Lipid composition and biosynthesis in the gingiva of the domestic cat

Periodontal disease in the domestic cat may assume debilitating and serious consequences; however, little is known of the biochemical composition or metabolism of feline gingiva in health or disease. In this report the chemical composition and metabolism of gingival lipids from inflamed an non-inflamed sites is presented and compared to other species with naturally occurring periodontitis. The neutral and phospholipid composition of feline gingiva was found to be distinct from that of porcine and human. As a measure of de novo lipid synthesis, the total incorporation of 14C-acetate into fractionated lipid components was determined and revealed an approximate 2 to 3 fold decrease in inflamed versus non-inflamed gingiva. The decrease in 14C-acetate incorporation appeared to result from a 2-fold increase in free acetate pools in inflamed compared to non-inflamed gingival samples, since total lipase and phospholipase activity were comparable in inflamed and non-inflamed gingiva and total lipid composition was not changed between inflamed and non-inflamed sites. These data are similar to those reported for periodontally involved human gingival tissue and suggest a common effect of periodontal inflammation on lipid metabolism in both species.

Optical cellular logic image processor: implementation and programming of a single channel digital optical circuit

A diode-laser driven all-optical iterative processor has been constructed and tested. Results are presented showing operation equivalent to a single channel of the cellular logic image processor architecture. Functional features of the circuit include optically programmable logic, thresholding, and data synchronization. Essential elements such as cascadability, logic-level restoration, and data feedback have been demonstrated with the optical processor controlled by a conventional electronic computer. Serial processing algorithms for word recognition, comparison, full addition, and subtraction have been implemented. Comments on the reliability of operation and future plans for expansion are made.

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.

Denture materials and acrylic base materials

Modifications in denture plastics, including acrylics containing butadiene-styrenes, block copolymers to increase toughness, and those with added soluble heavy-element salts to increase radiopacity are described. Developments in processing of denture bases by microwave, laser, and injection methods are described. Also reviewed are acrylics and their dimensional stability, including the effect of artificial salivas on properties. In addition, the rheological, glass transition, dynamic, impact, and fatigue properties of denture acrylics are presented. Adhesion of polymers to plastics and metals is reviewed, as well as the biocompatibility and adhesion of organisms to denture plastics. Soft denture materials are reviewed with respect to research on new materials and to clinical evaluations of existing products. Finally, studies on the wear of denture teeth are summarized.

Cytotoxicity of a BIS-GMA dental composite before and after leaching in organic solvents

Cell culture techniques were used to determine the source of cytotoxic agents in a commercial BIS-GMA composite. The material was polymerized according to the manufacturer's directions and leachable components were removed by room temperature extraction in ethanol, chloroform, or toluene. The leachable components in the extracts were identified using infrared spectrographic analysis. Thin layer chromatographic analysis was used to determine the number of constituents. These constituents were separated by gas chromatography and then identified by mass spectrographic analysis. Succinic dehydrogenase activity and radioactive labeling with tritiated leucine were used to evaluate cell metabolism and protein synthesis, respectively. The infrared analysis of the extracts showed that the primary component was unreacted BIS-GMA. Trace amounts of 2-hydroxy-4-methoxy-benzophenone, a light stabilizer, as well as a phenyl ester of benzoic acid which was probably degraded from BIS-GMA, were detected by the mass spectrographic method. The removal of leachable components caused a 90% decrease in toxicity compared to the nonextracted BIS-GMA samples. The extracted BIS-GMA samples showed no cellular response compared to the Teflon negative control.

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.

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.

Accuracy of impression materials measured with a vertical height gauge

The objectives of this study were to introduce a different method for evaluating the accuracy of impression materials using a vertical height gauge, and to determine the vertical (axial) and horizontal (transversal) changes of four impression materials. Comparison of means demonstrated the changes for addition and condensation type silicones, and larger changes for the agar/alginate combination and the visible light cured (polyetherurethanedimethacrylate) impression material. The results were in agreement with an earlier study of the agar/alginate combination, and the values for the condensation and addition silicones were about half those reported in previous studies. These small changes might indicate the use of a mandibular stock tray for the upper jaw when a putty/wash technique is employed. The findings suggest that, when the horizontal changes (delta X) of impressions taken with a mandibular stock tray have a negative sign (contraction), then the vertical changes (delta L) will have a positive value (expansion), and vice versa. Thus the pattern of distortion can be formulated as delta X/delta L less than 0.

All-optical programmable logic gate

Experimental results are presented showing all-optical programmability and operation of a multifunction Boolean logic gate. All eight symmetric two-input logic functions have been demonstrated. Comments on the practical implementation and usage of this gate within an optical circuit are made.

Comparison of commercial elastomeric impression materials

The properties of some recently marketed rubber impression materials were compared with some earlier products. In general, the qualities of addition silicones and polyethers were superior to polysulfides and condensation silicones. However, there were significant differences in the properties of products of the same type and class and thus the selection of a product for a particular application should be based on actual property data rather than on the type and class of rubber impression material.

Properties of a new polyether urethane dimethacrylate photoinitiated elastomeric impression material

The photoinitiated impression material is supplied premixed as a light-bodied material in a light-tight plastic syringe and as a heavy-bodied material in a tube. The impression material has excellent physical, mechanical, and clinical qualities with noteworthy long working times, short setting times, dimensional stability, accuracy, high tear strength, good wettability, biocompatibility, and ease of cold disinfection without loss of quality. The impression material is also compatible with gypsum and silver or copper metallizing baths. Accurate casts can be obtained by means of either a double-impression technique or a double-mix technique.

Finite element analysis of three- and four-unit bridges

A two-dimensional finite element model of a mandibular quadrant was used to examine differences in magnitude of the principal stresses from the placement of three- and four-unit bridges. The area of interest spanned the first premolar to the second molar. Loading conditions were (i) vertical and distributed and (ii) 30 degrees to the vertical and concentrated. The principal stresses were calculated and compared for: (i) the first molar removed with the remaining bone either cancellous or cancellous surrounded by a cortical shell; (ii) as in (i) but with the second premolar and first molar removed; (iii) a three-unit bridge spanning the second premolar to the second molar; and (iv) a four-unit bridge spanning the first premolar to the second molar. Each tooth was supported by periodontal ligaments, cortical and cancellous bone with each assigned the appropriate physical constants. Removal of the first molar resulted in considerable variation of the stresses especially when the cortical shell was replaced by cancellous bone. Because of the lower modulus of cancellous bone and its lower load-bearing capabilities the stresses were three to ten times lower and more uniform within the cancellous bone. Generally, the addition of a bridge resulted in lower and better distributed sigma min stresses. The bridge also resulted in higher tensile stresses distal to the abutment teeth which theoretically could result in bone deposition. No significant differences in magnitude were observed between the three- and four-unit bridge. From a stress standpoint the bridges resulted in more uniform stress distribution around the abutments and an increase in the tensile stress distal to the abutments. Such findings support the placement of a fixed bridge to maintain bone in an edentulous area.

The effect of powder/water ratio of irreversible hydrocolloid on the bond strength of irreversible hydrocolloid and agar combinations

This study investigated the effect of powder/water ratios of irreversible hydrocolloid on the tensile bond strength of several irreversible hydrocolloid and agar combinations. Each irreversible hydrocolloid was prepared in three different powder/water ratios as follows: (1) normal recommended ratio, (2) 10% more water than normally recommended, and (3) 10% less water than normally recommended. The irreversible hydrocolloid and the agar were joined together in a special loading assembly, which was subjected to tensile loading. The results suggest that except for one irreversible hydrocolloid and agar combination the powder/water ratio had no significant effect on the bond strength. In addition, the results indicate that for a successful bond it is important to choose not only a reformulated agar but a compatible irreversible hydrocolloid.

Insulin increases the steady state level of alpha-1(I) procollagen mRNA in the osteoblast-rich segment of fetal rat calvaria

Insulin at 3-100 nM increased the steady state level of alpha-1(I) procollagen mRNA and stimulated collagen synthesis in the osteoblast-rich segment of central bone from 21-day-old fetal rat calvaria. The increases in the level of procollagen mRNA and the rate of collagen synthesis were observed 18 h after the addition of insulin to the cultures. The removal of insulin from calvaria incubated for 24 h with 3 nM insulin caused collagen synthesis and the level of alpha-1(I) procollagen mRNA to return to control values within 5 h. Adding insulin back to calvaria withdrawn from insulin treatment for 3 h did not rescue the decay in collagen synthesis or the level of alpha-1(I) procollagen mRNA. Insulin increased the steady state levels of alpha-1(I) procollagen mRNA in the presence of the RNA synthesis inhibitor actinomycin-D. Our data suggest that in fetal rat bone, one mechanism by which insulin increases the steady state level of alpha-1(I) procollagen mRNA may be by altering its stability.

Solubility of zinc oxide-eugenol and calcium hydroxide cements in simulated dentinal fluid

The solubility of four dental cement bases was measured in simulated dentinal fluid and distilled water to evaluate the relevancy of the American Dental Association solubility test for cement bases in contact with vital dentine. A simulated dentinal fluid was formulated utilizing glucose, distilled water, and sterile human plasma. Cement-base samples were immersed in either distilled water or simulated dentinal fluid at 37 degrees C in a shaker water-bath for 1, 2, or 3 months. Weight loss values were compared utilizing a three-way analysis of variance. Zinc oxide-eugenol cements were significantly more soluble in simulated dentinal fluid than distilled water, while the calcium hydroxide cement bases were significantly more soluble in distilled water than simulated dentinal fluid.

Changes in whole body lipid composition in a murine model of insulin-dependent diabetes mellitus

To assess the effect of experimentally induced insulin-dependent diabetes mellitus (IDDM) on total body lipid composition, homogenates of neonatal (0-day) and 6-day Sprague-Dawley rat pups treated on day 0 with 65 mg/kg body weight of streptozotocin (STZ) or citrate buffer alone were compared using thin-layer and gas-liquid chromatographic techniques. STZ-treated littermates in a parallel study were markedly hyperglycemic, hypoinsulinemic and attained only 50% of the gain in weight of citrate-treated controls. Although both groups were similar in protein to body weight ratios, STZ-treated pups exhibited 60% of the total lipid content of citrate-treated littermates when compared by weight. The decrease in total lipid content in the STZ-treated group resulted specifically from decreased neutral and not phospholipid content, although a small increase in phosphatidic acid and sphigomyelin was observed in this group. The changes in relative whole body lipids with short-term, high-dose STZ parallel those reported in human IDDM.

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.

Wettability of a hydrophilic addition silicone impression material

Silicone impression materials, long noted for their poor wettability, have typically demonstrated contact angles with water greater than 90 degrees. This study compared the wettability of a new hydrophilic addition silicone with that of other impression materials. Specimens from various viscosities of polyether, polysulfide, hydrophobic addition silicone, and hydrophilic addition silicone were formed against a smooth surface. The advancing contact angle of a saturated aqueous solution of CaSO4 on the impression materials was measured after 1 minute. Mean contact angles were calculated and results were analyzed by ANOVA and a multiple comparison of means procedure. Differences between pairs of contact angle means were found to be statistically significant except for the polyether-hydrophilic addition silicone pair. The wettability of the hydrophilic addition silicone impression material was found to be not significantly different from that of a polyether impression material.

Finite element analysis of a mandibular model

A two-dimensional finite element model of a mandibular quadrant was used to examine the stresses and displacements resulting from a 100 N load placed as follows: (i) distributed on the second molar, (ii) concentrated at 30 degrees to the vertical on the second molar, and (iii) distributed on the second premolar and second molar. Each tooth was supported by periodontal ligaments, cortical and cancellous bone. The modulus and Poisson's ratios for each material were selected from accepted values. The principal stresses were determined throughout the model, with special emphasis being placed for elements in the immediate vicinity of the teeth mentioned above. It was found that for the case where the load was uniformly distributed on the second molar the stresses sigma min were mostly compressive (-) in nature while sigma max were mostly tensile (+). In the case where the load was concentrated and at 30 degrees to the vertical, the magnitude of the stresses were three to five times greater and the pattern less uniform than those resulting from the distributed load. The concentrated load at 30 degrees to the vertical resulted in higher bending stresses than the distributed load and hence higher sigma max stresses.

Physical properties of addition silicones as a function of composition

The effects of molecular weight of the base silicone, filler and copolymer concentrations on compression set, strain, creep and dynamic elastic modulus were determined. The molecular weight of the base silicone had the least effect on these properties although low molecular weights showed better properties. Chain extenders were detrimental to physical properties of creep, compression set and dynamic elastic modulus. Increased copolymer concentrations decreased compression set, strain and creep and increased the dynamic elastic modulus. The useful copolymer/base functional group ratio was from 1:1 to 3:1. Filler affected properties to a lesser extent than copolymer ratio. Compression set, strain, and creep decreased and the dynamic elastic modulus increased with increasing filler with the properties being directly proportional to the weight fraction. All properties were interrelated with ln strain linearly related to ln compression set, creep proportional to set, and the dynamic elastic modulus was inversely correlated with strain and creep.

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.

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.

Review of dental impression materials

Major advances in impression materials and their application have occurred during the last decade, with greater emphasis being placed on rubber impression materials than on dental compound, zinc oxide-eugenol, and agar and alginate. Of particular interest has been the effect of disinfection solutions on the qualities of impressions and the biocompatibility of impression materials. The principal advance in hydrocolloids has been the introduction of the agar/alginate impression technique, which has simplified the procedure and improved the quality of gypsum dies compared with those prepared in alginate impressions. The tear strength of some alginates has been improved, and some have been formulated so that the powder is dustless, thus reducing the health hazard as a result of patient inhalation of dust during the dispensing process. Polyether and silicone impression materials have been modified so that the working time, viscosity, and flexibility of the polyethers have been improved and, with the introduction of addition silicones, their accuracy has become exceptional. Although the early addition silicones liberated hydrogen after setting, thus delaying the pouring of models and dies, most addition silicones have been improved so that no hydrogen is released and dies can be poured immediately. The introduction of automatic mixing systems for addition silicones has simplified their manipulation, has reduced the number of voids in impressions, and has reduced the amount of material wasted. The incorporation of surfactants into addition silicones has made them hydrophilic, with wetting properties similar to those of polyethers, and has made pouring bubble-free gypsum dies easier.

This review is confined to published and unpublished information of the past decade. It will also suggest trends that should be anticipated in the near future based on this information. The review will not present information developed before 1975, which is available in several textbooks on dental materials by Craig (1985a), Phillips (1982), and Williams and Cunningham (1979).

Correlation of parameters used to estimate monomer conversion in a light-cured composite

The sensitivities of Fourier transform infrared spectroscopy, Knoop hardness, water sorption, and resin leaching were compared for their ability to distinguish differences between composite samples cured through different thicknesses of overlying resin. The method developed allowed samples of light-cured composite to be made with controlled conversion for parameter testing, and eliminated effects of resin lost to slurry during polishing or an increase in conversion as a result of heat generated during grinding. Sensitivity to differences was greatest and equal for FTIR spectroscopy and Knoop hardness, while resin leaching proved to have moderate sensitivity, and water sorption none. The ability of these parameters to predict monomer conversion as measured by FTIR spectroscopy was also determined. Knoop hardness proved the best conversion predictor, resin leaching the next best, and water sorption the worst. Water sorption values did not vary with changes in specimen conversion.

Force-displacement properties of a modified cross-linked silicone compared with facial tissues

A dimethyl siloxane triacetoxy terminated silane, Type A adhesive, was modified with the base component of a medium grade polydimethyl siloxane with vinyl groups, MDX 4-4210, to produce a more pliable maxillofacial prosthesis. Force-displacement curves of various ratios of Type A adhesive/MDX 4-4210 were determined and compared with force-displacement curves obtained from human subjects. Within the force range of 0.4 to 1.2 N, the force-displacement slopes obtained on human subjects compared favourably with some of the Type A adhesive/MDX 4-4210 test specimens. The force-displacement slopes for the elastomers and humans were not in agreement for forces below 0.4 N.