J Dent App. 2017; 4(1): 379-384.
A Comparative Evaluation of the Efficacy of Disinfectants on Patient Derived Irreversible Hydrocolloid Impressions and their Effect on the Dimensional Accuracy of the Impression Material
Verma K¹*, Mahesh GE², Parag D³, Rashima V4 and Ashish K5
1Graded Specialist, Division of Prosthodontics, MDC, BEG, India
2Commandant, Division of Prosthodontics, CMDC (WC), India
3Classified Specialist, Division of Prosthodontics, 14 CDU, India
4Dental Surgeon, ECHS Polyclinic, Kirkee, India
5Graded Specialist, Division of Prosthodontics, CMDC (CC), India
*Corresponding author: Kamal Verma, Graded Specialist, Division of Prosthodontics, MDC, BEG, India
Received: May 14, 2017; Accepted: June 07, 2017; Published: June 14, 2017
Purpose: Assessing the efficacy of disinfectants on irreversible hydrocolloid impressions and their effect on the dimensional accuracy.
Materials and Methods: The study was carried out to compare the efficacy of three commercially available disinfectants (Cidex – 2% Glutaraldehyde (Johnson & Johnson), 1% Sodium Hypochlorite (I - Dent), MD 520 – 0.5% Glutaraldehyde and 0.25% Ammonium chloride (Durr)) in eliminating or reducing the microbial colonies on patient derived irreversible hydrocolloid impressions and the resultant effect on the dimensional accuracy of the impression material when exposed to these agents.
Results: MD 520 system resulted in maximum (95.6%) removal of the visible colonies for all samples investigated and 1% sodium hypochlorite was found to cause the least amount of dimensional changes in irreversible hydrocolloid impressions.
Conclusions: It is entirely the clinician’s choice to select disinfecting agents to use considering all their advantages and disadvantages. It should be kept in mind that though MD 520 was shown to be the most effective disinfectant, sodium hypochlorite caused lesser dimensional changes in the alginate impressions.
Keywords: Disinfection; Irreversible Hydrocolloid; Dimensional stability
Disinfection of dental impressions has drawn much attention and research interest in recent years . To address cross contamination concerns, the American Dental Association has issued guidelines for disinfecting impressions while using spray or immersion disinfectants. Three important factors must be considered when dental impressions are disinfected - how are the impression material and resultant cast affected, how stable are the disinfectant solutions and how effective are the disinfection procedures . Very few studies have been undertaken till date which reveals answers to all these aspects together. Meanwhile, manufacturers claim disinfectants are better for disinfection of irreversible hydrocolloid impressions, but they do not mention about the dimensional accuracy of the impression. The idea behind conceptualizing this study was the fulfillment of the following objectives: (1) To clinically examine the carriage of oral pathogens on the impression surface. (2) To clinically evaluate the disinfection efficacy of three commercially available agents in removing oral pathogens from patient derived impressions. (3) To evaluate the effect of these disinfecting agents on the dimensional stability of irreversible hydrocolloid impressions.
The study was carried out at our centre to compare the efficacy of three commercially available disinfectants (Cidex – 2% Glutaraldehyde (Johnson & Johnson), 1% Sodium Hypochlorite (I - Dent), MD 520 – 0.5% Glutaraldehyde and 0.25% Ammonium chloride (Durr)) (Figure 1) in eliminating or reducing the microbial colonies on patient derived irreversible hydrocolloid impressions and the resultant effect on the dimensional accuracy of the impression material when exposed to these agents.
Figure 1: Three disinfectants used in the study.
The study was performed in two stages:
(A) Comparison of Antimicrobial Effect on Patient Derived Irreversible Hydrocolloid Impression Material Thirty dentulous subjects were randomly selected after getting their verbal consent and with following inclusion criteria: no denture on either jaw, more than 10 teeth present in the maxilla, age of 20 – 40 years with no systemic illness and the subjects should not have received oral hygiene or tooth brushing instructions.
Maxillary perforated metal stock trays were selected. Four impressions of the maxillary arch of each subject were obtained at an interval of 1 week. According to the manufacturer’s recommendations irreversible hydrocolloid powder (Plastalgin, Septodont, France) and distilled water was mixed utilizing vacuum mixer. Distilled water was used in lieu of tap water because for required standardization and ion concentrations present in tap water may interfere with irreversible hydrocolloid chemical reactions. The mixed irreversible hydrocolloid was then loaded on the tray and impression was made of each patient’s maxillary arch.
After setting of the impression, the impression was removed and washed under running tap water for 15–20 seconds. Impression was split sagittally down the middle with the help of sterile surgical blade (Figure 2). One half of separated impression was left untreated (Control) to evaluate the amount of microorganisms carried by the impression and the other half was subjected to one of the disinfectant treatment regimes (treated sample) (Figure 3, Table 1). The impressions were taken out of the disinfectant solution and rinsed with running water. Both the treated and the untreated samples were then carefully placed into a sterile plastic container partitioned into two compartments with boxing wax. Brain heart infusion (BHI) agar medium (M211- 500G, Himedia) was prepared at 50°C by mixing 52g of powder in 1000ml of distilled water. It was autoclaved (Runyer, Unicorn Denmart) at 121°C for 15 minutes at 15psi and poured onto the impression (Figure 4). The agar was allowed to cool for 1 hour at 4°C following which it was separated from the impression and was incubated at 37°C for 48 hours to facilitate adequate growth of the micro organisms (Figure 5).
No. of Impressions
Running tap water only
Rinsing under running water for 01 minute
Running tap water followed by Cidex
Rinsing followed by immersion for 05 minutes (as per manufacturer’s instructions)
Running tap water followed by Sodium Hypochlorite
1% Sodium hypochlorite
I – Dent
Rinsing followed by immersion for 05 minutes (as per manufacturer’s instructions)
Running tap water followed by MD 520
Rinsing followed by immersion for 05 minutes (as per manufacturer’s instructions)
Table 1: Disinfection treatment regimes used in the study.
Figure 2: Maxillary impression split sagittally with sterile surgical blade.
Figure 3: Impressions rinsed under running water and treated with disinfection treatment regimes.
Figure 4: Brain Heart Infusion (BHI) Agar Medium poured onto the impression.
Figure 5: Separated Agar samples.
The presence of colonies on the culture specimen was determined (Figure 6). The number of bacterial colonies appearing on each specimen was counted using a colony counter (Scope, India) and the results were tabulated. The procedure was repeated for each of the four groups included in the study for each patient. As a negative control, an irreversible hydrocolloid impression was also made of the maxillary arch of a sterilized typhodont to see if any colony growth was observed after 48hrs of incubation.
Figure 6: Colony growth on untreated and treated Agar samples after 48 hrs incubation at 37°C. (A) Samples washed under tap water, (B) Samples disinfected with 2% glutaraldehyde, (C) Samples disinfected hypochlorite with MD 520, (D) Samples disinfected with 1% sodium.
Selective isolation of oral microorganisms: The colonies on the surface of the BHI impression culture for control and treated samples were collected and were then suspended in 1 ml of sterile phosphatebuffered saline. The colony suspension was placed on selective agar medium plates to detect the presence of Streptococci, Staphylococci, Pseudomonas aeruginosa and Candida. After 48 hours of incubation at 37°C, the existence of positive colonies for each selective medium was determined visually (Figure 7).
Figure 7: Showing different microbial colonies on selective medium.
Data collection and statistical analysis: Descriptive statistics including mean, standard deviation and minimum and maximum values of microbial colonies were calculated for each group. A oneway analysis of variance (ANOVA) was used to determine whether significant differences in values existed among the various groups (Table 2). Non parametric test i.e. Kruskal-Wallis test was performed to determine significant differences in values of microbial colonies before and after disinfection (Table 3).
Sum of Squares
Table 2: Analysis of variance (ANOVA) for comparison of mean number of colonies between treated and untreated samples.
(B) Comparison of effect of disinfectants on the dimensional stability of irreversible hydrocolloid impression material
Impression making protocol was followed as per American Dental Association Specification No. 18 (ADA 18) for irreversible hydrocolloid impression materials. 120 impressions were made on standardized metal die (similar to those described in the specification) scored with three equidistant horizontal and two vertical lines with the same irreversible hydrocolloid that was used to record impressions of the patients. A metal ring mold with glass lid was also fabricated to fit over the die (Figure 8).
Figure 8: Round metal Test Die block (According to ADA specification 18).
To make the impressions, the ring mold was slightly overfilled with irreversible hydrocolloid and was centered and pressed over the test die for 3 minutes (as per manufacturer’s instructions). The irreversible hydrocolloid flash from the sides of the mold was removed. The set irreversible hydrocolloid impression was separated from the metal die (Figure 9). An alcohol swab was used to clean the die and its assembly before reuse. After impression removal, impressions were rinsed with tap water to simulate rinsing following impression removal from the mouth and the excess water was shaken off. The impressions were divided into 4 groups and subjected to different disinfection regimes as per the manufacturer’s instructions, as shown in Table 1. The impressions were taken out of the disinfectant solution and rinsed with running water.
Figure 9: Irreversible Hydrocolloid impression removed from Die.
Each impression was evaluated for dimensional change by measuring the linear scores (X-X’) between the reference lines obtained from the test die under a Universal Measuring Microscope (Figure 10). Three readings were obtained for each impression and a mean value was calculated. The percentage dimensional change of the irreversible hydrocolloid impression from the metal die was computed using the following equation: [(D-A)/ D] x 100, where A = mean irreversible hydrocolloid impression measurement and D = die measurements.
Figure 10: Measuring the linear scores between the reference lines obtained from the Test Die under a Universal Measuring Microscope.
Descriptive statistics including mean, standard deviation, and minimum and maximum values of irreversible hydrocolloid impression measurement and dimensional change were calculated for each group. A one-way analysis of variance (ANOVA) was carried out to determine whether significant differences in percentage dimensional change existed among the various groups (Table 4).
The use of the BHI impression culture detection method produced a large number of obvious colonies on the samples of the irreversible hydrocolloid impression which were distributed predominantly over the areas of the palate and the dental arch. In contrast, no colonies were observed on the BHI impression cultures from the negative controls obtained from sterilized typhodonts, thus indicating the reliability of sterilization procedures. The occurrence of different microorganisms on impression surfaces has been summarized in Figure 10. The split-impression culture method demonstrated that all disinfection procedures investigated reduced the number of microbial colonies versus the untreated samples (Graph 1). The reduction in the number of colonies was greatest following disinfection with the MD 520 system followed by 2% glutaraldehyde, 1% sodium hypochlorite, and least while rinsing with tap water. Disinfection using the MD 520 system resulted in maximum (95.6%) removal of the visible colonies for all samples investigated. In contrast, treatment with rinsing under tap water resulted in 46.7% reduction in the number of colonies.
Graph 1: The mean percentage dimensional change.
One-way ANOVA and Kruskal-Wallis Test were employed to statistically analyze the results.
A statistically significant difference was observed by ANOVA in the mean number of colonies between groups of treated samples. F values of 92.321 with 3 degrees of freedom were found to be significant (p<0.05), thus signifying a successful disinfection regime. The F values of 0.012 with 3 degrees of freedom between groups of mean number of colonies of untreated samples were found to be non significant (p=0.998) (Table 2).
A statistically significant difference was also observed by Kruskal Wallis test in the mean number of microorganisms between groups of untreated and treated samples. P values of treated microorganisms except Candida were significant (p value< 0.05) with 3 degrees of freedom (Table 3).
Table 3: Kruskal – Wallis test statistics of all microorganisms.
Effect of disinfectants on the dimensional accuracy of irreversible hydrocolloid impression material
A planned comparison approach with one way ANOVA (Table 4) was used to detect the differences in irreversible hydrocolloid impression measurements with each disinfectant. Irreversible hydrocolloid was found to be most stable when treated with 1% sodium hypochlorite followed by 2% glutaraldehyde (Graph 2). Impressions dipped in MD 520 exhibited greatest amount of dimensional change within groups. Few samples rinsed under tap water and treated with 1% sodium hypochlorite showed shrinkage as compared to expansion of samples treated with 2% glutaraldehyde and MD 520.
Graph 2: The mean percentage dimensional change.
The results of one way ANOVA revealed that there were significant differences in percentage dimensional change between groups of treated samples (F=35.755, P< 0.05). The F values of 2.287 with 3 degrees of freedom between groups of mean irreversible hydrocolloid measurement were found to be non significant (p=0.082) (Table 4).
Sum of Squares
Mean alginate impression measurement
Percentage dimensional change
Table 4: Analysis of variance (ANOVA) for comparison of percentage dimensional change between and within groups.
Prosthodontics is the field of dentistry where prevention of cross contamination seems to be an insurmountable problem. During impression making procedure, the material comes in contact with saliva and blood, which are sources of contamination and carries a great number of microorganisms of oral flora upon removal from mouth [3,4].
The ADA Council on Dental Therapeutics has recognized 32 brands of commercial products as being effective disinfecting or sterilizing agents for use in dentistry and immersion is the method most recommended . Immersion disinfection is based on the assumption that immersion is more likely to expose all surfaces of the impression to the disinfectant for the recommended time . Spraying disinfectant onto the surface of an impression reduces the chance of distortion but may not adequately reach the areas of undercuts. Bergman and Thomasz [6,7] reported that spraying method was compatible with the irreversible hydrocolloid impression material and produced clinically acceptable results. Though microbial contamination of patient-derived impressions has been documented; however, few studies have characterized the pathogenic microorganisms on the impressions [8-10].
The present study examined a total of 120 specimens for detection of pathogens on the patient-derived impressions. The isolation frequency of Streptococci, Staphylococci, Candida, and P aeruginosa species on untreated impressions was 97.5%, 60%, 11.6%, and 35.8% respectively. This result confirmed the ability of patient-derived dental impressions to carry pathogenic microbial contamination and was in accordance with the results of Al- Jabrah, and Egusa H [11,12].
The disinfection with 2% glutaraldehyde or 1% sodium hypochlorite was only partially successful against oral pathogens, but more effective with the MD520 system which achieved 95.7% reduction in colony growth as compared to 74.3% reduction with 2% glutaraldehyde and 70% with 1% sodium hypochlorite. But at the same time, irreversible hydrocolloid impressions were not as dimensionally stable in a solution of MD 520 as compared to 1% sodium hypochlorite and 2% glutaraldehyde. Though the dimensional changes of irreversible hydrocolloid were within the acceptable limits (0 – 0.15%, according to ADA specification 18) when dipped in any of the three disinfectants, it was observed that the mean values of percentage dimensional changes were the least when 1% sodium hypochlorite was used.
Another interesting finding was the irreversible hydrocolloid impressions exhibited a small amount of shrinkage when dipped in 1% sodium hypochlorite or rinsed in tap water. The above observations raise the question of the reason for shrinkage. Although irreversible hydrocolloid contains water, it may be due to an initial expansion caused by the ions present in the irreversible hydrocolloid (e.g. Na+, SO42-, PO43-) creating an osmotic potential. However, subsequently the ions diffuse out into the surrounding water, reversing the osmotic potential, so that some water diffuses out again. When the external solution itself contains ions i.e. in the case of sodium hypochlorite, then there will be a two way transport of ions, until the set irreversible hydrocolloid is in equilibrium with the external solution. These results are similar to those noted by Martin and Nallamuthu [13,14].
Within the limitations of this study, the following conclusions were drawn:
1. The irreversible hydrocolloid impression act as potential carriers of oral microbes by way of blood and saliva. Cross contamination through irreversible hydrocolloid impressions in the dental laboratory may pose serious health hazard threats to dental personnel. Therefore, adequate disinfection of irreversible hydrocolloid impressions is an important concern for the dentist.
2. Streptococcus was most commonly found on the impressions followed by Staphylococcus, P aeruginosa and Candida. Rinsing of the impressions with water alone is not effective in removing the microbial load adequately.
3. Distilled water should be used to mix alginate powder in order to prevent the reaction of ions that are present in tap water.
4. It should be kept in mind that though MD 520 was shown to be the most effective disinfectant, sodium hypochlorite caused lesser dimensional changes in the alginate impressions. It is entirely the clinician’s choice to select disinfecting agents to use considering all their advantages and disadvantages.
5. Though none of the disinfectants used in this study caused changes in dimensional accuracy beyond the permissible limits (0– 0.15%), 1% sodium hypochlorite was found to cause the least amount of dimensional changes in irreversible hydrocolloid impressions.
6. Further clinical studies are required to try out newer methods of disinfection like gaseous, where the factors like compromised dimensional stability never arise.
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Citation: Verma K, Mahesh GE, Parag D, Rashima V and Ashish K. A Comparative Evaluation of the Efficacy of Disinfectants on Patient Derived Irreversible Hydrocolloid Impressions and their Effect on the Dimensional Accuracy of the Impression Material. J Dent App. 2017; 4(1): 379-384.