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Biomedical subjects

C T Hanks

Publications and source records attributed to C T Hanks.

At least 55 records · Page 3Linked to original sources
PubMed1991

The in vitro effects of metal cations on eukaryotic cell metabolism.

The in vitro cytotoxicity of nine metal cations common in dental casting alloys was evaluated using Balb/c 3T3 fibroblasts and four toxicity parameters: total protein production, 3H-leucine incorporation, 3H-thymidine incorporation, and MTT-formazan production. Concentrations causing 50% toxicity compared to controls (TC50's) and reversibility of these effects were determined. The range of potency of the metal cations was 2-3 orders of magnitude, with Cd2+ showing the greatest potency and In3+ showing the least. Potency did not correlate with atomic weight for these metals. For each metal cation, the TC50's of the various toxicity parameters were similar in most cases. However, several cations (Cu2+, Ga3+) showed greater potency with 3H-thymidine incorporation. Reversibility of the toxic effects was observed for all cations; the effects generally became irreversible at concentrations in the range of the TC50 value for each cation. Several stimulatory effects were seen. Small but statistically significant stimulations were observed after 24 h of metal exposure for Ag1+, Au4+, Cu2+, Ga3+, and Ni2+. Residual stimulations 24 h after removal of the metal cations were observed for Au4+, Cd2+, Ni2+, and Zn2+. Stimulations always occurred at concentrations below the TC50 concentrations. This study should be useful in evaluating the potential cytotoxic effects of metal cations released from dental alloys.

3T3 Cells↗
PubMed1991

Modeling bacterial damage to pulpal cells in vitro.

There is increasing evidence that access to patent dentinal tubules by bacteria and their products rather than trauma from restorative materials is responsible for subsequent pulpitides. The purpose of this study was to compare the relative cytotoxicity of centrifugal fractions of two bacteria, Fusobacterium nucleatum and Treponema denticola, on L929 cells in monolayer cultures and in the "in vitro pulp chamber." Neutrophilic chemotaxis assays and Limmulus assays were performed to verify biological activity of the various fractions of these bacteria. It was found that T. denticola inhibits new protein synthesis in cultured cells to a much greater extent than F. nucleatum, but that only F. nucleatum fractions are chemoattractive for human neutrophils in the absence of serum. While the chemical nature and molecular weights of the "toxic" materials were not determined, it appeared that eukaryotic protein synthesis inhibition caused by the T. denticola pellet fraction in the in vitro pulp chamber was at least 1000 times less than that caused by the same concentrations in monolayer cultures.

Cells, Cultured↗
PubMed1991

The release of elements of dental casting alloys into cell-culture medium.

Ten dental casting alloys were tested for alloy-element release into cell-culture medium, and this release was related to alloy composition, alloy microstructure, and alloy cytotoxicity (previously determined). Cell-culture medium was analyzed for alloy elements by flame atomic absorption. Concentrations of elements in the medium were normalized by dividing them by their atomic abundance in the alloy, giving element medium-alloy ratios (EMA ratios). Results showed that Au, In, and Pd generally did not dissolve into the medium, but that Ag, Cd, Cu, Ga, Ni, and Zn frequently dissolved. Comparison of EMA ratios for Ag, Cu, and Zn showed that each element retained a behavioral identity in diverse metallurgical environments, but that these environments influenced the release behavior to some degree. Some EMA ratios in multiphase alloys were greater than those in solid solutions, and EMA ratios showed great diversity within all the alloys. Nominal composition seemed to be of little value in the prediction of metal release unless the composition supported multiple-phase formation. In addition, release of alloy elements did not, in itself, completely predict alloy cytotoxicity measured previously. However, cytotoxicity was associated with metal release in each case. The commercial alloys used in this study exhibited more complex and less predictable release behavior than did the simpler ternary alloy systems used by previous investigators. It is believed that the use of commercial preparations is necessary for their in vivo behavior to be modeled.

Copper↗
PubMed1991

Cytotoxic effects of resin components on cultured mammalian fibroblasts.

The objectives of this study were to determine the cytotoxic concentrations of 11 components of resin composites on monolayers of cultured Balb/c 3T3 fibroblasts, to study the inhibitory effects of these components on DNA synthesis, total protein content, and protein synthesis, and to determine whether effects were reversible when the components were withdrawn from the medium. These data were reported as concentrations which inhibited 10% (ID10) and 50% (ID50) of a particular metabolic process as well as the range of concentrations over which cell metabolism was irreversibly inhibited. For any individual component, the ID50 values for all three metabolic parameters were of the same magnitude. The same was true for the ranges of irreversibility. Ethoxylated Bis-phenol A dimethacrylate (E-BPA) was the most toxic molecule of the group (ID50 being between 1 and 10 mumol/L). The ID50 concentrations for three of the components, including Bis-GMA, UDMA, TEGDMA, and Bis-phenol A, ranged between 10 and 100 mumol/L, while the ID50 values of three components (N,N dihydroxyethyl-p-toluidine, camphoroquinone, and N,N dimethylaminoethyl methacrylate) were above 100 mumol/L. The concentrations to which the cells and tissues are exposed in vivo are not known. This study should help to identify the concentrations of organic composite components which pose clinical cytotoxic hazards.

Animals↗
PubMed1990

Cytotoxicity of experimental casting alloys evaluated by cell culture tests.

The cytotoxicity of a series of 29 experimental alloys and six pure metals was determined with cell culture techniques and succinic dehydrogenase histochemistry. The width of any ring of inhibition, optical density of the histochemically stained cells, and a visual ranking of the intensity of the blue color of the stained cells were compared for determination of cytotoxicity. Twenty-four of the 35 metals and alloys (approximately 70%) had the same rankings by the three methods. Of the pure metals, Au, Pd, and Ti were the least cytotoxic, followed by Ag, then Ni, and finally, Cu. Single-phase alloys with moderately high Cu and without high Pd and Au concentrations had high cytotoxicity, as did multiphase alloys, even when they were high in Au and Ag. High Pd was more effective in maintaining the biocompatibility of alloys containing Cu than was Au. Single-phase alloys with compositions typical of those to be used for porcelain-fused-to-metal restorations showed good biocompatibility, as did those base metal alloys that formed adherent oxide surface layers.

Animals↗
PubMed1989

Search for cyclotron resonance in cells in vitro.

There are a number of reports of the plasma membrane transport of Ca2+ in biological systems being enhanced by low frequency electromagnetic fields (EMF), including reports that the enhancement involves a resonance-type response at the cyclotron frequency for Ca2+ ions for geomagnetic values of the magnetic field. Using the fluorescent probe fura2, we find no evidence for changes in cytosolic calcium concentration in BALB/c3T3, L929, V-79, and ROS, a rat osteosarcoma cell line, at the application of both resonant and nonresonant EMF.

Animals↗
PubMed1989

Characterization of the "in vitro pulp chamber" using the cytotoxicity of phenol.

Phenol was found to be an acceptable positive control substance for cytotoxicity assays in a new device, the "in vitro pulp chamber" (IVPC). Various concentrations of phenol were used to study its biologic effects on Balb/c 3T3 cells as well as its diffusion characteristics through various thicknesses of dentin disks. The cells showed a linear cytotoxic response to direct contact with phenol between the concentrations of 5 x 10(-4) and 5 x 10(-2) M. When a dentin barrier was used in the IVPC, phenol concentrations in the lower chamber were reduced below that in the reservoir and were inversely proportional to the thickness of the dentin. In the IVPC with 0.5 mm dentin disks, Balb/c 3T3 cells growing on the bottom of the dentin disks still maintained new protein synthesis at 60% of control levels when the phenol concentration in the reservoir was 0.05 M. When in direct contact with the cells this phenol concentration depressed protein synthesis to basal levels.

Animals↗
PubMed1989

Morphological changes in taste buds of the fungiform papillae after a single dose of x-ray irradiation in rats.

The qualitative and quantitative changes occurring in the taste buds of the fungiform papillae of male Sprague-Dawley rats (aged 51-125 days old) after x-ray irradiation were studied. A single dose of 2000 Roentgen (R) was delivered and observations were made at 0, 3, 7, 14, 21 and 30 days after x-ray irradiation. The changes in taste bud morphology were interpreted first as degenerative and then as regenerative at various stages of the study. The degenerative process appeared at about the third day and reached a peak at 7 days. Regeneration then began after a further week and the taste buds appeared mature at about 30 days. While the number of fungiform papillae remained constant throughout the study, there was a marked loss of taste buds on these papillae at 7 days. At 14 days, the number of taste buds increased from this low level, and by 30 days the number approached the control values. Initial taste bud loss could be attributed to a direct irradiation damage leading to taste bud cell desquamation combined with a concomitant mitotic inhibition of the stratum germinativum.

Animals↗
PubMed1988

Cytotoxicity of dental composites and other materials in a new in vitro device.

Several in vitro methods have been developed over the years to improve correlation between screening tests and usage tests of dental restorative materials. Pulpal responses to restorative materials in usage tests are usually less severe than are responses of cells either in vitro screening tests or in implantation tests where there is direct contact between experimental materials and vital cells. In the "in vitro pulp chamber" device tested in the present study, dentin disks were interspersed between composite resins (as well as other dental materials) and the medium which served as the nutrient source for the Balb/c 3T3 test cell system. The dentin restricted the diffusion of materials into the "pulp chamber" to clinically relevant levels. The light-cured composite resins (Fulfil and P30), caused depression of protein synthesis only during the first 24 h postpolymerization, when placed on 0.5 mm but not 1.5 mm thick dentin dishes. The chemically-set composites (SILAR and P10) caused no significant inhibition of protein synthesis (as compared to negative controls) at any postpolymerization time on either 0.5 mm or 1.5 mm dentin disks.

Animals↗
PubMed1988

Reaction of fibroblasts to various dental casting alloys.

The cytotoxicity of a series of dental casting alloys in the as-cast and polished condition was determined with cell culture techniques involving phase contrast microscopy to examine cell morphology and the succinic dehydrogenase histochemical reaction to measure any ring of inhibition of Balb/c 3T3 cellular respiration around alloys. Crown and bridge casting alloys and a nickel- and a cobalt-base alloy were biocompatible in the polished condition, but less so in the as-cast condition. The only two exceptions were casting alloys containing 50-60 wt% Cu. Porcelain-fused-to-metal alloys were biocompatible in either the as-cast or polished condition. This direct contact method appeared satisfactory for evaluating biocompatibility of dental casting alloys, especially since these materials are in contact with gingival tissues.

Alloys↗
PubMed1988

Clinical effects of electromagnetic stimulation as an adjunct to periodontal therapy.

The clinical effects of electromagnetic stimulation (EMS) on periodontal soft tissues and alveolar bone level were studied among 23 patients. The sides of the arch to receive EMS were randomly selected and exposed for a period of eight weeks following periodontal surgery. The contralateral control sides received surgery only. The electromagnetic signal was a multiple pulse signal with 21 asymmetrical quasirectangular pulses per burst and a burst frequency of 16.9 Hz. The peak magnetic field strength reached 0.46 Gauss. Changes from baseline in clinical attachment level, probing depth, and radiographic alveolar bone level were assessed at six, 12, and 18 months postsurgically. A greater gain of clinical attachment level following EMS was observed only for pockets with initial depth of 1 to 3 mm. There were no consistent differences between test (EMS) and control sides in the change of clinical attachment level or probing depth for pockets deeper than 4 mm. Radiographically, the test sides demonstrated statistically significant gain of alveolar bone level compared with the control sides at six months following surgery. Hereafter, the rates of change were similar in the stimulated and unstimulated sides, and the total gain of alveolar bone level remained greater in the test side throughout the observation period. Within the limitations of this study, it was concluded that electromagnetic stimulation does not promote gains in clinical attachment or alveolar bone level to the extent that it can be recommended as an adjunct to conventional periodontal therapy.

Adult↗
PubMed1987

Morphological evidence of innervation of taste buds of rat fungiform papillae after acute X-ray irradiation.

An acute dose of 2000 Roentgens (R) of x-ray was delivered to the head and neck area of Sprague-Dawley rats. Groups of rats were sacrificed at 0, 3, 7, 14, 21 and 30 days after x-ray irradiation. Both general nerve staining and localization of cholinergic nerves by special staining of fungiform papillae were performed. No apparent change in number and distribution of nerve fibres were observed light microscopically within the fungiform papillae containing normal, degenerating and regenerating taste buds. Similarly, cholinesterase activity was present in all control and experimental groups. These preliminary findings do not support the theory that taste bud degeneration is due to x-ray irradiation causing damage to related nerve fibres. A theoretical model of taste bud degeneration after acute x-ray irradiation is proposed.

Animals↗
PubMed1986

Growth control of cultured rat calvarium cells by platelet-derived growth factor.

Platelet-derived growth factor (PDGF), which is released during the "clotting cascade", has a mitogenic effect on a variety of mesenchymal cells including those of the periosteum. Cell culture provides a method of studying these effects. In the present study, PDGF was studied for its ability to stimulate quiescent calvarium periosteal cells to enter G1, indicated by new protein synthesis. After addition of platelet poor plasma, these cells later entered S phase, indicated by uptake of 3H-thymidine. Three hours after PDGF stimulation, there were quantitative increases of at least 18 protein bands as compared to cells left in serum starvation medium. Two of these new protein bands (31K and 45K) required transcription. These data suggest that PDGF in extravasated blood may stimulate appositional bone formation beneath intact periosteum at the site of injury.

Animals↗
PubMed1983

Protein synthesis in vitro, in the presence of Ca(OH)2-containing pulp-capping medicaments.

Four Ca(OH)2-containing pulp-capping medicaments were compared for their effects on protein synthesis in early subcultures of monkey- and human-pulpal fibroblasts. While protein synthesis, as well as DNA synthesis, was depressed by three of the medicaments, the protein-synthetic rate in human-cell cultures in the presence of Life rose to control levels when the medium was changed daily, but was depressed when the medium was not changed. This suggests that serum proteins play a protective role for pulpal tissues under inflammatory conditions, at least in the case of Life, allowing odontoblasts to differentiate and make dentinal matrix without interference of either toxic components or excess alkalinity.

Animals↗
PubMed1981

Cytotoxic effects of dental cements on two cell culture systems.

Four dental cements and one bis-GMA composite were tested in cultures of human periodontal ligament fibroblasts and mouse 3T3 fibroblasts. It was found that these cell types reacted to the cements with different intensities, and that there were differences in evaluation by phase contrast microscopy and succinic dehydrogenase histochemistry.

Animals↗