This clinical and laboratory study evaluated the effect of two methods of disinfection in different modes at the volume changes of polysiloxane dental impressions and plaster models poured from them, as compared to the same parameters of plastic master models (PMM), using three-dimensional non-contact laser scanner and software. To determine the volume changes of sіlicone impressions, as a result of immersion and microwave methods of decontamination received 270 impressions from plastic master models (PMM) by 5 different polysiloxane materials: Stomaflex, Express, Speedex, Стомавід, Zeta Plus. After receiving the impressions were washed under running water for 2 minutes and separated into the groups depending on the method and mode of disinfection. Surfanios Premium UA and Аniosept Аctive were chosen for immersion disinfection on silicone impressions as the disinfectants. For immersion disinfection used plastic containers, the thickness of the layer of solution above the embedded fingerprint was at least 1 cm, the solution prepared according to the regulations and guidelines of selected disinfectants. For microwave method of decontamination as a source of microwave energy we used microwave oven Samsung MW87HR. For smooth power control of microwave radiation used setting «-UNDADENT" (patent # 102663). Each group consisted of 54 silicone impressions: the first group was control, the impressions were not subject to disinfection; in the second group - impressions were immersed in a solution of 0.25% "Surfanios Premium" for 15 minutes each time; in the third group - impressions were immersed in solution of 2% "Aniosept Aktiv" for 15 minutes each time also; in the fourth group – impressions were disinfected in the microwave oven using settings « - UNDADENT" at 486W power for 10 minutes - "dry smooth" microwave mode; in the fifth group – impressions were disinfected in the microwave oven and they were immersed in a container with distilled water using settings « - UNDADENT" at 243W power for 10 minutes - "wet smooth " microwave mode; in the sixth group – impressions were disinfected in the microwave oven and they were immersed in a container with solution of 0,05 % “Aniosept Aktiv” using settings « - UNDADENT" at 425W power for 4 minutes - " wet smooth combined express" microwave mode. The impressions were rinsed for 3 min. under running water after disinfection and then were cast plaster models in the ratio of 20 ml of water / 100 g plaster according to the manufacturer's instructions of Fuji Rock gypsum. After crystallization the plaster models were scanned using DAVID SLS-2. Scanned casts exported in the graphical editor Geomagic Studio 2013. There the teeth were separated from plaster models and the volume changes were calculated as a result. Research results processed by methods of variation statistics with the definition of medium size and its errors, Student's t test for multiple comparisons. Considered statistically significant value of P < 0.05. Volume changes in the II-III groups, resulting in a double immersion in solutions of chemical disinfectants exposure of 15 min. directed towards reduction (shrinkage) more than deviations in IV-VI study groups on average 0.2%, but significantly it was not confirmed, P>0.05 (5%). Except there were changes in the second group of Stomaflex impressions, which were statistically significantly greater than the volume deviation in the studied I and IV groups, P<0.05 (5%). The method of the microwave disinfection using settings "UndaDent" when used "dry smooth ", "wet smooth" and “wet smooth combined express” have modes of exposure, an average of 4 to 10 min. In all researched groups of silicone impressions that modes did not change volumetric parameters so that it was significantly noticeable, p> 0.05 (5%). Immersion in solutions of chemical disinfectants with an exposure of 15 minutes did not affect significantly the size of silicone impressions compared to the control group. But according to the regulations and guidelines on the use of selected chemical disinfectants, especially dangerous to destroy viruses and bacteria is necessary to prepare working solutions with high concentrations, but this is due to increased spending on this method, as well as increased hazard to medical staff. The method of the microwave disinfection using settings «-UNDADENT" when used "wet smooth combined express" mode reduces the cost of expensive disinfectants in the preparation of working solutions with low concentrations. That is possible through a dual effect on pathogens, namely chemical, thermal and microwave. Microwave method also makes it possible to dispense with all chemical disinfectants using ordinary distilled water and exposure time 10 min. Thus, according to the research results, with 95% confidence we can make assumptions about the safety of methods and disinfection regimes for volumetric parameters of used silicone impressions, besides, Stomaflex, that, in our view, necessary to choose other effective solutions of chemical disinfectants in which they could be immersed with exposure less than 15 min.
Keywords: silicone impressions, plaster models, 3d scanning, immersion disinfection, microwave disinfection, master model
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