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International Journal of Polymeric Materials andPolymeric Biomaterials

ISSN: 0091-4037 (Print) 1563-535X (Online) Journal homepage: http://www.tandfonline.com/loi/gpom20

Chemical analysis and microstructure examinationof extended-pour alginate impression versusconventional one (characterization of dentalextended-pour alginate)

Rasha Mohamed Abdelraouf

To cite this article: Rasha Mohamed Abdelraouf (2017): Chemical analysis and microstructureexamination of extended-pour alginate impression versus conventional one (characterizationof dental extended-pour alginate), International Journal of Polymeric Materials and PolymericBiomaterials, DOI: 10.1080/00914037.2017.1362636

To link to this article: http://dx.doi.org/10.1080/00914037.2017.1362636

Accepted author version posted online: 11Aug 2017.Published online: 11 Aug 2017.

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INTERNATIONAL JOURNAL OF POLYMERIC MATERIALS AND POLYMERIC BIOMATERIALS https://doi.org/10.1080/00914037.2017.1362636

Chemical analysis and microstructure examination of extended-pour alginate impression versus conventional one (characterization of dental extended-pour alginate) Rasha Mohamed Abdelraouf

Faculty of Oral and Dental Medicine, Cairo University, Cairo, Egypt

ABSTRACT Alginate impressions are not dimensionally stable. The recommended storage time for a conventional alginate is maximum 30 min. However, extended-pour alginate exhibits dimensional stability up to 100 h. For better understanding of the nature of extended-pour alginate, chemical analysis was performed by X-ray florescence spectrometer, compared to conventional alginate. Fourier transform infrared spectroscopy was used to determine the functional groups of both alginates. The organic content weights and microstructures were assessed. The higher Ca:Na ratio, lower organic content, and higher powder: water ratio might contribute in increasing the dimensional stability of the extended-pour alginate. Neither the functional groups nor the microstructure differed between both types.

GRAPHICAL ABSTRACT

ARTICLE HISTORY Received 16 November 2016 Accepted 29 July 2017

KEYWORDS Chemical analysis extended-pour alginate; microstructure

1. Introduction

Alginate hydrocolloid is one of the most widely used dental impression materials [1]. It could be used to generate gypsum casts used for numerous applications, including treatment planning for restorative and orthodontic care as well as fabricating removable prostheses [2].

Being hydrocolloids, the alginate impressions are dimen-sionally unstable. Conventional alginate impressions if left for more than 30 min may become inaccurate as shrinkage might occur [3]. For maximum accuracy, the model material should be poured as soon as possible [3].

On the other hand, manufacturers have marketed extended-pour alginate impression materials with dimensional

stability for up to 100 h [4]. Several studies compared the dimensional changes of conventional versus extended-pour alginate [2, 4–7]. It was concluded in a systematic review about the dimensional stability of alginate that the immediate pouring of traditional alginate was recommended, however, this may not be necessary for the extended-pour types [8].

In general, the powder of dental alginate is composed mainly of sodium or potassium alginate (≈18 wt.%) to be dissolved in mixing water and react with calcium ions of calcium sulfate dihydrate (≈14 wt.%) to form an insoluble calcium alginate gel [3]. Contrary to other ingredients present in smaller percentages, diatomaceous earth or silicate may be

none defined

CONTACT Rasha Mohamed Abdelraouf rasha.abdelraouf@dentistry.cu.edu.eg Faculty of Oral and Dental Medicine, Cairo University, 11 El-Saraya Street, Maadi, Cairo 12411, Egypt. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gpom. © 2017 Taylor & Francis

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added in weight percent about ≈56% to control the consistency of mixed alginate [3].

In a previous study, the calcium/sodium ratio was positively correlated to the dimensional stability (the higher Ca:Na ratios, the greater dimensional stability) [9].

In the present study, an extended-pour-type impression material was assessed in depth regarding its chemical compo-sition, functional group, organic content, and microstructure, compared to conventional alginate.

2. Materials

Two commercial regular set dental alginate powders were used; a conventional alginate (CA37, Cavex, Holland) and an extended-pour alginate (Vival NF, Ivoclar Vivadent, Italy), Table 1. Six samples per material were made for each analysis (n ¼ 6 per group).

Chemical compositions of the alginate powders were deter-mined using X-ray florescence spectrometer (XRF) (Axios, Panalytical, Netherland).

Fourier transform infrared spectroscopy (FTIR) (Nicolet 380, FTIR, Thermo Electron Corporation, USA) was used to assess the functional groups of the dental alginates in the pow-der form as well as set alginate impression materials, Figure 1. The latter was performed by mixing each alginate powder with water using the measures supplied by the manufacturers according to their instructions. These measures were a scoop for the powder and a graduated beaker for the water. For each one scoop of powder, one grade (1/3) of the beaker should be filled with water for mixing. The powder: water ratio for the extended-pour alginate (Vival) was 9 g: 18 mL, while that for the conventional one (CA37) was 9 g: 19.5 mL.

The resultant sols were poured in a Teflon mold (10 mm diameter � 5 mm thickness) until gelation occurred. This took 2 min 10 s for the extended-pour alginate and 3 min 30 s for the conventional one, and then removed from the mold in disk shape, Figure 1. The infrared spectra (FTIR) of the set alginate disks were recorded within the ranges of 400–4,000 cm� 1

immediately after alginate setting. Using a four-decimal digital balance (SBA 31, Scaltec,

Germany), the organic content of each alginate powder was determined by weighing the powder before and after being heated in a furnace under air at 650°C for 2 h. Then, subtract-ing the weights to get the organic content quantity lost during heating.

The inorganic content was examined by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) for microstructure and elemental analysis, respectively. SEM (Supra 40, Carl Zeiss NTS GmbH, Germany) was used to inspect the alginate powders sprayed on coded brass stubs. In addition, disk-shaped set alginate impression materials were also examined (manipulated as previous) immediately after setting. The constituents of the inorganic fillers were obtained

using EDX (Supra 40, Carl Zeiss NTS GmbH, Germany). An accelerating voltage of 20.0 to 30.0 kV was used.

3. Results

All the six samples of each alginate gave the same results, per analysis performed.

3.1. Chemical composition

The XRF results of the conventional and extended-pour alginate powders revealed that they contained common vari-ous elements, however, in different weight percentages (wt.%) (Table 2). On the other hand, some elements were present only in the conventional type (ZrO2 0.005, Nb2O5 0.001 wt.%), while others existed in the extended-pour type only (ZnO 0.272, CuO 0.006 wt.%). The following were present in both alginate types where the first number for the conventional alginate, while the second for the extended-pour one in wt.%: CaO (4.231, 5.173), Na2O (1.83, 1.695), MgO (2.951, 1.772), Al2O3 (1.075, 0.672), SiO2 (56.767, 49.761), P2O5 (0.46, 0.258), SO3 (4.549, 3.307), K2O (1.868, 0.525), TiO2 (1.779, 0.45), MnO (0.008, 0.007), Fe2O3 (0.797, 0.541), NiO (0.005, 0.004), F (0.01, 0.01), Cl (0.049, 0.019), SrO (0.016, 0.039). The Ca:Na ratios for the conventional and extended-pour alginate powders were 2.5 and 3.5, respectively.

Table 1. Materials, manufacturers, and lot number of the impression materials. Material Manufacturer Lot number Cavex CA37 Cavex, Holland 120310 Vival NF Ivoclar, Vivadent, Italy PL4053

Figure 1. Disc-shaped set alginate impression materials. (a) Conventional alginate (Cavex), (b) Extended-pour alginate (Vival).

Table 2. XRF results of conventional and extended-pour alginate powder. Element(wt.%) Conventional alginate (Cavex) Extended-pour alginate (Vival)

CaO 4.231 5.173 Na2O 1.83 1.695 MgO 2.951 1.772 Al2O3 1.075 0.672 SiO2 56.767 49.761 P2O5 0.46 0.258 SO3 4.549 3.307 K2O 1.868 0.525 TiO2 1.779 0.45 MnO 0.008 0.007 Fe2O3 0.797 0.541 NiO 0.005 0.004 F 0.01 0.01 Cl 0.049 0.019 SrO 0.016 0.039 ZrO2 0.005 – Nb2O5 0.001 – ZnO – 0.272 CuO – 0.006

XRF, X-ray florescence spectrometer.

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3.2. Functional groups

Both conventional and extended-pour alginate powders have almost the same FTIR spectrum approximately (Figures 2 and 3). Strong and weak bands were observed, either being broad or sharp in both powders (Table 3). The spectral analy-sis revealed the presence of very strong broad band of stretch-ing vibrations of C–O–C (saccharide structure) and Si–O–Si in diatomaceous silica at 1089–1076 cm� 1. In addition, stretching and bending vibration modes of Si–O–Si bonds in diato-maceous silica were detected at 792–93 cm� 1 as very sharp strong band, while at 617–18 cm� 1 by being sharp strong and at 472–67 cm� 1 as broad strong band. On the other hand, a very weak broad band of stretching vibration of OH-group of physically adsorbed water was observed at 3408–10 cm� 1, while, stretching vibration of C–H group of alginate weak

Figure 2. FTIR spectra of conventional alginate powder (Cavex).

Figure 3. FTIR spectra of extended-pour alginate powder (Vival).

Table 3. FTIR band positions and their assignments of conventional and extended-pour alginate impression powders.

Assignments Intensity Peak position

(cm� 1)

Stretching vibration of OH-group of physically adsorbed water

Very weak broad

3408–10

Stretching vibration of C–H group of alginate

Weak sharp 2,924

Bending vibration of OH-group of physically adsorbed water

Weak sharp 1,620

Stretching vibrations of C–O–C (saccharide structure) and Si–O–Si in diatomaceous silica

Very strong broad

1089–1076

Stretching and bending vibration modes of Si–O–Si bonds in diatomaceous silica

Very sharp strong

792–93

Sharp strong 617–18 Broad strong 472–67

FTIR, Fourier transform infrared spectroscopy.

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sharp were detected by weak sharp band at 2924 cm−1. Weak sharp band was also assessed at 1,620 cm� 1 for the bending vibration of OH-group of physically adsorbed water.

On mixing the impression powders with water, some changes in the spectra were noticed and must be taken into account. Very broad and strong bands at 3,331 cm� 1 and strong bands at 1639–33 cm� 1 appeared in the two alginate types (Figures 4 and 5). On the other hand, the bending vibration modes at lower frequencies completely disappeared.

3.3. Organic contents

After heating and reweighting both alginate powders, the organic contents for the conventional and extended-pour alginate powder were 16.2 and 14.7%, respectively.

3.4. Microstructure

Scanning electron microscopic micrographs and EDX of both conventional and extended-pour alginate showed inorganic fillers of various shapes and composition (diatomaceous earth fillers), Figures 6–10. The filler in Figure 8 was present only in the conventional alginate and composed mainly of zirconia, while the others (Figures 6, 7, 9, and 10) were found in both alginate types and consisted mainly of silica. The inorganic fillers were either mainly silica with different concentrations and various other elements (Si ¼ 50%, Ca ¼ 4.12%, O ¼ 42.8%), (Si ¼ 57.61%, C ¼ 11.74%, O ¼ 29.75%, Al ¼ 0.9%), (Si ¼ 43.38%, Mg ¼ 22.71%, Fe ¼ 2.05%, O ¼ 31.31%), (Si ¼ 55.92%, C ¼ 4.05%, O ¼ 38.58%, Ni ¼ 1.44%), or zirconia (Zr ¼ 36.27%, Na ¼ 24.29%, Si ¼ 6.5%, O ¼ 27.91%, C ¼ 5.03%).

Figure 4. FTIR spectra of mixed conventional alginate after setting (Cavex).

Figure 5. FTIR spectra of mixed extended-pour alginate after setting (Vival).

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4. Discussion

4.1. Chemical composition

In the extended-pour alginate impression material, the higher Ca:Na ratio might contribute in increasing its dimensional stability, compared to the conventional one, as in agreement with Fellows and Thomas [9]. This may be attributed to an increase in the divalent calcium ions, which increased the crosslinking between the alginate polymer chains [10,11]. There were other divalent ions as magnesium ions (Mg2þ), which may aid in crosslinking [11]. Contrary to the old thought that Mg ions may be nongelling ions for alginate, it was shown that Mg2þ induce alginate gelation [12]. However, it was reported that alginate network formation with Mg ions was very slow and was typically accomplished within 2–3 h [12]. This long time seems to be impractical for taking an impression in the patient’s mouth. Thus, calcium ions were considered the main divalent ions which crosslink the alginate rapidly within reasonable time. In addition, gelation with Mg ions was also strongly dependent on alginate chemical compo-sition and higher concentration of ions than that reported for calcium-based gels [12]. A previous study investigated the role

Figure 6. SEM micrograph of inorganic filler with composition: Si = 50%, Ca = 4.12%, O = 42.8%.

Figure 7. SEM micrograph of inorganic filler with composition: Si = 57.61%, C = 11.74%, O = 29.75%, Al = 0.9%.

Figure 8. SEM micrograph of inorganic filler with composition: Zr = 36.27%, Na = 24.29%, Si = 6.5%, O = 27.91%, C = 5.03%.

Figure 9. SEM micrograph of inorganic filler with composition: Si = 43.38%, Mg = 22.71%, Fe = 2.05%, O = 31.31%.

Figure 10. SEM micrograph of inorganic filler with composition: Si = 55.92%, C = 4.05%, O = 38.58%, Ni = 1.44%.

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of Mg oxide in alginate setting, where experimental alginates containing MgO were prepared with concertation 10% [11]. It was concluded that the role of MgO as a crosslinking agent was demonstrated [11]. This concentration may be a critical percentage where the effect of Mg ions aids in crosslinking. In the current study, the concentration of MgO in both algi-nates was below such value (2.951 in conventional alginate, 1.772 in extended-pour one). Yet, Donati et al. described Mg ions as diffusively bound rather than the strongly site-bounded Ca ions [13]. Thus, in this research, the main focus was on the divalent Ca ions which were higher in extended-pour type. In addition, elements present only in extended-pour alginate as zinc may increase the dimensional stability of the taken impression through interaction with the poured gypsum [14]. On the other hand, zirconia found in the conventional alginate only was in the filler form (Figure 8) affecting mainly the consistency, strength, and stiffness [15,16].

4.2. Functional groups

Regarding the FTIR, no difference was detected between the conventional and extended-pour dental alginate either in the powder form or the mixed impression after setting. It was noticed in the FTIR of two alginate types after mixing with water and gelation, the appearance of very broad and strong bands at 3,331 cm� 1 and strong bands at 1639–33 cm� 1. This may be attributed to the formation of hydrogen bonding between H2O and silica and that made the gel solid structure as well as the Ca2þ crosslink bridging in the alginate chain network [17–19]. This gelation and increased rigidity may aid in quenching of the stretching vibration Si–O–Si bands at 1089–1076 cm� 1 in the framework of diatomaceous silica.

4.3. Organic contents

Since the organic content is responsible for more dimensional instability in the composite system, contrary to the more stable inorganic diatomaceous earth or silicate [20], with decreasing the organic content of the extended-pour alginate, the dimen-sional changes may be reduced. This was in agreement with the previous study concluding that the high filler: polymer ratio, the more dimensional stability of the alginate [9].

4.4. Microstructure

Both conventional and extended-pour dental alginates revealed multishaped/composition diatomaceous earth fillers which were apart in the powder forms. While, after being mixed with water and gelation occurred in the disks, the inorganic fillers became compacted and held by the organic polymeric matrix (Figures 11 and 12). The observed micro-structure was in agreement with Guiraldo et al. who detected fillers with circular, cylindrical, helical, and stick-shaped particles with several perforations in dental alginates [16]. In addition, that research observed that silicon was the main component in all formulations [16]. This observation was nearly similar to that found in the present study, where most of the fillers were mainly silica. This may be due to the siliceous nature of the diatomaceous earth fillers which were

sedimentary rocks of fossilized cell walls of unicellular algae [15].

In regard to the powder: water ratio, it was noticed that the amount of water required for mixing 9 g powder was higher in the conventional alginate (19.5 mL) than that in extended- pour alginate (18 mL). This lower powder: water ratio of the conventional type may lead to increase its dimensional insta-bility if subjected to loss of water and syneresis. This was in agreement with Todd et al. who concluded that the alginate impressions mixed with higher water: powder ratios tend to be less stable [4].

5. Conclusion

The extended-pour dental alginate showed higher calcium/ sodium ratio, lower organic content, and higher powder: water ratio than the conventional one, which may contribute in increasing its dimensional stability. On the other hand, the functional groups and the microstructure did not show variation between both alginate types.

Figure 11. SEM micrograph of mixed conventional alginate after setting.

Figure 12. SEM micrograph of mixed extended-pour alginate after setting.

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Acknowledgment

The author would like to thank Professor Dr. Sabry A. El-Korashy, Professor of Inorganic Chemistry, Faculty of Science, Suez Canal University, Ismailia, Egypt for his help in interpreting FTIR results.

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