Biomedical subjects

R G Craig

Publications and source records attributed to R G Craig.

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↗

PubMed1991

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.

Acetates↗

PubMed1991

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.

Acrylic Resins↗

PubMed1990

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.

Biocompatible Materials↗

PubMed1990

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.

Agar↗

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

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.

Agar↗

PubMed1989

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.

Calcium Sulfate↗

PubMed1989

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.

Animals↗

PubMed1989

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.

Calcium Hydroxide↗

PubMed1989

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.

Alveolar Process↗

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

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.

Animals↗

PubMed1989

Effect of retarder on compression set of an addition silicone.

Use of a retarder with a light-bodied addition silicone according to the manufacturer's recommendations increased the working time but resulted in poorly fitting crowns fabricated from these impressions. The compression set of the retarded mixes at the recommended time of removal was 3.2% compared with 0.08% for the nonretarded control. Increasing the time for removal by one minute resulted in a satisfactory compression set of 0.19%. It is recommended that if a retarder is used with an addition silicone, the correct time of removal should be determined by the compression set.

Dental Impression Materials↗

PubMed1988

Two-dimensional photoelastic simulation of a castable ceramic fixed partial denture.

Two-dimensional photoelastic models were used to determine the optimum design and loading conditions for a three-unit castable ceramic fixed partial denture. Findings relating to design and material variables can be summarized as follows. 1. Higher modulus cements impart more rigidity to the fixed partial denture design and result in lower stresses. 2. A short connector results in higher stress than a long connector; however, the length of the connector should not exceed one half the mesial-to-distal length of the pontic. 3. An intermediate thickness of cement results in the best stress distribution. 4. The male connector is best attached to the bulkier abutment. 5. Occlusal cement eccentricity is less desirable than cervical eccentricity. 6. The most undesirable loading site is directly above the connector.

Dental Stress Analysis↗