Mary Frangou

Physical properties of a silicone prosthetic elastomer stored in simulated skin secretions

STATEMENT OF PROBLEM Facial prostheses worn over an extended time are exposed to various environmental factors, including sebaceous oils (sebum) and perspiration. PURPOSE This study investigated the physical properties of tensile strength and modulus, elongation, tear strength, hardness, weight, and color change, of a silicone facial elastomer after immersion for 6 months in simulated sebum and perspiration at 37 degrees C. MATERIAL AND METHODS Specimens made of Episil silicone elastomer were immersed in simulated alkaline or acidic perspiration as well as in sebum. Tensile and tear tests were conducted according to ISO specifications no. 37 and 39, respectively, in a Monsanto testing machine. Shore A hardness measurements were run according to ASTM D 2240. Weight changes were followed at 5, 15, 30, and 180 days, and color changes were determined in the CIE LAB system using a tristimulus colorimeter. RESULTS An improvement of mechanical properties for specimens immersed in acidic perspiration was attributed to facilitation of the propagation of cross-linking reaction during aging of the silicone samples. Some weight increase was observed for the specimens immersed into the aqueous solution, whereas for those immersed in sebum, weight loss was recorded, probably because of extraction of some compounds. In this latter case, the color change was lower than that corresponding to simulated perspiration. CONCLUSION The silicone specimens aged for a period, which simulates 1.5 years of clinical service, showed minimal changes with respect to the properties studied.

The effect of immersion cleansers on gloss, colour and sorption of acetal denture base material

OBJECTIVE To study the effect of peroxide and hypochlorite cleansers on gloss, colour and sorption of acetal denture resins. MATERIALS AND METHODS Pink acetal and thermoplastic acrylic resins were evaluated. Thirty-five specimens 39 × 39× 1.8 mm of each resin were prepared. Each group of specimens (n = 7) was then immersed into cleansers for 100 days. Group I immersed in tap water, Group II in Corega Extradent for 5 min, Group III in Corega Extradent for 8 h, Group IV in NitrAdine™ Seniors for 15 min and Group V in NaOCl 5.25%. Gloss, colour and weight measurements were taken initially and after 100 days. Data subjected to two-way anova and Tukeys test at α = 0.05. RESULTS Acrylic resin showed reductions of glossiness from -5 to -15 and acetal from -0.2 to -6. Colour changes (ΔΕ*) ranged from 2.64 to 7.64 for acrylic and 2.77 to 26.54 for acetal resin. Sorption for acrylic ranged from 11.64 to 17.06 μg/mm(3) and 9.18 to 24.79 μg/mm(3) for acetal resin. The results of (ΔΕ*) and sorption showed an interaction between denture resins and cleansers. CONCLUSIONS The gloss of acetal resin was less affected by water, peroxides and NaOCl 5.25% compared with acrylic resin. Acetal resin showed clinically acceptable (ΔΕ*) whereas acrylic resin unacceptable ones for water and peroxide solutions. The immersion of acetal resin in NaOCl 5.25% showed clinically unacceptable (ΔΕ*) and higher sorption and should be avoided or should be managed with care.

Effect of immersion cleansing in color stability and hardness of soft denture reliners.

AbstractHygienic care of removable prostheses is important, and denture cleansers selected must be efficient and maintain the physicomechanical properties of soft reliners. Microwave energy has been reported to increase the sanitation effectiveness of denture cleansers. The purpose of the study was to evaluate hardness and color stability of some visible light polymerized and autopolymerized soft reliners after exposure in different denture-cleansing treatments. Six soft denture reliners (2 autopolymerized silicones, 1 autopolymerized acrylic, and 3 visible light polymerized ones) were exposed to 4 cleansing treatments (Corega Whitening, Polident 5-Minute, Corega Whitening + microwaving, Polident 5-Minute + microwaving). Hardness was measured with a Shore A durometer, and color changes were evaluated by a tristimulus colorimeter. The results were subjected to 2-way analysis of variance and Scheffé test for post hoc comparisons at a confidence level of &agr; = 0.05. Sofreliner showed the smallest hardness change, and LightLiner the greatest. Versasoft and Sofreliner seem to have the lowest color change for every cleansing treatment examined, whereas LightLiner and Eversoft presented the greatest. Silicone-based materials demonstrated the smallest changes in both hardness and color, either when using water or with any of the other cleansing treatments.

Evaluation of the frequency and temperature dependence of the dynamic mechanical properties of acetal resins

The purpose of this study was to evaluate and compare the dynamic mechanical properties of two acetal resins (different colored samples of the same resin), an autopolymerized reline resin, and a heat-polymerized denture base resin. Measurements were obtained in two conditions, the frequency- and temperature-dependent conditions, using a dynamic viscoelastometer. The acetal resins exhibited lower loss tangent values than the autopolymerized reline resin and heat-polymerized denture base resin. With respect to temperature dependence, all of the materials displayed stable viscoelastic properties in the temperature range found in the oral environment. The acetal resin had both a glass transition temperature and a melting point, whereas the autopolymerized reline resin and heat-polymerized denture base resin had only glass transition temperatures. The results of this study suggest that acetal resin displays elastic properties when compared with the other 2 materials.