Contribution of fibroblasts to the mechanical stability of in vitro engineered dermal-like tissue through extracellular matrix deposition.

Tissue-engineered skin with mechanical and biological properties that match the native tissue could be a valuable graft to treat non-healing chronic wounds. Fibroblasts grown on a suitable biodegradable scaffold are a feasible strategy for the development of a dermal substitute above which epithelialization may occur naturally. Cell growth and phenotype maintenance are crucial to ensure the functional status of engineered tissue. In this study, an electrospun biodegradable polymer scaffold composed of a terpolymer PLGC [poly(lactide-glycolide-caprolactone)] with appropriate mechanical strength was used as a scaffold so that undesirable contraction of the wound could be prevented when it was implanted. To enhance cell growth, synthetic PLGC was incorporated with a fibrin-based biomimetic composite. The efficacy of the hybrid scaffold was evaluated by comparing it with bare PLGC in terms of fibroblast growth potential, extracellular matrix (ECM) deposition, polymer degradation, and mechanical strength. A significant increase was observed in fibroblast attachment, proliferation, and deposition of ECM proteins such as collagen and elastin in the hybrid scaffold. After growing fibroblasts for 20 d and 40 d, immunochemical staining of the decellularized scaffolds showed deposition of insoluble collagen and elastin on the hybrid scaffold but not on the bare scaffold. The loss of mechanical strength consequent to in vitro polymer degradation seemed to be balanced owing to the ECM deposition. Thus, tensile strength and elongation were better when cells were grown on the hybrid scaffold rather than the bare samples immersed in culture medium. Similar patterns of in vivo and in vitro degradation were observed during subcutaneous implantation and fibroblast culture, respectively. We therefore postulate that a hybrid scaffold comprising PLGC and fibrin is a potential candidate for the engineering of dermal tissue to be used in the regeneration of chronic wounds.

Effect of resin matrix ratio, storage medium, and time upon the physical properties of a radiopaque dental composite.

Three light curing composite pastes with varying resin matrix ratios [bisphenol A-glycidyl methacrylate (BIS-GMA)/urethane tetramethacrylate (UTMA) 25:75, BIS-GMA/UTMA 50:50, and BIS-GMA/UTMA 75:25 w/w%] were prepared in combination with a radiopaque glass powder and camphorquinone photoinitiator. Cured samples were aged at 37 degrees C in three food simulating media such as citrate buffer (pH 4.0), PBS buffer (pH 7.4), and 75% ethyl alcohol. Samples were withdrawn at specific intervals of 1, 15, 30, 45, and 60 days and tested for changes in mechanical properties, sorption, and solubility characteristics. Statistical calculations revealed significant changes in compressive strength (CS) for composites depending on the resin matrix ratio and type of medium used for aging. While diametral tensile strength (DTS) was affected adversely in citrate medium for composites with higher urethane content, samples stored in alcohol medium showed deterioration of transverse strength (TS) and microhardness (VMH) for all composites studied. Increase in BIS-GMA content in the resin matrix and storage in alcohol medium resulted in higher sorption and solubility values and lower microhardness.

Three body wear studies of five dental composites preconditioned in food simulating media.

Progressive three body wear up to 30 min for five dental composites (Concise, Heliomolar, Occlusin, P-30, Profile, TPH) stored for 9 months at 37 degrees C in citrate, lactate and PBS buffers, 25 and 75% ethanol media, has been measured using a wear tester. Particle size of the filler and the storage media are found to play dominant roles in determining the extent of wear. Heliomolar, which is a microfilled composite, shows maximum wear whereas wear is least in composites containing filler particles of conventional and hybrid size such as P-30 (> 1 micron). The storage media is found to attack and degrade glass filler particles compared to composites having quartz fillers.

Development and evaluation of radiopaque light cure composite.

After the development of a two-paste chemical cure composite, evaluation of its physicochemical properties, toxicological evaluation and in-vivo experiments in dogs teeth with histopathological study of dental tissues, a clinical trial was carried out and commercial production recommended. As the shelf life of the material was not enough, a light cure composite was developed, its material characteristics, toxiclological study, in-vivo experiments in dogs with histopathological evaluation and clinical trials carried out. However, the material was radiolucent, and could not be seen in an x-ray and differentiated from a cavity after filling was done. This led to the development of radiopaque light cure composite. Compressive strength, diametral strength, and microhardness were tested with 200-250 phr range of incorporated radiopaque glass particle filler of the size 0.7 to 1.0 micron this improved the properties when compared to conventional composites. The composite was non-toxic and suitable for animal studies. In vivo studies are underway in dogs with histopathological studied of the pulp and dentin. The material awaits clinical trials prior to commercial production.

Effect of amine activators on the properties of chemical cured dental composites.

The purpose of this study was to evaluate the reactivity and the effect of concentration of three tertiary amines upon the mechanical properties of a chemical curing dental composite. Chemical cured composite pastes were prepared by keeping peroxide concentration constant at 1 wt% (by weight of resin mixture) and by varying the amine/peroxide molar ratio from 0.25 to 1.5. Composite samples were prepared for all three amine pastes aged for 1, 15, 30, 45, and 60 d stored at 8, 22, and 37 degrees C. The loss in activity of the tertiary amine with time was measured. Changes in compressive strength, diametral tensile strength, and microhardness were also measured. A sharp decrease in working and setting times corresponding to increased activity was noticed with an increased amine content. The activity was found to vary in the order N,N-dimethyl p-toluidine (DMPT) > 2-(4-dimethylaminophenyl)ethanol (DMAPEA) > N,Ndiethanol p-toluidine (DEPT). DMPT is found to be more temperature sensitive than DMAPEA and DEPT. However, DEPT is found to provide better storage stability out of all three amines tested. Each amine was found to possess optimum concentrations at which the mechanical properties showed maximum values. DEPT is preferred for long-term storage stability in chemical-cured dental composites where aging tends to reduce the activity of the amine.

Development and clinical evaluation of Chitra visible light cure composite.

Two paste, self cured BIS-GMA based resin was developed and physicochemical and biological characterization carried out. Its suitability and safety for clinical use were evaluated. Clinical trials for direct bonding of Orthodontic brackets conducted at the College of Dental Surgery, Manipal showed a success rate of 83% against 85% with "Right On" adhesive used as control. Further research to improve shelf life of the material led to the development of light cure-BIS-GMA based resin. It was evaluated for physicochemical characteristics which included setting time, compressive strength, diametral tensile strength, microhardness, water sorption and exothermic reaction. Biological characterization studies on material toxicity and biocompatibility on animal models established the safety and suitability of this composite for clinical use in dentistry. Clinical evaluation for direct bonding of Orthodontic brackets in comparison to Ultralight (T.P Orthodontics, USA) showed its handling characteristics to be superior to control. Flash removal was easier around bracket bases bonded with Chitra light cure. However, bond strength of light cure composite was 66% as compared to 79% with Ultralight. Subsequent improvement of the material increased the bond strength significantly. Failure rate with the new material was 11% against 13% with control in the ongoing clinical trials.

Effect of diluent upon the properties of a visible-light-cured dental composite.

Four long-chain aliphatic organic diluents, triethylene glycol dimethacrylate (TEGDMA), ethylene glycol dimethacrylate (EDMA), triethyleneglycol diacrylate (TEGDA) and tetraethylene glycol diacrylate (TTEGDA) were used as diluents for preparing a visible-light-cured dental composite. Cured samples of pastes prepared using the above diluents were stored separately for a period of 60 days in distilled water at 37 degrees C and tested for changes in compressive strength, diametral tensile strength and microhardness at specific intervals of 1, 7, 14, 21, 28 and 60 days. Samples prepared using TEGDMA showed better strength values initially compared with the composite specimens prepared using the rest of the diluents although they are found to deteriorate slowly upon storage in distilled water up to 60 days. Samples prepared using EDMA showed retention in properties whereas samples prepared using TEGDA and TTEGDA showed large deviations in strength values during the first 28 days, did not deteriorate further and were found either to show improvement upon ageing or to remain constant. Sorption values seem to reach a maximum for all composites and then to decrease further after 14 days whereas solubility is found to increase with time.

Studies on microleakage associated with visible light cured dental composites.

The objective of this investigation was twofold: 1) to determine the extent of microleakage associated with two visible light cured dental composites, one of which is an indigenously developed light cure composite (chitra light cure system) compared with a commercially available control material (Prisma APH light cure system), and 2) to study the effect of using bonding agents upon the above phenomena. The bonding agents used along with the above composites during restoration were chitra bonding agent system containing chitra primer/chitra resin and a control (Probond) which was purchased commercially. A comparison of microleakage in freshly restored human premolar teeth by silver nitrate staining technique was made during the above study. Cavities were restored with both composites with and without bonding agents, stored in 50 percent silver nitrate, and sections were cut after developing. The microtomed sections were observed under the optical light microscope and scanning electron microscope. Results indicate that bonding agents are mandatory for effective bonding at the tooth/resin interface and subsequent reduction in marginal leakage. Chitra bonding agent showed excellent adhesive bonding characteristics at the dentine/composite interface with minimal marginal leakage compared to the control bonding system. The chitra light cure composite material also showed lower shrinkage characteristics compared to Prisma APH composite.

Synolite as a base resin for dental composites and related biomaterials.

Synolite resin was analysed using FTIR, NMR and HPLC to determine its components and purity. The resin was found to be predominantly BIS-GMA containing traces of its two isomers. The analysis indicated that there was no unreacted methacrylic acid or other impurities.

Radiation grafting of hydrophilic monomers on to plasticized poly(vinyl chloride) sheets. II. Migration behaviour of the plasticizer from N-vinyl pyrrolidone grafted sheets.

The grafting of N-vinyl pyrrolidone, a hydrophilic monomer, on to flexible poly(vinyl chloride) sheets used in medical applications using ionizing radiation from a 60Co source was studied. The graft yield was found to increase linearly with monomer concentration and also with increasing radiation doses. The migration of the plasticizer di-(2-ethylhexyl)phthalate into a strong organic extractant such as n-hexane was studied at different time intervals for different grafted systems of poly(vinyl chloride) at 30 degrees C. The results indicated a drastic reduction in the leaching of the plasticizer from grafted systems versus ungrafted controls. Incorporation of ethylene dimethacrylate cross-linker during grafting did not seem to affect the graft yield considerably but appeared to further reduce the plasticizer migration. Surface energy calculations of the grafted samples indicate that the surfaces are highly hydrophilic compared to ungrafted poly(vinyl chloride) and the polar and dispersion components tend to vary with increasing cross-linker concentration.