disinfection techniques of impressions in prosthodontics

disinfection of various impressions and impression materials used in prosthodontics

1. Comprehensive review and comparison of the disinfection techniques currently available in the literature Ahila S. Chidambaranathan , MDS & Muthukumar Balasubramanium , MDS journal of prosthodontics , VOL 28, issue 2 - 2019 , AJAY YERRAMSETTI

2. CONTENTS INTRODUCTION LEVELS OF DISINFECTION CHOICE OF DISINFECTION FOR IMPRESSIONS DISINFECTANTS USED IN DENTISTRY ANALYSIS OF STERILIZATION METHODS ALTERNATIVE METHODS DISCUSSION CONCLUSION

3. INTRODUCTION Public awareness of the spread of microorganisms and infectious diseases in the dental office among the dentist, auxillaries and laboratory personnel has increased significantly. Some microorganisms may cause opportunistic infections in immuno-compromised persons such as those with hepatitis, tuberculosis, herpes, and AIDS. Dental impressions contaminated with a patient’s saliva or blood can cross-contaminate stone casts and serve as a source of infection to dental personnel who handle the impression or cast.

4. Spray and immersion disinfection using solutions and the incorporation of antibacterial chemicals into the gypsum or die stone during mixing may influence the mechanical properties including setting time and dimensional accuracy. Immersion disinfection ensures that all surfaces of the dental impression are exposed to the disinfectant; however, hydrocolloids and polyether materials cannot be immersed in disinfectants due to the imbibition phenomenon. The spray method of disinfection reduces the chance of distortion, especially in hydrocolloids and polyether, and also uses less disinfectant solution, but it may not reach the areas of undercuts and also releases air, leading to occupational exposure.

5. Antimicrobial agents have been incorporated into impression materials by the manufacturer, increasing the risk of dermal and mucosal irritation of the patient when multiple impressions are made. Many methods have been tested for disinfection of casts. These methods include incorporation of disinfectants into dental casts and disinfection of casts using a microwave oven in controlled settings.

6. LEVELS OF DISINFECTION High-level Intermediate level Low-level Capable of inactivating bacterial spores and all other microbial forms, an essential criteria for high-level disinfectants like ethylene oxide gas or glutaraldehyde solutions. Namely formaldehyde , chlorine compounds , iodophors, alcohols, and phenolic compounds, destroy microbes like tubercle bacilli, but they do not inactivate spores. With narrow antibacterial activity namely, quaternary ammonium compounds,simple phenols ,and detergents , which are unacceptable for impressions disinfection Chemical disinfectants can be classified into three categories based on their efficiency against vegetative bacteria, tubercle bacilli, fungal spores, and viruses.

7. IMPRESSION MATERIAL DISINFECTANT AGENT DURATION Alginate Iodophors and diluted sodium hypochlorite 10 minutes Compound Iodophors and diluted sodium hypochlorite 10 minutes Polyether Iodophors and diluted sodium hypochlorite, complex phenolics 10 minutes Polysulphide Iodophors and diluted sodium hypochlorite, complex phenolics 10 minutes Silicone Iodophors and diluted sodium hypochlorite, complex phenolics 10 minutes Agar Iodophors and diluted sodium hypochlorite 10 minutes Zinc-oxide eugenol Iodophors 10 minutes

8. DISINFECTION SOLUTIONS USED IN DENTISTRY Iodophor , discovered by H. A. Shelanskiand , M.V.Shelanski , is a complex of polyvinyl pyrolidone (povidone, PVP) and elemental iodine. These compounds are bactericidal, sporicidal, virucidal , and fungicidal but require more disinfection time. They also have been used for the disinfection of blood culture bottles, hydrotherapy tanks, thermometers, and endoscopes. The disinfective ability of iodine is neutralized in the presence of organic material, and hence frequent applications are needed for thorough disinfection. 1.IODOPHOR

9. Glutaraldehyde is a pungent colorless oil used to sterilize medical and dental instruments. It is used as preservative in industries. Glutaraldehydes are bactericidal, virucidal , fungicidal, sporicidal, and parasiticidal and can be highly toxic. They are used as disinfectant in both liquid and gas forms. 2.GLUTARALDEHYDE

10. 3.SODIUM HYPOCHLORITE Sodium hypochlorite is a chemical with the formula of NaOCl . It is composed of sodium cation and hypochlorite anion. It is soluble in water. NaOCl is a compound that can be used for purification. It is used for surface purification, bleaching, odour removal, and water disinfection in industry. Hypochlorite removes stains from clothes at room temperature.

11. 4.ALCOHOLS ISOPROPYL ALCOHOL It is a colorless chemical compound with strong odor. It is commonly used as a topical antiseptic. It is also used to disinfect the surface of medical equipment. Alcohols are flammable, hence must be stored in a cool, well-ventilated area. Alcohol irritates the tissues and evaporates rapidly. It is very expensive for general use as a surface disinfectant.

12. ETHYL ALCOHOL Ethyl alcohol is more bactericidal than bacteriostatic, also tuberculocidal, fungicidal, and virucidal against enveloped viruses. Alcohols are not effective against bacterial spores and non-enveloped viruses. They denature the bacterial proteins, thereby inactivating the microorganisms. The optimum bactericidal concentration in water is 60% to 90%, and the cidal activity drops when diluted below 50% concentration. Ethyl alcohol also can be used for hand washing. The drying effect of alcohols on the hands can be blocked by the addition of emollients and skin-conditioning agents. Ethanol has shown clear bacterial growth inhibition, especially when used in high concentrations against S. mutans and S. aureus.

13. CHLORHEXIDENE Chlorhexidine (CHX) is a positively charged molecule that binds with the negatively charged sites of the cell wall and destabilizes. Hence, it interferes with osmosis of the cell wall. The CHX then attacks the cytoplasmic membrane and leaks the components that lead to cell death. In high concentrations, CHX causes the cytoplasm to congeal or solidify. The bacterial intake of CHX is very rapid (<20 seconds). No antifungal activity of CHX has been observed in the agar diffusion test in low concentrations, but 2% CHX showed antimicrobial activity against S. aureus, E. coli, and B. subtilis, but not C. albicans.

14. Analysis of sterilization methods STERILIZATION Sterilization means complete elimination of microorganisms and spores, and requires an immersion period of 6 to 10 hours. Sterilization of elastomers by autoclave and microwave is associated with mild linear dimensional changes.

15. UV LIGHT ON IMPRESSION The effectiveness of UV rays in disinfection depends upon the time, intensity, humidity, and access to the microorganism. Since dental prostheses provide a number of sites for housing microorganisms, UV light must be reflected from many directions. UV light exposure has been shown to drastically reduce C. albicans colonies as compared to direct-current glow discharge. It has been observed that a higher-watt UV light tube decreases the colony count in less time. The maximum killing efficiency with UV light exposure has been obtained with 24 watts (3750 µw/cm 2). The higher wattage required less time to decrease the colony count of C. albicans to zero.

16. DIRECT CURRENT GLOW DISCHARGE A glow discharge is plasma formed by passing electric current between two metal electrodes in a glass tube containing low pressure gas at 1 to 10 torr (argon). Direct-current glow discharge has been shown to decrease the count of C. albicans colonies, but UV light could be a better disinfection method than direct-current glow discharge.

17. STEAM AUTOCLAVE An autoclave is a device used to sterilize equipment by subjecting them to high saturated steam pressure at 121°C or more for 15 to 20 minutes. An autoclave also works at 115°C/10 p.s.i , 121°C/15 p.s.i ., and 134°C/30 p.s.i . The standard settings can kill most bacteria, spores, viruses, and fungi at 134°C, which can be achieved in 3 minutes. Digitalized autoclaves use an F0 (F- nought ) value to monitor the sterilization cycle. Addition or condensation silicone materials could be sterilized without any significant dimensional changes using stock metal trays at 132°C and producing lessthan 0.5% dimensional change at 134°C without producing clinically relevant changes in tear strength.

18. ETHYLENE OXIDE GAS AUTOCLAVE Holtan et al noted that ethylene oxide gas sterilization allowed gas inclusions into the polyvinyl siloxane(PVS) impression material, which produced bubbles in dies poured immediately. This kind can be avoided by pouring the dies after 24 hours. They also stated that steam autoclaving was a suitable method if the impressions were used for removable prostheses. Olin et al reported that the use of ethylene oxide gas autoclaving of heavy- and light-body addition silicone impression material in custom trays showed significant structural changes (>0.5%change) due to the distortion of the trays or incapability of preventing expansion of the impression material.

19. ARGON RADIO FREQUENCY GLOW DISCHARGE Plasma glow discharge is created by evacuating a reaction chamber, then refilling with a low-pressure gas. The gas is the energized by radiofrequency microwaves using alternating current or direct current. Argon radio frequency glow discharge (RGD) improves the wettability of impression materials. Recently, RGD has been advocated for disinfecting procedure for PVS impressions, but it is not clear if glow discharging results in sterilization.

20. MICROWAVE STERILIZATION Microwave irradiation improves the strength and hardness of the cast, but cracks or porosities in the surface have been noted to occur when type III gypsum is exposed to irradiation with 1450 W and 5 minutes of microwave oven irradiation in a household microwave oven set at 900 W. Studies have also demonstrated that the exposure of bacterial suspensions to microwave irradiation caused reduction of viable cell counts and increased leaching of DNA and protein. These results suggest that microwaves affect cell membrane integrity and permeability and cell metabolism, which leads to cell death. Microwave irradiation (10 minutes/720 W) has been noted to have little effect on impression accuracy of impressions, and hence has been recommended as a suitable technique for sterilizing rubber impressions.

21. ALTERNATIVE METHODS OF IMPRESSION DISINFECTION TO PREVENT CROSS CONTAMINATION IN PROSTHODONTICS Incorporation of disinfectant into the alginate powder Nanotechnology Disinfection or sterilization of dental cast Disinfectant incorporated into the gypsum product

22. INCORPORATION OF DISINFECTANT INTO THE ALGINATE POWDER Water soluble antimicrobial compounds such as quaternary ammonium compounds, bisquanidine compounds, dialkyl quaternary compounds, quinoline compounds, substituted phenols, chlorhexidine, didecyldimethyl ammonium chloride, and a mixture of these materials are generally employed. Disinfectants that are either physically blended or coated onto the alginate powder have been made in the form of microcapsules, which will release the disinfectant on mixing with the liquid. Similarly, disinfectants can also be added to the mixing liquid. Among these,CHX was the most widely used and efficient disinfectant without affecting handling of alginates.

23. NANOTECHNOLOGY Nanotechnology has been used for dental applications in several forms. Jafari et al compared solutions containing nano silver colloid 1000 ppm and 500 ppm with 2% chlorhexidine solution and sterile distilled water. The 500 ppm nano-silver showed the widest range of zone of inhibition (ZOI).

24. DISINFECTANT INCORPORATED INTO THE GYPSUM PRODUCT Addition of 0.5% sodium hypochlorite to distilled water for disinfection of dental stone casts can decrease the setting time, increase the compressive strength, and have no significant effect on setting expansion of stone models. The setting expansion of type V gypsum mixed with 0.5% calcium hypochlorite has proven to be higher than that of type V gypsum mixed with distilled water. Surface hardness of type V gypsum stone mixed with 0.5% calcium hypochlorite was less than that of type V gypsum mixed with distilled water. Sodium hypochlorite is not recommended for type IV gypsum disinfection in a concentration more than 0.5%. Iodine is not suitable for type IV gypsum disinfection in any concentration equal or more than 2%.

25. Dental stones mixed with chemical disinfectant agents have shown high average roughness (Ra); however, the additions of gumarabic and calciumhydroxide to the hemihydrate powders before mixing maintain the roughness values to the level of the control.

26. DISCUSSION Impressions must be treated with disinfectants that do not affect their dimensional stability. The most effective means of minimizing infection risks is chemical disinfection of impressions. The quality of the stone casts obtained from irreversible hydrocolloid impressions disinfected by the immersion method has improved. Chemical disinfection and autoclave sterilization do not significantly increase surface roughness. Chemical agents suitable for the disinfection of dental impressions, like chlorine compounds, glutaraldehydes , phenols, and iodophors, have been effective against viruses, spores, and bacteria.

27. The ADA recommended using at minimum a medium-level disinfectant for dental impressions. Sodium hypochlorite has a medium level of action. So the surface has to be exposed to a concentration of 1% active chlorine (10,000 ppm) for 10 minutes, but it corrodes the metal trays. Glutaraldehyde is a high-level disinfectant and is not as corrosive as hypochlorite. Neutral and alkaline glutaraldehydes are less corrosive than the acidic glutaraldehyde. They are suitable for use in a concentration of 2% for 10 minutes. Ten minutes of irradiation at high power can sterilize the impressions made from PVS impression materials. Microwave irradiation can be used for gypsum cast disinfection.

28. CONCLUSION Impression sterilization is expensive and time consuming, and potentially damaging to the dental materials, since surface disinfection with chemical solution is an alternative method of disinfecting hydrocolloid and silicone impression materials. Iodophor is a recommended disinfectant for all types of impression materials. The dentist should realize the importance of disinfection to prevent the cross contamination of microorganisms via impression to patients, dental auxiliaries, and the laboratory technician.

29. REFERENCES Leung RL, Schonfield SE: Gypsum casts as a potential source of microbial cross contamination. J Prosthet Dent 1983;49:210-211 Council on dental materials: instrument and equipment disinfection impressions. J Am Dent Assoc 1991;122:110 Council on scientific affairs and council on dental practice: infection control recommendations for the dental practice and the dental laboratory. J Am Dent Assoc 1996;127:672-680 Drenon DG, Johnson GH: The effect of immersion disinfection of elastomeric impressions on the surface detail reproduction of improved gypsum casts. J Prosthet Dent 1990;63:233-241

30. Comprehensive review and comparison of the disinfection techniques currently available in the literature Ahila S. Chidambaranathan , MDS & Muthukumar Balasubramanium , MDS journal of prosthodontics , VOL 28, issue 2 - 2019 , AJAY YERRAMSETTI