In daily dental practice, to avoid cross-contamination from potentialpathogenic bacteria of oral flora, dental impression materials are disinfected byimmersion in liquid disinfection solutions. In the present study ozone disinfection wasapplied, by means of a prototype automated disinfection device. The aim of thepresent dissertation is to compare the effectiveness of a new method that uses thedisinfective properties of ozone with the effectiveness of immersion disinfection inliquid solutions. The method was tested not only in terms of laboratory conditions, butin daily dental practice conditions, as well. In addition, dimensional stability andsurface degradation that dental impression materials possibly encounter during ozonedisinfection, were examined.A prototype ozone disinfection apparatus for dental impression materials wasconstructed combining various devices, including a corona discharge ozone generator,an air dryer, a varying flow air pump, a moisture indicator, a high precision flowmeter, a disinfection chamber, a manganese dioxide-copper oxide catalyst and Teflonpipework (Greek patent office registration number: 20110100194/2013).For the bacteriological study, dental light-body addition-cured silicone wasinoculated with liquid inoculum of the Gram (-) and Gram (+) bacteria Klebsiellapneumoniae and Staphylococcus aureus, respectively. 10mm diameter discs wereremoved and were disinfected using ozone for various time intervals, with immersionin benzalkonium chloride solution or served as controls. Furthermore, sixteenaddition-cured silicone impressions were obtained from four volunteers and afterarranging them into groups, the same disinfection procedure was followed. Theeffectiveness of each disinfection method was evaluated by using the viable platecount method (in triplicate). The dishes were incubated at 37μC for 24h or 48h inaerobic or/and anaerobic conditions.Subsequently, possible impression materials dimensional changes wereexamined, after ozone disinfection or immersion disinfection (sodium hypochlorite orbenzalkonium chloride solutions). 120 specimens from 4 different elastomericimpression materials were constructed via a special die. Specimens were measuredbefore and after disinfection under a measuring microscope and the dimensionalchange percentage was counted. Accordingly, 30 light-curing resin custom trayspecimens were constructed via a specially designed edentulous maxillary cast, inwhich 4 removable die pins were incorporated. Specimens were measured before andafter disinfection (6 distances in between the pins) via a digital micrometer and thedimensional change percentage of each distance was counted. In addition, the totaldimensional change percentage of the custom trays was counted in accordance to thesurface change percentage that was defined by the 4 pins that were incorporated into the custom trays.Finally, possible elastomeric impression materials surface degradationinspection was conducted by fabricating 32 specimens, 1mm in thickness, from 4different elastomeric impression materials that were either ozone disinfected, eitherimmersion disinfected in sodium hypochlorite or benzalkonium chloride solution, byusing 2 disinfection time intervals for each disinfection method or served as controls.A 7mm disc was removed from each specimen and after attaching it to a special stubvia a suitable conductive cement, it was gold-coated in a sputter-coater. Thespecimens were examined in a Scanning Electron Microscope set at x2000magnification. The statistical analysis of the microbiological study results was conducted viaone way-ANOVA, with significance threshold at 0,05 based on the log10transformations of the colony-forming units (CFU). Pairwise comparisons of thevarious treatments were conducted by the Tukey‟s test. The statistical analysis of theresults of the impression materials and custom trays dimensional stability study wasconducted via the non-parametric Wilcoxon test, regarding the change of eachspecimen group separately, with significance threshold at 0,05. Pairwise comparisonsof various specimen groups were conducted via the non-parametric Mann-Whitneytest, with significance threshold at 0,05.During the bacteriological study, a reduction of the bacterial load of at least 3logarithmic units was observed after the first 3min of ozone exposure. Thebacteriological study of the impressions revealed that after ozone disinfection, thebacterial load was reduced by ≈1log10. The ozone disinfection method proves fullyeffective and safe, since a similar high bacterial load was observed for the immersiondisinfected impressions (≈4log10), especially regarding the anaerobic conditions. Theozone disinfection method proves to be at least equal to that of immersion disinfectionin liquid solutions.During the impression materials dimensional stability study, the ozonedisinfection method showed the smallest dimensional changes designating remarkableaccuracy. During the elastomeric impression materials surface degradation study, itwas concluded that in almost all disinfection treatments, either liquid or airborne byozone, similar, very small, insignificant changes appear on the specimens‟ surface,establishing ozone disinfection completely efficient.The current study designated dental impression materials‟ ozone disinfectionmethod equal and in some cases more effective than current established disinfectionmethods. It is a fast, efficient, safe, accurate and fully automated disinfection methodfor dental impression materials that can be established, having in addition theadvantages of low operating cost and environmental friendliness, since there will beno use of disinfection solutions with all the hazardous consequences they possess forthe environment, through their daily, in global level, usage.
Evaluation of dimensional stability and details reproduction of alginate molds storage in different times and temperature
