Wettability, imbibition, and mass change of disinfected low-viscosity impression materials

Disinfection efficacy of sodium hypochlorite and glutaraldehyde and their effects on the dimensional stability and surface properties of dental impressions: a systematic review

Objective

To systematically evaluate the disinfection efficacy of the two most frequently used disinfectants, sodium hypochlorite and glutaraldehyde, and their effects on the surface properties of four different dental impression materials.

Methods

A systematic literature search was performed in four databases until May 1st, 2022 to select the studies which evaluated disinfection efficacy of disinfectants or surface properties of dental impressions after chemical disinfection.

Main results

A total of 50 studies were included through electronic database searches. Of these studies, 13 studies evaluated disinfection efficacy of two disinfectants, and 39 studies evaluated their effects on the surface properties of dental impressions. A 10-minute disinfection with 0.5-1% sodium hypochlorite or 2% glutaraldehyde was effective to inactivate oral flora and common oral pathogenic bacteria. With regard to surface properties, chemical disinfection within 30 min could not alter the dimensional stability, detail reproduction and wettability of alginate and polyether impressions. However, the wettability of addition silicone impressions and the dimensional stability of condensation silicone impressions were adversely affected after chemical disinfection, while other surface properties of these two dental impressions were out of significant influence.

Conclusions

Alginate impressions are strongly recommended to be disinfected with 0.5% sodium hypochlorite using spray disinfection method for 10 min. Meanwhile, elastomeric impressions are strongly recommended to be disinfected with 0.5% sodium hypochlorite or 2% glutaraldehyde using immersion disinfection method for 10 min, however, polyether impression should be disinfected with 2% glutaraldehyde.

Improved water absorption behaviour of experimental hydrophilic vinyl polysiloxane (VPS) impression materials incorporating a crosslinking agent and a novel surfactant

OBJECTIVES

To study the effects of incorporating a further crosslinking agent and a novel surfactant on the water absorption behaviour of experimental VPS impression materials.

METHODS

Part 1: The water uptake behaviour of Aquasil-Ultra-Monophase (AqM) was studied gravimetrically in three media (DW, 1%NaOCl and Perform ID), at 23 °C and 37 °C, over a period of one and four-months (n = 5) to gain information on long-term immersion. Part 2: Five experimental materials were formulated: Exp-I and II as hydrophobic and Exp-III-V as hydrophilic, containing an additional cross-linking agent (TFDMSOS) and Rhodasurf CET-2 surfactant. Their water uptake and desorption (both at 23 °C) properties (gravemetrically), solubility, pH and diffusion coefficient (DC) data were compared with three commercial, hydrophilic VPS impression materials, over seven days (n = 5). The results were analysed statistically.

RESULTS

Part 1: Significant differences in water absorbed by AqM were observed in the three media at 23 °C. Aq M had a significantly higher uptake in 2% Perform ID, than in DW and NaOCl. At 37 °C, over four-months the uptake profiles were more enhanced and differed. Part 2: All Exp and commercial materials significantly increased in weight in both media (DW and 1% NaOCl at 23 °C), with differing uptake profiles and non-reached equilibrium. Exp-VPS absorbed significantly less water than commercial-VPS. Desorption of all VPS from both parts was faster than absorption, followed Fickian diffusion kinetics and reached equilibrium within 1-3 days. Desorption DCs for Exp-VPS were higher than commercial materials (10^-10 versus 10^-11 m² s^-1). The solubility was higher in 1% NaOCl compared to DW. The pH of DW after immersion of samples significantly increased compared to 1% NaOCl.

SIGNIFICANCE

The incorporation of novel cross-linking agent, TFDMSOS and non-ionic surfactant, Rhodasurf CET-2, (ethoxylated-cetyl-oleyl alcohol) improved the dimensional stability of hydrophilic Exp-VPS in DW and 1% NaOCl. These materials merit further research in producing accurate casts of the patient's anatomy following disinfection.

The effect of disinfectants on the accuracy, quality and surface structure of impression materials and gypsum casts: A comparative study using light microscopy, scanning electron microscopy and micro computed tomography

The aim of this study was to compare the effect of several commercially available disinfectants on the accuracy of various types of impression materials and their compatibility with gypsum including surface quality and structure evaluation. Four alginate and three elastomeric impression materials in combination with disinfectants Aseptoprint Liquid, Zeta 7 solution, Silosept and Dentaclean Form were tested. The dimensional changes, detail reproduction, the compatibility with gypsum and surface/subsurface morphology were evaluated using light microscopy, scanning electron microscopy and micro computed tomography. Two alginate materials disinfected in Dentaclean Form exhibited the most significant differences (p<0.0001). The loss of detail on some alginate impressions in combination with this disinfectant including deterioration and change of morphology of gypsum surfaces was observed. Porosity in subsurface area and exposed large particles were detected. It was confirmed that the desired properties of impressions may be negatively affected in combination with some disinfectants.

The effect of prolonged storage and disinfection on the dimensional stability of 5 vinyl polyether silicone impression materials

PURPOSE

Vinyl polyether silicone (VPES) has a different composition from other elastomeric impression materials as it combines vinyl polysiloxane (VPS) and polyether (PE). Therefore, it is important to study its properties and behavior under different test conditions. This study investigated the dimensional stability of 5 VPES consistencies when stored for up to 2 weeks, with and without using a standard disinfection procedure.

MATERIALS AND METHODS

40 discs of each VPES consistency (total 200) were made using a stainless steel die and ring as described by ANSI /ADA specification No. 19. 20 discs of each material were immersed in a 2.5% buffered glutaraldehyde solution for 30 minutes. Dimensional stability measurements were calculated immediately after fabrication and repeated on the same discs after 7 and 14 days of storage. The data was analyzed using two-way ANOVA with a significance level set at α = 0.05.

RESULTS

The discs mean contraction was below 0.5% at all test times ranging from 0.200 ± 0.014 to 0.325 ± 0.007. Repeated measures ANOVA showed a statistically significant difference after 2-week storage between the disinfected and non-disinfected groups (P < .001). Although there was no statistically significant difference between the materials at the time of fabrication, the contraction of the materials increased with storage for 1 and 2 weeks.

CONCLUSION

The dimensional changes of VPES impression discs after disinfection and prolonged storage complied with ANSI/ADA standard. The tested VPES impression materials were dimensionally stable for clinical use after disinfection for 30 minutes in glutaraldehyde and storage for up to 2 weeks.

Evaluation of dimensional accuracy for different complete edentulous impressions immersed in different disinfectant solutions

OBJECTIVE

The aim of this study was to evaluate the effects of two different disinfectant solutions' immersion on the dimensional accuracy of different complete edentulous impressions.

MATERIALS AND METHODS

A specific custom-made metallic cast template was constructed and used for making both 120 alginate and zinc oxide eugenol (ZOE) paste impressions (60 for each). Disinfectants with 1% sodium hypochlorite and 2% glutaraldehyde were used for 10 and 60 min immersion of both impressions. After immersion time, the impressions were used for constructing 120 completely edentulous master stone models and divided into different groups according to the study. An electronic caliper was used for dimensional accuracy measurements of the casts. The data were collected and statistically analyzed according to the independent paired sample t-test at statistically significant level P < 0 05. One-way ANOVA test was used to compare between significant different groups.

RESULTS

There is no statistically significant difference in dimensional accuracy of alginate and ZOE paste impressions as disinfection with 1% sodium hypochlorite and 2% glutaraldehyde for 10 min and ZOE paste impressions for 60 min, where there is statistically significant difference in alginate impressions dimensional accuracy as disinfection with 1% sodium hypochlorite and 2% glutaraldehyde for 60 min.

CONCLUSIONS

Possibility of ZOE impressions paste disinfected with 1% sodium hypochlorite and 2% glutaraldehyde for 10 or 60 min, not affecting on dimensional stability, while alginate impressions, only 10 min immersion in disinfectant not affecting the dimensional stability.

Dimensional changes in stone models simulating full crown preparations with adjacent teeth resulting from long-term immersion of medium-viscosity addition-type silicone rubber impressions in disinfectant solutions

If impression materials could be immersed in disinfectant solutions for a longer period, then this form of disinfection would be easier to incorporate into dental preparation procedures. This study investigated the dimensional changes in stone models resulting from immersion of medium-viscosity hydrophilic addition-type silicone rubber impression material in disinfectant solutions for 30 min and 24 h. Impressions of a master die designed to simulate a full crown preparation with adjacent teeth were immersed in 2% glutaraldehyde and 0.55% ortho-phthalaldehyde solutions. The dimensional changes in the mesiodistal and buccolingual dimensions in the stone models were then measured using a three-dimensional coordinate system. It was found that the dimensional changes in the stone models caused by immersion of the impression materials were less than 15 μm. Immersion in 2% glutaraldehyde or 0.55% ortho-phthalaldehyde for 24 h was as clinically acceptable for medium-viscosity hydrophilic addition-type silicone rubber impressions as immersion for 30 min.

Surface Detail Reproduction and Effect of Disinfectant and Long-Term Storage on the Dimensional Stability of a Novel Vinyl Polyether Silicone Impression Material

PURPOSE

This study investigated the surface detail reproduction and dimensional stability of a vinyl polyether silicone (VPES) in comparison to a vinylpolysiloxane (VPS) material as a function of prolonged storage for up to 2 weeks.

MATERIALS AND METHODS

Heavy-body VPES (EXA'lence(TM) Fast Set) and VPS (Imprint(TM) 3 Quick Step) were compared. Forty impression ingots of each material were made using a stainless steel die as described by ANSI/ADA specification No. 19. Twenty impressions of each material were disinfected by immersion in a 2.5% buffered glutaraldehyde solution. Surface quality was assessed and scored immediately after making the ingots. Dimensional stability measurements were made immediately and repeated on the same ingots after 7 and 14 days storage in ambient laboratory conditions. Data were analyzed using the D'Agostino and Pearson omnibus normality test followed by two-way repeated measures ANOVA with post hoc Bonferroni tests. Values of p < 0.01 were deemed to be significant.

RESULTS

Disinfected VPES and VPS specimens had significantly reduced dimensional changes at 7 and 14 days when compared with the nondisinfected ones (p < 0.0001). The dimensional stability of both materials was within ANSI/ADA specification No. 19's acceptable limit throughout the 2-week test period, regardless of whether they were disinfected. Out of the initial 80 ingots, 8 VPES and 1 VPS ingot scored a 2 on the surface detail test, while the remaining 71 ingots scored 1.

CONCLUSIONS

Heavy-body fast-set VPES experienced minimal contraction in vitro after prolonged storage, though surface detail scores were not as consistent as those of the VPS tested. The least contraction occurred when the material was examined immediately after ingot production.

Impression materials in fixed prosthodontics: influence of choice on clinical procedure

The purpose of this article is to review impression materials used for fabricating fixed restorations in dentistry. Their compositions, properties, advantages, and disadvantages are presented and compared. How these properties influence clinical decisions is also described. This review helps the clinician choose which material is more suitable for a specific case. A broad search of the published literature was performed using Medline to identify pertinent current articles. Textbooks, the Internet, and manufacturers' literature were also used to supplement this information. It is limited to impression materials used in fixed prosthodontics. The review gives basic knowledge of ideal impression material properties and discusses traditional and, primarily, more recently developed products, such as polyethers, poly(vinyl siloxane), polysulfides, and condensation silicone materials. Clear advantages and disadvantages for these impression materials are provided along with the role that compositional variations have on the outcome of the impression. This should enable clinicians and technicians to easily identify the important physical properties of each type of impression material and their primary clinical indications.

The effect of disinfection by spray atomization on dimensional accuracy of condensation silicone impressions

BACKGROUND AND AIMS

The condensation silicone impression materials are available, but there is little knowledge of their accuracy after disinfection. The objective of this study was to evaluate the effect of the disinfection by spray atomization on dimensional accuracy of condensation silicone impressions.

MATERIALS AND METHODS

Impressions were made on a stainless steel master model containing a simulated two complete crown preparation with an edentulous space interposed using Spidex® and Rapid® impression materials. 44 impressions were made with each material, of which 16 were disinfected with 5.25% sodium hypochlorite, 16 were disinfected with 10% iodophor and 12 were not disinfected. Three dimensional measurements of working casts, including interpreparation distance, height, and diameter, were calculated using a measuring microscope graduated at 0.001 mm. Dimensional changes (mm) between the disinfected and non-disinfected working casts were compared. One-way analysis of variance (ANOVA) was employed to analyze the data (α=0.05).

RESULTS

Disinfection of each condensation silicone material by spraying atomization with two different disinfectant material resulted in significant change in interpreparation distance (p<0.05). Changes in height and diameter were only significant in Spidex® impressions (p<0.05).

CONCLUSION

Significant changes in the mean dimensions were seen as a result of disinfection by spraying; however, the dimensional changes do not seem great enough to cause critical positional distortion of teeth when fixed partial denture restorations are made.

The elastomers for complete denture impression: A review of the literature

This article reviews the current trends in materials used for complete denture impression. Peer-reviewed articles, published in English and in French between 1954 and 2007, were identified through a MEDLINE search (Pubmed and Elsevier) and a hand search of relevant textbooks and annual publications. Emphasis was made on the characteristics of the elastomers, their manipulation, the different techniques used, and the quality of the impression obtained. The combination of excellent physical properties, handling characteristics, and unlimited dimensional stability assures the popularity of these impression materials.

The dynamic interaction of water with four dental impression materials during cure

PURPOSE

The purpose of this work was to investigate the interaction of water with four different dental impression materials: Aquasil (Ultra XLV Type 3), Take 1 (Wash Regular Set), Genie (Light Body, Standard Set), and Impregum Garant (Soft Light Bodied Consistency).

MATERIALS AND METHODS

Apparent contact angles of de-ionized water made against thin horizontal sample films of the different materials under different conditions were measured from analysis of profile images of symmetrical sessile drops of water placed on the sample films using a Model FTA200 dynamic drop shape analysis system, which included a JAI M30 high speed CCD camera combined with a zoom microscope. Data were taken for specimens of dry ages (times following mixing) from a minimum of 20 seconds up to 1220 seconds. Imaging was started before the initial water/impression material contact, and lasted for at least 420 seconds in each case. The interval at the beginning of each run was 0.033 second, and then increased by a factor of 1.012 to the end. During the initial 3 seconds following the drop deposition, the drop's shape oscillated due to inertial effects, so apparent contact angle data during this period were neglected in all cases. All measurements were made at room temperature. The drops were enclosed in a humidified chamber that suppressed evaporation. All data were repeated at least five times, and results were analyzed where appropriate using one-way ANOVA. Microscopic images of the water/impression material interactions for fresh (uncured) materials were acquired to reveal the destructive interactions that resulted from such contact. Finally, surface tension measurements were made of water that had been contacted with material of varying dry age using the pendant drop method capability of the drop shape analysis system. These helped to assess the origin of hydrophilicity development for the different materials.

RESULTS

For short curing times (dry ages), water showed a destructive effect on the integrity of all of the impression materials, as evidenced by the formation of a crater beneath the water drop and a scum of material at its surface. These effects diminished with dry age until a critical curing time was reached, beyond which such destructive interactions were no longer detectable. These critical curing times were determined to be 80, 140, 110, and 185 seconds for Aquasil, Take 1, Genie, and Impregum, respectively. The initial contact angle following the respective critical curing time was lowest for Impregum, at 66 degrees ; while values for Aquasil, Genie, and Take 1 were 93 degrees , 104 degrees , and 110 degrees , respectively. Beyond the critical curing times for the different materials, different degrees of hydrophilicity were observed. Aquasil showed the lowest final contact angle (<10 degrees ), with Impregum, Take 1, and Genie showing 31 degrees , 34 degrees , and 40 degrees , respectively. Measurements of the surface tension of water after contact with the different materials suggested that for Aquasil, hydrophilicity appears to be developed through the leaching of surfactant from the material, whereas for Impregum, Take 1, and Genie, hydrophilicity is developed at least in part through a change in surface structure in contact with water. Impregum and Aquasil materials of dry ages well beyond the critical curing time exhibited a stick-slip behavior in their interline movement or contact angle evolution. This was believed to be due to the slowness in the leaching of surfactant (in the case of Aquasil) or the re-orientation of unleachable surface groups (in the case of the other materials) in comparison to the inherent kinetics of water drop spreading.

CONCLUSIONS

All materials investigated in the fresh, uncured state showed qualitative decomposition when put in contact with water through the formation of a crater beneath the water drop and a scum of material at its surface. These effects diminished with curing time until beyond a critical value, no such effects were evident. The initial hydrophilicity of the materials as determined by the contact angles obtained at their respective critical dry ages was greatest for Impregum. Beyond the critical curing time, different degrees of hydrophilicity were observed, with Aquasil showing the lowest final contact angle.

Accuracy and stability of impression materials subjected to chemical disinfection - a literature review

Disinfection of impressions by immersion or spraying with disinfecting solutions is considered nowadays mandatory for effective infection control. The purpose of this review was to examine existing evidence on the effects that chemical disinfection may have on critical qualities of impressions, namely dimensional accuracy and stability over time. A PubMed search was conducted to include original laboratory research articles written in English, published between 1980 and 2005 in peer-reviewed journals and investigating the effect of chemical disinfection, by immersion or spraying, on the dimensional changes that the impression materials experience after setting. Studies were also sought manually, by tracing the references cited in the retrieved articles. The reports on dimensional changes of disinfected impression materials, although rather numerous, are difficult to compare and analyze because of variations of the experimental design. The investigations broadly agree that the disinfection process does not generally affect the dimensional integrity of the impressions, in spite of the statistically significant differences occasionally found. However, the immersion in the disinfecting solution encourages water absorption phenomena in the case of the so-called hydrophilic impression materials, especially after the long-term immersion. Chemical interactions between impressions and disinfectants may occur, but they do not appear to influence the dimensional behaviour of the former. The overall effect of the disinfection is influenced not only by the changes experienced by the impression per se, but also by the alterations of the acrylic tray containing the impression and of the gypsum product poured in it.

Surface Quality and Long-term Dimensional Stability of Current Elastomeric Impression Materials after Disinfection

PURPOSE

The objectives of this investigation were to evaluate the effect of disinfection on surface quality and dimensional stability of more recent, reformulated vinylpolysiloxane (VPS) and polyether (PE) materials.

METHODS

Using ANSI/American Dental Association (ADA) specification 19 protocols, 50 impressions of stainless steel dies were made with each material. Ten impressions of each material were randomly assigned to a treatment group: (1) no disinfectant; (2) 10-minute dual phenol immersion; (3) 1-hour dual phenol; (4) 10-minute sodium hypochlorite (NaOCl); and (5) 1-hour NaOCl. Impression surface quality immediately after disinfection was categorized as smooth/shiny, matte, or wrinkled/sticky. Dimensional stability was evaluated by measuring dimensional accuracy according to specification 19 after 24-hour, 1-week, and 2-week storage at ambient laboratory conditions.

RESULTS

The PE material surface quality was significantly affected (Pearson Chi-square, p<or= 0.05) by NaOCl with a mottled surface on 30% of the impressions after 10-minute immersion and a matte/sticky surface on 100% of the PE impressions after 1-hour immersion. Separate 2-factor analyses of variance (ANOVA) and Bonferroni post hoc tests of dimensional accuracy within each material indicated a significant difference (p<or= 0.05) between non-disinfected and disinfected PE impressions, which exhibited expansion. There were also significant differences (p<or= 0.05) in both VPS and PE dimensional accuracy as a function of measurement time related to increasing shrinkage over time in non-disinfected and disinfected impressions.

CONCLUSIONS

Despite PE expansion following disinfection and continued shrinkage of both the non-disinfected and disinfected VPS and PE impressions over a 2-week period, all dimensional accuracy measurements met the ADA standard, <or=0.5% dimensional change. Based on this evidence, neither NaOCl nor dual phenol disinfectants used for varying time periods adversely affected the dimensional stability of the more recent formulations of VPS and PE; however, Impregum PentaSoft PE surface quality appeared to be adversely affected by increasing exposure to NaOCl.

Pre- and Post-set Hydrophilicity of Elastomeric Impression Materials

PURPOSE

To evaluate the hydrophilicity of one polyether, four poly(vinyl siloxanes), and one condensation silicone before and after setting under simulated clinical conditions, and to correlate the findings to the contact angle values of these materials.

MATERIALS AND METHODS

The hydrophilicity before and after setting, as well as the contact angle values of the elastomeric impression materials were evaluated. Part I: A freshly extracted tooth, which was prepared for a full coverage restoration, was kept in saliva for 15 minutes and was then rinsed for 10 seconds. Impressions were taken without any drying of the tooth. A total of ten samples were taken for each material. The specimens were evaluated at a 10x magnification for defects. Part II: After the evaluation, the impressions were poured with a type IV dental stone and were left for 1 hour before separation. The stone specimens were then evaluated at a 10x magnification for negative voids. A total of 60 specimens were tested. Part III: Sixty identical 10 x 10 x 4 mm(2) plastic molds were used for the fabrication of the impression material specimens. Contact angle measurements of each specimen were made 1 hour after separation from the plastic mold. A calibrated pipette was used to place a drop (0.05 ml) of saturated calcium sulfate dehydrate onto each specimen. Digital images were taken for each specimen, and contact angle values were measured with appropriate software.

RESULTS

Part I: One-way ANOVA revealed significant differences among the materials (F = 15.526, p < 0.0005). Polyether had the fewest voids. The poly(vinyl siloxanes) did not present any significant differences among them, according to Tukey's HSD test (p < 0.05). Part II: One-way ANOVA revealed significant differences among the materials (F = 46.164, p < 0.0005). Polyether (Impregum) was the material which produced stone specimens with the fewest voids. Part III: One-way ANOVA indicated significant differences among the elastomeric impression materials (F = 494.918, p < 0.0005). Polyether displayed the smallest contact angle values.

CONCLUSIONS

Polyether was the most hydrophilic of all materials tested.

The dimensional stability of dental impression materials following immersion in disinfecting solutions

OBJECTIVES

This investigation examined the effect of several disinfectant systems upon the dimensional stability of a range of common dental impression materials. A new disinfection process based upon hypochlorous acid was one of those examined (Sterilox).

METHODS

Test specimens of commercially available impression materials from the following categories were investigated: alginates, addition-cured silicones, condensation-cured silicones and polyether. Three disinfection regimes were tested: sodium hypochlorite 5.25%, Perform ID and Sterilox. A custom-built automatic laser micrometer was used to measure the dimensions of sample discs of the test materials before disinfection, immediately after and then following 24h storage. Analysis of variance was employed to identify statistically significant differences within groups and across groups.

RESULTS

All the disinfection routines tested resulted in acceptable levels of dimensional stability within the category of normal use of each impression material. All the materials tested can be disinfected with 10% Sterilox without undergoing unacceptable levels of dimensional change.

SIGNIFICANCE

All the disinfection routines tested resulted in acceptable levels of dimensional stability within the category of normal use of each impression material.

Hydrophilicity of elastomeric non-aqueous impression materials during setting

OBJECTIVES

Clinically relevant accuracy of dental impressions depends on flowing and wetting properties of the applied impression materials. The major objective of this study was to develop an experimental set-up and an analysis strategy for wettability measurements of impression materials during their working time.

METHODS

High-resolution drop shape analysis was used to study contact angles on thin unset films of two polyether and two vinyl polysiloxane (VPS) impression materials. Qualitative and quantitative analysis of the contact angle evolution in terms of initial values and the equilibrium state of hydrophilicity, as well as in terms of kinetics of hydrophilization were extended using a mathematical model approach.

RESULTS

Compared to VPS impression materials, polyethers show pronounced and constant initial hydrophilicity throughout prescribed working time. The kinetics of the VPS impression materials towards more hydrophilic equilibrium surface states is very fast compared to polyethers. This possibly balances the disadvantage of the initial VPS impression materials hydrophobicity. Generally, the experimental and analytical methods have proven to yield detailed insights into the wetting characteristics during setting.

SIGNIFICANCE

Both, high initial and a fast kinetics towards increased hydrophilicity may improve flowing and wetting processes during impression taking. Therefore, time-resolved wettability studies should be regarded when developing advanced impression materials and defining working times. They may supplement rheological studies.

The effect of surface moisture on detail reproduction of elastomeric impressions

STATEMENT OF PROBLEM

Monophase and dual-viscosity impression techniques are available with little knowledge of which one might render better quality under wet and dry surface conditions.

PURPOSE

The purpose of this study was to determine whether type of material, viscosity selection, and presence of moisture affect detail reproduction of elastomeric impressions.

MATERIALS AND METHODS

Single-viscosity systems were polyether (Impregum Penta) and vinyl polysiloxanes (President MonoBody, Extrude MPV, and Aquasil). Dual-viscosity systems included polyether (Impregum Penta/Permadyne Garant) and vinyl polysiloxanes (Dimension Penta H/Dimension Garant L, Extrude Extra/Extrude Wash, and Aquasil/Aquasil LV). Impressions were made of a surface analyzer calibration standard possessing a uniform "saw-tooth" pattern with a mean roughness (Ra) of 2.87 mum, which was one fourth of the peak-to-valley height. Each of the 8 impression groups was subjected to dry (control) and wet conditions. The wet condition consisted of 3 mL of distilled water applied to the surface of the standard but allowed to escape during the procedure. Eighty impressions were made, 5 for each test group. After setting, the surface of each impression was scanned at 5 locations using a Surfanalyzer 4000. A 3-factor ANOVA and Student-Newman-Kuels test were used to analyze the data (alpha=.05).

RESULTS

There were significant differences between polyether and vinyl polysiloxane materials, dual and monophase techniques, and the 2 surface conditions (P<.05). Cross-product interactions were not significant, allowing comparison of mean values for each factor. The mean Ra for single viscosity was 2.21 mum versus 1.67 mum for dual viscosity; polyether was 2.12 mum versus 1.89 mum for addition silicone; and under dry conditions, the mean was 2.04 mum versus 1.86 mum for wet conditions.

CONCLUSION

Single-viscosity systems reproduced the standard saw-tooth pattern better than the dual-viscosity systems, as did polyether impression materials compared to addition silicones. Moisture led to a lower Ra or less detail compared to dry conditions.

Temperature effects on the rheological properties of current polyether and polysiloxane impression materials during setting

STATEMENT OF PROBLEM

Rheological tests of elastomeric impression materials during setting have been most often conducted at room temperature rather than at intraoral temperature. Because temperature may affect properties and the setting kinetics, clinically relevant inferences may not be accurate with studies conducted at room temperature.

PURPOSE

The purpose of this study was to determine the viscoelastic properties of new low- and medium-viscosity elastomeric impression materials during setting at 33 degrees C and to evaluate the medium-viscosity materials at 3 additional temperatures.

MATERIAL AND METHODS

The impression materials investigated at 33 degrees C were 2 polyvinylsiloxanes (PVS) (Aquasil Deca and Aquasil LV) and 5 polyethers (PE) (Impregum Penta, Impregum Penta Soft H, Impregum Penta Soft L, Impregum Garant Soft L, and Permadyne Garant L). Three impression materials (Aquasil Deca, Impregum Penta, and Impregum Penta Soft H) were also investigated at 25 degrees, 29 degrees, and 37 degrees C. Time-dependent oscillatory rheometry was carried out on these materials (n=3) with a rheometer with a 25-mm diameter parallel plate cell. The storage modulus (G') and the loss tangent (tandelta) were determined as functions of time over a period from 0 seconds to 900 seconds, commencing 40 seconds after mixing. Induction time (t(ind)) or initial setting time and tandelta, the relative liquidlike behavior, were also computed. A single-factor analysis of variance (ANOVA) was used for the properties determined at 33 degrees C and a 2-factor ANOVA was used for the temperature studies, with hypothesis testing at alpha=.05.

RESULTS

The G'(t) curves for all materials displayed the expected sigmoidal shape with time, with the solid-like behavior rising slowly, then more rapidly, and again slowly to final set. The initial setting time (t(ind)) was found to be approximately 2.8 minutes for the PVS materials and for Impregum Penta and Impregum Penta Soft H, but was significantly longer for the remaining 3 PE low viscosity materials. The solid-like behavior (G') at final set or shear modulus differed among all materials, ranging from 1.0 MPa for Aquasil Decca, 1.69 for Impregum Penta Soft H, and 1.8 MPa for Impregum Penta. G' for low-viscosity materials ranged from 0.66 MPa for Aquasil LV and 0.79 MPa for Permadyne Garant L to 1.2 MPa for Impregum Penta Soft L. The loss tangent at 40 seconds tandelta (t(0)) varied among medium and low viscosity materials, ranging from liquid-like behavior of 4.3 for Permadyne Garant and less than unity or significant solid-like behavior for Impregum Penta. All materials showed tandelta values less than unity at their setting times. The temperature studies revealed significant changes in the kinetics of setting, with the setting time decreasing more than 3-fold between 25 degrees and 37 degrees C for the Aquasil Deca and the Impregum Penta Soft H and more than 2-fold for the Impregum Penta. At room temperature of 25 degrees C, the storage modulus for Impregum Penta Soft H and Aquasil Deca was 1.1% and 37.5% lower than Impregum Penta, respectively.

CONCLUSION

The development of the viscoelastic rheological properties with time for 3 medium- and 4 low-viscosity impression materials at 33 degrees C showed significant differences in the setting time and the magnitude of the storage modulus. Compared with Impregum Penta, the new Impregum Penta Soft H was 6% less stiff when set, compared with 44% lower stiffness for the medium viscosity addition silicone. Temperature studies between 25 degrees C and 37 degrees C revealed strong temperature sensitivity of the kinetics of setting and evolution with time of their rheological properties.