Thermal and PH Changes, and Dimensional Stability in Irreversible Hydrocolloid Impression Material during Setting

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1 Original paper Dental Materials Journal 21 (2): , 2002 Thermal and PH Changes, and Dimensional Stability in Irreversible Hydrocolloid Impression Material during Setting Funda BAYINDIR, Nuran YANIKOGLU and Zeynep DUYMUS Ataturk Universitesi, Dis Hekimligi Fakultesi, Protetik Dis Tedavisi Anabilim Dali, Erzurum, Turkey Received November 26, 2001/Accepted March 26, 2002 Present study the relation between ph, thermal changes and dimensional stability during setting of irreversible hydrocolloid impression materials was investigated. Ten specimens of each product were prepared for different measurements: Thermal, ph changes and dimensional stability (mass and linear). Thermal and ph readings for 20min and dimensional measurements for a 2hr period were taken after mixing. It was observed that ph and thermal values changed in relation to different materials, while they did not change with the time according to variance analysis results. On the other hand, dimensional stability showed significant differences with time in all tested impression materials. A continuous ph change was observed with the time of gelation in all irreversible hydrocolloid impression materials tested. Dimensional stability also showed significant differences with time in all impression material and as a result hydrocolloids with a high ph showed better dimensional stability than those with a low ph. Key words: Irreversible hydrocolloid impression material, Thermal changes, PH changes INTRODUCTION Dental impression materials are necessary for prosthodontic treatment to replicate oral structures and construct negative forms to subsequently create positive casts. Important requirements of impression materials are ease of manipulation, precise replication of oral tissue, dimensional stability and compability of cast materials1). Irreversible hydrocolloid impression materials were first used in 1940's, and various improvements have been recorded since2,3). Irreversible hydrocolloid impression materials were used for first impressions of total or removable dentures, and the preparation of orthodontic models, antagonistic arch models and study models4,5) Many clinical and laboratory studies have been related to the use of alginate (irreversible hydrocolloid) as an impression material4-9),11-14). But few studies focused on the chemical events during setting. So, the purpose of the present study was to investigate dimensional stability, ph and thermal changes in various irreversible hydrocolloid impression materials during the setting process. In addition, the hydrocolloid providing the best dimensional stability was searched for by examining how the ph changes of hydrocolloid impression materials during setting affected dimensional stability.

2 BAYINDIR et al. 201 MATERIALS AND METHODS The irreversible hydrocolloid materials used in the present study are listed in Table 1. All materials used were of recent production dates and were first opened at the beginning of the study. Distilled water was used for all mixing materials. The waterto-powder ratio was that recommended by the manufacturers of the materials. The temperature of the water mixed with irreversible hydrocolloid powder was 21 }1 Ž. All experimental procedures were carried out by a single operator at an environmental temperature of 22 }1 Ž and a relative humidity of 50 }10%. Ten specimens of each product were prepared for each of the three groups of measurements made. The first group consisted of 10 cylindrical irreversible hydrocolloid specimens with a height of 10 }1mm and a diameter of 45 }1mm prepared for mass measurements. Ten minutes after mixing, all the specimens of the first group were weighed with a balance accurate to g (Sartorius AG., Gottingen, Germany), and subsequent measurements were made at 10-min intervals to detect loss of mass. The second group of linear measurements consisted of ten specimens; 1cm long, cross-sectioned in a 1cm equilateral oblong triangle. Ten minutes after mixing, all specimens were measured using a Vernier microscope (Tokyo, Japan). Table 1 Irreversible hydrocolloid materials used in the study Fig. 1 PH changes with time for the tested irreversible hydrocolloid impression materials.

3 202 THERMAL AND PH CHANGES IN HYDROCOLLOID One person made all measurements. The first and second groups had dimensional (mass and linear) measurements read for a 2-hr period following mixing. The ph meter was used for measurements of both ph and thermal changes. Each irreversible hydrocolloid specimen was placed in a plastic cylinder. A small imprint was made on the surface of the gel to implant the glass electrode of the ph meter (Universal meter Multiline P4, Weilheim, Germany) into the mass. The surface of the imprint was covered with 0.2ml of water to keep to the ph meter electrode in continuous contact with the gel's aqueous phase. The ph and thermal changes were recorded at 20-sec intervals over the duration of the experiments. The initial ph value of each material's mass was recorded for 50sec after the start of mixing. The third group consisted of ph and thermal readings made 20min after the mixing of the powder with distilled water. PH changes ceased completely after 20min, and it was feasible to record these changes at 20-sec intervals. For the statistical evaluation of ph changes, thermal changes and dimensional changes (linear and mass), variance analysis and multiple comparison tests (LSD: Least significant difference) were used. Linear regression analysis was also used in the evaluation of linear dimensional changes15). RESULTS The results were averaged to give mean values of ph, thermal, linear and mass changes. In this study, there was a significant difference between initial ph values recorded in alginate impression materials and ph values during setting (Fig. 1). The results of variance analysis of the ph changes showed that the time and interaction of the irreversible hydrocolloid type used became significant (P<0.01). According to the multiple-comparison test, it was found that the values of Deguprint (Degussa, Frankfurt, Germany) and CA37 (Cavex, Haarlem, Holland) were similar, and that ph values of Alginoplast (Heraeus Kulzer, Dormagen, Holland) and Orthoprint (Zhermack, Rovigo, Italy) were significantly different (Table 2). The initial temperature of irreversible hydrocolloid impression materials decreased and subsequent gradual increases were observed (Fig. 2). The variance analysis results of the temperature changes occurring during the setting of hydrocolloid impression material showed that the thermal changes of the irreversible hydrocolloid impression materials used became significantly different Table 2 The means, standard deviations, and multiple comparison test results of ph changes in the impression materials : The distinction between the means a different letter is statistically significant (P<0.01)

4 BAYINDIR et al. 203 Fig. 2 Thermal changes with time for the tested irreversible hydrocolloid impression materials. Table 3 The means, standard deviations, and multiple comparison test results of the thermal changes of the impression materials : The distinction between the means a different letter is statistically significant (P<0.01) (P<0.001). The means, standard deviations and multiple comparison test results are shown in Table 3. According to the multiple-comparison test, it was found that the thermal values of Alginoplast and Deguprint were similar, and that thermal values of CA37 and Orthoprint were significantly different from this and from each other. According to the regression analysis results used in the evaluation of linear dimensional changes seen in irreversible hydrocolloid impression materials with time, Determination coefficient: R2=R-Sq=75.5%, t= ) (P<0.001) was obtained; it was found that linear dimensional changes were significantly different. The least dimensional change found was -5.60ƒÊm (P<0.001) in Alginoplast (mean ph value: 8.14) and Orthoprint (mean ph value: 7.94) followed -6.25ƒÊm (P<0.001) contraction and the largest dimensional change was in Deguprint (mean ph value: 7.55) with a ƒÊm (P<0.001) contraction per time interval (Table 4). As a result

5 204 THERMAL AND PH CHANGES IN HYDROCOLLOID Table 4 Regression analysis of linear dimensional change for the impression materials : p< Table 5 The means, standard deviations, and multiple comparison test results of the linear dimensional changes of the impression materials : The distinction between the means a different letter is statistically significant (P<0.01) Table 6 The means, standard deviations, and multiple comparison test results of the mass changes of impression materials : The distinction between the means a different letter is statistically significant (P<0.01) hydrocolloids with a high ph showed better dimensional stability than those with a low ph. According to multiple-comparison test results, the linear dimensional changes in the four irreversible hydrocolloids used were significantly different (Table 5). The result of variance analysis of the mass changes showed that the time and irreversible hydrocolloid type used were observed significant different (P<0.001). According to the multiple-comparison test results, while the mass changes seen in Deguprint and Orthoprint were similar to each other, the difference between CA37 and Alginoplast was significant (P<0.01) (Table 6). Linear and mass changes are illustrated in Figs. 3 and 4.

6 BAYINDIR et al. 205 Fig. 3 Linear dimensional changes with time for the tested irreversible hydrocolloid impression materials. Fig. 4 Mass dimensional changes with time for the tested irreversible hydrocolloid impression materials. DISCUSSION During the impression phase, irreversible hydrocolloid material may cause varying degrees of clinical and histological change due to ph changes6,7). Moergeli and Vermilyea7) evaluated that the ph characteristics of the irreversible hydrocolloids from the time of mixing to the final setting. As a result of their study one ophthalmic irreversible hydrocolloid material became more basic during its

7 206 THERMAL AND PH CHANGES IN HYDROCOLLOID setting where as another ophthalmic irreversible hydrocolloid material remained stable throughout the setting. The other dental materials tested decreased in ph with time. In view of this result, any materials with a ph lower than 6.6 or higher than 7.8 may cause a subjective response. In addition, Moergeli et al.6) stated that the dental irreversible hydrocolloid impression materials produced a more severe acute inflammatory response than the ophthalmic irreversible hydrocolloid impression materials. Anastassiadou et al.8) reported that ph changes with initial ph values of irreversible hydrocolloid material during the setting process became significantly different. In another study, Anastassiadou et al.11,12) recorded the thermal and ph changes in irreversible hydrocolloid material throughout 20-min periods, and detected that the ph was reduced significantly in the first few minutes, and the alchalic medium rapidly became neutral and reached an acid ph. They suggested that the fast reduction of ph increased stepwise few minutes later, and that chemical events during gelation and colloidal formation of the alginate resulted in thermal and ph changes. In addition, these researchers found that some irreversible hydrocolloid material ph changes occurred in the alkaline phase while ph changes occurred in the acidic phase. Depending on the findings obtained, they divided the material into two groups; ph changes occurring in the acidic phase, and those occurring in the alkaline phase. In the present study only dental irreversible hydrocolloid impression materials were evaluated. The findings obtained parallel those mentioned above, and we determined that there was a significant difference between the initial ph values recorded in dental irreversible hydrocolloid impression materials and the ph values during their setting. When mixed with water, impression materials showed alkaline features, and the ph became neutral when setting was complete. Chemical events during gelation and the colloidal structure of irreversible hydrocolloid material resulted in thermal changing and ph changing. Kim et al.1) stated that, the dimensional accuracy of all materials is affected by thermal changes. Impression materials shrink during the change from mouth temperature (37 Ž) to room temperature (23 Ž). During the setting of the irreversible hydrocolloid impression materials used in the present study, we determined that the thermal changes occurred depending on gelation. This result parallels the findings of Anastossiadou et al.11). Anastossiadou et al.9) reported that differences in the final gel structures of the irreversible hydrocolloid materials were shown to be related to the differences in thermal and ph changes during setting. This could be expected from their various chemical compositions such as the variety of components, the chemical forms of the principal components and the proportion of each component. Thermal and ph changes are related both to the chemical phenomena occurring during gelation and the colloidal nature of alginates9,11). If the chemical composition of the used materials is known, clinicians can chose the most appropriate materials for dental application.

8 BAYINDIR et al. 207 The majority of the gel volume in irreversible hydrocolloid impression materials consists of water. Since the impression is kept in open air before the necessary preparations this leads to the loss of some part of the water with water loss, fibrill in hydrocolloids undergo impression contraction by shrinkage. Unlike this event, if gel directly contacts the water, it will swell by absorbing water. This event is defined as imbibation. Since there is no exact parallel between these two events, to dimensional changes which may occur, plaster should be cast to obtain the model, immediately after the impression is taken,10). While gelling of irreversible hydrocolloid material continues, a situation known as hydrogen bonding results by mutual extraction between the H and OH groups involved. As a result of this, the liquid occurring in gell is seen on the surface of the jell as an exuda. This situation is termed synerezis. In addition, this exuda affects the surface quality of the plaster model, and it causes late setting13). In addition irreversible hydrocolloid ph evaluation during setting will influence the accuracy of the cast surface detail12). It is a known that irreversible hydrocolloid materials undergo shrinkage13). According to Milller13), and Coleman et al.14) there are two reasons for the shrinkage: One is the evaporation of water from the gell structure, and the other is synerezis. The amount of the shrinkage synerezis causes is high13). The evaporation of water from the Bell can be prevented in a 100% moisture medium. However, the models must immediately be cast in order to obtain the best result. According to Anastassidou et al.8), dimensional changes originate from the combination of two factors: 1-PH change occurring while the chemical reaction progesses during setting, 2-The loss of water or other liquids from the material, the second factor is associated with the structure of initial chemical reaction, and it can be determined from the composition of the material. Anastasidou et al.8) determined that linear dimensional changes of irreversible hydrocolloid materials with alkaline ph values were clearly higher than materials with acidic ph values, while the mean mass changes appeared to be greater with alkaline materials. They also observed that the closer the ph values were to neutral ph, the smaller the ph range. The linear change variance was greater in materials with acidic ph values than in materials with alkaline ph values. They did not clearly define the mass change. We found that hydrocolloids with alkaline ph (Alginoplast) provided better dimensional stability than the other tested hydrocolloids. It was determined that there were fewer linear dimensional changes in those which were in the neutral phase from hydrocolloid impression materials used. (Figs. 1 and 3) CONCLUSION Thermal and ph changes and dimensional measurements of four irreversible hydrocolloid impression materials during setting were studied. As a result the

9 208 THERMAL AND PH CHANGES IN HYDROCOLLOID following results were found: 1-A continuous ph change was observed throughout gelation in all the irreversible hydrocolloid materials tested. 2-The ph values of Deguprint and CA37 were similar, but those of Alginoplast and Orthoprint were different. 3-The thermal values of Alginoplast and Deguprint were similar but those of values of CA37 and Orthoprint were significantly different from each other and from Alginoplast and Deguprint. 4-Dimensional stability showed significant differences with time among all irreversible hydrocolloid impression materials. 5-The least dimensional change with -5.60ƒÊm (P<0.001) contraction was in Alginoplast and Orthoprint followed it with a -6.25ƒÊm (P<0.001) contraction and that the largest dimensional change was in Deguprint with a ƒÊm (P<0.001) contraction in per minute interval. As a result hydrocolloids with a high ph showed better dimensional stability than those with a low ph. As a result, it is important to know the chemical compositions of dental material for dental applications. It will help clinicians chose the most adequate materials. ACKNOWLEDGMENTS Presented as a poster at the 24th Annual Conference of the European Prosthodontic Association, Groningen, Netherlands, August REFERENCES 1) Kim, K.M., Lee, J.S., Kim, K.N. and Swin, S.W.: Dimensional changes of dental impression materials by thermal changes, J Bio Med Mare Res 58: , ) Cru, R.G. and Peyton, F.A.: Restorative dental materials, 5th ed., The CV Mosby, St. Louis ) Guide to dental materials and devices, 6th ed. American Dental Association (ADA), ) O'Brien. J.W.: Dental materials: Properties and selection. Quintessence, pp ) Scotti, R., Lugli, M, and D'Elia, A.: Reliability of antagonistic arch impression in dental prostheses: Clinical evaluation of different preimpression preparation procedure, J Prosthet Dent 74: , ) Moergeli, J.R., Fraleigh, E.M., Ostrowski, J.S. and Pelleu, G.B.: Irritation of ocular tissue by irreversible hydrocolloid, J Prosthet Dent 54: 286, ) Moergeli, J.R. and Vermilyea, S.G.: Change in ph of irreversible hydrocolloid impression materials during setting, J Prosthet Dent 56: , ) Anastassiadou, V., Dolopoulou, V. and Kaloyannides, A.: Relationship between ph changes and dimensional stability irreversible hydrocolloid impression material during setting, Int J Prosthodont 8: , ) Anastassiadou, V., Dolopoulou, V. and Kaloyannides, A.: The relation between thermal and ph changes in alginate impression materials, Dent Mater 11 (3): , ) Anderson, J.N.: Applied dental materials sed, Blachwell scientific publications, Oxford, ) Anastassiadou, V., Dolopoulou, V. and Kaloyannides, A.: The relation between thermal and ph changes in alginate impression materials, Dent Res 71, Abstract No: 30,

10 BAYINDIR et al ) Anastassiadou, V., Dolopoulou, V. and Kaloyannides A,: The effect of ph changes at the impression stone cast interface during setting, J Prosthet Dent 74: , ) Miller, M.W.: Syneresis in alginate impression materials, Br Dent J 139: , ) Coleman, R.M., Hembree, J.H. and Weber, F.: Dimensional stability of irreversible hydrocolloid impression materials, Am J Ortho 5: , ) Draper, N., and Smith, N.: Applied regression analysis, John Wiley, New York, London, Sidney, 1966.