Automotive

Sterilization of Gypsum Cast and Dies by Microwave Irradiation -An in Vitro Study

Description
Introduction: Disinfection of casts after obtaining them from the impressions is important to prevent cross contamination and spread of infections. The study was carried out to evaluate the effect of microwave irradiation method of disinfection on
Categories
Published
of 5
0
Categories
Published
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Share
Transcript
   www.ijcmr.com International Journal of Contemporary Medical Research Volume 3 | Issue 4 | April 2016 | ICV: 50.43 | ISSN (Online): 2393-915X; (Print): 2454-7379 982 Sterilization of Gypsum Cast and Dies by Microwave Irradiation -An in Vitro Study Neha Malaviya 1 , Kishore Ginjupalli 2 , Deepthi Kalahasthi 3 , Ashish Yadav 4 , Deepika Kapoor 5 , Deepanshu Garg 6 ORIGINAL RESEARCH ABSTRACTIntroduction: Disinfection of casts after obtaining them from the impressions is important to prevent cross contamination and spread of infections. The study was carried out to evalu-ate the effect of microwave irradiation method of disinfection on surface details reproducibility and compressive strength of dental casts. Material and Methods: Type III and IV gypsum samples were subjected to microwave irradiation method of disinfec-tion. Microwave irradiation was given for 3 min at full pow-er of 900 Watts and 2450 MHz’s. The control and test group casts were examined to evaluate the effect of disinfection pro-cedure on surface details. Surface details of casts were evalu- ated under low angle light at X10 magnication with a stereo zoom microscope in terms of degradation of the reproduced 0.05-mm-wide line and graded. The compressive strength test was conducted on an Instron universal testing machine with a 10kg load cell at a crosshead speed of 0.05cm/min. Results:  Microwave irradiation of type III and IV gypsum samples after one hour of pouring reduced the strength of materials signicantly (p<0.05) with loss of surface details. The compressive strength values of dental stone and die stone were not signicantly affected by irradiation at the end of 24 hours (p>0.05). Microwave irradiation of the samples at the end of one hour resulted in changes in the surface details but surface details were not altered signicantly when irradiated at the end of 24 hours. Conclusion:  We suggest the use of microwave irradiation af-ter 24 hours of air drying to decontaminate the casts prepared  by using type III and IV gypsum products since it does not  produce signicant changes in surface details and is conven -ient. Keywords: microwave irradiation, dental casts, disinfection, compressive strength, surface details INTRODUCTION Increased awareness of the potential for transmission of nu-merous infectious microorganisms during dental procedures have led to an increased concern for, and attention to, infec-tion control in dental practice. 1  Patient derived dental im- pressions and gypsum casts are contaminated with numerous microbes including Candida , MRSA,  P. aeruginosa which are known as opportunistic pathogens responsible for noso-comial and /or life threatening infection in immuno-compro-mised hosts. 2 Impression making is one widely used procedure where clinicians must balance the requirement to maintain an in-tact barrier system with the need to produce accurate dental casts. 3  Dental impressions become contaminated with the micro organisms from patients’ saliva and blood, which can cross infect gypsum casts poured against them. Movements of these organisms into dental casts while setting have been demonstrated. 4  Some microbes have been shown to remain viable within gypsum cast materials for up to seven days. 5 Various methods to disinfect dental casts have been pro- posed and carried out. These include immersing the casts in disinfecting solutions, spraying the casts with disinfecting solutions, 6,7  incorporating chemicals into gypsum at the time of mixing 3  or using die stone containing disinfectant. It was observed that physical properties such as setting time and setting expansion were affected by incorporating disinfect-ants into gypsum. 8,9 Microwave irradiation as an alternative to conventional methods has been reported in literature. 10,11  It is found out that this method is effective and practical and eliminates cross contamination via the cast because it can be repeated at every stage as and when required. 10 The ideal disinfection procedure should not affect the physi-cal and chemical properties of the gypsum cast unchanged to achieve accuracy of the nal prosthesis. 12  This study was done to explore the effect of microwave ir-radiation on the mechanical properties, that is, compressive strength properties and surface detail reproduction of type III and type IV gypsum samples. MATERIAL AND METHODS Two types of dental gypsum products were subjected to two methods of disinfection. The gypsum products tested includ-ed: Type III gypsum product (Kalstone, Kalabhai Dental P Lim - ited, Mumbai) and Type IV stone (Kalrock, Kalabhai Dental P Limited,Mumbai). Die fabrication:  An aluminium die according to ADA spec- 1 Assistant Professor, Department of Prosthodontics, Universal Col-lege of Dental Surgery, 5 Lecturer, Department of Pedodontics, Col -lege of Medical sciences, Bharatpur, 6 Lecturer, Department of Oral Medicine and Radiology, College of Medical Sciences, Bharatpur,  Nepal, 2 Reader, Department of Prosthodontics, Manipal College of Dental Sciences, Manipal, 3 Reader, Department of Prosthodon-tics,Vydehi institute of Dental Sciences, Bangalore, 4 Senior Lec -turer, Department of Prosthodontics, Government Medical College, Azamgarh, India Corresponding author: Dr. Deepika Kapoor, Lecturer, Depart -ment of Pedodontics, College of Medical sciences, Bharatpur, Ne- pal How to cite this article:  Neha Malaviya, Kishore Ginjupalli, Deepthi Kalahasthi, Ashish Yadav, Deepika Kapoor, Deepanshu Garg. Sterilization of gypsum cast and dies by microwave irradia-tion -an in vitro study. International Journal of Contemporary Med-ical Research 2016;3(4): 982-986.  Malaviya, et al. Sterilization of Gypsum Cast and Dies International Journal of Contemporary Medical Research ISSN (Online): 2393-915X; (Print): 2454-7379 | ICV: 50.43 | Volume 3 | Issue 4 | April 2016 983 ication No. 25 13  was fabricated to be used as a test die for evaluation of surface detail. The test die had a diameter of 30 mm. All its surfaces were polished. 3 parallel lines, x, y, and z, to a depth of 50, 20, and 75 mm, respectively are inscribed for evaluation of surface details. Cross lines cd and c’d’ are provided for the determination of dimensional stabil- ity ( Figure 1 ). For the measurement of compressive strength measurement, an aluminium split mould die with guide screws was machine milled. It had 3 compartments for sam- ple preparation, each with 40mm length and 20mm diameter, according to ANSI /ADA specication No. 25 ( Figure 2 ). Mixing and pouring of gypsum samples:  The gypsum prod-ucts were mixed according to manufacturer’s instructions. One hundred grams of type III and type IV were weighed to the nearest +/- 0.1 grams using a physical balance and 32 and 24 ml of water was measured to the nearest +/- 0.1 ml for type III and type IV respectively. The powder was added to distilled water in a clean rubber mixing bowl, allowed to soak in water and then hand spatulated for 10 seconds with a round headed steel blade spatula, followed by spatulation for 20 seconds in a mechanical mixer (Motova SL, BEGO, Bremen,Germany) connected to vacuum to obtain a creamy,  bubble free mix. The mixed dental stone was poured on to the metal die in small increments placed on a mechanical vibrator (Vibro - master; BEGO, Bremen, Germany). The vibration frequency and amplitude were set at 6000 cycles/min and step 3 am-  plitude (0.4 mm) respectively to prevent formation of air  bubbles. The collar was covered with a glass slab to ensure that the base was parallel to the test surface. The casts were allowed to set for 1 hour at room temperature. The casts that were to be checked after 24 hours were removed from the die and allowed to air dry for 24 hours on a table top. Disinfection using microwave irradiation:  The prepared samples of the microwave irradiation group were kept on the glass plate in the microwave oven and timer set to 3 min at full power of 900 Watts and 2450 MHz (Onida Power Con - vection Microwave). After irradiation the casts were allowed to cool down to room temperature and then subjected to the tests respectively. A pilot study done to establish the opti-mum time for microwave irradiation of dental casts revealed that the specimens were completely dried with the remov-al of excess water within 3 minutes. Hence for the present study 3 minutes of irradiation time was selected. (a)   Sample preparation for surface detail evaluation:  A collar was fabricated with elastic material (Impregum Pen - ta Soft Polyether Impression Material; 3M ESPE, St. Paul, Minn) to box the test die to retain the poured gypsum prod -uct.The test casts that did not reproduce the entire length of the 0.05-mm-wide line were discarded. Thirty test casts each of the type III and IV were reproduced from the metal die di-rectly. The samples, thus prepared were classied into 2 groups as follows: • Group 1 (Microwave irradiation for 3 minutes at 900 W, 2450 MHz). Ten samples of each type were tested at 1 hour. • Group 2 (Microwave irradiation for 3 minutes at 900 W, 2450 MHz). Ten samples of each type were tested at 24 hours. Compressive strength evaluation:  The compressive strength test was conducted on an Instron universal testing machine (Instron Corp.,Canton, Mass.) with a 10kg load cell at a crosshead speed of 0.05cm/min. The samples were  placed on the platform and the load applied. The samples were then crushed between the load and the platform. The results obtained were recorded in MPa. (b) Sample preparation for compressive strength evalu-ation: Compressive strength of type III and IV was deter-mined on the cylindrical samples made according to ANSI/ ADA specication. The split metal mould were lled with dental stone under mechanical vibration. The cylindrical test samples were allowed to set for 1 hour and then retrieved.The samples prepared for each type of gypsum products were classied into four groups as follows and were then crushed ( Figure 3 ):• Group 1 (control). Ten samples of each type were tested at 1 hour. • Group 2 (control). Ten samples of each type were tested at 24 hours. • Group 3 (Microwave irradiation for 3 minutes at 900 W, 2450 MHz). Ten samples of each type were tested at 1 hour. • Group 4 (Microwave irradiation for 3 minutes at 900 W, 2450 MHz). Ten samples of each type were tested at 24 hours. Figure-1: Aluminium die for surface detail evaluation Figure-2: Aluminium split mold die for compressive strength eval-uation  Malaviya, et al. Sterilization of Gypsum Cast and Dies International Journal of Contemporary Medical Research Volume 3 | Issue 4 | April 2016 | ICV: 50.43 | ISSN (Online): 2393-915X; (Print): 2454-7379 984 Surface detail evaluation: The control and test group casts were used to evaluate the effect of disinfection procedure on surface details. The effect on the casts in terms of degrada-tion of the reproduced 0.05-mm-wide line was examined un- der low angle light at X10 magnication with a stereo zoom microscope (Motic® type 102 M Stereozoom microscope, Vancouver, Canada). Same investigator performed all the microscopic studies of the casts. The casts were evaluated  based on the graded scoring system with rating values of 1 through 4 ( Figure 4 ).• Rating 1 indicated a well-dened, sharp continuous line• Rating 2 indicated a continuous line, but with some loss of sharpness • Rating 3 indicated a loss of continuity of the line • Rating 4 indicated complete obliteration of the line. STATISTICAL ANALYSIS The observations made on compressive strength of each sample were statistically evaluated using independent t test for one hour groups and one way ANOVA multiple compar  -ison Tukey HSD post hoc test for 24 hours groups. For sta-tistical analysis of the surface details the chi-square test was used to determine the signicance of relationship between the numbers of scores. All computations were conducted in the SPSS software (version 11.5). RESULTS The effects of microwave irradiation on samples were eval-uated. Compressive strength Table – 1 shows the readings of compressive strength eval-uation after microwave irradiation of dental stone and die stone. Type III stone samples:  At one hour interval, the mean compressive strength of samples of control group was sig- nicantly higher compared to microwave irradiation group (p<0.05). However at 24 hours, compressive strength val - ues of dental stone showed no signicant difference between control group and microwave irradiated group (p>0.05). Type IV die stones: At one hour interval, the mean compres- sive strength of samples of control group was signicantly higher compared to microwave irradiation group (p<0.05). At 24hours compressive strength values of control group and microwave irradiated samples were not signicantly differ  - ent (p>0.05). Surface details Summary of results obtained for the detail reproduction of dental stone and die stone samples subjected to microwave irradiation are presented in Table 2. All the samples of dental stone and die stone in the control group exhibited better surface detail reproduction and were able to reproduce a line of 50µm thick clearly as indicated by 100% score in score 1. When the samples were microwave irradiated at one hour, dental stone samples have shown min-imum changes in the surface details as noted from the scored obtained which lie mainly between score 1 and 2. With die stones, microwave irradiation did not cause any change in the surface detail as seen in 90% samples having score score 1. Both dental stone and die stone did not show much change in the surface detail when subjected to microwave irradiation at 24 hours as is clear from the 90% and 80% sample having Figure-3: Compressive strength evaluation using Instron Universal testing machine (Instron corp, Canton, Mass) Figure-4: Surface detail evaluation of prepared samples with Motic type 102 M stereozoom microscope (Motic stereozoom, Canada) Description1Hr Control1Hr Mi-crowave24Hr Control24Hr Mi-crowave Dental Stone Mean (MPa) 18.5715.9323.9523.25S.D1.163.032.181.34Die Stone Mean (MPa) 24.0416.8033.8133.49S.D3.041.451.861.75 Table-1: Readings of compressive strength evaluation after microwave irradiation of dental stone and die stone DescriptionDental StoneDie stone12341234 1Hr Control10---10---1Hr Microwave451-91--24Hr Control10---10--- Table  – 2: Scores for surface detail evaluated after microwave irradiation of the dental stone and die stone.  Malaviya, et al. Sterilization of Gypsum Cast and Dies International Journal of Contemporary Medical Research ISSN (Online): 2393-915X; (Print): 2454-7379 | ICV: 50.43 | Volume 3 | Issue 4 | April 2016 985 score 1 respectively for dental stone and die stone. DISCUSSION Since the autoclaving process would be damaging to a den- tal cast, the American Dental Association (ADA) and the Centers for Disease Control and Prevention 14  have suggested methods for the disinfection of dental casts, including im-mersion or spraying with the disinfectant. It is important that these procedures and materials have no effect on the physi-cal properties of the dental casts. 15  It was observed that the immersion disinfection process affects the surface quality of the casts/dies. It has been shown by Rudd et al (1970) 16  that immersing a stone cast even in tap water for 15 min altered surface properties. Studies undertaken to evaluate the disinfection potential of microwave irradiation of dental casts have proved it is an effective method. 10,11  Microwaves comprise the portion of the electromagnet-ic spectrum extending from the frequency of 300 MHz to 3,00,000 MHz. Most commercial microwave ovens oper-ate at 2450 MHz. Microwaves are generated by magnetron and propagated in a strong line along the wave guide what is called the dominant mode. Microwaves are absorbed in materials containing water and produce friction of water molecules in an alternating electrical eld. The energy thus  produced is transformed into heat and it is supposed that mi-croorganisms with high water content can be consequently killed in short time. However, microwave irradiation was found to cause enlarge-ment of the pores on the surface of the cast because of the rapid loss of water as steam which may have an inuence on the mechanical characteristics and reproducibility of the surface details. 17  Since the fabrication of a dental prosthesis requires the dental cast to undergo various laboratory proce-dures, the strength of the dental cast and its ability to retain the surface details is of utmost importance. Effect of microwave irradiation on compressive strength The results obtained for compressive strength for one hour were subjected to independent t test whereas the 24 hours samples were subjected to One way ANOVA multiple com - parisons Tukey HSD post hoc test. It was noted in the present study, that both dental stone and die stone had a decrease in the compressive strength when subjected to microwave irra-diation at one hour. This decrease was more prominent in die stone as compared to that seen for dental stone.This could be explained by the differences in the crystal shape, density, intermeshing and entanglement of dehydrate crystals in the gypsum tested. In die stone, the number of crystal nuclei formed is much greater and the amount of intermeshing and entanglement is greater compared to den-tal stone. Such an arrangement results in the formation of a dense mass with less amount of porosity. When type IV gypsum casts are subjected to microwave irradiation, excess water used during mixing, although less compared to den-tal stone, forms steam and creates cracks or porosities while leaving the surface. Because structure of die stone is dense, the escape of steam creates stress in the material which prob-ably leads to formation of minor cracks in the material. For-mation of porosities or micro cracks could be the reason why die stone failed at low stress values. Dental stone, on the other hand, is not as dense as die stone, allows easy escape of the steam and there by showing little change in compressive strength. Compressive strength of dental stone and die stone specimens measured at 24 hours is not signicantly different from the compressive strength of microwave irradiated spec-imens. This is understandable as most of the excess water would have evaporated from the material with 24 hours. Mi-crowave irradiation in these samples may not produce steam which may create cracks or porosities. In a study conducted by Leubke and Schneider  16  (1985), it was noted that at 2 hours, there was no signicant difference in compressive strength of type III dental stone dried in mi-crowave oven when compared with the air dried stone. They also suggested that microwave ovens should not be used to disinfect extremely wet or water soaked casts because rapid  boiling of free water may crack the casts. They also observed that the die stones were physically changed by microwave drying because of the appearance of cracks and holes on the surface. In our study we noticed the same effect. Many holes and cracks were easily seen on the outer surface of the spec-imens, which was easily broken by handling. 16 Setting the oven at lowest power level has been advocated  by Leung RL et al (1983). 4  In a study done by Tuncer et al (1993) 18  it was observed that highest power level resulted in a decrease in the compressive strength of type IV die stone. A pilot study, done to establish the optimum time for micro-wave irradiation of dental casts showed that. specimens were completely dry with the removal of excess water within 3 minutes after heating in microwave. Hence for the present study 3 minutes of irradiation time was selected after air dry-ing the samples Effect of microwave irradiation on surface detail reproduction: Microwave irradiation of dental stone and die stone samples at the end of one hour resulted in changes in the surface de-tails in about 60% samples. However, this effect was not sig- nicant when the samples were irradiated with microwaves GroupDependent Variable(I) Class(J) ClassMean Difference (I-J)p Dental StoneHR 24ControlMicro0.70000.802Die StoneHR 24ControlMicro0.31900.991 Table–3: One way ANOVA multiple comparisons Tukey HSD post hoc test between 24 hours samples for compressive strength for dental stone and die stone. TestValuep Dental stone Pearson Chi-Square39.5310.001 vhsDie stone Pearson Chi-Square33.4240.001 vhs Table–4: Chi-Square Tests for surface detail comparison  between the 24 hours microwave and hypochlorite immersion groups of dental stone and die stone  Malaviya, et al. Sterilization of Gypsum Cast and Dies International Journal of Contemporary Medical Research Volume 3 | Issue 4 | April 2016 | ICV: 50.43 | ISSN (Online): 2393-915X; (Print): 2454-7379 986 at the end of 24 hours. The loss of surface details at one hour can be explained on the basis of porosity or microcracks formed by the steam during microwave irradiation. Microwave irradiation of samples after one hour of pouring reduced the strength of the materials signicantly (p<0.05) and also there was loss of surface detail. The compressive strength values of samples were not signicantly affected by microwave irradiation at the end of 24 hours (p>0.05). Mi -crowave irradiation of the samples at the end of one hour re-sulted in changes in the surface details in about 60% samples  but the surface details were not altered signicantly when the samples were irradiated with microwaves at the end of 24 hours. CONCLUSION Based on the observations of this study, it can be inferred that microwave irradiation of dental casts after one hour of pouring reduced the strength of materials signicantly (p<0.05) and also there was loss of surface detail. The sur  -face details and compressive strength were not altered signif-icantly when the samples were irradiated with microwaves at the end of 24 hours. In view of the seriousness of the diseases like HIV and hep-atitis it is worth waiting for 24 hours when using microwave irradiation. We, therefore, recommend the use of microwave irradiation after 24 hours of air drying to decontaminate the dental casts till better alternatives are available REFERENCES 1. Hiroshi Egusa,Takao Watamoto,Keiko Abe, Munemasa Kobayashi, Yoshitoshi Kaneda, Shunji Ashida, Takuya Matsumoto, Hirofumi Yatani. An Analysis of the Per  - sistent Presence of Opportunistic Pathogens on Pa -tient-Derived Dental Impressions and Gypsum Casts. Int J Prosthodont 2008;21:62–68.2. Hiroshi Egusa, Takao Watamoto, Takuya Matsumoto, Keiko Abe, Munemasa Kobayashi, Yoshihiro Akashi, Hirofumi Yatani. Clinical Evaluation of the Efcacy of Removing Microorganisms to Disinfect Patient Derived Dental Impressions. Int J Prosthodont 2008;21:531– 538.3. Hall BD, Muñoz-Viveros CA, Naylor WP, Sy J. Effects of a chemical disinfectant on the physical properties of dental stones. Int J Prosthodont. 2004;17:65-71.4. Ralph L. Leung, Steven E. Schonfeld. Gypsum casts as a potential source of microbial cross contamination. J Prosthet Dent 1983;49:210-211.5. Seymour S. Block. Disinfection, Sterilization and Pres-ervation. 5 th  edition, Lippincott publications, page 1060. 6. Sarma AC, Neiman R.A study on the effect of disin-fectant chemicals on physical properties of die stone. Quintessence Int. 1990;21:53-9.7. Bass RA, Plummer KD, Anderson E. The effect of a surface disinfectant on a dental cast. J Prosthet Dent. 1992;67:723-5.8. Lucas MG, Arioli-Filho JN, Nogueira SS, Batista AU, Pereira Rde P. Effect of incorporation of disinfectant solutions on setting time, linear dimensional stability, and detail reproduction in dental stone casts. J Prostho-dont. 2009;18:521-6.9. Abdullah MA. Surface detail, compressive strength, and dimensional accuracy of gypsum casts after repeat-ed immersion in hypochlorite solution. J Prosthet Dent. 2006;95:462-8.10. Davis DR, Curtis DA, White JM. Microwave irradia-tion of contaminated dental casts. Quintessence Int. 1989;20:583-585.11. Einar Berg, Oyunn Nielsen, Nils Skaug. High-Level Microwave Disinfection of Gypsum Casts. Int J Prost-hodont 2005;18:520-525.12. S. Ahmad, C. J. Tredwin, M. Nesbit and D. R. Moles. Effect of immersion disinfection with Perform-ID on alginate, an alginate alternative, an addition cured sili-cone and resultant type three gypsum casts. British Den-tal Journal 2007;202:1-7.13.  New American Dental Association Specication no. 25 for dental gypsum products- JADA 1972;84:640-644.14. American Dental Association reports, council on dental materials, instruments and Equipment -1991. 15. Twomey JO, Abdelaziz KM, Combe EC, Anderson DL. Calcium hypochlorite as a disinfecting additive for den-tal stone. J Prosthet Dent. 2003;90:282-8.16. Rudd KD, Morrow RM, Brown CE Jr, Powell JM, Rahe AJ. Comparison of effects of tap water and slurry on gypsum casts. J Prosthet Dent 1970;24:563:70.17. R. J Leubke, R. L Schneider. Microwave oven drying in articial stone. J Prosthet Dent 1985;53:261-265 18. N.Tuncer, H.B. Tufekeioglu, S.Callikkocaoglu. Investi-gation on the compressive strength of several gypsum  products dried by microwave oven with different pro-grams. J Prosthet Dent. 1993;69:333-339. Source of Support:  Nil; Conlict of Interest:  None Submitted: 11-02-2016; Published online : 09-03-2016
Search
Similar documents
View more...
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks
SAVE OUR EARTH

We need your sign to support Project to invent "SMART AND CONTROLLABLE REFLECTIVE BALLOONS" to cover the Sun and Save Our Earth.

More details...

Sign Now!

We are very appreciated for your Prompt Action!

x