This in-vitro study was designed and conducted in the Department of Prosthodontics, College of Dentistry, King Khalid University, Abha, KSA during 2019. Ethical approval was obtained from the scientific research committee of College of Dentistry, King Khalid University with a registration number SRC/ETH/20, 17-/18/52.
Test Materials:
1. Impression Materials:
Three commercially available hydrocolloids were selected namely, Hydrogum 5, Chroma print (extended pour alginates) and Tropicalgin (conventional alginate). These materials were evaluated by testing dimensional stability and surface details reproduction accuracy of their produced master casts. A die was prepared for the impression making procedures.
(Fig. 1)
Figure 1
Different Alginate Impression Materials
2. Dental Stone:
Type IV dental stone was used to pour the alginate impressions.
Different materials used in the test are illustrated in Table 1.
Table 1
Test materials | Manufacturer | Material Type |
Hydrogum 5 | Zhermak | Irreversible Hydrocolloid (Extended pour time) |
Chroma print | Coltene | Irreversible Hydrocolloid (Extended Pour time) |
Tropicalgin | Zhermak | Irreversible Hydrocolloid (Conventional) |
Durone IV | Dentsply | Type IV Dental Stone |
3. Custom Stainless Steel Die: |
Impressions using the three alginate materials were prepared over a custom-made metal die (300 mm outer diameter and 270 mm internal diameter). The die includes three parallel lines 25, 50, and 75 µm wide and 25 mm in length and spaced 2.5 mm apart, with two lines intersecting the three lines to determine the dimensional accuracy and surface detail reproduction on the 25 µm line. (Fig. 2)
Figure 2
Custom stinless steel die used for making impression
- Test Procedures:
Impression and disinfection Procedures:
The impression trays used were custom-made perforated metal trays which fit to the die with a uniform thickness space. After mixing the impression materials according to the manufacturer’s instructions, they were loaded in the trays and joined to the die and pressed using a 1 kg weight to allow excess material to escape, until completion of setting time. The tests were performed in accordance with the American National Standards Institute/ American Dental Association (ANSI/ADA) Specifications Nos. 18 and 19. (Figs. 3, 4, 5)
Figure 3
custom-made perforated metal tray
Figure 4
A 1 kg weight placed over the tray to allow even pressure
Figure 5
Completed impression
The trays then were removed 1 minute after gelation (the gelation time was consistent with the minimum time recommended by the manufacturers) and then disinfected either by:
1) No treatment with disinfectant solution (as control group).
2) Spraying with 5.25% sodium hypochlorite disinfectant as recommended in manufacturer’s instructions.
2) Immersion in 2% glutaraldehyde for 10 minutes as recommended in manufacturer’s instructions.
Storage of Impressions:
All disinfected and control impressions were rinsed under tap water for 10 seconds then stored in a sealed plastic bag with a damp cotton roll (to ensure a relative humidity) at the room temperature for the storage periods of 0, 72 or 120 hours (h). (Figs. 6, 7)
Figure 6
A group of stored impression samples
Figure: 7: A group of poured casts
Table 2
Disinfection method | Storage time | Experimental groups |
Alginate impression material (Brand) |
Hydrogum 5 (Extended pour) | Chroma print (Extended pour) | Tropicalgin (conventional) |
No disinfection | Immediate | Group 1 | Group 2 | Group 3 |
72 hours | Group 4 | Group 5 | Group 6 |
120 hours | Group 7 | Group 8 | Group 9 |
Spraying (5.25% NaOCL) | Immediate | Group 10 | Group 11 | Group 12 |
72 hours | Group 13 | Group 14 | Group 15 |
120 hours | Group 16 | Group 17 | Group 18 |
Immersion (2% Gluteraldehyde) | Immediate | Group 19 | Group 20 | Group 21 |
72 hours | Group 22 | Group 23 | Group 24 |
120 hours | Group 25 | Group 26 | Group 27 |
Casting Procedure:
After the specified storage periods, impressions were immediately poured with type IV dental stone to generate casts. After one hour of mixing stone, the casts were separated from the molds and permitted to dry for 24 hours.
Assessments:
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Assessment of Surface Details Reproduction:
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Evaluations were performed on the stone casts using a (× 10) magnifying lens to assess the 25 µm-line, whether it was reproduced completely through its full length in the casts. The procedure was repeated three-times for each cast and the results were recorded on a scale of 1 to 4 as proposed by Owen in 1986.[30]
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Assessment of Dimensional Stability:
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On The stone cast, the 25 µm- line was measured for dimensional changes compared to the original dimensions of the stainless steel die using an electronic digital caliper. (Fig. 8) The measurement procedure was repeated 3 times for each cast.
Figure 8
Electronic digital caliper used for measuring the dimensional changes.
Statistical Analysis:
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Means and standard deviations were calculated for each experimental group. A one-way analysis of variance (ANOVA) was used to assess the effects of each of material brand, disinfection technique, and storage time on the dimensional stability, followed by a Tuckey’s post-hoc test among groups. Moreover, for evaluating the surface details reproduction, KrusKal Wallis test was used followed by Mann-Whitney’s test. The level of significance was predetermined at P ≤ 0.05.
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Data was statistically analyzed using SPSS version 24 software (SPSS Inc., Chicago, IL, USA).