Stability and release of antiviral drugs from ethylene vinyl acetate (EVA) copolymer.

The use of polymer based drug delivery systems in dentistry is a relatively new area of research with the exception of the inhibition of secondary caries by the release of fluoride ions from polyalkenoate cements and their predecessors silicate cements. The present study was to test on orally biocompatible material, ethylene vinyl acetate copolymer (EVA), for release of antiviral drugs at oral therapeutic levels over extended periods of time. We also determined their stability during film casting and release. Materials studied include gancyclovir (GCY), acyclovir (ACY), dichloromethane (DCM), and ethylene vinyl acetate (EVA). The square films (3 x 3 x 0.1 cm) were prepared from the dry sheet obtained by solvent evaporation of polymer casting solutions. These solutions were made of EVA and the drug (40:1) in 70 ml of dichloromethane at 38 degrees C. Then drug release characteristics from the drug loaded films were examined at 37 degrees C for a minimum of 14 days in 10 ml medium (ddwater) replaced daily. Kinetics of drug release were followed by spectral measurements using previously determined lambda(max) values (GCY = 250 nm; ACY = 253 nm). A minimum of three samples was tested and reproducible results were obtained. Drug stability (ACY) during film casting and its release was determined using 1H NMR spectrometer (Bruker DRX-500 and 400). Rate of drug release was determined from the part of the curve (rate vs. time) after the onset of the "burst." Although GCY has a larger molecular weight (255) than ACY (225), GCY exhibited about three times higher rate of release than ACY. This difference in rate values may be explained due to its relatively greater solubility in EVA, facilitating faster diffusion of the molecules through the channels present in EVA. This is consistent with the observation that the rate at which drug molecules diffuse through the channels of the polymer, can be increased by decreasing the molecular weight. In the case of ACY, the molecules may be undergoing molecular associations, perhaps dimerization or trimerization in addition to its lower solubility in EVA. The diffusion of ACY tends to be slower under these circumstances compared to GCY resulting in lower rate value than in the case of GCY. Biological studies revealed that ACY exhibited a remarkable decrease in a number of viral organisms present in virus infected cell culture system using real-time polymerase chain reaction (RT-PCR). NMR analysis indicates that the chemical structure of the drug remains stable during film casting process and release.

[Adaptation of acrylic resin dentures polymerized using various activation modes].

The purpose of this in vitro study was to compare the dimensional accuracy of maxillary dentures made using a conventional heat-activated PMMA resin, a pour resin, a visible light-activated resin, and a microwave-activated acrylic resin. Two simple methods for measuring dimensional accuracy were used: (1) weight of impression material entrapped between the base and master die and (2) measurement of the posterior border gap at five locations. The volume of space between the denture base and the master die was determined by (1) computation and (2) estimation. Statistical analysis (Bartlett, ANOVA and Tukey's Tests) supported the following conclusions: (1) all groups showed a processing contraction, most apparent from buccal flange to buccal flange, (2) the poorest fitting group was processed in a brass flask and a water bath at a temperature which rose from 70 to 100 degrees C, using a heat activated resin (Acron), (3) the visible light activated resin (Triad) produced dentures of intermediate accuracy, as did Acupac 20 when either heat or microwave activated, (4) the two best fitting groups were prepared from a chemically activated resin system using pressure at low heat (PER form), and the resin developed for microwave activation (Acron MC).

Evaluation of color changes of silicone maxillofacial materials after exposure to sunlight.

A number of authors have listed the following qualities as ideal for maxillofacial material: (1) original physical and mechanical properties comparable to the human tissue that they are replacing, (2) the ability to sustain these properties during service, (3) compatibility with human tissues and the adhesives used to adhere the prostheses to tissue, and (4) the quality of being easy to process and an insensitivity to processing variables. Clinical experience has indicated that there is frequent and for the replacement of maxillofacial appliances because of rapid discoloration in the service environment and/or degradation of the physical and dynamic properties of the base elastomer. Color stability in the service environment may be the most important factor in patient acceptance of the prosthesis. The results of this study suggested that aging rather than exposure to sunlight results in most of the color changes observed in the HTV and RTV base polymers studied.

Resin denture bases: review of accuracy and methods of polymerization.

Traditional compression molding and heat-activation methods for polymerization of denture base resins have been widely used. Studies have shown that stresses introduced during processing can lead to the distortion of denture bases. Chemical-, microwave-, and light-energy activation, and various combinations (including polymerization under pressure) have been offered as alternative ways to make dentures. These methods have been attempts to improve the accuracy of fit of the dentures, but sometimes the goal has also been to provide a more convenient laboratory technique. This extensive review covers studies that have investigated the accuracy of acrylic and other types of resins for making dentures using the known range of fabrication methods.

Adaptation of acrylic resin dentures as influenced by the activation mode of polymerization.

With the advent of newer methods of activation of the polymerization of denture base resins, there is a need to compare dentures constructed using various modes of activation such as heat, light, and microwave energy. This study compares the dimensional accuracy of a conventional heat-activated acrylic resin poly (methyl methacrylate) with a new pour resin, a visible light-activated resin, and microwave-activated acrylic resin, all polymerized for denture bases. All groups showed a processing contraction; the poorest-fitting group was processed in a brass flask and a water bath at 70-100 C, using a heat-activated resin (Acron); the relatively new light-activated resin (Triad) produced dentures of intermediate accuracy, as did Acupac 20, when either heat- or microwave-activated. The two best-fitting groups were prepared from an autopolymerizing resin (PERform) and the microwave-activated resin (Acron MC).

The application of Moire topography to removable prosthodontics.

The study was designed to assess the dental research potential of moire topography--the use of geometrically regular light patterns for measuring three-dimensional objects. One hundred thirty-nine maxillary edentulous casts and 20 mounted cast pairs were evaluated. Results demonstrated that the moire topography techniques can be used to quantitatively evaluate edentulous arch forms, compare edentulous ridge forms and surfaces, determine the amount of overlap of mounted maxillary and mandibular casts, and confirm prime areas for positioning posterior teeth.