Biomedical subjects

S Kalachandra

Publications and source records attributed to S Kalachandra.

12 recordsLinked to original sources

PubMed2002

Development of butyl elastomer/methacrylate monomer systems as denture soft lining materials.

Previous studies have shown elastomer/methacrylate monomer formulations to have good strength; however, water uptake was high and they also suffered from oxidation. This study has looked at the use of three different butyl elastomers, well known for their oxidation resistance, butyl (PB), chlorobutyl (PCB) and bromobutyl (PBB). The tensile and water uptake properties of the three elastomers gelled with ethyl hexyl methacrylate containing 1% ethylene glycol dimethacrylate and 1% lauryl peroxide (5+ formulation from previous studies) were studied. Water uptake of the pure elastomers was also measured. Tensile strengths were low (PCB5+ = 3.09+/-0.12 MPa and PBB5+ = 3.90+/-0.36 MPa); however, elongation to break values were high (PCB5+ = 797+/-17% and PBB5+ = 599+/-13%). Water uptake was high and protracted with none of the formulations reaching equilibrium. The PCB5+ had the highest uptake (approximately 6% at 203 days) with that for PBB5+ and PB5+ at a similar level (approxiamtely 4% at 203 days). None of the materials showed any sign of oxidation. The PBB proved to be the most suitable of the three elastomers for further development in soft lining formulations.

Denture Liners↗

PubMed2000

Analysis of a dimethacrylate copolymer (bis-GMA and TEGDMA) network by DSC and 13C solution and solid-state NMR spectroscopy.

In this work the effect of dilution with TEGDMA on the kinetics of Bis-GMA polymerization and on the extent of polymerization or degree of conversion was studied using (a) DSC and (b) NMR. The systems with lower viscosity and lower Tg exhibited higher extent of polymerization. For Bis-GMA/TEGDMA mixtures the calculated Tg values were found to be higher than the experimental values suggesting that a dilution effect is predominant rather than intermolecular hydrogen bonding. Solid state NMR has been shown to be a convenient method for measuring the total amount of conversion in a mixed monomer system. The disappearance of the NMR solution spectrum was used to reveal overall polymerization kinetics.

Biocompatible Materials↗

PubMed1998

Evaluating the effect of soft lining materials on the growth of yeast.

STATEMENT OF PROBLEM: Soft lining materials continue to have a place in clinical removable prosthodontics. However, there is an increased probability of yeast colonization on soft lining materials. PURPOSE: This study (1) assessed a method of evaluating the effect of long-term soft lining materials on the growth of yeast and (2) investigated the effect five soft lining materials had on the growth of three species of yeast. MATERIAL AND METHODS: Coe Supersoft, Novus, and three experimental soft lining materials were investigated together with Candida albicans, Candida tropicalis, and Issatchenkia orientalis (formerly Candida krusei) yeasts. Strips of soft lining material incubated on blood agar plates were examined for inhibition of the growth of yeast. Soft lining materials soaked in sterile trypticase soya broth or water were inoculated with yeast and incubated. The change in colony forming units per milliliter from the initial load of yeast at 3 days was measured. Statistical analysis was performed with an independent paired Student t test. RESULTS: Inhibition of yeast growth occurred for two soft lining materials. Despite the presence of sufficient viable organisms, differences between the initial load of yeast and the 3-day results were mostly small, both for the test and control groups, suggesting that the material does not support the growth of the tested yeast during this period. CONCLUSIONS: The often described increased prevalence of yeast associated with soft lining materials in the oral environment is likely related to readily available nutrients in the mouth and the difficulty in maintaining and cleaning these materials.

Acrylic Resins↗

PubMed1998

Relationship between composite matrix molecular structure and properties.

The synthesis of three novel dimethacrylate esters for use as the monomer phase in dental composites was studied. The monomers were prepared by the reaction of glycidyl methacrylate with phthalic, isophthalic and terephthalic acids, respectively, and the reaction products were found to be mixtures of isomers. The monomers obtained from the reaction of phthalic and isophthalic acids were low-viscosity liquids and the relationship between viscosity and molecular structure was studied. The low viscosity of these di-hydroxyl containing monomers was shown to be due to intramolecular hydrogen bonding. This reduced monomer viscosity compared with BisGMA allowed a reduction in the quantity of diluent monomer triethyleneglycoldimethacrylate (TEGDMA) required to give standard viscosities of 1 and 2 Pas resulting in a modest decrease (ca. 10%) in polymerization shrinkage compared with that exhibited by BisGMA/TEGDMA solutions of equivalent viscosities. A number of properties relevant to the use of these as potential core monomers in dental composites were determined for both monomer and polymer systems.

Biocompatible Materials↗

PubMed1997

Influence of additives on the water uptake of hydrosilanized silicone rubbers.

Water uptake characteristics of a silicone polymer containing additives of varying solubility have been investigated. A hydrophobic silica, a sparingly soluble agent and a soluble catalyst were added to a stoichiometrically balanced hydrosilanized silicone polymer (the inherent absorption of which was 0.09 wt%). The diffusion coefficients for desorption of all materials were of the order 10(-6) cm2s-1, whereas the diffusion coefficients for absorption showed a decrease with increasing hydrophilicity and solubility of the additive. The greater the solubility of the additive, the more prolonged the uptake and the greater the deviation from classic diffusion theory.

Absorption↗

PubMed1992

Water sorption and mechanical properties of light-cured proprietary composite tooth restorative materials.

Seven light-cured proprietary composite restorative materials, P-50 (3M), P-10 (3M), P-30 (3M), FulFil (Caulk), Herculite (Kerr), Silux Plus (3M) and Silux (3M) were characterized in terms of water uptake at 37 degrees C. For several of the systems, elastic modulus and glass transition temperature were evaluated with a dynamic mechanical analyser (Autovibron DDV-II-C). Model systems such as bis-GMA (75%) + triethylene glycol dimethacrylate (25%), bis-GMA (30%) + triethylene glycol dimethacrylate (10%) + lithium aluminium silicate (60%), bis-GMA + triethylene glycol dimethacrylate (14%) + barium glass (silanated) (86%) and bis-GMA + triethylene glycol dimethacrylate (14%) + zinc glass (silanated) (86%) were also studied with reference to water sorption. It was concluded that the changes in elastic modulus tend to confirm the hypothesis that the matrix-filler interface contains water. Silux and Silux Plus accommodated the greatest amount of water at the interface. Silux Plus displayed a dramatic reduction in elastic modulus c. 0 degrees C, indicating possible melting of water clusters. It appeared that the only available hole for water clusters was at the matrix-filler interface.

Adsorption↗

PubMed1989

Water sorption of plasticized denture acrylic lining materials.

The objective was to characterize water sorption of plasticized denture acrylic lining materials, with determination both of uptake and diffusion coefficient (D). Feasibility was investigated first for simple binary mixtures of poly(methyl methacrylate), PMMA, and various phthalate plasticizers prepared by radiation polymerization of methyl methacrylate/plasticizer solutions. These were shown to be tractable when samples were saturated with water and then characterized in desorption measurements. Plasticizers were found to decrease the uptake of water. This decrease was attributed to the hydrophobic nature of the plasticizers and also to their ability to fill microvoids in PMMA which, in their absence, would be available to water. Values of D increased monotonically with increasing volume fractions of plasticizer. It appeared that values of D increased more rapidly in cases where large proportions of plasticizer resulted in samples which were above their glass transition temperature, Tg, at the temperature of testing water sorption. Desorption measurements were extended satisfactorily to a model system made from poly(ethyl methacrylate) powder, methyl methacrylate, and dibutyl phthalate, which was polymerized with a conventional redox initiator. Water desorption results were compared with various proprietary materials which were also characterized with respect to Tg and, cursorily, to composition.

Acrylic Resins↗

PubMed1989

Influence of fillers on the water sorption of composites.

The main objectives of this work were to characterize the water sorption of dental composites in terms of water uptake, diffusion coefficients (D), and polymer content, and to study how these parameters are influenced by the nature of the filler and the presence of 4-META (4-methacryloxy ethyl trimellitic anhydride). Four anhydrous composites--(1) tribasic calcium phosphate (TCP 50%) and triethylene glycol dimethacrylate (TEGDM), (2) silanated lithium aluminum silicate (SS, 75%) and TEGDM, (3) barium sulfate [BaSO4 (70%) and poly(methyl methacrylate) (PMMA)], and (4) silane-coated barium glass (SBG) (75%)--and PMMA were employed in the water-sorption studies at 37 degrees C. The effect of 5% 4-META on the diffusion and uptake of water was studied at 37 degrees C. The data conformed approximately to Fick's laws of diffusion. The values of D were found to be significantly smaller with SS, suggesting an effective coupling. Polymer contents in the latter two composites were determined by incineration of the samples to constant weight. The uptake of water by the filled specimens was about two-fold that which would be expected on the basis of the PMMA content. These filled specimens took nearly twice as much water as unfilled PMMA. An additional amount of water is perhaps accommodated at the interface between the filler and PMMA matrix. The D values for water in filled specimens were considerably larger than those in the unfilled specimens. It appears that the filler-matrix interface provides paths of facile diffusion similar to grain boundary diffusion.

Acrylates↗

PubMed1987

Water sorption of polymethacrylate networks: bis-GMA/TEGDM copolymers.

Polymethacrylate networks were made by copolymerization of a range of compositions of bis-GMA and triethylene glycol dimethacrylate (TEGDM). Polymerization was initiated both by heating with benzoyl peroxide or by photopolymerization (lambda greater than 400 nm) using camphoroquinone as sensitizer. The uptake of water increased from 3 to 6% as the proportion of TEGDM increased from 0 to 1.0. Intermediate compositions took up less water than would be predicted from the law of mixtures. Volumetric changes were determined and clinical significance discussed. A copolymer prepared by photopolymerization took up more water as the temperature was increased from 24-60 degrees C. In this range, values of the diffusion coefficient (D) conformed to the Arrhenius equation, D = Do exp (-E/RT), giving E = 42-46 kJ/mol and Do = 0.13 cm2 s-1.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1985

Lubrication and surface chemical properties of ophthalmic solutions.

Surface chemical and lubrication parameters such as contact angle, surface tension, and coefficient of friction, together with viscosity, were measured for commercial ophthalmic solutions. A sensitive friction-testing instrument was employed to measure the coefficient of friction between low-energy polymeric surfaces, e.g., polymethylmethacrylate (PMMA). The viscosity of ten commercial tear substitutes employed in the present study ranged from 2 to 25 cp. The results showed that there is no correlation between the coefficient of friction and viscosity, surface tension, or contact angle of these tear substitutes. The coefficient of friction of tear substitutes appears to depend upon the structure, conformation, and adsorption characteristics of polymer as well as surface characteristics of sliding surfaces. A systematic study was undertaken to evaluate the effect of speed and load on the coefficient of friction between different sliding surfaces, namely PMMA/nylon and PMMA/PMMA. The analysis of data established that our system was operating in the region of "boundary lubrication." In general, a PMMA/PMMA system exhibited a lower coefficient of friction as compared with the PMMA/nylon system.

Lubrication↗

PubMedDate not supplied

Relationship between filler and matrix resin characteristics and the properties of uncured composite pastes.

The relationships between filler type, filler content, matrix resin composition and viscosity and the flow characteristics of composite paste formulations have been investigated. BIS-GMA and 10 experimental BIS-GMA analogues were diluted as needed with TEGDMA to produce 1000 and 2000 cp solutions corresponding to the viscosity range of commercial composite matrices. All of these resins were mixed with a silanated hybrid-filler and a silanated micro-filler. For each combination the maximum filler content was determined, as well as the paste consistencies (plasticities) at a series of filler contents. Paste consistencies were measured by a modification of the ADA specification methods developed for determining standard test consistencies for zinc phosphate and silicate cements. For each monomer-filler combination increasing filler contents resulted in monotonically reduced plasticities. The maximum filler contents appeared to be an attribute of the particular filler rather than matrix resin characteristics. For the materials used, the maximum contents were approximately 86 wt% (83 vol%) filler for the hybrid filler, and 36% wt% (24 vol%) for the microfilled material. At lower filler contents, plasticity differences unexpectedly existed even at equal filler contents and matrix viscosities. Evidence was found that the plasticity varied both with the base monomer composition and the amount of TEGDMA present. The results imply that compositional interactions between the filler and matrix influence the results when all known mechanical factors are controlled.

Absorption↗

PubMedDate not supplied

Water uptake of soft lining materials from osmotic solutions.

OBJECTIVES: The water uptake characteristics of soft lining materials are of obvious importance in that they are expected to function in the oral environment. Results for Novus (Hygenic Corp., Akron, OH, USA) show a very high uptake from distilled water. Despite this high uptake, Novus appears to function satisfactorily in the mouth. High water uptake of soft lining materials has been attributed to the presence of water soluble impurities that, on immersion, form solution droplets; the driving force for the uptake being the osmotic gradient between the droplets and the external solution. Uptake should therefore be less from ionic solutions. The object of this study was to test the applicability of this theory to Novus and two experimental soft lining materials. METHODS: Water uptake of two experimental materials and Novus has been determined from distilled water and two saline solutions (0.45 and 0.9 M). After 196 days specimens were desorbed to constant weight and then subjected to a second sorption cycle. RESULTS: Novus had the highest uptake from distilled water at approximately 18%, the experimental materials having an uptake approximately 7%. Desorptions were all rapid, minimum weight being reached within 1-2 days. Uptakes of the second sorptions from water were all higher. Uptake from saline solutions was approximately 12% for all materials, uptake from 0.9 M saline being the lowest. Second sorption results from solution were similar to the first. CONCLUSION: The results obtained support the theory that the high water uptake of elastomeric materials is osmotically driven.

Adsorption↗