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Biomedical subjects

G L Polyzois

Publications and source records attributed to G L Polyzois.

At least 19 recordsLinked to original sources
PubMed2001

Influence of curing method, sealer, and water storage on the hardness of a soft lining material over time.

PURPOSE: The purpose of this study was to determine the hardness of plasticized acrylic resin soft lining materials over time when curing procedures were modified and when surface sealers were either used or omitted. MATERIALS AND METHODS: A chairside plasticized acrylic resin material and a heat processed plasticized resin material were made into disks 40 mm in diameter and 10 mm in thickness. Materials were cured by processing at an elevated temperature or at mouth temperature. Five samples were used with each processing method. Half of all samples were treated with a surface sealer, whereas the other samples received no surface treatment. After processing, the samples were immersed in 37 degrees C water for a total time of 1 year. Specimens were tested to determine hardness on a monthly basis. Testing was accomplished using a Shore A durometer. RESULTS: Hardness testing showed differences relative to material and to time after processing. The heat-processed plasticized resin material showed significantly higher Shore A hardness values than the chairside over the entire experimental period (p <.01). Increased hardness was seen for all materials over time, but this was more pronounced with plasticized acrylic resin in which the hardness increased from 28.4% to 115.8% depending on processing method and surface treatment. Surface treatment showed significant softening only when the samples were cured at simulated mouth temperature (p <.05). CONCLUSIONS: Processing method and time after processing have an effect on surface hardness of the tested materials, but neither of these effects is as profound as the initial choice of material. J Prosthodont 2001;10:42-45.

Acrylic Resins↗
PubMed2000

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.

Absorption↗
PubMed2000

Irritation test of tissue adhesives for facial prostheses.

STATEMENT OF PROBLEM: Adhesives are commonly used to improve the retention of a facial prosthesis to the skin. Although no requirement exists for facial prosthetic adhesives, an adhesive should be nonirritating and nontoxic. PURPOSE: This study assessed the irritative potential of facial prosthetic adhesives by using an in vitro technique for detection of eye-irritating chemicals. MATERIAL AND METHODS: Ten adhesives were evaluated by the hens egg test chorioallantoic membrane method. Adhesives were applied to the chorioallantoic membrane in fertilized hen eggs, and the membrane examined by a photomacroscope for injury to the blood vessels. The average irritation score was calculated from the recorded times for the debut of hemorrhage, lysis, and coagulation, and the products were classified as being non, slight, moderate, or strong irritants, based on the irritation score. RESULTS: The predominant injury to the membrane was coagulation of blood vessels, and the exposure time needed to initiate the reaction was dependent on the composition of the product. Four products were classified as strong irritants, 1 as moderate, and the remaining 5 as slight or nonirritant. CONCLUSION: On the basis of a test for eye irritation, the irritant potential of tissue adhesives varied from non to severe. The most severe reactions were mainly seen in products containing the solvent ethyl acetate.

Acetates↗
PubMed1999

Color stability of facial silicone prosthetic polymers after outdoor weathering.

STATEMENT OF PROBLEM: Color deterioration of silicone prosthetic elastomers affects the life expectancy of facial prostheses in a service environment. PURPOSE: This study investigated the color stability of 3 nonpigmented silicone elastomers (Silskin 2000, Elastosil M3500, Ideal) exposed to outdoor weathering for 1 year. MATERIAL AND METHODS: A tristimulus colorimeter was used to evaluate the color differences (DeltaE*) of the silicone elastomers every 2 months. Ten disk-shaped specimens for each material were tested. Data were analyzed with a repeated measures ANOVA and Student-Newman-Keuls test at a significance level of alpha = .05. RESULTS: All silicone elastomers showed visually detectable, mean color differences (DeltaE* > 2.0), that ranged from 2.13 to 3.98. Silskin 2000 showed greater color differences (P <.05) compared with Elastosil M3500 and Ideal, which showed similar behavior (P >.05). CONCLUSION: Outdoor exposure of silicone facial elastomers for 1 year resulted in visually detectable color differences. Duration of exposure and silicone elastomer were significant factors that affected color stability. Silskin 2000 was significantly less color stable than Elastosil M3500 and Ideal, which were not statistically significantly different from each other.

Analysis of Variance↗
PubMed1999

Wettability of silicone rubber maxillofacial prosthetic materials.

STATEMENT OF PROBLEM: Maxillofacial prosthetic materials that contact skin or mucosa should have good wettability. A material that is easily wetted will form a superior lubricating layer between the supporting tissues and, thus, reduce friction and patient discomfort. The surface energy of a maxillofacial prosthetic material will give an indication of the amount of energy available for adhesion and of the susceptibility of the material to bacterial adhesion. PURPOSE: This study evaluated the wettability and surface energies of a range of commercially available silicone rubber maxillofacial prosthetic materials. MATERIAL AND METHODS: Contact angles and surface energies were measured by using a dynamic contact angle measuring technique. Four commonly used silicone maxillofacial materials were tested and their properties compared with those of an acrylic resin denture base material and a widely used denture soft lining material. RESULTS: There were no significant differences in the wettability of the silicone rubber materials. All materials were significantly less wetted than the denture acrylic resin material. There were no significant differences in the surface energies of the silicone rubber materials, but all were significantly lower than denture acrylic resin material. CONCLUSIONS: The Cahn dynamic contact angle analyzer was a quick and reproducible method for determining the contact angles and surface energies of maxillofacial materials. Further work is needed to improve the wettability of silicone rubber materials used for maxillofacial prostheses, thus, reducing their potential to produce friction with tissues.

Acrylic Resins↗
PubMed1998

Color stability of provisional resin restorative materials.

STATEMENT OF PROBLEM: Use of temporary crowns and fixed partial dentures is especially relevant when the treatment plan requires restorations for long interim periods, and the in-service discoloration of provisional restorative materials is a major drawback. PURPOSE: This study evaluated the discoloration effect of coffee and tea on some materials that are commonly used in the fabrication of provisional restorations. MATERIAL AND METHODS: Six commercially available provisional resins (Jet, Caulk TBR, Protemp Garant, Luxatemp Solar, Provipont DC and SR-Ivocron-PE) were evaluated after 1 day, 7 days, and 30 days of immersion in various staining solutions. Color measurements were obtained by using a Dr Lange Micro Color tristimulus colorimeter and color differences (delta E*) were estimated. RESULTS: The 2 chemically activated resins (Jet and Caulk TBR) and the heat-cured resin (SR-Ivocron PE) exhibited the least color changes, whereas the Provipont-DC resin was the least color stable. After immersion for 30 days, the combination with the coffee solution resulted in unacceptable discoloration for all the tested materials. CONCLUSIONS: Provisional restorative materials, staining solutions, and immersion time were significant factors that affected color stability. After immersion for 7 days, all materials showed observable color changes. The composite-based materials, especially light-curing composites, were the least color stable. The coffee solution exhibited more staining capacity than the tea solution.

Analysis of Variance↗
PubMed1998

Physicomechanical and cytotoxic properties of room temperature vulcanizing silicone prosthetic elastomers.

The physicomechanical and cytotoxic properties of two newly introduced room temperature vulcanizing (RTV) silicone prosthetic elastomers, Ideal and Silskin 2000, were investigated. Another RTV silicone, Elastosil M3500, was also investigated as a potential facial material. The in vitro cytotoxicity was assessed with the agar diffusion test and mouse fibroblast cells (L929). The properties investigated were tensile strength, percentage elongation, modulus, tear strength, hardness, and color changes (deltaE*). The properties tested were selected because of their clinical significance in fabricating facial prostheses. The results indicate that Elastosil M3500 has a better combination of high tear strength, elongation at break, and low hardness than Ideal and Silskin 2000. All materials demonstrated a low cytotoxic profile. Elastosil M3500 warrants further attention with clinical trials.

Agar↗
PubMed1996

Acrylic resin denture repair with adhesive resin and metal wires: effects on strength parameters.

The fracture of acrylic resin dentures is an unresolved problem in prosthodontics. In this study one brand of denture base acrylic resin was used to make specimens in the form of strips and maxillary denture bases. The specimens were cut and repaired with one type of an autopolymerizing adhesive resin and metal wires. The mechanical properties of the repaired specimens were measured, and the efficiency of each method was evaluated. The statistical results of this study revealed that geometric characteristics of a maxillary denture combined with the shape and pretreatment of reinforcement were the controlling factors for the overall mechanical behavior. Furthermore this study revealed that data with clinical significance can only be obtained by testing specimens similar to the original items used in dental practice.

Acrylic Resins↗
PubMed1996

A comparison of microwave and dry-heat curing methods on the bond strength of silicone facial materials applied to acrylic resin.

PURPOSE: This study compared two curing methods (microwave irradiation and dry heat) on the tensile bond strength of silicone facial materials to cured acrylic resin. The facial materials studied were Mollomed, Silskin II, MDX4-4210, and A-2186. MATERIALS AND METHODS: The samples were processed with microwaves for 13 minutes at 90 W plus 2 minutes at 500 W and dry heat for 3 hours at 100 degrees C to cured acrylic resin. Facial materials 3-mm thick were processed between two half-dumbbells of acrylic resin. The bonding surfaces were treated with a primer. The samples were placed in tension until failure. RESULTS: The results showed that the bond strength was affected by the type of silicone material and not by the curing methods used. CONCLUSIONS: Mollomed had the highest bond strength of all materials tested. MDX4-4210 and A-2186 showed the lowest, and Silskin II had intermediate bond strength. Microwave irradiation has the potential of saving time, energy, and resources during the fabrication of facial prostheses, but further laboratory studies and clinical trials are indicated.

Acrylic Resins↗
PubMed1995

Evaluation of a new silicone elastomer for maxillofacial prostheses.

PURPOSE: Although numerous advances in maxillofacial materials have been made in the past several years, the need for improvement continues. Currently, the most widely used materials are the silicones, especially the room temperature-vulcanizing type. This study compared the physical properties of a new silicone material Cosmesil K10 (Cosmedica Ltd, Cardiff, United Kingdom) with those of MDX4-4210 (Dow Corning Corporation, Midland, MI), a popular material for maxillofacial prostheses. MATERIALS AND METHODS: The properties that were investigated were tensile strength, modulus at 100% elongation, percentage of elongation, tear strength, and hardness. The properties tested were selected because of their clinical significance for fabricating maxillofacial prostheses. Tensile strength and elongation were measured with a Monsanto Tensometer (Monsanto Ltd, Swindon, England) and dumbell-shaped specimens according to the International Organization for Standardization (ISO) specification no. 37. The tear test was performed on the Monsanto machine with unnicked 90 degree angle-shaped specimen following the ISO specification no. 34. The type A Shore durometer was used to measure hardness on specimens 25 x 25 x 10 mm according to the American Society for Testing Materials specification no. D2240. RESULTS: The results showed that MDX4-4210 had a greater tensile strength and modulus (P = .0002; P = .0015). No significant difference (P = .1986) was found for the percentage of elongation between MDX4-4210 and Cosmesil K10. Cosmesil K10 had a greater tear strength and was slightly harder (P = .0022; P = .0421) than MDX4-4210. CONCLUSIONS: Cosmesil K10 showed physical properties similar to those of MDX4-4210. An improvement in the predictability of the mechanical behavior of Cosmesil K10 would further enhance the value of the material.

Elasticity↗
PubMed1995

Using an existing orbital prosthesis in the construction of a new one.

A procedure for fabrication of a new orbital prosthesis using an existing one and keeping its acceptable characteristics is described. The procedure saves time without depriving the patient of the existing prosthesis for a long period and can be applied in the remaking of other types of facial prostheses.

Eye, Artificial↗
PubMed1995

Biological testing of dental materials: development of national and international standards.

Testing of dental materials helps to ensure that they are of satisfactory quality. Most standardized testing programs have focused on the physical, chemical, and mechanical properties of the materials, and started at the National Bureau of Standards, USA, in 1919. The need for biological evaluation of dental materials became evident after some material-related adverse incidents. The first document concerning standardized testing of the biological properties of dental materials was published by the American Dental Association in 1972. During the last twenty-five years, increased attention has been focused on the evaluation of biological properties by standardized testing. The development of standards concerning biological testing of dental materials since 1972 at the national and international level is described.

American Dental Association↗
PubMed1995

Repair strength of denture base resins using various methods.

The object of this study was to measure the repair strength of denture base resins repaired using, (a) standard heat activated polymerising resin, (b) a denture base resin especially formulated for microwave-activated polymerisation, and (c) an autopolymerising resin. Comparisons were made between conventional water bath and microwave curing and autopolymerised resin repairs, using transverse bend and impact tests. Repairs with the two heat-activated denture base resins were carried out using conventional dental flasking procedures, whereas autopolymerised resin repairs were carried out in open gypsum moulds. The results indicate that the transverse strength, and impact resistance of the resin specimens repaired with microwave irradiation were generally superior to specimens repaired by using a water bath curing cycle or the use of an autopolymerising resin.

Acrylic Resins↗
PubMed1995

Reinforcement of denture acrylic resin: the effect of metal inserts and denture resin type on fracture resistance.

This study investigated the fracture load and deflection of acrylic resin specimens with different types of metal inserts. A metal adhesive denture resin (Meta Dent) and a conventional denture resin (Meliodent) were used with round metal, braided wires and mesh as inserts. There were eight groups and each group contained ten specimens. Each specimen was broken on a Monsanto testing machine using a three point load after storage in water at 37 degrees C for 48 hours. The results indicated that metal inserts enhanced the fracture resistance of both denture resins. No significant differences were found between the metal adhesive and conventional denture resin.

Acrylic Resins↗
PubMed1994

Repair of denture base resins using visible light-cured materials.

Specimens of denture base resins were repaired with autopolymerizing and visible light-cured (VLC) repair materials. Flexural properties were measured and revealed that the highest strength and toughness of joint are obtained by the autopolymerizing repair material and are independent on the base resin. The VLC materials exhibited a lower repair strength (22% to 58%) and toughness (9% to 33%) than those of the autopolymerizing resin. No interaction between base and repair material was detected, which was attributed to poor adhesive bonding created at the interface.

Acrylic Resins↗
PubMed1994

An assessment of the physical properties and biocompatibility of three silicone elastomers.

The physical properties of two room-temperature vulcanizing (RTV) silicones, A-2186 and Silbione 71556, and one high-temperature vulcanizing (HTV) material, Mollomed, were compared. The potential cytotoxicity of the silicone materials was assessed with the agarose overlay test. The properties that were investigated were tensile strength, percentage elongation, modulus, permanent set, tear strength, and hardness. The properties tested were selected because of their clinical significance for fabricating facial prostheses. The results of this study indicate that the A-2186 material has a better combination of high tear strength and elongation at break with a softer surface compared with Mollomed silicone, and Silbione 71556 silicone proved to be the weakest material. All materials demonstrated absence of cytotoxicity in the cell culture tests.

Analysis of Variance↗
PubMed1994

Effects of RTC-silicone maxillofacial prosthetic elastomers on cell cultures.

The use of a wide variety of materials in the construction of maxillofacial prostheses makes biocompatibility testing a necessity. However, the dental literature contains few reports of biocompatibility testing of maxillofacial prosthetic materials. The cytotoxic profiles of five room-temperature cross-linking (RTC)-silicone elastomers were investigated by means of two in vitro cell culture techniques. Mouse fibroblast cells (L929) were used, and the results indicated that RTC-silicone elastomers adversely affected cells in culture and that storage of samples for 1 week in saline solution did not alter this effect. Clinical follow-up of patients wearing prostheses made of these silicone materials is warranted to evaluate host reactions in long-term contact with human mucous membrane and skin tissue.

Animals↗