Biochemical and Morphological Studies of Rat Submandibular Gland: I. Centrifugal Fractionation of Granule-Rich Fraction

Submandibular glands from male rats were homogenized in 0.34 M sucrose and 0.5 mM ethylenediaminetetraacetic acid in 10 mM HEPES buffer at a pH of 7.4. The extract was centrifuged and filtered through nuclepore filters to prepare a granule-rich fraction. Electron dense zymogen granules constituted approximately 85% of the particles in this fraction which also contained about a third of the total alkaline esterase activity in the gland.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68103/2/10.1177_00220345750540053201.pd

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total protein content, and protein synthesis, and to determine whether effects were reversible when the components were withdrawn from the medium.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 μmol/L). The ID50 concentrations for three of the components, including Bis-GMA, UDMA, TEGDMA, and Bis-phenol A, ranged between 10 and 100 μmol/L, while the ID 50 values of three components (N,N dihydroxyethyl-p-toluidine, camphoroquinone, and N,N dimethylaminoethyl methacrylate) were above 100 μmol/L. The concentrations to which the cells and tissues are exposed in uiuo are not known. This study should help to identify the concentrations of organic composite components which pose clinical cytotoxic hazards.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66623/2/10.1177_00220345910700111201.pd

The Effects of Cleaning on the Kinetics of in vitro Metal Release from Dental Casting Alloys

The kinetics of the release of elements from six dental casting alloys into cell-culture medium was assessed by means of atomic absorption spectroscopy. Alloys were evaluated in the polished and polished-cleaned conditions so that the effects of cleaning could be determined. Auger scanning microscopy was used for analysis of the surfaces of selected alloys before and after exposure to the cell-culture medium. Release patterns for each element were characterized by the shape of the dissolution us. time curve, concentration of the element at 12 h as a percentage of the 72-hour concentration, and the relative slope of the curve from 48 to 72 h. Three patterns of release were observed for elements in these alloys. Type I patterns had logarithmic shapes with relatively large 12-hour concentrations and low 48-72-hour slopes. Type II patterns had logarithmic shapes but with moderate 12-hour concentrations and 48-72-hour slopes. Type III patterns were polynomial in shape, had relatively low 12-hour concentrations, and had large 48-72-hour slopes. Cleaning did not change the pattern of release but did generally significantly decrease the quantities of elements released (p = 0.05). The type of dissolution vs. time curve appeared to be dependent upon the element and the composition of the alloy. When cleaning reduced dissolution, surface analyses showed that the cleaning process increased the abundance of elements such as Au and Pd and reduced the abundance of Ag and Cu. Elements which were released from the alloys were more abundant on the surface than in the bulk in both polished and polished-cleaned conditions. Auger analyses of alloy surfaces after exposure to medium showed the presence of organic films up to 50 nm thick. This study demonstrated the importance of consideration of the cleaning method and kinetic release pattern when in vitro tests which assess the cytotoxicities of these alloys are planned.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67010/2/10.1177_00220345920710071101.pd

Cytotoxic Interactive Effects of Dentin Bonding Components on Mouse Fibroblasts

Previous studies have shown a wide range of pulpal reactions to dentin bonding systems and a poor correlation between in vitro and in vivo toxicity of dentin bonding agents. Because dentin bonding agents are composed of multiple components which may diffuse through dentin, we hypothesized that these components may cause cytotoxicity through interactive (synergistic) effects. We investigated the cytotoxicities of four dentin bonding components-HEMA, Bis-GMA, TEGDMA, and UDMA-and interactive effects for three binary combinations of the dentin bonding components-HEMA and Bis-GMA, Bis-GMA and TEGDMA, and TEGDMA and UDMA. Cytotoxicities to Balb/c 3T3 mouse fibroblasts were measured by the MTT assay. Concentrations which caused 50% toxicity compared with controls (TC50 values) were compared, and the interactive effects were determined by evaluation of the differences between observed and expected MTT activities of the cells. The ranks of toxicity of the dentin bonding components in terms of TC50 values were as follows: Bis-GMA > UDMA > TEGDMA >>> HEMA (least toxic) after 24- and 72-hour exposures. As binary combinations, the three combinations of dentin bonding components interacted in three ways—synergism, additivism, and antagonism-which were influenced by the concentrations of both components. The longer period of exposure resulted in a significant increase in the cytotoxicity of the dentin bonding components and combinations. The findings indicate that both exposure time and the interactions between the dentin bonding components may be important parameters in determining the cytotoxicity of dentin bonding agents in vivo.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66489/2/10.1177_00220345950740091601.pd

Cytotoxicity of components of resins and other dental restorative materials

Cytotoxicity testing of dental restorative materials must be viewed as an assessment of hazards, that is the potential of the material to cause pulpal problems. In this context, composites, glass ionomers, amalgams, zinc-based cements and peroxide bleaching agents are all possible hazards to the pulp. The risks that these materials will cause pulpal toxicity in vivo can be partly estimated by assessing the cytotoxicity of the substances which are released from these materials in vitro and comparing these cytotoxic concentrations with those concentrations that are present in vivo . The resin components of composites, metal ions and hydrogen peroxide, all of which are released from dental restorative materials, have been shown to be cytotoxic in vitro in sufficient concentrations. The potencies of these substances are quite diverse. However, the Cytotoxicity of these substances in usage tests, and therefore the risks of pulpal toxicity, depends on their ability to diffuse through the dentine and accumulate in the pulp.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74183/1/j.1365-2842.1994.tb01159.x.pd

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.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67738/2/10.1177_00220345910700060301.pd

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 (-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.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67442/2/10.1177_00220345900690081801.pd

Permeability of biological and synthetic molecules through dentine

The diffusion through dentine by a number of biological and synthetic molecules, including resins and dyes, is reported. In vitro measurements were derived by experiments with a modified ‘split-chamber device’. Diffusion was found to be indirectly proportional to dentine thickness for all molecules. Permeability of water-soluble molecules and ethanol-soluble molecules was proportional to the molecular weights, except for fluorescein, hydrogen peroxide (H 2 O 2 ) and urethane dimethacrylate. The resin components tested are not soluble enough in an aqueous medium to diffuse through 0.5 mm dentine at sufficient concentrations to cause cytotoxicity to pulpal cells.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71760/1/j.1365-2842.1994.tb01162.x.pd