| Abstract|| |
Purpose: The aim of this study was to determine the effect of disinfectant procedures on the dimensional stability and surface quality of a tissue conditioner used as a functional impression material.
Materials and Methods: A tissue conditioner (Visco-gel) used as a functional impression material was disinfected by immersion in 5.25% sodium hypochlorite or 2% glutaraldehyde solutions for 10 or 20 minutes, respectively. The control group consisted of specimens (n=10) that were not treated by disinfectants. For testing the dimensional stability, impressions of an aluminum edentulous arch with three reference points were made. After 24 hours of storage in distilled water, the specimens were treated by one of the disinfection procedures. Impressions were poured and, subsequently, 50 stone casts were measured with a Nikon profile projector. For surface roughness evaluation, disks that contained Visco-gel were pressed against glass slides. The disks were then stored in distilled water for 24 hours. After disinfection, 50 disk-shaped dental stone casts were prepared. Surface roughness values were determined using a profilometer. For each test, data were subjected to two-way analysis of variance (ANOVA) followed by Tukey's test (α = 0.05).
Results: The results of the dimensional stability test showed that immersion of Visco-gel impressions in 5.25% sodium hypochlorite solution or 2% glutaraldehyde solution did not significantly change the anteroposterior (AP) and cross-arch (CA) distances of the resultant stone casts when compared to the control group (P>0.05). The surface quality of dental stone casts formed by Visco-gel did not change significantly when impressions were immersed in the disinfectant solutions for either 10 or 20 minutes, or when stored in distilled water (P>0.05).
Conclusion: The results showed that the disinfectant solutions used in this study did not have a significant effect on the surface quality and dimensional accuracy of Visco-gel as a functional impression material.
Keywords: Dimensional stability, disinfection, functional impression, surface roughness, tissue conditioners
|How to cite this article:|
Khaledi A, Borhanihaghighi Z, Vojdani M. The effect of disinfectant agents on dimensional stability and surface roughness of a tissue conditioner material. Indian J Dent Res 2011;22:499-504
Tissue conditioners are soft resilient materials used for the conditioning of inflamed, irritated tissues abused by ill-fitting dentures. They are also used as interim reliners during the healing phase after implant placements and as functional impression materials for the relining procedure or fabrication of new dentures. ,, However, some of these materials are incapable of performing the dual functions of tissue conditioning and the creation of functional impressions due to their viscoelastic and chemical properties. That is, if the material is ideal for one purpose it may not be suitable for another.  Among the tissue conditioner materials tested, Visco-gel has been reported to be more dimensionally stable and more capable of producing smoother surfaces on dental stone.  Visco-gel also has a satisfactory plastic flow, elastic recovery, and compressibility.  Therefore, Visco-gel seems to be a suitable material for making a functional impression.
|How to cite this URL:|
Khaledi A, Borhanihaghighi Z, Vojdani M. The effect of disinfectant agents on dimensional stability and surface roughness of a tissue conditioner material. Indian J Dent Res [serial online] 2011 [cited 2019 Sep 16];22:499-504. Available from: http://www.ijdr.in/text.asp?2011/22/4/499/90277
When tissue conditioner materials are used for impression taking as is done with other impression materials they should be disinfected before the impression is sent to the dental laboratory.  Numerous contagious diseases such as AIDS, hepatitis, herpes simplex I and II, and tuberculosis can be prevented by simple and practicable infection control measures in dental offices and laboratories.  The American Dental Association (ADA) has issued guidelines regarding impression disinfection that stipulate which disinfectants should be used for different impression materials and also specify the dilution, time, and temperature needed for each agent's optimal performance , because it has been observed that materials differ widely in terms of the properties of microbial absorption and retention.  The guidelines recommend using an ADA-accepted spray or immersion technique with an approved disinfectant. , However, a recent review concluded that disinfection by immersion is preferred because sprayed disinfectant tends to pool and therefore the entire impression surface may not be adequately covered.  This is especially true for hydrophilic and porous materials. ,, On the other hand, it is critical to weigh the effectiveness of the disinfection procedure against possible negative side effects on the material.  Several studies have concluded that there is no adverse effect of various disinfecting media on the different impression materials, ,, but other studies have indicated adverse effects of disinfectants on the dimensional stability of some impression materials. ,
Another important property that should not be adversely affected by disinfection procedures is the surface quality of the resultant stone casts. Peutzfeldt and Asmussen observed that some disinfectant/impression combinations may produce changes in the surface texture of dental stone.  Therefore, the ideal disinfectant should be determined for each impression material.
There has been much attention and research interest in recent years on disinfection of dental impressions in order to prevent cross-contamination. ,, However, there have been no investigations on the effect of disinfectants on the dimensional stability and surface roughness of tissue conditioners when used as functional impression materials. It has been hypothesized that disinfection procedures will not significantly affect dimensional stability and surface quality of the resultant stone casts. The objective of this study was to evaluate both the dimensional stability and surface quality of stone casts made from Visco-gel as an impression material when these are immersed in disinfectants for the prevention of cross-contamination.
| Materials and Methods|| |
For each of the tests of surface roughness and dimensional change, 50 specimens of Visco-gel (Dentsply De Trey GmbH, Germany) were prepared. Specimens in each group (n=10) were subjected to disinfection procedures as follows:
- C: no immersion in disinfectant solutions (control group)
- H 10 : 10-minute immersion in 5.25% sodium hypochlorite solution (Pakshoo Corp., Ghazvin, Iran)
- H 20 : 20-minute immersion in 5.25% sodium hypochlorite solution (Pakshoo Corp., Ghazvin, Iran)
- G 10 : 10-minute immersion in 2% glutaraldehyde solution (Behsa Corp., Arak, Iran)
- G 20 : 20-minute immersion in 2% glutaraldehyde solution (Behsa.Corp., Arak, Iran)
For the dimensional stability test, specimens were obtained from impressions of an aluminum master model that represented an edentulous arch. Reference points for the measurements consisted of the central incisor and two other symmetrical points in the left and right posterior regions. Individual acrylic resin trays were fabricated on the artificial stone cast of the master model which provided a uniform 2-mm thickness of the impression material. Visco-gel powder and liquid were mixed according to the manufacturer ' s recommendations. The mixture was poured into the trays, which were subsequently seated over the master model. Each impression assembly was stored in distilled water at 37°C for 24 hours. After removal from distilled water all impressions, with the exception of the control group (C), were subjected to one of the disinfecting procedures. For each procedure, new solutions of each of the disinfectants were prepared. After the immersion period, impressions were washed for 15 seconds in running water and dried gently. Then the impressions were immediately poured with dental stone (New Plastone Type 3, GC Corp., Tokyo, Japan). The dental stone was hand spatulated and then vacuum mixed for 15 seconds before being poured into the impressions with vibration. The casts were allowed to set for 1 hour prior to their removal from the impressions. Distances between the left anteroposterior (AP) and cross-arch (CA) references [Figure 1] were measured in triplicate with a Nikon profile projector (Nikon Corporation, Tokyo, Japan) at a precision of 0.001 mm. The average of the distances was calculated. Measurements of the master model were made in a similar manner.
|Figure 1: Dimensional accuracy of casts were determined by measuring the distances between the reference points|
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The surface roughness test was carried out according to the procedure described by Murata et al.  The mixed tissue conditioner was poured into aluminum rings, with diameters of 18 mm and thicknesses of 2 mm, until slightly overfilled. A flat glass plate was immediately centered above the rings and pressed down onto the mass of Visco-gel. To reach a maximum state of elasticity, all specimens were stored in distilled water at 37°C for 24 hours. Specimens in the experimental groups were then treated by one of the disinfection procedures. The control group was untreated.
Visco-gel-containing rings were rinsed under running water for 15 seconds, air dried, and boxed with wax (Heraeus Kulzer, South Bend, Ind.). The dental stone and water were mixed by hand in a water/powder ratio according to the manufacturer's recommendation and then mechanically mixed under vacuum for 15 seconds. Dental stone mixture was poured over the surface of the specimens with gentle vibration and stored at room temperature for 1 hour. After the impressions were removed from the dental stone casts; the surface roughness was measured in micrometers at three areas of each cast with the use of a profilometer (Surfcorder SE-1700, Kozaka Industry, Japan) that had been calibrated with a cutoff value of 0.8 mm and tracing length of 2.5 mm. Then the mean surface roughness values were measured (in μm) and recorded. The examiner was blinded to the treatments the casts had received.
Data on the dimensional stability and surface roughness were subjected to two-way analysis of variance (ANOVA) followed by Tukey 's tests (α=0.05).
| Results|| |
Taking the control group as the baseline we can asses the influence of treatments on the tested material. Group mean values of the AP and CA distances of casts made from Visco-gel impressions, according to time period and disinfectant solution, and the result of the two-way ANOVA for dimensional change are shown in [Table 1] and [Table 2], respectively.
|Table 1: Mean values of the AP and CA distances (mm) of casts made from Visco-gel impressions|
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The results for the dimensional stability test demonstrated that disinfection treatments did not significantly change the AP and CA dimensions of the resultant stone casts when compared to the control group (P>0.05). With regard to the 'disinfectant' and cross-product interaction of 'disinfectant × time,' there were no significant differences between disinfected vs nondisinfected for both the AP and CA distances (P>0.05). Results for the 'time' factor indicated that a significant difference existed for the CA dimension. According to Tukey's test [Table 3], the only significant difference was observed between the average value of the CA distance when the specimens were immersed in 2% glutaraldehyde for both 10 and 20 minutes (P=0.02).
The mean changes and percentage deviations from the master model for both the AP and CA dimensions were determined. There was a contraction of 0.006mm in both the AP and CA distances of visco-gel in the control group.
With immersion in 5.25% sodium hypochlorite solution, the AP and CA distances decreased by 0.015 mm (0.07%) and 0.033 mm (0.11%), respectively, after 10 minutes. However, the group that was immersed for 20 minutes showed an expansion of 0.05 mm (0.23%) in the AP distance and 0.03 mm (0.10%) in the CA dimension. On the other hand, 10-minute immersion in 2% glutaraldehyde caused a decrease of 0.08 mm (0.37%) in the AP distance and 0.09 mm (0.30%) in the CA distance. With 20-minute immersion in the same solution, the resultant stone casts displayed an increase of 0.015 mm (0.07%) in the AP distance and 0.084 mm (0.28%) in the CA distance.
The mean values of surface roughness of dental stone casts from nondisinfected and disinfected specimens and the result of ANOVA are shown in [Table 4] and [Table 5], respectively. The least surface roughness was seen when Visco-gel was disinfected by 2% glutaraldehyde for 20 minutes, followed by casts immersed in the same agent for 10 minutes. The difference of surface roughness between casts made from Visco-gel immersed in 2% glutaraldehyde and those made from visco-gel immersed in sodium hypochlorite solution was not statistically significant (P>0.05). Generally, with respect to surface roughness, none of the disinfection treatments were shown to differ statistically from the control group (P>0.05).
|Table 4: Mean values of surface roughness (μm) of casts made from Visco-gel impressions|
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| Discussion|| |
Compared with the control, casts made from Visco-gel impressions and disinfected by immersion were found to maintain accuracy in both the AP and CA dimensions. The reproduction of surface quality was also unaffected by treatments. Therefore, the hypothesis that disinfection procedures would not significantly affect the dimensional stability and surface quality of the Visco-gel material was not rejected.
With 24-hour storage in water and 10-minute immersion in disinfectant solution, the AP and CA distances decreased; however, groups that were immersed for 20 minutes showed increase in both dimensions. These changes were not significant. They may be attributed to the chemical composition, molecular weight, and particle size distribution of polymer powders, in addition to the composition of the liquids. , Tissue conditioners are available as powder and liquid packaged separately. The liquid is an ester plasticizer of 4%-50% by wt. ethyl alcohol, while the powder consists of poly (ethyl methacrylate) or a related copolymer.  Jones et al. have reported that ethyl alcohol was completely lost within 24 hours of storage in water. The leaching out of alcohol and plasticizer into water would be associated with shrinkage, whereas expansion would be caused by water absorption.  Tissue conditioners, when used as functional impression materials, should have dimensional stability in addition to compatibility with dental stones.  These properties should remain unchanged following treatment with disinfectants. To avoid distortion of the impression surface, the material should reach its maximum state of elasticity before the cast is poured. It would seem that a functional impression should remain intraorally for approximately 24 hours. This amount of time may be a more important factor than the selection of the material. With this time period, the elasticity of the material reaches a sufficient value. , However, during the time needed for impression taking tissue conditioners, more than any other material, are in close contact with saliva, blood, or food particles that have been consumed by patients. Therefore, disinfection of tissue conditioners when they are used as impression materials is significantly important.
In accordance with ADA guidelines, the present study used immersion in 2% glutaraldehyde and 5.25% sodium hypochlorite solutions to disinfect impression materials.  Glutaraldehyde solutions act by fixating cell membranes, blocking the release of cellular components, and consequently killing the microorganisms. The performance of sodium hypochlorite is based on cell oxidation.  The method implemented in this study took into account the recommendations of several investigators that 10 minutes of immersion in the two test solutions would be enough to eliminate viable bacteria from the surface of the impression material and, additionally, allow an impression with a virus-free surface. However, we checked the effects when this time period was increased to 20 minutes because this longer duration is necessary for an anti-spore effect ,, .
The material should have sufficient thickness of approximately 2 mm in order to create an accurate functional impression.  In addition, the efficacy of tissue conditioners as functional impression materials is influenced by rheological properties, dimensional stability, durability, and compatibility with dental stone. Therefore, some materials may not be suitable for creating functional impressions. , When these materials are immersed in water they experience a marked loss of their properties due to leaching out of the plasticizers and ethyl alcohol components, as well as absorption of water into the material. , Murata et al. have evaluated the linear dimensional change, absorption, and solubility of six tissue conditioners during water storage. After 24 hours, significant differences were found in the percentage changes in the linear dimensions of all the materials. A positive linear relationship between dimensional changes and the weight changes of tissue conditioners was observed. However, Visco-gel was more dimensionally stable, with the least weight change and lowest percentage of solubility, than the other materials. 
In another study, Visco-gel produced smoother surfaces on dental stone when compared with other tissue conditioner materials and exhibited only minimal changes on surface roughness over a period of time.  Visco-gel liquid consists of a considerably lower percentage of ethyl alcohol (4.9% wt.) and higher-molecular-weight esters [butyl phthalyl butyl glycolate (mol. wt. 336)], which result in the least weight and dimensional change and the lowest percentage of solubility.  In addition, it has been observed that Visco-gel has the lowest elastic recovery and most compressibility when compared with other tissue conditioners.  Therefore, from the standpoint of surface quality, viscoelastic properties, and dimensional stability, it seems that Visco-gel is a suitable material for making functional impressions. ,,,
Although to ensure the stability of functional impressions, they must be poured as soon as possible after removal from the patient's mouth,  the results of our study showed that immersion of impressions for 10-20 minutes in disinfectants did not have a significant effect on the dimensional stability of the dental stone casts. In addition, surface roughness was unaffected when compared to the control group. The mean changes and percentage deviations from the master model for both the AP and CA distances were neither statistically nor clinically significant. For comparison, 0.1% corresponds to 0.022 mm in the AP and 0.03 mm in the CA dimensions. The amount of distortion in the mandible during opening and impression taking is in the range of 0.1-0.5 mm  and is larger than the dimensional changes during the disinfection process (0.015-0.09 mm).
The results of the current study cannot be extrapolated to other combinations of tissue conditioners, disinfectants, and dental stones. Therefore, further research on the compatibility of different disinfection methods with other tissue conditioners is necessary.
| Conclusion|| |
This study tested the effect of 5.25% sodium hypochlorite and 2% glutaraldehyde solutions on Visco-gel as a functional impression material. Within the limitations of this study, it can be concluded that immersion for 10-20 minutes does not significantly impact either dimensional stability or surface roughness of stone casts that have been formed by Visco-gel.
| Acknowledgment|| |
We would like to thank the Office of Vice Chancellor of Research at Shiraz University of Medical Sciences for providing financial support.
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Department of Prosthodontics, Faculty of Dentistry, Shiraz University of Medical Sciences, Shiraz
Source of Support: Vice Chancellor of Research at Shiraz University of Medical Sciences, Conflict of Interest: None
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]