Faculty of Dentistry, Kırıkkale University Celebi Sokak No: 1, 71451 Yahsihan, Kırıkkale TURKEY Email: [email protected] Copyright © 2019 by the Editorial Council for The Journal of Prosthetic Dentistry. https://doi.org/10.1016/j.prosdent.2019.09.001
Sahin et al
Effect of storage time on mechanical properties of extendedpour irreversible hydrocolloid impression materials Volkan Sahin, DDS, PhD,a Hossein Jodati, MSc,b and Zafer Evis, MSc, PhDc
ABSTRACT Statement of problem. Recent commercial extended-pour irreversible hydrocolloid impression materials (EPIHIMs) claim to maintain dimensional stability up to 120 hours. However, data regarding their mechanical properties and performance after 120 hours of storage are lacking. Purpose. The purpose of this in vitro study was to test the elastic recovery, strain in compression, and tear strength properties of 5 commercially available EPIHIMs, immediately after preparation and after 120 hours of storage under specific storage conditions. Material and methods. A total of 150 specimens were prepared in accordance with the ISO 21563:2013 standard from 5 commercially available EPIHIMs (Blueprint Xcreme, Kromopan, Alginmax, Hydrogum 5, and Alginelle). The specimens were subjected to elastic recovery, strain in compression, and tear strength tests immediately after specimen preparation (n=5) and after 120 hours of storage inside clear plastic zipper bags held at 23 C (n=5). Data were analyzed with a multivariate analysis of variance (MANOVA) test for brand and duration parameters. Normality of data was analyzed with the Shapiro-Wilk test. The Duncan test or Games-Howell test was used for multiple comparisons (a=.05). Results. Elastic recovery and strain in compression values of the EPIHIMs tested were affected by brand and duration parameters (P<.001). Tear strength values of the EPIHIMs tested were affected by brand (P<.001); however, they were not affected by duration (P>.05). Data distribution was normal except for Alginmax in terms of the elastic recovery values and Blueprint Xcreme in terms of the strain in compression values (P<.05). Significant interactions were present between brand and duration for the strain in compression and tear strength values of the EPIHIMs tested (P<.05). Statistically significant difference was not found among mean elastic recovery values of the tested EPIHIM brands (P<.001). Moreover, a statistically significant increase was present in elastic recovery values of the tested EPIHIMs after 120 hours of storage (P<.001). Statistically significant difference was not found among mean strain in compression values of the tested EPIHIM brands tested immediately after preparation (P>.05). However, 120 hours of storage led both to a statistically significant decrease in mean strain in compression values of the tested EPIHIMs (P<.001) except for Alginelle (P>.05) and a statistically significant difference among mean strain in compression values of the tested EPIHIM brands (P<.001). Storage time did not influence mean tear strength values of the EPIHIMs tested (P>.05). However, statistically significant differences were present among mean tear strength values of the tested EPIHIM brands tested immediately after preparation (P<.001) and after 120 hours of storage (P<.001). Conclusions. Despite variations in elastic recovery, strain in compression, and tear strength properties of the EPIHIMs tested, all the materials fulfilled the requirements to comply with the ISO 21563:2013 standard even after 120 hours of storage. (J Prosthet Dent 2019;-:---)
Irreversible hydrocolloid impression materials (IHIMs) are made in 2 phases: sol and gel. In the sol phase, IHIM powder is mixed with water and forms liquid or semiliquid. Later in the gel phase, semisolid, gel-like material
is formed through a chemical reaction,1 where soluble sodium alginate reacts with calcium sulfate and produces insoluble calcium alginate gel. Meanwhile, the rate of production of calcium alginate is regulated by presence
This study was financially supported by Türkiye Bilimsel ve Teknolojik Aras¸tırma Kurumu (The Scientific and Technological Research Council of Turkey) with the project #215M056. a Professor, Department of Prosthodontics, Faculty of Dentistry, Kırıkkale University, Kırıkkale, Turkey. b Doctoral student, Biomedical Engineering Department, Middle East Technical University, Ankara, Turkey. c Professor, Engineering Sciences Department and Biomedical Engineering Department, Middle East Technical University, Ankara, Turkey.
THE JOURNAL OF PROSTHETIC DENTISTRY
1
2
Volume
Clinical Implications Decrease in mean strain in compression values of the irreversible hydrocolloid impression materials after 120 hours of storage might require additional attention during removal of the gypsum cast because decreased strain in compression values led to impressions with increased stiffness.
and amount of a third soluble salt, such as sodium phosphate.2 However, alginates are composed of guluronic acid and mannuronic acid monomers, and only the guluronic acid monomers are believed to participate in intermolecular cross-linking with divalent cations to form hydrogels. The composition (mannuronic acid and guluronic acid monomer ratio), sequence of the monomers, guluronic acid block length, and molecular weight are factors that affect the physical properties of alginate and its resultant hydrogels.3 Hydrogels derived from alginates with higher guluronic acid monomer content have higher stiffness.3 The ISO 21563:2013 standard4 refers to hydrocolloid impression materials, and IHIMs are required to provide adequate elastic recovery, strain in compression, and tear strength values to comply with this standard. The elastic recovery test determines the ability of the IHIMs to recover from deformation with a minimum admissible value of 95%.4 The strain in compression test is used to determine the required flexibility to allow the removal of the impression from the mouth without injury to the oral tissues and the appropriate stiffness of the impressions to withstand deforming forces. Strain in compression value in a range of 5% to 20% is acceptable as stated in the ISO 21563:2013 standard.4 Dental impressions might tear during impression removal from the mouth or cast removal from the impression.5 Defects in the impression influence precision of the casts.6 Therefore, imposed tensile stresses must be endured by IHIMs to prevent rupture.7 Tear strength acts as an indicator for the stability of these impressions, and having high tear strength at the time of removal is necessary to make accurate gypsum casts. Conventional IHIMs usually need to be poured within 12 minutes after removal of the impression from the mouth; otherwise unacceptable distortion occurs.8,9 Recently introduced extended-pour irreversible hydrocolloid impression materials (EPIHIMs) were developed to postpone pouring impressions so they can be sent to a dental laboratory. The manufacturers claim these materials maintain their dimensional stability up to 120 hours.10,11 The purpose of this in vitro study was to test elastic recovery, strain in compression, and tear strength THE JOURNAL OF PROSTHETIC DENTISTRY
-
Issue
-
Table 1. Extended-pour irreversible hydrocolloid impression materials tested
Manufacturer
Lot #
Recommended Powder-to-Water Ratio
Blueprint Xcreme
Dentsply Sirona
1511228928
25 mL/17 mL
Kromopan
Lascod S.p.A
Alginmax
Major Prodotti Dentari S.p.A.
Hydrogum 5
Zhermack S.p.A.
Alginelle
Lascod S.p.A
Brand Name
0166291163.207
9 g/20 mL
16117
9.5 g/20 mL
260391
7 g/15 mL
0164320149.207
9 g/20 mL
properties of 5 commercially available EPIHIMs immediately after preparation and after 120 hours of storage under specific storage conditions. The null hypothesis was that storage time would have no influence on the elastic recovery, strain in compression, or tear strength properties of the EPIHIMs tested. MATERIAL AND METHODS A total of 150 specimens were prepared in accordance with the ISO 21563:2013 standard4 from 5 commercially available EPIHIMs (Blueprint Xcreme, Kromopan, Alginmax, Hydrogum 5, and Alginelle). Manufacturer information, lot numbers, and water-to-powder ratios used during specimen preparation are provided in Table 1. Specimen preparation and test procedures were carried out under ambient laboratory conditions of 23 ±2 C and 50 ±10% relative humidity in accordance with the ISO 21563:2013 standard.4 Ten specimens were produced from each EPIHIM for each test procedure. The specimens were divided into 2 groups (n=5); the first group provided the base line measurements, which were tested instantly after specimen preparation, and those in the second group (n=5) were individually stored inside clear plastic zipper bags held at 23 C for an additional 120 hours after fabrication. Sample size was based on the ISO 21563:2013 standard4 as the standard requires preparation of either 3 or 5 specimens for each test procedure, so 5 specimens prepared for each EPIHIM brand were used in each test for the duration of the storage tested. A 2piece split mold with a fixation ring was used for preparation of specimens for the elastic recovery and strain in compression tests, where the specimens (Fig. 1) have a cylindrical shape with a diameter of 12.50 mm and height of 20.00 mm (Fig. 2). A polymeric tear test mold (Fig. 3) was used to prepare specimens with a length of 102.00 mm, width of 19.00 mm, and a thickness of 4.00 mm for the tear strength test (Fig. 4). Specimen-forming molds were conditioned in a laboratory oven (Protherm PLF 130/18; Alser Teknik) at 35 ±2 C for at least 15 minutes before the specimen-forming step. EPIHIM powder was mixed with deionized water (23 C) by using a mixer unit (AM100; Shanghai Foshion Medical Instrument Co Ltd) Sahin et al
-
2019
3
Figure 1. Specimen-forming split mold with fixation ring used for preparation of specimens subjected to elastic recovery and strain in compression tests. A, Disassembled. B, Assembled.
Figure 2. Elastic recovery test specimens of Blueprint Xcreme EPIHIM.
Figure 4. Tear strength test specimens of Blueprint Xcreme EPIHIM.
Figure 3. Polymeric tear test specimen forming plate for tear strength test specimens.
for 15 seconds. After removal of the mold from the oven, the mold cavity was slightly overfilled with the EPIHIM, and the specimen-containing mold was transferred to a hot water bath held at 35 ±2 C. For the elastic recovery test, the specimen was aligned with the dial indicator spindle, deformed 4.0 ±0.1 mm, and released within 5 seconds. The elastic recovery (K) for each specimen was to the nearest 0.1% calculated 2 from the equation K = 100− 100 h1h−h 0
Sahin et al
, where h0 is the
initial length of the specimen (20.00 mm), h1 is the length recorded by the dial indicator 10 seconds after the indicator spindle contacted the top of the specimen before deformation, and h2 is the length recorded by the dial indicator 40 seconds after deformation. For the strain in compression test, the specimen was axially aligned with the center of the loading shaft foot. The strain in compression (E) for each specimen was calculated to the nearest 0.1% from the equation E= 100
h1 −h2 h0
, where E is the percentage of strain in
compression, h0 is the height of the split mold, h1 is the dial indicator reading 30 seconds after application of the initial load of 1.2 ±0.1 N, and h2 is the dial indicator reading at 30 seconds after application of the total load of 12.2 ±0.1 N. For the tear strength test, a dial indicator (2112-101F; Insize Inc) was used to measure the thickness of the specimen at a point centered on and just inside the apex of the 90-degree angle edge. The specimen was loaded in tension until rupture with a crosshead speed of 500 mm/ min within 90 seconds after removal of the mold THE JOURNAL OF PROSTHETIC DENTISTRY
4
Volume
Table 2. Multivariate analysis of variance (brand, storage) of elastic recovery, strain in compression, and tear strength tests F
P .001
69.05
<.001
Brand×duration
1.12
.361
Kromopan
94.69 ±0.69
Brand
9.56
<.001
Alginmax
144.35
<.001
Hydrogum5
Brand Duration
Strain in compression
Duration Brand×duration Tear strength
6.21
.001
55.51
<.001
Duration
0.98
.329
Brand×duration
4.01
.008
Brand
Brand
Statistic
df
P
Blueprint Xcreme
0.88
10
.135
Kromopan
0.90
10
.238
Alginmax
0.73
10
.002*
Hydrogum 5
0.88
10
.113
Strain in compression
Alginelle
0.85
10
.063
Blueprint Xcreme
0.83
10
.030*
Kromopan
0.88
10
.139
Tear strength
Alginmax
0.92
10
.327
Hydrogum 5
0.86
10
.077
Alginelle
0.92
10
.341
Blueprint Xcreme
0.91
10
.278
Kromopan
0.93
10
.492
Alginmax
0.92
10
.392
Hydrogum 5
0.86
10
.068
Alginelle
0.92
10
.335
*P<.05 indicates significant difference.
containing the specimen from the water bath. The force required to achieve rupture was recorded. The tear strength Ts, for each specimen was calculated to the nearest 0.01 N/mm from the equation Ts = Fd, where F is the maximum force (N) applied to cause rupture of the specimen and d is the specimen thickness (mm). The same test procedure was applied for the specimens in the second group, which were stored inside clear plastic zipper bags held at 23 C for an additional 120 hours. Data were analyzed with a multivariate analysis of variance (MANOVA) test for brand and duration parameters by using a statistical software (SPSS v. 15.0; SPSS Inc). Normality of data was analyzed with the Shapiro-Wilk test. The Duncan test or Games-Howell test was used for multiple comparisons (a=.05). RESULTS Elastic recovery and strain in compression values of the EPIHIMs tested were affected by brand and duration parameters (P<.001). Tear strength values of the EPIHIMs tested were affected by brand (P<.001); however, they were not affected by duration (P>.05). Significant THE JOURNAL OF PROSTHETIC DENTISTRY
Baseline
Blueprint Xcreme
Alginelle
120 h of Storage
95.56 ±0.40A
b
97.45 ±0.26B
a
b
97.41 ±0.52B
a
93.41 ±2.56A
b
96.18 ±0.30Ba
95.62 ±0.30A
b
97.31 ±0.24B
a
b
96.56 ±0.53B
a
95.09 ±0.12
A
A
Different superscript uppercase letters indicate statistically significant differences among brands. Different subscript lowercase letters indicate statistically significant differences among storage durations.
Elastic Recovery (%)
Table 3. Shapiro-Wilk test results for normality of data Elastic recovery
-
Elastic Recovery (%) Brand
P<.05 indicates significant difference.
Effect
Issue
Table 4. Mean values, standard deviations, and multiple comparison results of elastic recovery test
6.00
Effect Elastic recovery
-
100 90 80 70 60 50 40 30 20 10 0 Blueprint Xcreme
Kromopan Alginmax Hydrogum5 Alginelle
Brand Baseline
120 hours of storage
Figure 5. Interaction plot for elastic recovery test.
interactions were present between brand and duration for the strain in compression and tear strength values of the EPIHIMs tested (P <.05) (Table 2). Data distribution was normal except for Alginmax in terms of the elastic recovery values and Blueprint Xcreme in terms of the strain in compression values (P<.05) (Table 3). Multiple comparisons were performed by using the GamesHowell test for the elastic recovery and tear strength properties because the Levene test indicated significant differences for these properties (P<.001). Multiple comparisons were carried out by using the Duncan test for the strain in compression property because the Levene test did not indicate a significant difference for this property (P>.05). A statistically significant difference was not found among the mean elastic recovery values of the tested EPIHIM brands (P<.001), but a statistically significant increase was found in the elastic recovery values of the tested EPIHIMs after 120 hours of storage (P<.001) (Table 4). Statistically significant interaction was not found between the brand and duration parameters for this test (P>.05) (Fig. 5). A statistically significant difference was not found among the mean strain in compression values of the tested EPIHIM brands tested immediately after preparation (P>.05). However, 120 hours of storage led to a statistically significant decrease in the mean strain in Sahin et al
2019
5
Table 5. Mean values, standard deviations, and multiple comparison results of strain in compression recovery test Strain in Compression (%) Brand Blueprint Xcreme
Baseline
120 h of Storage
14.49 ±1.08A
a
8.81 ±0.43D
a
11.53 ±0.63C 12.12
A
b
Kromopan
15.03 ±1.40
Alginmax
16.33 ±1.25A
a
Hydrogum5
14.55 ±1.85A
a
9.02 ±0.39D
b
a
13.12 ±1.09B
a
Alginelle
14.23 ±1.84
A
b ±0.70BCb
Different superscript uppercase letters indicate statistically significant differences among brands. Different subscript lowercase letters indicate statistically significant differences among storage durations.
Strain in Compression (%)
-
100 90 80 70 60 50 40 30 20 10 0 Blueprint Xcreme
Kromopan Alginmax Hydrogum5 Alginelle
Brand Table 6. Mean values, standard deviations, and multiple comparison results of tear strength test
Baseline
Figure 6. Interaction plot for strain in compression test.
Tear Strength (N/mm) Baseline
120 h of Storage
Blueprint Xcreme
1.14 ±0.19A
a
1.03 ±0.17F
a
Kromopan
0.91 ±0.06B
a
0.84 ±0.06G
a
Alginmax
0.70 ±0.08C
a
0.89 ±0.07FGa
Hydrogum5
1.09 ±0.05A
a
1.18 ±0.12E
a
Alginelle
0.53 ±0.02D
a
0.57 ±0.04H
a
Different superscript uppercase letters indicate statistically significant differences among brands. Different subscript lowercase letters indicate statistically significant differences among storage durations.
compression values of the tested EPIHIMs (P<.001), except for Alginelle (P>.05), to a statistically significant difference among the mean strain in compression values of the tested EPIHIM brands (P<.001) (Table 5), and to a statistically significant interaction between brand and duration parameters for this test (P<.001) (Fig. 6). Alginelle maintained its strain in compression value even after 120 hours of storage (baseline: 14.23 ±1.84%, after 120 hours: 13.12 ±1.09%, P>.05). Mean strain in compression values of the Kromopan and Alginmax decreased (Kromopan: baseline: 15.03 ±1.40%, after 120 hours: 11.53 ±0.63%, P<.05, Alginmax: baseline: 16.33 ±1.25%, after 120 hours: 12.12 ±0.70%, P<.05). The highest decrease in the mean strain in compression values of all the tested EPIHIMs was observed for Hydrogum 5 and Blueprint Xcreme materials (Hydrogum 5: baseline: 14.55 ±1.85%, after 120 hours: 9.02 ±0.39%, P<.05, Blueprint Xcreme: baseline: 14.49 ±1.08%, after 120 hours: 8.81 ±0.43%, P<.05). Storage time did not influence the mean tear strength values of the EPIHIMs tested (P>.05). However, statistically significant differences were found among the mean tear strength values of the EPIHIM brands tested immediately after preparation (P<.001) and after 120 hours of storage (P<.001) (Table 6). At baseline measurements, Blueprint Xcreme and Hydrogum 5 had the highest mean tear strength values (1.14 ±0.19 N/mm, 1.09 ±0.05 N/mm), followed by Kromopan (0.91 ±0.06 N/mm) and Alginmax (0.70 ±0.08 N/mm), whereas Alginelle had the lowest mean tear strength values (0.53 ±0.02 N/mm). Hydrogum 5 had the highest mean tear Sahin et al
Tear Strength (N/mm)
Brand
120 hours of storage
1.2 1 0.8 0.6 0.4 0.2 0 Blueprint Xcreme
Kromopan Alginmax Hydrogum5 Alginelle
Brand Baseline
120 hours of storage
Figure 7. Interaction plot for tear strength test.
strength value after 120 hours of storage (1.18 ±0.12 N/mm), followed by Blueprint Xcreme (1.03 ±0.17 N/mm), Alginmax, and Kromopan (0.89 ±0.07 N/mm, 0.84 ±0.06 N/mm), whereas Alginelle had the lowest mean tear strength values (0.57 ±0.04 N/mm). Variations in the mean tear strength values of the EPIHIMs subjected to prolonged storage time led to a statistically significant interaction between brand and duration parameters for this test (P<.001) (Fig. 7). DISCUSSION This in vitro study investigated the elastic recovery, strain in compression, and tear strength properties of 5 commercially available EPIHIMs immediately after preparation and after 120 hours of storage under specific storage conditions. The null hypothesis was accepted for the tear strength property because storage time had no influence on this property. However, the null hypothesis was rejected for the elastic recovery and strain in compression properties because 120 hours of storage led to a statistically significant increase in mean elastic recovery values of all the tested EPIHIMs and a decrease in THE JOURNAL OF PROSTHETIC DENTISTRY
6
the mean strain in compression values of the tested EPIHIMs except Alginelle. The EPIHIMs tested in the present study were chosen from available materials that the manufacturers claimed to be dimensionally stable up to 120 hours in controlled storage conditions. The ISO 21563:2013 standard4 refers to hydrocolloid impression materials, and the tests mentioned refer to conventional IHIMs. Therefore, the tests applicable to IHIMs simulate clinical conditions, where the impressions removed from the mouth undergo the testing procedures immediately. However, testing procedures for the EPIHIMs have not yet been specified. In this study, modified test procedures were applied to determine the elastic recovery, strain in compression, and tear strengths of EPIHIMs after prolonged storage. Any alteration in strain in compression and tear strength of EPIHIMs after prolonged storage might result in damaging gypsum casts during removal. The results of the present in vitro study indicated that prolonged storage led to an increase in the mean elastic recovery values of all the EPIHIMs tested, which indicates prolonged storage improved recovery capabilities of these impression materials. This increase may be because prolonged storage time enabled progress of the gelation reaction of the EPIHIMs tested, where the additional gelation reaction provided the increased mean elastic recovery values. Prolonged storage led to a statistically significant decrease in mean strain in compression values of the tested EPIHIMS, except for Alginelle. This decrease may also be related to the fact that prolonged storage time enabled progress of the gelation reaction of the EPIHIMs tested, where the additional gelation reaction provided more guluronic acid monomers to interact with calcium cations to form hydrogels with increased stiffness. The difference in behavior of the Alginelle material may be because the alginate component had lower guluronic acid monomers. Although the decreased strain in compression values of the EPIHIMs are still in the acceptable 5% to 20% range as stated in the ISO 21563:2013 standard,4 care during removal of the gypsum cast is recommended because decreased strain in compression values lead to impressions with increased stiffness. The effect of EPIHIM brand on mechanical properties such as tear strength is possibly dependent on the materials’ chemical composition, especially the composition of the alginate component, and needs further investigation. As there was an increase in the elastic
THE JOURNAL OF PROSTHETIC DENTISTRY
Volume
-
Issue
-
recovery and decrease in the strain in compression properties of the tested EPIHIMs, setting new standards applicable to this specific impression material type should be considered. Limitations of this in vitro study included that the procedure used for determining tear strength values of EPIHIMs excluded a measurement of the thickness of the specimen at the moment of tearing. This value is not required to calculate tear strength in the ISO 21563: 2013 standard.4 CONCLUSIONS Based on the findings of this in vitro study, the following conclusion was drawn: 1. Despite variations in elastic recovery, strain in compression, and tear strength properties of the EPIHIMs tested, all the materials complied with the requirements of the ISO 21563:2013 standard, even after 120 hours of storage. REFERENCES 1. Fu S, Thacker A, Sperger DM, Boni RL, Buckner IS, Velankar S, et al. Relevance of rheological properties of sodium alginate in solution to calcium alginate gel properties. AAPS PharmSciTech 2011;12:453-60. 2. Anusavice KJ, Shen C, Rawls HR. Phillips’ science of dental materials. 12th ed. St. Louis: Elsevier Saunders; 2013. p. 171-7. 3. Lee KY, Mooney DJ. Alginate: properties and biomedical applications. Prog Polym Sci 2012;37:106-26. 4. International Organization for Standardization. ISO 21563: 2013. Dentistryhydrocolloid impression materials. Geneva: International Organization for Standardization; 2013. Available at: http://www.iso.org/iso/home.html. 5. Phoenix RD, Cagna DR, DeFreest CF. Stewart’s clinical removable partial prosthodontics. 4th ed. Hanover Park: Quintessence; 2008. p. 271-7. 6. Lee EA. Impression material selection in contemporary fixed prosthodontics: technique, rationale, and indications. Compend Contin Educ Dent 2005;26: 780, 2-4, 6-9. 7. Vrijhoef M, Battistuzzi P. Tear energy of impression materials. J Dent 1986;14: 175-7. 8. Donovan TE, Chee WW. A review of contemporary impression materials and techniques. Dent Clin North Am 2004;48:445-70. 9. Miller MW. Syneresis in alginate impression materials. Br Dent J 1975;139: 425-30. 10. Jamani KD. The effect of pouring time and storage condition on the accuracy of irreversible hydrocolloid impressions. Saudi Dent J 2002;14:126-30. 11. Walker MP, Burckhard J, Mitts DA, Williams KB. Dimensional change over time of extended-storage alginate impression materials. Angle Orthod 2010;80:1110-5. Corresponding author: Dr Volkan Sahin Department of Prosthodontics, Faculty of Dentistry, Kırıkkale University Celebi Sokak No: 1, 71451 Yahsihan, Kırıkkale TURKEY Email: [email protected] Copyright © 2019 by the Editorial Council for The Journal of Prosthetic Dentistry. https://doi.org/10.1016/j.prosdent.2019.09.001
Sahin et al