| Abstract|| |
Background: Most of the materials (casts, impressions, etc.) that are sent to the dental laboratories show the presence of numerous pathogenic microorganisms. All the spray disinfectants are not equally effective against these microorganisms.
Aims and Objectives: The aim was to compare the effectiveness of different spray disinfectants on irreversible hydrocolloid impressions and to find out the most effective dilution, contact time, and effect against each microorganism studied.
Materials and Methods: The effects of four spray disinfectants, 5.25% sodium hypochlorite, 0.525% sodium hypochlorite, 1:213 (1 part in 213 parts of water) povidone iodine, and 2% glutaraldehyde along with control (distilled water) on irreversible hydrocolloid impressions contaminated with Staphylococcus aureus, Bacillus subtilis and Streptococcus viridans were studied.
Results: Sodium hypochlorite, 5.25%, showed 1-min exposure time which was able to effect a 4log10 reduction in bacterial counts against S. aureus and S. viridans followed by 0.525% sodium hypochlorite and 2% glutaraldehyde for 10 min. None were able to effect a 4 log10 reduction against B. subtilis.
Conclusion: Sodium hypochlorite with a concentration of 5.25% was the most effective disinfectant and required the shortest contact time (1 min). Not all ADA-approved concentrations of surface disinfectants work equally well on irreversible hydrocolloid impression materials.
Keywords: Irreversible hydrocolloid impression, spray disinfectants, dental casts
|How to cite this article:|
Doddamani S, Patil RA, Gangadhar S A. Efficacy of various spray disinfectants on irreversible hydrocolloid impression materials: An in vitro study. Indian J Dent Res 2011;22:764-9
Infection control has assumed prime importance in dentistry. It is a matter of concern in prosthodontics as well, where impression materials are most commonly used.
|How to cite this URL:|
Doddamani S, Patil RA, Gangadhar S A. Efficacy of various spray disinfectants on irreversible hydrocolloid impression materials: An in vitro study. Indian J Dent Res [serial online] 2011 [cited 2013 Dec 12];22:764-9. Available from: http://www.ijdr.in/text.asp?2011/22/6/764/94662
Dental personnel are exposed directly or indirectly to a wide variety of microorganisms. Majority of these organisms pose significant risk to dental personnel, such as hepatitis C, HIV virus, etc.  An indirect source of disease transmission is contaminated impressions.  The casts made of dental stone poured against contaminated impressions may be a medium for cross-contamination between patients and the dental personnel. 
To prevent cross-infection, many products are being developed. Among them, 0.5% sodium hypochlorite and 2% glutaraldehyde in a spray form are considered effective against both Gram-positive and Gram-negative microorganisms.  In this study, an effort has been made to evaluate spray-form sodium hypochlorite with different concentrations and contact periods. Also, it is compared with povidone iodine and glutaraldehyde.
| Materials and Methods|| |
Making an impression
A regular set, irreversible hydrocolloid (Alginoplast® , Regular set, batch number 76678441; Heraeus Kulzer GmbH, Hanau, Holland-) impression material has been used in this in vitro study. Powder and water are measured according to the manufacturer's instructions, and for mixing we used a clean, flexible bowl and a stiff-bladed spatula. The measured quantity of powder was sprinkled in the measured amount of water and then rapid spatulation was done. Vigorous figure-of-eight motion can also be used. Then the material was loaded on a sterilized, maxillary perforated stock metal tray.
Contamination of the metal model
The microorganisms used for this study were Staphylococcus aureus, NCIM no. 2079, Bacillus subtilis, NCIM no. 2063 (National Centre for Industrial Microorganisms, Pune, Maharashtra, India), and Streptococcus viridans (Department of Oral Pathology). Letheen broth, sterile, high culture collecting device, and blood agar base (HiMedia Laboratories Ltd., Mumbai, Maharashtra, India) were used for the culture.
Microorganisms were inoculated from the culture to normal saline with an inoculating loop (platinum loop). The numbers of microorganisms were measured with McFarland standard to approximate a cell density of 1 × 10 9 organisms/ ml. A metal model of a maxillary dental arch (sterilized by autoclaving) was then dipped into a normal saline suspension containing approximately 10 9 bacteria/ ml of one of the microorganisms for 2 min (S. aureus, S. viridans, and B. subtilis; [Figure 1]).
|Figure 1: Sterilized metal model kept in a container having the known number of bacteria|
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An impression of the contaminated model was made and allowed to set at room temperature for 3 min before removing the model. The impression was then rinsed slowly (approximately 15 s) with 250 cc sterile water to simulate the rinse performed by the dentist and was gently shaken to remove excess water.
Cultures and disinfection
Sodium hypochlorite (VIP Vensons India, Dental Division, Bangalore, Karnataka, India), povidone iodine (Merind, Wochardt Ltd., Mumbai, Maharashtra, India), and 2% glutaraldehyde (Bioclenz G., Karnataka, India) were used as spray disinfectants.
The predisinfection swabs which simulate viable bacterial transfer were verified by culturing the impression sites of teeth 16 and 26 (FDI system of tooth numbering) using sterile swabs soaked in the Letheen broth [Figure 2].
|Figure 2: Culturing the impression sites of 16 and 26 with a sterile swab|
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These swabs were then placed into 1 ml Letheen broth. After these initial cultures, the impression was sprayed with one of the test disinfectant to fully cover all surfaces. The impression was then sealed in a "Zip Lock" plastic bag and stored at room temperature for the contact time [Table 1]. Immediately following the prescribed contact time, the impression was removed from the plastic bag and rinsed as before with 250 cc of sterile water and then was gently shaken to remove excess disinfectant and water.
|Table 1: Mean pre-disinfection and post disinfection colony forming units count for each micro-organisms|
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The postdisinfection swabs at the sites of teeth 17, 13, 27, and 23 (FDI system) in the impression were then cultured as before. All cultures were plated directly on to sheep blood agar (SBA) from the Letheen broth; cultures were incubated aerobically at 37°C for 24-48 h. After incubation, all plates were examined for growth and colonies were counted manually with a magnifying lens. This procedure was repeated until seven impressions contaminated with each microorganism for each disinfectant. As a control, three additional impressions contaminated with each microorganisms were made and sterile water was used as the "disinfectant." This provided 28 test impressions and 3 control impressions for each of the 3 microorganisms for a total of 93 impressions, and for 1 impression, 2 cultures were made before disinfection and 4 swabs were taken after disinfection. A total of 6 cultures were made for each impression; hence the total number of cultures for 93 impressions was 558.
The minimum parameter for success was 4 log10 reduction in colony forming units (CFU) between pre- and postdisinfection impressions. This means that to be considered effective, a disinfectant had to produce a 99.99% reduction in bacterial counts.
All the pre- and postdisinfection values are quoted separately. The means of these values are shown in [Table 1] and presented in the Graphs 1-3.
| Observations and Results|| |
For one alginate impression, with one disinfectant for one particular microorganism, two swabs were made before disinfection (in relation to the maxillary right and left canine) and four swabs were made after disinfection in relation to the maxillary first and second molar on both the sides.
| Discussion|| |
It is felt that there may be great differences between the behaviors of various brands of impression materials and disinfectants. It would be wise to test a specific combination of impression material, disinfectant, and a gypsum product to confirm their compatibility before using them clinically.
It was reported that the commercially available, irreversible hydrocolloid impression material in "factory sealed containers" showed viable organisms which may pose potential hazards in immunocompromised patients.  One of the ADA reports  recommends spray disinfection and storage in sealed plastic bags for alginate impressions, and says that casts can be more accurately obtained with spray disinfection than immersion. Centre of Disease Control (ADA policy statement 1988) recommended that body fluids from all patients must be treated as though they are infected with blood-borne diseases. 
In this study, the most commonly used impression material alginate is used but, it has got its own disadvantages like porous nature and high water content; the material requires special considerations in the disinfection treatment. It has also been shown that irreversible hydrocolloid impressions retain two to three times more bacteria than elastomeric impression and retention of bacteria on dentate impressions is greater than edentulous. 
In this study, we have selected S. aureus, B. subtilis, and S. viridans because of the following reasons:
- S. viridans: It is the more commonly found Gram-positive, anaerobic coccus. It is normally present in the mouth and upper respiratory tract. It is ordinarily nonpathogenic but can cause disease on occasions. In persons with preexisting cardiac lesions, it may cause bacterial endocarditis. Following tooth extractions or other dental procedures, it can cause transient bacteraemia and get implanted on damaged or prosthetic valves or in a congenitally diseased heart and grow to form vegetations. 
- S. aureus: Staphylococci are among the more resistant of nonsporing bacteria. Dried on threads, they retain their vitality for 3-6 months. They have been isolated from dried pus after 2-3 months. They can withstand a temperature of 60°C for 30 min. They resist 1% phenol for 15 min. Mercury perchloride kills them in 10 min. They are Gram-positive, catalase-positive organisms that occur in grape-like clusters. They are ubiquitous and form the most common cause of localized suppurative lesions in human beings. They may cause endocarditis and postoperative infections. They gain resistance to penicillin and other antibiotics by producing beta-lactamase. This enhances their importance as human pathogens, especially in the hospital environment. 
- B. subtilis: They are nonpathogenic aerobic spore-bearing bacilli appearing as common contaminants in cultures and having general resemblance to anthrax bacilli. They are called pseudoanthrax or anthracoid bacilli. They have also been isolated from individuals suffering from septicemia, meningitis, endocarditis, and pneumonia, wound infections, and other suppurative lesions.  These are less hazardous to use in an in vitro study.
We have used 5.25% sodium hypochlorite for a contact period of 1 min and 0.525% sodium hypochlorite for a contact period of 10 min. It was one of the objectives of this study. If we can get same disinfection with a contact period of 1 min, it would be of great help for a speedy process. One pilot study showed that disinfection of irreversible hydrocolloid impressions in a 0.6% solution of sodium hypochlorite for 2 min was as effective as the ADA's protocol of using a 0.5% sodium hypochlorite solution for 10 min to destroy the test bacteria. 
The results of this study for various spray disinfectants against S. aureus, B. subtilis, and S. viridans can be shown in a decreasing order as follows: 5.25% sodium hypochlorite > 0.525% sodium hypochlorite > 2% glutaraldehyde > 1:213 (1 part in 213 parts of water) povidone iodine > distilled water (control; [Table 1], Graphs 1-3).
Seven impressions were made for each disinfectant with one microorganism and two swabs were made before disinfection and four swabs were made after disinfection. Hence, the total number of predisinfection swabs was 14 and that of postdisinfection swabs was 28.
Each swab was checked for a 4 log10 reduction in colony counts. The effect against S. aureus with 5.25% and 0.525% sodium hypochlorite and 2% glutaraldehyde showed a 4log10 reduction in all the 28 swabs, that is, 100% effec. Povidone iodine showed 4 log10 reductions in 5 swabs out of 28 (i.e., 17.85% effec).
None of the spray disinfectants tested were effective against B. Subtilis, i.e., they did not produce a 4 log10 reduction in any swabs out of 28. Sodium hypochlorite, 0.525%, was effective in two swabs. Further studies are necessary to investigate the disinfectants, which can successfully reduce the B. subtilis counts in a shorter duration of time.
The effect against Streptococcus viridans with 5.25% and 0.525% sodium hypochlorite, and 2% glutaraldehyde showed 4 log10 reductions in all 28 swabs (100%).
Povidone iodine, 1:213, showed a 46.42% effect, i.e., it produced 4 log10 reductions in 13 swabs out of 28. So overall in this study, 1:213 povidone iodine showed less effect against any of the microorganisms. Sodium hypochlorite, 5.25%, was much effective in a shorter period of 1 min. A similar study showed that the use of 0.525% sodium hypochlorite sprayed onto the surface of alginate effectively disinfected 96.6% of the samples. 
Overall, 5.25% sodium hypochlorite was the effective disinfectant in this study. In addition, it has several advantages over other disinfectants:
- least expensive
- readily available through many retail sources
- shown to be 100% effective in decontaminating objects immersed in it for 5 min or longer 
- fast-acting broad-spectrum disinfectant; 5% sodium hypochlorite diluted with an equal amount of bioburden is reported to kill HIV in 2 min and 1 min without bioburden 
- bactericidal, virucidal, and fungicidal disinfectant.
Glutaraldehyde is an irritant and some individuals develop acute sensitivities.  These sensitivities may be displayed as itching of the skin with slight redness, to redness and swelling or yellowing of the skin with prolonged exposure, or irritation to eyes and nasal membranes, headache, coughing, sneezing, and asthma-like symptoms. Glutaraldehyde can be absorbed by inhalation, ingestion, and through the skin. It has a detectable odor at 0.04 parts per million volume (ppmv) and is irritating to skin and mucous membranes at 0.3 ppmv.  Vapors are released whenever solutions are disturbed and the surface tension is broken. Mixing, adding, and removing equipment, or disposing of a glutaraldehyde solution can cause a break in the surface tension.  Whenever the glutaraldehyde solution is not being accessed, it should be covered with a tight-fitting lid. 
A recent study evaluated the antimicrobial efficacy of a chlorite disinfectant (Presept) and a new formulation (chlorine dioxide-based disinfectant Aseptrol) on an irreversible hydrocolloid (alginate) impression material. There was a consistent significant reduction (99.99%) in all tests of vegetative organisms after immersion in the Aseptrol for 30 s, and for spores after 1.5 min. It was effective against vegetative organisms for up to 27 days for a 30-s exposure. Presept significantly reduced (99.99%) Candida albicans, S. aureus and Streptococcus mutans in 30 s, and Pseudomonas aeruginosa in 60 s, but for B. subtilis spores took at least 5 min. Within the limits of this study, it was found that both compounds effectively disinfected the alginate in the presence of the organic material, but that Aseptrol did so after an immersion time of only 1.5 min. The short action time of Aseptrol may make it ideal for the disinfection of alginate impressions, and it may also find many uses in disinfection and possible sterilization. 
| Conclusion|| |
From this study, the following inferences can be drawn:
- Not all the ADA-approved concentrations of surface disinfectants work equally well on an irreversible hydrocolloid (alginate) impression material.
- S. aureus and S. viridans were effectively destroyed by 2% glutaraldehyde.
- Dilution in a 1:10 ratio of sodium hypochlorite with water (0.5%) for 10 min was very effective against S. aureus, S. viridans (5 log10 reduction), and B. Subtilis (3log10 reduction, 99.9%).
- Full strength (5.25%) sodium hypochlorite was the most effective disinfectant overall and required the shortest contact time (1 min).
- None of these disinfectants produced 4log10 reductions for B. subtilis.
Limitations of the study
The study had the following limitations:
- This study did not include the effect of disinfectants on virus and fungi.
- The effect of disinfectants on physical properties of impression materials, like dimensional stability and surface detail, is not included.
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Department of Prosthodontics, Bapuji Dental College and Hospital, Belgaum, Karnataka
[Figure 1], [Figure 2]