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: firstname.lastname@example.org 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. 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