Panagiota N. Eleni

The effect of artificial accelerated weathering on the mechanical properties of maxillofacial polymers PDMS and CPE

The effect of UVA-UVB irradiation on the mechanical properties of three different industrial types of polydimethylsiloxane and chlorinated polyethylene samples, used in maxillofacial prostheses, was investigated in this study. Mechanical properties and thermal analysis are commonly used to determine the structural changes and mechanical strength. An aging chamber was used in order to simulate the solar radiation and assess natural aging. Compression and tensile tests were conducted on a Zwick testing machine. Durometer Shore A hardness measurements were carried out in a CV digital Shore A durometer according to ASTM D 2240. Glass transition temperature was evaluated with a differential scanning calorimeter. Simple mathematical models were developed to correlate the measured properties with irradiation time. The effect of UVA-UVB irradiation on compressive behavior affected model parameters. Significant deterioration seems to occur due to irradiation in samples.

Effects of outdoor weathering on facial prosthetic elastomers

Physical weathering is usually responsible for the degradation of maxillofacial prosthetic elastomers and the replacement of prostheses. The purpose of this study was to investigate the effects of outdoor weathering on the physical properties of four nonpigmented facial prosthetics after 1 year of exposure. In addition, simple mathematical models were developed to correlate the measured properties with irradiation time, including parameters with physical meaning. Three different medical-grade polydimethyl siloxanes (PDMSs) and an experimental chlorinated polyethylene (CPE) were examined in this study. The samples were exposed to solar radiation for 1 year in Athens, Greece. Mechanical tests (compression and tensile) were performed using universal-type testing machine, and hardness measurements were performed with a durometer (Shore A). Thermal tests were also performed with a differential scanning calorimeter. Simple mathematical models were developed to describe the examined properties. Changes observed in the properties of examined materials, before and after the exposure, reflected the effect of weathering. More specifically, two of the silicone prosthetics (Elastomer 42, TechSIL 25) seemed to become harder and more brittle, different from the other silicone (M511) sample and the CPE sample, which became softer and more ductile. Moreover mathematical models correlate the measured properties with irradiation time, and their constants indicate that duration of exposure seems to increase the degradation. Significant changes in the mechanical and thermal properties of the examined materials were observed as a result of outdoor weathering. The effect of weathering on samples’ properties was introduced through its effect on the mathematical models’ parameters.

Effect of different disinfecting procedures on the hardness and color stability of two maxillofacial elastomers over time

Objective: Disinfection procedures often cause deterioration in a maxillofacial prosthesis. Color and hardness alterations could lead to a replacement of the prosthesis. Material and Methods: An experimental chlorinated polyethylene (CPE) and a commercial polydimethyl siloxane (PDMS) sample were treated with four different disinfection procedures for a period which simulates 1 year of clinical service. The applied disinfection procedures included microwave exposure and immersion in three solutions, sodium hypochlorite, neutral soap and a commercial disinfecting soap. Shore A hardness (ΔΗ) and color differences (ΔΕ) were determined before and after each procedure. All data were analyzed by Two Way Analysis of Variance (ANOVA) and Tukeys post hoc tests at a level of α=0.05. Results: The samples presented significant alterations in color and hardness after the different disinfection treatments. The color differences (ΔΕ) were at least eye detectable in all cases and clinically unacceptable in most of the cases, with values ranging from 1.51 to 4.15 and from 1.54 to 5.92 for the PDMS and CPE material, respectively. Hardness was decreased after all the disinfection procedures in the PDMS, while for the CPE, a decrement was observed after disinfection with sodium hypochlorite and neutral soap and an increment after microwave exposure and the disinfection with a commercial antimicrobial agent. The PDMS samples presented greater alterations in color and hardness after disinfection with sodium hypochlorite solution, while the microwave exposure caused negligible effects. The CPE samples were affected most after disinfection when treated with neutral soap, and more slightly when disinfected with sodium hypochlorite solution. Conclusions: The disinfection procedures caused alterations in color and hardness of the examined materials. The most suitable disinfection procedure for the PDMS material is microwave exposure, while disinfection with sodium hypochlorite solution is not recommended. The CPE material is suggested to be disinfected with sodium hypochlorite solution and the use of neutral soap is not recommended. Comparing the two materials, the PDMS material is most color stable, while the CPE material presented fewer changes in hardness.

Effect of time passage on some physical properties of silicone maxillofacial elastomers.

Objectives: Changes in color and other physical properties of silicone facial prosthesis are the main reasons for its replacement. The purpose of this study was to investigate the effect of time passage on some physical properties such as tensile strength, modulus of elasticity, elongation at break, tear strength, hardness, color stability, and contrast ratio (CR) of 2 silicone facial elastomers after being sealed in glass containers and kept in the dark for 1 year. Materials and Methods: Specimens from 2 silicone elastomers (Silasto 30 and Premium 2) were made and stored in the dark. Tensile and tear strength tests were conducted according to International Organization for Standardization specification nos. 37 and 39, respectively, in a universal testing machine. Shore A hardness was measured according to the American Society for Testing Materials specification D 2240. Color changes (&Dgr;&Egr;*) were determined in the CIE L*a*b* system using a tristimulus colorimeter, and CR also was calculated. Data were analyzed by paired and unpaired t-tests at a significance level of &agr; = 0.05. Results: Elongation at break, modulus of elasticity, and hardness were significantly changed, whereas changes in CR were observed only in 1 of the 2 elastomers. Tensile and tear strengths were not significantly changed for both of them. Within the limitations of this study, color changes (&Dgr;&Egr;) were unacceptable. Conclusions: Most of the physical properties studied were significantly affected because of time passage. Mechanical and physical properties of silicone maxillofacial elastomers can be changed with time passage (natural aging in the dark). The average time of replacing a facial prostheses is 6 to 18 months; thus, it is important that the findings of this study covered a period of 12 months. Time passage seems to be a critical factor contributing to the overall deterioration of a silicone maxillofacial elastomer.

Thermal, textural, and physicochemical analysis of corn extrudates enriched with broccoli or olive paste

The growing consumers’ demand for healthier snacks is of high importance and is driving research and industry towards developing novel ready to-eat expanded products. Thus, it would be interesting to enrich these products with additives that possibly lead to highly nutrient products. In the present study, extruded snacks based on corn flour enriched with broccoli or olive paste were developed and studied. Although the addition of broccoli or olive paste in extruded snacks can improve their nutritional properties, the final properties of these products must also be considered. Textural analysis (compression tests), thermal analysis (glass transition temperature), and moisture sorption measurements (sorption isotherms) were performed. A Guggenheim–Anderson–de Boer model has been applied to describe moisture sorption isotherms. Moreover, simple mathematical models were developed in order to correlate textural properties (maximum stress, maximum strain, elasticity parameter, number of cracks) with the process conditions during the extrusion (screw speed, temperature) and the raw materials’ characteristics (moisture content, concentration of broccoli or olive paste). Regression analysis was used to estimate mathematical models’ parameters. The influence of process conditions and raw materials’ characteristics on the measured properties of corn-based snacks enriched with broccoli or olive paste was presented based on the alterations of the estimated parameters.

Material properties of a maxillofacial chlorinated polyethylene elastomer stored in simulated skin secretions.

STATEMENT OF PROBLEM Facial prostheses deteriorate in a service environment primary due to exposition to various environmental factors, including sebaceous oils (sebum) and perspiration. PURPOSE This study investigated the physical properties of an experimental, facial prosthetic after immersion for 6 months in simulated sebum, and perspiration at 37 degrees C. MATERIAL AND METHODS Chlorinated polyethylene (CPE) specimens were immersed in simulated perspiration as well as in sebum. Compression tests were conducted on a Zwick testing machine. Shore A hardness measurements were carried out in a CV digital Shore A durometer. Melting and glass transition temperatures were evaluated with a differential scanning calorimeter. Weight changes were measured and color changes were determined in the CIE LAB system using a MiniScan XE spectrophotometer. Simple mathematical models were developed to correlate the measured properties with immersion time. The data were also subjected to analyses of variance (ANOVA) and the Tukey multiple range tests at a level of alpha = 0.05. RESULTS Specimens immersed in perspiration became harder due to facilitation of the propagation of cross-linking reaction that probably occurred during aging of the CPE samples. Some weight increase was observed for the specimens immersed into the aqueous solutions, whereas for those immersed in sebum, weight loss was recorded, probably because of extraction of some compounds. The color change was higher for the specimens immersed in sebum than that corresponding to simulated perspiration. CONCLUSIONS The chlorinated polyethylene specimens aged for a period, which simulates 1.5 years of clinical service1, showed significant deformations in their physical properties.

Dynamic mechanical thermal analysis of maxillofacial prosthetic elastomers: the effect of different disinfecting aging procedures.

AbstractIn this study, dynamic mechanical thermal analysis was used to evaluate the changes that occurred in maxillofacial elastomers subjected to different disinfecting regimens. A commercial polydimethyl siloxane (PDMS) and an experimental chlorinated polyethylene (CPE) were treated with different disinfection procedures for a period that simulates 1 year of clinical service: microwave exposure (D1), hypochlorite solution (D2), neutral soap (D3), and a commercial disinfecting solution (D4). A fifth group was kept in dark storage as control. Dynamic mechanical thermal analysis tests operated in a fixed frequency (1 Hz) over a range of temperatures (−130°C to 20°C for PDMS, −60°C to 120°C for CPE). Loss modulus (G″), storage modulus (G′), and loss factor (tan&dgr;) were recorded as a function of temperature. The obtained glass transition temperature (Tg) values were subjected to statistical analysis. Dynamic mechanical thermal analysis revealed changes in Tg values for both materials, which reflect the possible changes in their chemical and physical structure, after different disinfection procedures. The PDMS and CPE samples seem to have less dense structure maybe because of chain scission reaction that probably occurred during the disinfection procedures. According to statistical analysis, Tg values presented significant changes from the control samples among the different materials and disinfecting procedures. Microwave exposure and hypochlorite solution affect CPE significantly, whereas PDMS exhibited significant changes after being treated with a commercial antimicrobial agent, concerning changes that occurred in Tg. In all cases, Tg values were decreased compared with the untreated samples, which were stiffer, presenting higher Tg and G′ values.

Effects of storage in simulated skin secretions on mechanical behavior and color of polydimethylsiloxanes elastomers.

Background: Among the deteriorations that occur in maxillofacial prosthesis due to exposure in various environmental factors, sebaceous oils (sebum) and perspiration are also responsible for several alterations. Purpose: Mechanical properties and color changes of 3 different medical-grade polydimethylsiloxanes were investigated in this study (Elastomer 42, Techsil 25, and M511), after immersion for 6 months in simulated sebum and perspiration at 37°C. The purpose of this study was to determine the effects of storage in their physical properties. The null hypothesis investigated was that immersion time did not affect the measured properties. Methods: Polydimethylsiloxane specimens were immersed in simulated perspiration and in sebum. Compression tests were conducted on a Zwick testing machine. Shore A hardness measurements were carried out in a CV digital Shore A durometer. Weight changes were measured, and color changes were determined in the CIELAB system, using a MiniScan XE spectrophotometer. Simple mathematical models were developed to correlate the measured properties with the immersion time. The data were analyzed by analysis of variance and Tukey multiple range test at a level of &agr; = 0.05. Results: Specimens immersed in simulated skin secretions became harder because of facilitation of the propagation of cross-linking reaction that probably occurred during aging of the polydimethylsiloxane samples, except for Elastomer 42, which seems to become more soft and ductile after immersed in sebum. Some weight increase was observed for the specimens immersed into the aqueous solutions, whereas for those immersed in sebum, weight loss was recorded, probably because of extraction of some compounds. The color change was higher for the specimens immersed in sebum than that corresponding to simulated perspiration. According to statistical analysis, all measured properties changed significantly after immersion in simulated perspiration and in sebum. Moreover, mathematical models reveal major alterations as well, which were introduced through their constants. Thus, the hypothesis investigated was rejected. Conclusions: Significant changes were observed in all the examined elastomers. The elastomers were aged for a period, which simulates 1.5 years of clinical service. Within the limitation of this study, concerning the mechanical behavior and mostly the color changes, sebum and perspiration greatly affect the examined elastomers.