Storing Alginate

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					    Dental Materials Journal 2010; 29(3): 309–315



The influence of storing alginate impressions sprayed with disinfectant on
dimensional accuracy and deformation of maxillary edentulous stone
models
Hisako HIRAGUCHI1,2, Masahiro KAKETANI1,2, Hideharu HIROSE1,2 and Takayuki YONEYAMA1,2
1
 Department of Dental Materials, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan
2
 Division of Biomaterials Science, Dental Research Center, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-
8310, Japan
Corresponding author, Hisako HIRAGUCHI; E-mail: hiraguchi@dent.nihon-u.ac.jp


This study investigated the effects of storing impressions for 3 hours after spraying them with a disinfectant solution on dimensional
change and deformation of maxillary edentulous stone models. Three brands of alginate impression materials, characterized by a
small degree of contraction in 100% relative humidity, were used. The spray disinfectants used were 1% sodium hypochlorite solution
and 2% glutaraldehyde solution. A stone model taken from an impression that had not been sprayed or stored was prepared as a
control. The results indicated that the differences in dimensional change between the control and disinfected stone models were less
than 24 µm, and that no deformation was observed in the stone models.

Keywords: Alginate impression materials, Spray disinfection, Dimensional accuracy


                                                                          product characterized by smaller contraction in 100%
                        INTRODUCTION
                                                                          relative humidity9).
During the process of dental treatment, it is important                        In light of the encouraging result obtained in the
to disinfect impressions as well as equipment so as to                    previous study9), the purpose of the present study was
prevent infection1-4). However, immersion disinfection                    to investigate the effect of storing alginate impressions
of alginate impressions has been reported to deteriorate                  for 3 hours, after spraying them with disinfectant, on
the dimensional accuracy of resultant stone models due                    the dimensional accuracy of maxillary stone models.
to imbibition of the impressions during immersion5,6).                    This experiment was carried out using an edentulous
Consequently, protracted immersion of alginate                            study model and commercially available stock trays.
impressions has been shown to cause large dimensional
changes in impressions7). To overcome these distortion
                                                                                          MATERIALS AND METHODS
issues, the American Dental Association (ADA)
recommended that alginate impressions be sprayed                          Materials used
with an ADA-approved disinfectant, and then sealed in                     Materials used in this study were listed in Table 1, and
a plastic bag according to the recommended disinfection                   they were used according to the manufacturers’
time1).                                                                   instructions. For the alginate impression materials,
     With regard to the spray disinfection method, it                     three product brands —characterized by their small
was mooted that if thus-disinfected impressions could                     degree of contraction in 100% relative humidity based
be stored for a long time after disinfectant spraying,                    on the results of a previous study8), which examined
they could then be carried back to a dental clinic to                     the dimensional changes of 10 brands of alginate
have stone models made for elderly patients receiving                     impression products under 100% relative humidity for
dental treatment at home. On the effect of long-term                      4 hours— were used as test materials: Algiace Z (ACZ;
storage on the dimensional accuracy and deformation                       Dentsply-Sankin, Tochigi, Japan), Star-Mix (STM;
of stone models, a previous study reported that under a                   Nippon Shiken Dental, Tokyo, Japan), and Alginoplast
relative humidity of 100%, the degree of dimensional                      EM (APE; Heraeus Kulzer Japan, Osaka, Japan).
change in alginate impressions varied according to the                         An automatic mixer (Super Rakuneru, GC, Tokyo,
different alginate impression products tested8).      In                  Japan) was used to mix the alginate impression
addition, the effect of storage period of alginate                        materials and a type V dental stone (New Plastone,
impressions —in a sealed bag after being sprayed with                     GC, Tokyo, Japan). An adhesive (Technicol Bond, GC,
disinfectant— on the dimensional accuracy of stone                        Tokyo, Japan) was used for the retention of alginate
models was also investigated9). This investigation9) was                  impression materials to the metal impression trays.
carried out using metal trays and a master model to                            The disinfectants investigated in this study were
simulate a sectional form of a residual ridge. It was                     1% sodium hypochlorite solution and 2% glutaraldehyde
then found that storage up to 3 hours after spraying                      solution. Two disinfectant product brands were used
was clinically acceptable for an alginate impression                      as test materials: Purelox (6% sodium hypochlorite;

Received Sep 8, 2009: Accepted Jan 14, 2010
doi:10.4012/dmj.2009-083 JOI JST.JSTAGE/dmj/2009-083
310                                         Dent Mater J 2010; 29(3): 309–315


Table 1     Materials used in this study
           Code              Brand name                     Manufacturer                      Lot No.     W/P (ml/g)

  Alginate impression material
      ACZ                  Algiace Z           Dentsply-Sankin, Tochigi, Japan               379-402         2.27
      STM                  Star Mix            Nippon Shiken Dental, Tokyo, Japan            3020619         2.33
      APE                  Alginoplast EM      Heraeus Kulzer Japan, Osaka, Japan            19 58861        2.38

  Dental stone
      ―                    New Plastone        GC, Tokyo, Japan                              0505091         0.24

  Sodium hypochlorite
      SH                   Purelox             Oyalox, Tokyo, Japan                          3633              ―

  Glutaraldehyde
      GA                   Sterihyde           Maruishi Pharmaceutical, Osaka, Japan         3X09A             ―



Oyalox,    Tokyo,    Japan)    and    Sterihyde   (20%
glutaraldehyde, Maruishi Pharmaceutical, Osaka,
Japan). These sodium hypochlorite and glutaraldehyde
disinfectants were then diluted with deionized water to
concentrations of 1% and 2% respectively.

Fabrication of stone models
Figure 1 shows a master die (Dental Study Model G1-
402, Nissin Dental Products, Kyoto, Japan) and a
perforated metal tray (Coe DC STO-K Tray U-4-0, GC
America, Chicago, IL, USA) with the apparatus
mounted on a stand, which was adjusted to an
impression thickness of 5 mm at the top of the alveolar
ridge. This equipment was used in the stone model            Fig. 1   Master die fixed on a plate with stand (left) and
fabrication system10) for standardized coordinate                     perforated tray (right).
positioning outside a stone model for a three-
dimensional analysis of the dimensional changes and
deformation of stone models. A diagram depicting the
setup of the master die and stand, including the tray,
is shown in Fig. 2. In this system, the master die and
stone model had the same standardized coordinates
positioned on the stand, whereby they could be replaced
with each other at the same location in relation to the
stand.
     The procedure used to make a stone model was as
follows. The perforated metal tray, overfilled with a
mixed alginate impression material, was seated on the
master die and immediately secured to the stand with
three set screws. At five minutes after the start of
alginate mixing, this assembly was inverted, and three
set screws which secured the stand to the plate were
removed. At seven minutes after the start of alginate
mixing, the master die was removed in an upward
direction using a pullout handle attached to a screw, at
a crosshead speed of 500 mm/min using a universal            Fig. 2   Diagram depicting the setup of the master die and
testing instrument (Model 5567, Instron, Canton, MA,                  stand, including the perforated tray.
USA).                                                                 A: Master die; B: Stand; C: Perforated tray; D:
     The impression was rinsed under tap water for 60                 Clamp to hold tray on stand; E: Tray guide; F:
seconds, and then sprayed for 30 seconds to coat the                  Plate used to secure master die to stand; and G:
impression surface with disinfectant. The impression                  Screw of the pullout handle used to remove the
                                                                      master die.
was then stored in a sealed plastic bag for 3 hours9),
                                            Dent Mater J 2010; 29(3): 309–315                                         311


                                                              coordinate measurement system (XYZAX GC400D,
                                                              Tokyo Seimitsu, Tokyo, Japan) in the same manner as
                                                              described in previous studies6,11). As shown in Fig. 3,
                                                              the standardized coordinates were positioned on the
                                                              stand. The profiles of the X-Y sections (Z=15 mm), Y-Z
                                                              sections (X=50, 60, and 70 mm), and X-Z sections
                                                              (Y=55, 70, and 89 mm) of the master die and stone
                                                              models were measured at a 0.5-mm pitch using a
                                                              touch-trigger electron probe fitted with a 1.0-mm feeler
                                                              ball. Cubic curve interpolation12) was performed on the
                                                              data of the master die, and nominal values at 0.5-mm
                                                              intervals were obtained. The distance between the
                                                              nominal values of the master die and the profile
                                                              determined by cubic curve interpolation of the stone
                                                              model’s measurement data were calculated (hereafter:
                                                              deviation). Sectional profiles based on the nominal
                                                              values of the master die were plotted graphically, and
                                                              so were profiles based on the measured data of the
                                                              stone models —including the deviations. Deformation
                                                              of the stone models for each condition was evaluated
                                                              from the latter.
                                                                   Dimensional changes in the stone models were also
                                                              evaluated. The mean value of the deviations of six
                                                              nominal values6) at each intersection point (1, 3, 4, 5, 6,
                                                              7, 9, 10, 12, 13, 14, 15, 16, 18, 19, 21, 22, 23, 24, and 26
                                                              in Fig. 3) of the measured profiles was defined as the
                                                              dimensional change of each intersection. For the other
                                                              points (2, 8, 11, 17, 20, and 25 in Fig. 3), the mean
                                                              value of the deviations of three nominal values6) of the
                                                              measured profiles was defined as the dimensional
Fig. 3   Upper diagram: X and Y axial directions and          change of each point. On dimensional change signs, a
         measured profiles of the X-Y sections (Z=15 mm),     positive (+) sign indicated displacement toward the
         Y-Z sections (X=50, 60, and 70 mm), and X-Z          tray, whereas the opposite direction was given a
         sections (Y=55, 70, and 89 mm) of the master die     negative (−) sign. Dimensional change data at points
         and stone models.
                                                              1−26 of the stone models were subjected to Tukey’s
         Lower diagram: X and Y axial directions and the
                                                              multiple comparison tests (α=0.05) for statistical
         measured positions (points 1–26) of the master die
                                                              comparison among the conditions.
         and stone models.
                                                                   The entire experiment was conducted at a room
                                                              temperature of 23±1°C and with a relative humidity of
                                                              50±10%.
with the impression surface facing downward. After
storage, the impression was rinsed under tap water
                                                                                      RESULTS
again for 60 seconds to remove the disinfectant.
Temperature of the water used was 23±1°C.                     Deformation of the stone models
    A dental stone mixture was poured into the                The sectional profiles of the X-Y section (Z=15 mm), X-
impression and allowed to set. At 1 hour after the            Z section (Y=55 mm), and Y-Z section (X=60 mm) as
start of stone mixing, the stone model was removed            based on the nominal values of the master die are
from the impression and stored at room temperature            shown in Fig. 4, and so are the measured profiles —
for 24 hours prior to the taking of three-dimensional         including the deviations— of the stone models obtained
measurements. For the control, it was also a stone            from ACZ impressions. The deviations were magnified
model prepared from the impression but which was              25 times so that the deformation of the stone models
neither sprayed nor stored. Finally, five stone models        could be evaluated.
were prepared for each condition: the control (C), 3-              As seen in Fig. 4, results of the control (C), 3-hour
hour storage after spraying with 1% sodium                    storage after spraying with 1% sodium hypochlorite
hypochlorite solution (SH), and 3-hour storage after          solution (SH), and 3-hour storage after spraying with
spraying with 2% glutaraldehyde solution (GA).                2% glutaraldehyde solution (GA) are shown
                                                              respectively.    The measured profiles —including
Three-dimensional measurement for dimensional                 deviations— of C, SH, and GA revealed a displacement
changes                                                       of the stone models toward the tray. However, the
Measurements were made using a three-dimensional              measured profiles showed no differences between the
312                                       Dent Mater J 2010; 29(3): 309–315




Fig. 4   Sectional profiles of stone models obtained from ACZ impressions (α) and master die (β). The deviations were
         magnified by 25 times for the expression.
         Left diagram: Impression was neither sprayed nor stored (C). Deviations were magnified by 25 times for the
         expression.
         Center diagram: Impression was stored for 3 hours after spraying with 1% sodium hypochlorite solution (SH).
         Right diagram: Impression was stored for 3 hours after spraying with 2% glutaraldehyde solution (GA).



control and the other models, regardless of the
                                                                                  DISCUSSION
disinfectant solution used.
     As for the measured profiles —including the             In a previous study , it was reported that impressions
                                                                                 9)

deviations— of the stone models obtained from STM            which underwent a large degree of contraction in 100%
and APE impressions, similar results were obtained.          relative humidity should not be stored for even one
                                                             hour. Conversely, impressions which underwent a
Dimensional changes of the stone models                      small degree of contraction in 100% relative humidity
The dimensional changes at points 1−26 on the stone          could be stored up to 3 hours because they exhibited
models obtained from ACZ, STM, and APE impressions           clinically acceptable dimensional changes9). However,
are shown in Figs. 5, 6, and 7 respectively.                 these results were obtained by means of a simplistic
     In the stone models obtained from ACZ                   master model and an accompanying metal tray. The
impressions, the dimensional changes with SH at              master model was surrounded completely by the metal
points 3, 4, and 11 were significantly smaller than          tray. In a clinical setting, many impressions are taken
those of C (Fig. 5). In the stone models obtained from       when a complete set of dentures is to be made, and
STM impressions, the dimensional changes with SH             stock trays are often used. Therefore, it is important
and/or GA at points 3, 4, and 6 were significantly           to investigate the dimensional changes of stone models
smaller than those of C (Fig. 6). In the stone models        using an edentulous study model and commercially
obtained from APE impressions, the dimensional               available stock trays.
change with GA at point 1 was significantly larger than           When an impression is firmly attached to the tray,
that of C (Fig. 7).                                          the stone model displaces toward the tray due to an
     For all the stone models within each alginate           expansion of the stone while setting and a contraction
impression material group, there were no significant         of the impression. On the other hand, when the stone
differences between the disinfectant solutions, except       model displaces in the opposite direction from the tray,
for the dimensional changes of stone models obtained         it is due to an expansion of the impression as a result
from the STM impressions at point 4.                         of water absorption from rinsing and disinfectant
                                                             spraying13).
                                                                  In the present study, the impression tray was open
                                                             at the posterior portion of the edentulous model
                                          Dent Mater J 2010; 29(3): 309–315                                     313




Fig. 5   Dimensional changes at points 1–26 on stone        Fig. 6   Dimensional changes at points 1–26 on stone
         models obtained from ACZ impressions.                       models obtained from STM impressions.
         *: Significant difference at p<0.05.                        *: Significant difference at p<0.05.



impression. Thus, expansion of the impression at the        caused by an expansion of the impression at the
posterior portion due to water absorption was               posterior part due to disinfectant solution remaining on
anticipated to be larger than that at the anterior          the impression surface, in addition to expansion
portion of the edentulous model14). Results of the stone    resulting from a second rinsing after storage.
models obtained from ACZ impressions indicated that              For the stone models obtained from STM
the dimensional changes with SH were significantly          impressions, the dimensional changes with SH and/or
smaller than those of C at points 3, 4, and 11 —and         GA were significantly smaller than those of C at points
these points were defined at the posterior portion of the   3, 4, and 6. Similarly, these points were defined at the
edentulous model. This result was thought to be             posterior portion of the edentulous model, and thus this
314                                       Dent Mater J 2010; 29(3): 309–315


                                                            and SH was merely 11 µm. Furthermore, there were
                                                            no significant differences between the disinfectant
                                                            solutions for the stone models obtained from the other
                                                            two impression materials. This latter result agreed
                                                            with a previous study9) in that stone models obtained
                                                            from alginate impressions showed no significant
                                                            differences between the different types of disinfectants
                                                            after spray disinfection. In light of all these results, it
                                                            was thus suggested that the type of disinfectant had a
                                                            small effect on the dimensional changes of stone
                                                            models.
                                                                 For the stone models obtained from APE
                                                            impressions, the dimensional change with GA at point
                                                            1 was significantly larger than that of C. This result
                                                            was thought to be caused by a contraction of the
                                                            impression during storage in a sealed bag. For APE
                                                            impressions, there were no significant decreases in
                                                            dimensional changes caused by the effect of expansion
                                                            of the impression. This meant that the significant
                                                            increases in dimensional change were caused by the
                                                            contraction of the impression. At point 1, the difference
                                                            in dimensional changes of the stone models between
                                                            GA and C was 11 µm. In contrast, this was not so for
                                                            ACZ and STM impressions in that there were no
                                                            significant increases in the dimensional changes of SH
                                                            or GA from that of C. In light of these findings, it was
                                                            thus suggested that contraction of impressions stored
                                                            in sealed bags had little influence on the dimensional
                                                            changes of stone models.
                                                                 As a guideline for infection control, the Japan
                                                            Prosthodontic Society recommended that alginate
                                                            impressions be immersed in 0.1−1.0% sodium
                                                            hypochlorite solution for 15−30 minutes4). For alginate
                                                            impressions characterized by small dimensional change
                                                            in water, the dimensional accuracy of their resultant
                                                            stone models was only slightly affected by immersion
                                                            disinfection15). In a previous study6), it was reported
                                                            that the immersion of an alginate impression —
                                                            characterized by small dimensional change in water—
                                                            in a 0.5 or 1.0% sodium hypochlorite solution for 15
                                                            minutes did not result in large-scale deformation of the
                                                            resultant stone models. Notably, the differences in
                                                            dimensional change between the stone models produced
                                                            with disinfected impressions and those of the control
                                                            were less than 45 µm6).
                                                                 In the present study, the spray disinfection method
Fig. 7   Dimensional changes at points 1–26 on stone
                                                            also did not lead to serious deformation of the stone
         models obtained from APE impressions.
                                                            models. The differences in dimensional change between
         *: Significant difference at p<0.05
                                                            the stone models produced with disinfected impressions
                                                            and those of the control were less than 24 µm. These
                                                            results indicated that spray disinfection of alginate
result was also thought to be caused by an expansion        impressions, which were characterized by small
of the impression at the posterior part. In particular at   dimensional change under 100% relative humidity, did
point 4, the dimensional change with GA was                 not adversely influence the dimensional accuracy of the
significantly smaller than that with SH. This result        resultant stone models when compared to immersion
indicated that expansion of the impression due to 2%        disinfection.
glutaraldehyde solution remaining on the impression              In terms of practical applications, the immersion
surface was larger than that with 1% sodium                 disinfection method has a niche in dental offices where
hypochlorite solution.    However, the difference in        dental stone is poured into a mold immediately after
dimensional changes of the stone models between GA          taking an impression.       For the spray disinfection
                                               Dent Mater J 2010; 29(3): 309–315                                              315


method, it is an effective and handy means to enable                6) Hiraguchi H.        Influence of immersion of alginate
alginate impressions to be carried from elderly patients’              impressions in disinfectant solutions on the reproducibility
                                                                       of maxillary edentulous working casts. Nihon Univ Dent J
homes to dental clinics for the fabrication of stone
                                                                       2001; 75: 269-280.
models.                                                             7) Motegi T. Dimensional stability of alginate impression
                                                                       materials —Effect of immersion in disinfectant solutions. J
                                                                       J Dent Mater 1987; 6: 747-761.
                      CONCLUSION                                    8) Hiraguchi H, Nakagawa H.           Storage of impressions
For alginate impressions which were characterized by                   following spray with disinfectant solutions in dental
                                                                       treatment for elderly patients at home. Part 1. Effect of
small dimensional change under 100% relative
                                                                       long-term storage of alginate impressions in sealed bag on
humidity, storage for 3 hours after spraying them with                 the dimensional accuracy and deformation of stone models.
a disinfectant solution was a feasible disinfection                    J J Gerodont 2004; 18: 309-316.
method.                                                             9) Hiraguchi H, Nakagawa H, Wakashima M, Miyanaga K,
                                                                       Sakaguchi S, Nishiyama M. Effect of storage period of
                                                                       alginate impressions following spray with disinfectant
                 ACKNOWLEDGMENTS                                       solutions on the dimensional accuracy and deformation of
                                                                       stone models. Dent Mater J 2005; 24: 36-42.
This study was supported in part by a grant from the
                                                                   10) Hiraguchi H, Kobayashi K, Sekiguchi E, Habu H. Three
Dental Research Center, as well as by the Sato Fund                    dimensional measurement of stone cast deformation —A
from the Nihon University School of Dentistry.                         pilot study. J J Dent Mater 1985; 4: 1-10.
                                                                   11) Hashimoto K.         Three-dimensional analysis on the
                                                                       reproducibility of denturous working models —The
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