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Biomedical subjects

G L Polyzois

Publications and source records attributed to G L Polyzois.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1994

In vitro evaluation of dental materials.

Biocompatibility has been described as the ability of a material to perform with an appropriate host response in a specific application. Appropriate host response means no (or a tolerable) adverse reaction of a living system to the presence of such a material. An adverse reaction may be due to the toxicity of a dental material. Therefore toxicity may be regarded as one reason for nonbiocompatibility of a dental material. The toxicity of a dental material can be evaluated by in vitro tests, animal experiments and clinical trials. There exists a variety of different in vitro test methods. The most widely used biological systems for toxicity screening of dental materials are cell cultures. Cell cultures for toxicity screening of dental materials are valuable tools for understanding their biological behavior, if the limitations of the methods are taken into consideration, especially concerning the interpretation of the results. Further research should concentrate on better simulations of the in vivo situation in cell cultures. In this review the applications of various cell culture methods to evaluate the cytotoxicity of a wide range of dental materials, e.g. metals, alloys, polymers and cements, are described.

Animals↗
PubMed1993

Some physical properties of an improved facial elastomer: a comparative study.

An attempt was made to evaluate some properties of clinical importance of a new facial elastomer, Cosmesil HC2. A comparative study versus Silskin II and Cosmesil SM4 was also carried out and took into account the effect of weathering after exposure to ultraviolet radiation. The results showed that Cosmesil HC2 is a resilient material and yet displays good tensile characteristics. The results also showed that weathering does not significantly affect Cosmesil HC2 elastomer's tear strength. The overall effect of irradiation was moderate in all materials tested.

Chemical Phenomena↗
PubMed1993

Tensile bond strength of maxillofacial adhesives.

A common technique for fixation of facial prostheses is the use of skin adhesives. The present study compared the tensile bond strength of five RTV-silicone elastomers used with four different skin adhesives to human skin. The elastomers were: Silskin II, MDX4-4210, Cosmesil, Cosmesil HC2, and RS 330 T-RTV. The adhesives were: Dow Corning 355 medical adhesive, PSA 1, Daro, and 9874 3M double-coated medical tape. The RTV silicones were cured as described by the manufacturer, fixed in circular metal holders, and glued to the skin (inner aspect of forearm) with the various adhesives. The specimens were pulled off 20 seconds after fixation by use of a universal testing machine with a crosshead speed of 1 mm/minute. Eight specimens of each silicone and adhesive combination were tested, and a mean bond strength was calculated for each combination and compared by Duncan's multiple range test on a personal computer. Significant differences were observed among the various combinations of silicones and adhesives. Dow Corning 355 adhesive showed the highest bond strength with all materials, and the medical tape had the lowest. Differences between the RTV silicones were also significant. The strongest bond with all adhesives was MDX4-4210 elastomer and the weakest for RS 330 T-RTV elastomer.

Adhesives↗
PubMed1993

Effect of microwave polymerisation on indentation creep, recovery and hardness of acrylic denture base materials.

With the advent of newer methods of activation of the polymerisation of denture base resins, there is a need to compare their physical properties using various modes of activation. Indentation creep, recovery and hardness of denture base resins polymerised either by microwave irradiation or heat were compared. A microwave curing cycle of 3 minutes at 500W was used. The Wallace microhardness tester and an indentation creep test were employed in order to evaluate the denture base resins. Under the experimental conditions of the study the results indicated that indentation creep, recovery and cyclic loading-deloading were similar in the resins polymerised by the two methods. Hardness was either similar or a softer produce was produced by microwave irradiation for two of the resins used. Hardness seems to be more sensitive to residual monomer levels, and for this reason a suitable microwave curing cycle should be employed to optimise all the physical properties.

Acrylic Resins↗
PubMed1993

Bonding of synthetic resin teeth to microwave or heat activated denture base resin.

Bonding between acrylic resin teeth and a denture base material was investigated after microwave and hot water-bath curing. The specimens were tested according to the methods of the International Organisation for Standardisation (ISO 3336-1977 Dentistry-Synthetic Resin Teeth) using a universal testing machine. Superior bonding was found after hot water-bath curing. The generation of more porosities during microwave curing is the most likely explanation for the bond failures in this group. This finding is of clinical importance as the choice of curing method could influence the risk of loosening of acrylic teeth from the denture. No statistically significant difference in the fracture load between the two types of curing was found, which was expected as the load at fracture is not only related to the binding forces but also to factors such as the contact area and the fracture type.

Acrylic Resins↗
PubMed1992

Adhesion properties of resilient lining materials bonded to light-cured denture resins.

This study compared the adhesive strength of three resilient denture lining materials with different chemical compositions when bonded to visible light-cured (VLC) denture base resin. Shear adhesive strength was evaluated using a simple overlap-joint model. Three different bonding agents were used and the effect of water on the bonding strength was evaluated by a series of samples tested after storage for 4 months. The findings showed that all of the lining materials were acceptable for clinical use but that water storage reduced their bond strength to VLC resin.

Acrylic Resins↗
PubMed1992

Light-cured combination obturator prosthesis.

A technique for the fabrication of an open combination (hard-resilient) obturator prosthesis with VLC materials for patients undergoing partially edentulous maxillectomy is described. VLC denture resins and resilient liners are an exciting innovation in prosthodontic treatment and offer the maxillofacial prosthodontist a wider choice of treatment modalities. The technique and the resultant obturator prosthesis have the following advantages: 1. The ease and rapidity of the technique saves time for both the patient and the maxillofacial prosthodontist by introducing the open obturator prosthesis at the earliest opportunity. 2. The combination open obturator prosthesis provides a stable record base for securing jaw relation records. 3. The thickness and resiliency of the obturator prosthesis can be managed more easily. Flexibility and resiliency can be modified by the thickness of the resilient liner or by adding a rigid scaffolding according to the clinical requirements. 4. Prostheses are easy to repair or modify by using increments of VLC hard or resilient materials. 5. The combination VLC obturator prosthesis provides stability, retention, and decreased weight and obduration of residual palatal defects. 6. The technique can be used for partially edentulous or edentulous patients after maxillary resection.

Acrylic Resins↗
PubMed1991

Cephalometrically predicted occlusal plane: implications in removable prosthodontics.

Although the determination of the occlusal plane is crucial in clinical removable prosthodontics, none of the existing methods gives sufficient guidelines for that purpose. The aim of this investigation was to check the hypothesis that the angulation of the occlusal plane is generally related to the skeletal base of the maxillae. Statistical analysis revealed (1) no strong linear correlation (p greater than 0.05) between the following variables: (a) the length of Cook's plane to Cook's occlusal plane angle, (b) the length of the maxillary plane to the maxillary occlusal plane angle, and (c) the Po Na ANS angle to the occlusal Frankfort plane angle; (2) no parallelism between the occlusal and HIP plane with a mean angle of 4.57 degrees, SD 2.57 degrees, and range of 0 to 9.5 degrees; and (3) no correlation between the predicted and clinically determined occlusal planes (r0.267, t1.797, p greater than 0.05).

Adult↗
PubMed1991

Boundary lubrication and maxillofacial prosthetic polydimethylsiloxanes.

Polydimethylsiloxanes exhibit hydrophobic behaviour and poor wettability. These features impose some problems with the clinical performance of the material when used for the construction of intraoral and extraoral facial prostheses. Surface active agents were added to modify the surface energy of the polydimethylsiloxane and contact angle measurements were carried out to observe wetting characteristics. Five siloxane-alkene oxide block copolymers, one organosilicon quaternary ammonium chloride and an epoxyalkyl silane ester were used as surfactants. The best surfactant in terms of permanency and contact angle lowering achieved a value of 24 degrees when added at 10% level compared with 57 degrees for the unmodified silicone. The fairly high viscosity, combined with a comb-like structure, together with the high hydroxyl number of 75 provided the correct balance of permanence and wetting characteristics.

Dimethylpolysiloxanes↗
PubMed1991

Repairs with visible light-curing denture base materials.

Visible light-curing interpenetrating networks are newly developed materials suitable for several dental applications. These materials have several advantages, including versatility and good physicomechanical properties, but also present some weaknesses, such as increased water sorption and poor adhesion to plastic teeth. The suitability of a visible light-curing resin as a repair material, ie, its bending strength, was examined. Results were compared to those obtained with a self-curing acrylic resin. The visible light-curing resin led to repairs with lower strength.

Acrylic Resins↗
PubMed1990

[Two part siloxane, acrylic obturators for edentulous patients].

Patients who have undergone extensive maxillary resection due to malignant tumors, suffer from severe limitation of speech, deglutition and mastication. Loss of structure in the oral cavity not only causes a loss of function but can cause a great psychological and aesthetic change. One of the most difficult prosthodontic procedures is to construct a functional obturator prosthesis. This paper describes a method for the construction of prostheses which incorporates a removable flexible obturator. This technique overcomes the anatomical problems which limit conventional restoration and provides dentures which are retentive and stable in function and comfortable for the patient to wear.

Acrylic Resins↗
PubMed1990

Improving the adaptation of denture bases by anchorage to the casts: a comparative study.

The purpose of this study was to investigate the adaptation of complete maxillary dentures to stone casts processed by the conventional, and two anchoring, methods. The anchoring methods used holes drilled on the cast and a special flange extended onto the posterior aspect of the maxillary cast. Both anchoring methods improved the adaptation of denture bases by minimizing the discrepancy between the denture base and cast. The greatest discrepancies observed in all methods were at the central portion of the posterior border.

Denture Bases↗
PubMed1987

Dimensional stability of dentures processed in boilable acrylic resins: a comparative study.

An investigation was conducted to evaluate and compare the dimensional stability of three fast boilable denture resins with a conventional and a high-impact denture resin processed with a long-curing cycle. Although the boilable denture resins have been introduced to the dental profession and offer merits such as faster processing, saving time for the dentist, patient, and technician, reduction of energy costs, and dramatic increase in denture laboratory production without adding personnel or purchasing new equipment, the relevant dental literature is sparse. The results of this investigation indicate that all five denture resins produced dentures that shrink. Also measurements between certain teeth showed shrinkages. Linear shrinkages of denture bases and teeth distances were less than 1%. Flange-to-flange and molar-to-molar changes were less than 0.5 mm and 0.2 mm respectively. Maxillary complete dentures processed in boilable resins presented less distortion in the midpalatal area across the posterior section than dentures processed in the conventional heat-cured resin. Although linear changes reported in this investigation were thought to be clinically insignificant, clinical studies should be conducted to establish correlation with laboratory findings.

Acrylic Resins↗
PubMed1987

A study of the occlusal plane orientation in complete denture construction.

A cephalometric study was conducted on eighteen dentulous subjects and fifty-six complete denture wearers to determine the location of the natural and artificial occlusal planes as related to Camper's plane. The results indicated that both the natural and artificial occlusal planes were not parallel to Camper's plane. However, the final anteroposterior inclination of the artificial occlusal plane in complete dentures was almost the same as the inclination of the natural occlusal plane.

Cephalometry↗