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 modelsHisako HIRAGUCHI1,2, Masahiro KAKETANI1,2, Hideharu HIROSE1,2 and Takayuki YONEYAMA1,2

1Department of Dental Materials, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan2Division of Biomaterials Science, Dental Research Center, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, JapanCorresponding 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�

INTRODUCTION

During the process of dental treatment, it is important to disinfect impressions as well as equipment so as to prevent infection1-4). However, immersion disinfection of alginate impressions has been reported to deteriorate the dimensional accuracy of resultant stone models due to imbibition of the impressions during immersion5,6). Consequently, protracted immersion of alginate impressions has been shown to cause large dimensional changes in impressions7). To overcome these distortion issues, the American Dental Association (ADA) recommended that alginate impressions be sprayed with an ADA-approved disinfectant, and then sealed in a plastic bag according to the recommended disinfection time1).

With regard to the spray disinfection method, it was mooted that if thus-disinfected impressions could be stored for a long time after disinfectant spraying, they could then be carried back to a dental clinic to have stone models made for elderly patients receiving dental treatment at home. On the effect of long-term storage on the dimensional accuracy and deformation of stone models, a previous study reported that under a relative humidity of 100%, the degree of dimensional change in alginate impressions varied according to the different alginate impression products tested8). In addition, the effect of storage period of alginate impressions —in a sealed bag after being sprayed with disinfectant— on the dimensional accuracy of stone models was also investigated9). This investigation9) was carried out using metal trays and a master model to simulate a sectional form of a residual ridge. It was then found that storage up to 3 hours after spraying was clinically acceptable for an alginate impression

product characterized by smaller contraction in 100% relative humidity9).

In light of the encouraging result obtained in the previous study9), the purpose of the present study was to investigate the effect of storing alginate impressions for 3 hours, after spraying them with disinfectant, on the dimensional accuracy of maxillary stone models. This experiment was carried out using an edentulous study model and commercially available stock trays.

MATERIALS AND METHODS

Materials usedMaterials used in this study were listed in Table 1, and they were used according to the manufacturers’ instructions. For the alginate impression materials, three product brands —characterized by their small degree of contraction in 100% relative humidity based on the results of a previous study8), which examined the dimensional changes of 10 brands of alginate impression products under 100% relative humidity for 4 hours— were used as test materials: Algiace Z (ACZ; Dentsply-Sankin, Tochigi, Japan), Star-Mix (STM; Nippon Shiken Dental, Tokyo, Japan), and Alginoplast EM (APE; Heraeus Kulzer Japan, Osaka, Japan).

An automatic mixer (Super Rakuneru, GC, Tokyo, Japan) was used to mix the alginate impression materials and a type V dental stone (New Plastone, GC, Tokyo, Japan). An adhesive (Technicol Bond, GC, Tokyo, Japan) was used for the retention of alginate impression materials to the metal impression trays.

The disinfectants investigated in this study were 1% sodium hypochlorite solution and 2% glutaraldehyde solution. Two disinfectant product brands were used as test materials: Purelox (6% sodium hypochlorite;

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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 modelsFigure 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 fabrication system10) for standardized coordinate 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 testing instrument (Model 5567, Instron, Canton, MA, USA).

The impression was rinsed under tap water for 60 seconds, and then sprayed for 30 seconds to coat the impression surface with disinfectant. The impression was then stored in a sealed plastic bag for 3 hours9),

Fig. 1 Master die fixed on a plate with stand (left) and perforated tray (right).

Fig. 2 Diagram depicting the setup of the master die and stand, including the perforated tray.

A: Master die; B: Stand; C: Perforated tray; D: Clamp to hold tray on stand; E: Tray guide; F: Plate used to secure master die to stand; and G: Screw of the pullout handle used to remove the master die.

Code Brand name Manufacturer Lot No. W/P (ml/g)

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

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

Sodium hypochloriteSH Purelox Oyalox, Tokyo, Japan 3633 ―

GlutaraldehydeGA Sterihyde Maruishi Pharmaceutical, Osaka, Japan 3X09A ―

Table 1 Materials used in this study

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with the impression surface facing downward. After storage, the impression was rinsed under tap water again for 60 seconds to remove the disinfectant. Temperature of the water used was 23±1°C.

A dental stone mixture was poured into the impression and allowed to set. At 1 hour after the start of stone mixing, the stone model was removed from the impression and stored at room temperature for 24 hours prior to the taking of three-dimensional measurements. For the control, it was also a stone model prepared from the impression but which was neither sprayed nor stored. Finally, five stone models were prepared for each condition: the control (C), 3-hour storage after spraying with 1% sodium hypochlorite solution (SH), and 3-hour storage after spraying with 2% glutaraldehyde solution (GA).

Three-dimensional measurement for dimensional changesMeasurements were made using a three-dimensional

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 change of each point. On dimensional change signs, a positive (+) sign indicated displacement toward the tray, whereas the opposite direction was given a negative (−) sign. Dimensional change data at points 1−26 of the stone models were subjected to Tukey’s multiple comparison tests (α=0.05) for statistical comparison among the conditions.

The entire experiment was conducted at a room temperature of 23±1°C and with a relative humidity of 50±10%.

RESULTS

Deformation of the stone modelsThe sectional profiles of the X-Y section (Z=15 mm), X-Z section (Y=55 mm), and Y-Z section (X=60 mm) as based on the nominal values of the master die are shown in Fig. 4, and so are the measured profiles —including the deviations— of the stone models obtained from ACZ impressions. The deviations were magnified 25 times so that the deformation of the stone models could be evaluated.

As seen in Fig. 4, results of the control (C), 3-hour storage after spraying with 1% sodium hypochlorite solution (SH), and 3-hour storage after spraying with 2% glutaraldehyde solution (GA) are shown respectively. The measured profiles —including deviations— of C, SH, and GA revealed a displacement of the stone models toward the tray. However, the measured profiles showed no differences between the

Fig. 3 Upper diagram: X and Y axial directions and measured 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.

Lower diagram: X and Y axial directions and the measured positions (points 1–26) of the master die and stone models.

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control and the other models, regardless of the disinfectant solution used.

As for the measured profiles —including the deviations— of the stone models obtained from STM and APE impressions, similar results were obtained.

Dimensional changes of the stone modelsThe dimensional changes at points 1−26 on the stone models obtained from ACZ, STM, and APE impressions are shown in Figs. 5, 6, and 7 respectively.

In the stone models obtained from ACZ impressions, the dimensional changes with SH at points 3, 4, and 11 were significantly smaller than those of C (Fig. 5). In the stone models obtained from STM impressions, the dimensional changes with SH and/or GA at points 3, 4, and 6 were significantly smaller than those of C (Fig. 6). In the stone models obtained from APE impressions, the dimensional change with GA at point 1 was significantly larger than that of C (Fig. 7).

For all the stone models within each alginate impression material group, there were no significant differences between the disinfectant solutions, except for the dimensional changes of stone models obtained from the STM impressions at point 4.

DISCUSSION

In a previous study9), it was reported that impressions which underwent a large degree of contraction in 100% relative humidity should not be stored for even one hour. Conversely, impressions which underwent a small degree of contraction in 100% relative humidity could be stored up to 3 hours because they exhibited clinically acceptable dimensional changes9). However, these results were obtained by means of a simplistic master model and an accompanying metal tray. The master model was surrounded completely by the metal tray. In a clinical setting, many impressions are taken when a complete set of dentures is to be made, and stock trays are often used. Therefore, it is important to investigate the dimensional changes of stone models using an edentulous study model and commercially available stock trays.

When an impression is firmly attached to the tray, the stone model displaces toward the tray due to an expansion of the stone while setting and a contraction of the impression. On the other hand, when the stone model displaces in the opposite direction from the tray, it is due to an expansion of the impression as a result 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

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).

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impression. Thus, expansion of the impression at the posterior portion due to water absorption was anticipated to be larger than that at the anterior portion of the edentulous model14). Results of the stone models obtained from ACZ impressions indicated that the dimensional changes with SH were significantly smaller than those of C at points 3, 4, and 11 —and these points were defined at the posterior portion of the edentulous model. This result was thought to be

caused by an expansion of the impression at the posterior part due to disinfectant solution remaining on the impression surface, in addition to expansion resulting from a second rinsing after storage.

For the stone models obtained from STM impressions, the dimensional changes with SH and/or GA were significantly smaller than those of C at points 3, 4, and 6. Similarly, these points were defined at the posterior portion of the edentulous model, and thus this

Fig. 5 Dimensional changes at points 1–26 on stone models obtained from ACZ impressions.

*: Significant difference at p<0.05.

Fig. 6 Dimensional changes at points 1–26 on stone models obtained from STM impressions.

*: Significant difference at p<0.05.

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result was also thought to be caused by an expansion of the impression at the posterior part. In particular at point 4, the dimensional change with GA was significantly smaller than that with SH. This result indicated that expansion of the impression due to 2% glutaraldehyde solution remaining on the impression surface was larger than that with 1% sodium hypochlorite solution. However, the difference in dimensional changes of the stone models between GA

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 also did not lead to serious deformation of the stone models. The differences in dimensional change between 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 impressions, which were characterized by small dimensional change under 100% relative humidity, did not adversely influence the dimensional accuracy of the resultant stone models when compared to immersion disinfection.

In terms of practical applications, the immersion disinfection method has a niche in dental offices where dental stone is poured into a mold immediately after taking an impression. For the spray disinfection

Fig. 7 Dimensional changes at points 1–26 on stone models obtained from APE impressions.

*: Significant difference at p<0.05

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method, it is an effective and handy means to enable alginate impressions to be carried from elderly patients’ homes to dental clinics for the fabrication of stone models.

CONCLUSION

For alginate impressions which were characterized by small dimensional change under 100% relative humidity, storage for 3 hours after spraying them with a disinfectant solution was a feasible disinfection method.

ACKNOWLEDGMENTS

This study was supported in part by a grant from the Dental Research Center, as well as by the Sato Fund from the Nihon University School of Dentistry.

REFERENCES1) Council on Dental Materials, Instruments, and Equipment,

Council on Dental Practice, Council on Dental Therapeutics. Infection control recommendations for the dental office and the dental laboratory. J Am Dent Assoc 1988; 116: 241-248.

2) Council on Dental Materials, Instruments, and Equipment. Disinfection of impressions. J Am Dent Assoc 1991; 122: 110.

3) Blair FM, Wassell RW. A survey of the methods of disinfection of dental impressions used in dental hospitals in the United Kingdom. Br Dent J 1996; 180: 369-375.

4) The Japan Prosthodontic Society. A Guideline for Infection Control Protocol in Prosthodontic Practice. Ann Jpn Prosthodont Soc 2007; 51: 629-689.

5) Rueggeberg FA, Beall FE, Kelly MT, Schuster GS. Sodium hypochlorite disinfection of irreversible hydrocolloid impression material. J Prosthet Dent 1992; 67: 628-631.

6) Hiraguchi H. Influence of immersion of alginate impressions in disinfectant solutions on the reproducibility of maxillary edentulous working casts. Nihon Univ Dent J 2001; 75: 269-280.

7) Motegi T. Dimensional stability of alginate impression materials —Effect of immersion in disinfectant solutions. J J Dent Mater 1987; 6: 747-761.

8) Hiraguchi H, Nakagawa H. Storage of impressions following spray with disinfectant solutions in dental treatment for elderly patients at home. Part 1. Effect of long-term storage of alginate impressions in sealed bag on the dimensional accuracy and deformation of stone models. J J Gerodont 2004; 18: 309-316.

9) Hiraguchi H, Nakagawa H, Wakashima M, Miyanaga K, Sakaguchi S, Nishiyama M. Effect of storage period of alginate impressions following spray with disinfectant solutions on the dimensional accuracy and deformation of stone models. Dent Mater J 2005; 24: 36-42.

10) Hiraguchi H, Kobayashi K, Sekiguchi E, Habu H. Three dimensional measurement of stone cast deformation —A pilot study. J J Dent Mater 1985; 4: 1-10.

11) Hashimoto K. Three-dimensional analysis on the reproducibility of denturous working models —The influences of various impression materials evaluated by the normal deviation. J J Dent Mater 1988; 7: 386-405.

12) Tokyo Seimitsu Co. Ltd. Software operating instructions: Profile measurement program. Tokyo: 1986. p. 100-102.

13) Ogura H, Takahashi H, Miyazaki T, Oda Y, Unemoto K, Kozono Y. Essentials of dental materials science, 1th ed. Tokyo: Ishiyaku Publishers Inc; 2008. p. 42.

14) Sekiguchi E. Study on the dimensional stability of alginate impression materials —Effects of impression thickness, impression diameter and retentive condition with a tray. J J Dent Mater 1988; 7: 861-874.

15) Hiraguchi H, Nakagawa H, Uchida H, Tanabe N. Disinfection of impressions in dental treatment for elderly patients at home —Effect of W/P ratio of alginate impression materials on the dimensional accuracy and deformation of stone models. J J Dent Mater 2002; 21: 313-322.