The oral cavity is a reservoir for opportunistic and pathogenic microorganisms. During routine orthodontic and dental practice, there is a high risk of cross-contamination and infection that may even cause systemic infections [
Omitting a proper disinfection of orthodontic equipment might increase the risk for transmission of communicable diseases and facultative pathogenic microorganisms. Dental technicians show a higher rate of hepatitis-B-infestation compared to the average population [
The need to disinfect orthodontic equipment before and after contact with patients is theoretically an obligation [
There are no agents produced specifically for disinfection of orthodontic equipment. However, disinfecting agents originally produced for disinfection of dental impressions are used commonly. In the majority of cases, aldehydes are the utilized agents for disinfecting orthodontic equipment and acrylic dentures. The disinfecting effect of dentures using aldehydes is adequate, although the material safety data sheets give no direct information regarding disinfection of orthodontic equipment and acrylic dentures [
Thus, the purpose of this
The hypothesis of this study is that the investigated chemical disinfecting agents have a significant influence under simulated practice conditions (single use disinfection) on the modulus of elasticity, the flexural strength, the macro hardness, the micro hardness, the average roughness, and colour change of different orthodontic acrylics.
For this investigation, 260 specimens consisting of two different orthodontic acrylics were fabricated. The cold-curing polymer Orthocryl in the colours green and colourless (Dentaurum, Ispringen, Germany) and the cold-curing polymer Forestacryl in the colours pink and colourless (ForestaDent, Pforzheim, Germany) were used. Test specimens were designed prismatically according to DIN EU ISO Norm 3167:2003 by using spreading technology and were constructed with dimensions of 80x10x4 mm. All test specimen surfaces were ground and polished, using granulation sizes of 220, 320, 800, 1200, and 2400 (RotoPol-35, Struers GmbH, Willich, Germany) (Figure
Cold-curing orthodontic acrylics after polymerisation. (A) Orthocryl colourless; (B) Orthocryl green; (C) Forestacryl colourless; and (D) Forestacryl pink.
The test specimens were distributed into test groups. Ensuring standardized water saturation and for appearing the maximum water sorption, 198 test specimens were inserted at 22°C in distilled water for 24 hours and finally incubated at 22°C (WTC Binder, Tuttlingen, Germany) aerobically for 24 hours. Finally, the influence of the disinfecting agents, consisting of Impresept (3M Espe, 3M Company, St. Paul, Minnesota, U.S.A.), Stammopur DR (Dr H Stamm, Berlin, Germany) and D 050 Instru-Gen (ad-Arztbedarf GmbH, Frechen, Germany), on the elastic modulus (E-Modulus), flexural strength, macro hardness, micro hardness, average roughness, and colour change of the test specimens was investigated. The active components of Impresept are oxalaldehyde and 1,5-pentanedial. These active components are enclosed to the chemical group of aldehydes. Didecyl-dimethylammonium chloride (quaternary ammonium cation) and 1,5-pentanedial are mentioned as active components of Stammopur DR. Sodium perborate and sodium benzoate with the chemical effect of oxidizing connections are the active substances of D 050 Instru-Gen. The used disinfecting agents were prepared with respect to the concentrations and exposure times regarding the manufacturer instructions, for conditioning of the test specimen. Impresept disinfected the test specimen for ten minutes and was used with a concentration of 100%. The Stammopur disinfecting solution was used with an exposure time of 60 minutes and was prepared in a concentration of 3%. The D 050 Instru-Gen disinfecting solution was prepared in a concentration of 2% and the disinfection time of the test specimens was 60 minutes. Dry storage on one hand and distilled water on the other hand were used in addition to the disinfecting agents as control groups. Test specimens, which were used in the distilled water group, were stored for 60 minutes in distilled water. After expiration of the storage period (dry storage control group) and disinfecting period (including the test specimens of the distilled water control group), the test specimens were rinsed with distilled water for one minute and dried manually. Subsequent, the influence on the E-Modulus, flexural strength, macro hardness, micro hardness, average roughness and color change was investigated.
The E-Modulus and the flexural strength were measured using the three-point bending test as per DIN EN ISO 178:2003.
120 test specimens were distributed into test groups. The test specimens of the first test group consisted of the stored dry control group. The single storage liquid of the second test group was distilled water. These two test groups were applied as control groups. In the third test group Impresept was used as disinfecting agent. In the fourth test group the influence of Stammopur DR on the test specimens was investigated. The fifth test group was utilized to perform the impact of D 050 Instru-Gen on the test specimens. Following the preparation of each orthodontic acrylic test specimen, three-point bending tests were performed using Zwick machine (ZWICKI TMZW, Zwick GmbH & Co. KG, Ulm, Germany) (Figure
Three-point bending device on the Zwick universal testing machine (ZWICKI TMZW, Zwick GmbH & Co. KG, Ulm, Germany) and Forestacryl colourless test specimen.
Zwick universal testing machine was constructed performing numerous tests on materials and structures. The investigated test specimens were placed in the universal testing machine between the clamps and the inspection stamp. Each of the tested specimens was mounted on two 5 mm diameter support posts 64 mm apart from each other. This distance was selected to be 16 times the specimens’ thickness of 4 mm. A plunger was used to apply a vertical force up to a maximum of 2 kN to the center of the test specimen. The E-Modulus and flexural strength were determined at a cross-head speed of 2 mm/min. The radii of the abutments and plunger were 5 mm. For determination of the E-Modulus and flexural strength, the test speed was kept at a consistent 2 mm/min. Analysis of the resulting data was performed using the test and calibration software testXpert II (Zwick GmbH & Co. KG, Ulm, Germany).
The macro hardness of 60 test specimens of the investigated cold-curing orthodontic acrylics was measured by testing the indentation hardness as per DIN EN ISO 2039-1 using the Instron Wolpert-Macro Hardness K-Testors 2524 (Wolpert Wilson Instruments, Pfungstadt, Germany) (Figure
Instron Wolpert- Macro Hardness K-Testors 2524 (Wolpert Wilson Instruments, Pfungstadt, Germany) including a Forestacryl pink test specimen.
The test load varies between the minimum test force of 49 N and the maximum test force of 961 N unless otherwise stated in the specific testing procedure. The measuring method is according to a measurement under load to evaluate the complete deformation of the investigated orthodontic acrylics. The determined hardness values include elastic, viscoelastic, and plastic deformation components. The distance between each test specimen was 10 mm to avoid the influence of adjacent hardness dots.
The micro hardness of 40 test specimens of the investigated cold-curing orthodontic acrylics was measured using a micro hardness test device (Fischerscope H 100C XYp, Helmut Fischer GmbH, Sindelfingen, Germany). The test procedure was performed according to DIN EN ISO 14577-1, 2 and 3. The micro hardness of test specimens was measured in an area of checking which was selected microscopically (Video-Measuring-and Inspection system VMZM-40, 4H-Jena engineering, Jena, Germany). Every single test specimen was charged with a rate of loading of 50mN/s to a maximum strength of 1000mN. Test specimen was discharged after 20 seconds. The depth of impression and the stress of the indenter were registered simultaneously and displayed graphical.
For conducting the average roughness investigations, 40 test specimens were used. The average roughness was performed according to DIN EN ISO 4287, 4288, and DIN 4760 using a surface measuring device (Perthometer PGK, Mahr GmbH, Göttingen, Germany) and an evaluation device (Perthometer S3P, Mahr GmbH, Göttingen, Germany) (Figure
Surface measuring station Perthometer S3P (Perthometer S3P, Mahr GmbH, Göttingen, Germany) measuring a Forestacryl pink test specimen.
The measurements were performed before and after storing in the test liquid. The test track had a distance of 5.6 mm. The entire measuring length was 4.0 mm. The cut-off wavelength
Colour change of all 260 test specimens of the investigated cold-curing orthodontic acrylics was quantified spectrophotometrically (Spectrophotometer VITA Easyshade, VITA Zahnfabrik, Bad Säckingen, Germany). The test groups were analogue loaded as described above. The spectrophotometer was calibrated prior to collecting colour data from the test specimens. Measurements were performed at ten different positions of each test specimen before and after storing in the test liquid for the defined reaction time of the investigated disinfection agents (Figure
Adapter with sensor tip (Spectrophotometer VITA Easyshade, VITA Zahnfabrik, Bad Säckingen, Germany) measuring an Orthocryl green test specimen.
For standardized positioning of the spectrophotometer, a 1.5 mm thick transparent suck-down template was fabricated (Erkodur, Erkodent GmbH, Pfalzgrafenweiler, Germany). A white paper board was used as the background for the specimens during the measurement process to guarantee standardized conditions.
Means were calculated, and data were evaluated statistically. Statistical analyses were performed using SPSS 17.0 for Windows (SPSS Inc., Chicago, IL, U.S.A.). Normal distribution of the data was attested (Kolmogorov-Smirnov-test) and significant differences between the groups were detected using the Student’s t-test and the single factor variance analysis (ANOVA) was used. The level of significance was set to 5% (p≤0.05). Significant results were analysed using the post-hoc test (Bonferroni).
Results are given as means ± standard deviation (Figure
Modification of the elastic modulus of the denture base resins according to the disinfection agents. Results are given as means ± standard deviation.
Results are given as means ± standard deviation (Figure
Modification of the flexural strength of the denture base resins according to the disinfection agents. Results are given as means ± standard deviation.
Results are given as means ± standard deviation (Figure
Modification of the macro hardness of the denture base resins according to the disinfection agents. Results are given as means ± standard deviation.
Results are given as means ± standard deviation (Figure
Modification of the micro hardness of the denture base resins according to the disinfection agents. Results are given as means ± standard deviation.
Results are given as means ± standard deviation (Figure
Modification of the average roughness of the denture base resins according to the disinfection agents. Results are given as means ± standard deviation.
Results are given as means ± standard deviation (Figure
Modification of the colour change of the denture base resins according to the disinfection agents. Results are given as means ± standard deviation.
In the present
Single use disinfection of orthodontic acrylics had no significant effect on elastic modulus and flexural strength (Figures
Regarding the results of the flexural strength measurements, the outcome of this investigation is hardly comparable to other findings in literature. Therefore, the proof stress limit
In contrast to the results of the elastic modulus and flexural strength, the material-related analysis of the macro hardness, micro hardness, and average roughness of the investigated orthodontic acrylics performed partly significant structural changes after single-shot disinfection (Figures
However, it has to be considered, if the measured effects on the test specimens are results of the disinfecting process or whether the material related-properties of the cold-curing orthodontic acrylics are responsible for these findings [
All investigated disinfecting agents performed significant changes of the macro hardness on the following orthodontic acrylics: Orthocryl colourless, green and Forestacryl colourless compared to the dry storage control group (Figure
The used disinfecting agents performed significant changes of the micro hardness on the orthodontic acrylics Orthocryl colourless and Forestacryl colourless compared to the values of the dry storage control group (Figure
The high standard deviation of the micro hardness results should be critically considered. It is shown that the single values were subjected to strong fluctuations (Figure
Taken together, the increase of the macro and micro hardness induces an embrittlement of the orthodontic acrylics. This leads to enhanced fracture susceptibility. However, a decrease of the macro and micro hardness stands for a softening of orthodontic acrylics that may cause changes of the shape [
At the beginning of the measurements of the average roughness, Forestacryl had a higher value (0.89 ± 0.43
The data analysis of the colour measurement shows that the disinfection of the four investigated orthodontic acrylics did not perform any significant colour changes (Figure
In summary, some orthodontic acrylics disinfection caused significant changes of the measured parameters. Changes were specific for the applied disinfectant and the tested orthodontic acrylic [
In principle it is difficult to estimate how often a denture is disinfected during its clinical service time. Dental prostheses have to be disinfected for the first time before delivery [
Thus, in this study the influence of single use disinfection was tested. In general, disinfecting agents should carry a wide application range. The disinfecting agent Impresept is recommended by the manufacturer for the disinfection of dental impression materials and is certified as surface disinfectant [
The objective of all infection control procedures is to prevent transmission of infections between treated patients, orthodontic staff, and orthodontic technicians. Removable orthodontic appliances are subjected to enormous stresses during clinical treatment. Even while integrating and excluding the appliances, additional stress of orthodontic acrylics will proceed. Therefore, it is essential that orthodontic acrylics maintain the elastic modulus and flexural strength after multiple disinfecting processes. In some orthodontic acrylics disinfection caused significant changes of the measured parameters. Changes were specific for the applied disinfectant and the tested acrylic. Thus, from manufacturers of orthodontic resins recommendations for appropriate disinfectants would be desirable.
A limitation of this present
The data used to support the findings of this study may be released upon application to the Department of Prosthodontics, Martin-Luther-University Halle-Wittenberg, that can be contacted at Dr. Arne Boeckler, Department of Prosthodontics, University Hospital Halle, Magdeburger Straße 12, 06112 Halle, Germany.
The present study was performed as part of the employment of the authors of the Department of Prosthodontics, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany.
The authors declare that they have no conflicts of interest.
The authors thank Dr. Seth Bozarth, DMD, Tufts University, Boston, and Dr. Jamie N. Amir, DDS, Ocala, Florida, USA for their technical support and for their comments regarding the manuscript.