Effect of air/water rinse versus water only and of five rinse times on resin-to-etched-enamel shear bond strength

This study compared the shear bond strength of composite resin bonded to etched, flattened enamel that had been rinsed for 0, 1, 2, 3, 5 or 20 seconds with either a water stream or an air/water spray. One hundred seventy-six molars were separated into mandibular and maxillary groups, then divided equally into 11 groups of 16 teeth each. The facial enamel surfaces were ground flat and etched for 20 seconds with 37% phosphoric acid gel. In one group, the etching gel was dried but not rinsed. In five groups the gel was rinsed with a direct stream of water at 22 psi. In the remaining five groups the gel was rinsed with an air/water spray (air at 53 psi, water at 22 psi). One tooth from each group was removed for scanning electron microscopy evaluation, leaving 15 specimens in each group for shear bond testing. Teflon tape with a 3 mm in diameter window was placed over each etched area, a light-curing liquid resin was applied and polymerized for 10 seconds, and a cylinder of light-curing composite resin was polymerized over the window. Specimens were thermocycled from 5 to 50 degrees C for 500 cycles (30-second dwell time). After 30 days' hydration at room temperature, the teeth were mounted and the composite resin cylinders were loaded in shear to failure with an Instron machine at a cross-head speed of 5 mm/min. Mean load to failure was calculated for each group. Specimens that were not rinsed had significantly (P < 0.001) less bond strength (mean 0.53 MPa) than any of the rinsed specimens (mean 18.7 MPa).(ABSTRACT TRUNCATED AT 250 WORDS)

The same genomic region is disrupted in two transgene-induced limb deformity alleles

Mutations of the mouse limb deformity locus, ld, map to Chromosome (Chr) 2 and result in defects in the morphogenesis and patterning of the limb and kidney. Complementation studies have defined the existence of five recessive ld alleles. Remarkably, two of these, ldTgHd and ldTgBri, are transgene-induced mutations. Recovery of the first transgene insertional allele, ldTgHd, facilitated the molecular cloning of a large (greater than 200 kb) candidate gene at the ld locus. This gene is broadly transcribed and encodes a set of novel protein isoforms, termed formins. Here we present characterization of the ldTgBri mutation that supports the molecular identification of the ld gene. We show that the ldTgBri fails to complement both the ldTgHd and the ldOR alleles and that it has undergone a genomic deletion that disrupts the cloned ld gene and its transcripts. Curiously, the ldTgBri deletion encompasses the same 11-kb interval in which the ldTgHd insertion occurred and in which a chromosomal rearrangement has been identified in a third allele, ldIn2. These findings suggest that this region of the ld gene is a preferential site for illegitimate recombination.

Long-term fluoride release from glass ionomer-lined amalgam restorations

This in vitro study evaluated the amount of fluoride released from glass ionomer-lined amalgam restorations over a period of 1 year. Class V cavities (2 x 2 x 7 mm) were prepared on the facial and lingual surfaces of 50 extracted human molars randomly distributed into 5 groups: Group 1: No restorations; Group 2: Dispersalloy amalgam alone; Group 3: same as Group 2 except 1 mm of Ketac-Silver was placed on the axial wall before amalgam insertion; Group 4: GC Lining/amalgam; and Group 5: Miracle Mix/amalgam. After restoration, each tooth was thermocycled (100x) at 5 degrees C and 55 degrees C with a dwell time of 30 seconds for baseline fluoride release levels. The teeth were placed in a polyethylene vial containing 4 ml of deionized water. At weekly intervals, each tooth was transferred to a fresh vial. Fluoride release was measured with a fluoride ion specific electrode for 10 consecutive weeks and then again at the end of 1 year. Calibration curves for low level measurements were prepared so the readings could be expressed in micrograms/ml F. At 1 year, fluoride released in micrograms/ml was: Group 1: less than 0.08; Group 2: less than 0.08; Group 3: 0.28; Group 4: 0.68; Group 5: 1.12. An ANOVA was used to evaluate the statistical difference between the groups. At the end of 1 year, measurable amounts of fluoride were recorded for all glass ionomer-lined groups with Miracle Mix and GC Lining releasing significantly more fluoride than Ketac-Silver (P less than 0.002).

Evaluation of fluoride release from an orthodontic bonding system

Decalcification around brackets is sometimes observed after orthodontic treatment. Fluoride-releasing orthodontic adhesives have been developed in an attempt to reduce the frequency and severity of decalcification. This study evaluated, in vitro, a light-activated, fluoride-releasing composite resin adhesive, FluorEver OBA. The findings indicate that FluorEver OBA released small concentrations of fluoride ions over time. A mean of 2.6 ppm was released on day 1, decreasing to a mean of 0.42 ppm by day 2 and to 0.04 ppm by day 43. The clinical implications of these findings are discussed.

Hardening of dual-cured cements under composite resin inlays

This study was conducted to determine the extent of hardening of three dual-cured cements under composite resin inlays and to determine the effectiveness of a light-reflecting wedge in promoting curing of the cements in the proximal margin. The exposure times needed to optimally harden the cements were determined by directly exposing the cements to the curing light. Composite resin inlays were bonded in an extracted molar with Dual cement, Dicor light-activated cement, and Duo cement. Cure-Thru reflective wedges were placed in the gingival embrasure of half of the specimens. None of the cements hardened completely by 24 hours when we used an exposure time that met or exceeded that recommended by the manufacturers. The chemical-cure component did not completely cure the cements when light was attenuated by the tooth and restoration. The light-transmitting wedge had little effect on hardening of the cements.

Transmembrane form of the kit ligand growth factor is determined by alternative splicing and is missing in the Sld mutant

The ligand (KL) for the c-kit receptor is a growth factor encoded at the mouse steel (Sl) locus. KL exists in both cell surface and soluble forms, though little is known of the regulation and functional significance of these forms. We show here that tissue-specific alternative splicing gives two types of KL mRNA. Both encode a transmembrane domain, but in transfected cells one produced the soluble form of KL at relatively high levels, whereas the other preferentially gave the cell surface form. Cell surface KL not only stimulated proliferation, but also mediated cell-cell adhesion. The SId allele, which impairs development of hematopoietic cells, melanocytes, and germ cells, has a deletion in the KL gene removing the transmembrane and intracellular domains. Expression of a corresponding cDNA gave a soluble protein that stimulated cellular proliferation but was not associated with the cell surface. These results provide evidence that cell surface KL has a critical role in the intact organism.

In vitro evaluation of a fluoride-releasing orthodontic resin

Decalcification around brackets is sometimes observed following orthodontic treatment. Fluoride-releasing orthodontic adhesives have been developed and used for reduction of the frequency and severity of decalcification. This study evaluated a light-activated, fluoride-releasing resin composite adhesive, FluorEver OBA. Our findings indicate that FluorEver OBA released small concentrations of fluoride ions over time. However, the adhesive had significantly lower tensile bond strengths than a conventional composite cement. Microhardness testing indicated that the resin underneath metal orthodontic brackets was not thoroughly polymerized, which may have contributed to cohesive failures of the resin composite. Despite its lower tensile bond strength, FluorEver OBA may be indicated for cases where decalcification is expected.

Genome regulation in mammalian cells

A theory is presented proposing that genetic regulation in mammalian cells is at least a two-tiered effect; that one level of regulation involves the transition between gene exposure and sequestration; that normal differentiation requires a different spectrum of genes to be exposed in each separate state of differentiation; that the fiber systems of the cell cytoskeleton and the nuclear matrix together control the degree of gene exposure; that specific phosphorylation of these elements causes them to assume a different organizational network and to impose a different pattern of sequestration and exposure on the elements of the genome; that the varied gene phosphorylation mechanisms in the cell are integrated in this function; that attachment of this network system to specific parts of the chromosomes brings about sequestration or exposure of the genes in their neighborhood in a fashion similar to that observed when microtubule elements attach through the kinetochore to the centromeric DNA; that one function of repetitive sequences is to serve as elements for the final attachment of this fibrous network to the specific chromosomal loci; and that at least an important part of the calcium manifestation as a metabolic trigger of different differentiation states involves its acting as a binding agent to centers of electronegativity, in particular proteins and especially phosphorylated groups, so as to change the conformation of the fiber network that ultimately controls gene exposure in the mammalian cell. It would appear essential to determine what abnormal gene exposures and sequestrations are characteristic of each type of cancer; which agonists, if any, will bring about reverse transformation; and whether these considerations can be used in therapy.

Microleakage of indirect composite inlays

The purpose of this in vitro study was to evaluate the microleakage of indirect composite inlays and to compare leakage of inlays with directly placed composite restorations. Standardized MOD preparations were cut in 50 extracted human molars. One gingival margin was placed in enamel above the CEJ, and the other was placed in dentin below the CEJ. Two groups of teeth were directly filled with composites (P-30 and Heliomolar) after being etched, and dentin bonding agents were applied. Two groups of teeth were restored with composite inlays that were fabricated on stone dies. The inlays were made and luted with the same two composites. The last group of teeth was restored with Heliomolar inlays luted with Dual cement. The specimens were thermocycled 300 times between 5 and 50 degrees C. Microleakage was evaluated by use of the silver-nitrate staining technique. The depth of leakage was measured microscopically after the teeth were sectioned. Both direct restorations and inlays showed substantial leakage at gingival-dentin margins; however, there was only superficial leakage at enamel margins. P-30 inlays and Heliomolar inlays cemented with Dual leaked less than direct restorations at the gingival-dentin margins. There was no difference in leakage of enamel margins of inlays and direct restorations, except that direct Heliomolar restorations leaked more than the others. There was no difference in leakage between Heliomolar restorations luted with light-cured or dual-cured cement.

Intrahepatic assembly of very low density lipoproteins: immunologic characterization of apolipoprotein B in lipoproteins and hepatic membrane fractions and its intracellular distribution

Monoclonal antibodies, prepared against rat apoB, were used to examine apoB structure in serum lipoproteins and characterize the forms and localization of apoB in liver membrane fractions and cultured hepatocytes. Of the several antibodies obtained, four, having separate epitopes, were characterized. Western blot analysis showed that three (DB11, F4, and LB14) antibodies recognized both apoBL and apoBS. One antibody (HB41) recognized only apoBL. This antibody showed unusual properties. Competition ELISA assays showed that the epitope recognized by HB41 was more effectively expressed on low density lipoproteins (LDL) compared to very low density lipoproteins (VLDL). In addition, treatment of lipoproteins with detergents and sulfhydryl reducing agents also increased the expression of the HB41 epitope. Since HB41 has been found to inhibit LDL binding to hepatocyte receptors, these data indicate that the HB41 epitope is located on the carboxy-terminal side of the apoBS junction (probably within the LDL receptor binding domain). Western blotting hepatic microsomal subfractions showed that in the rough and smooth microsomes, HB41 recognized only apoBL, while in the Golgi it recognized both apoBL and a protein having a molecular weight slightly smaller. In contrast, Western blotting with a polyclonal antibody known to recognize both apoBL and apoBS showed that, in rough and smooth microsomes, proteins in addition to apoBL and apoBS having molecular weights between 120,000 and 30,000 were recognized. These proteins, likely to be proteolytic fragments of apoB, were barely detectable in the Golgi. Additional biosynthetic studies show that the [35S]methionine-labeled proteins smaller than apoB were immunoprecipitated from the rough microsome subfraction. Pulse-chase experiments show that these are produced with the same kinetics as full-size apoBL and apoBS, indicating that they are not incomplete nascent chains. Finally, immunofluorescence microscopy was used to determine the localization of monoclonal epitopes. ApoB monoclonal antibodies that recognized exclusively apoBL (HB41) and apoBL and apoBS (DB11) produced an immunofluorescence pattern characteristic of the endoplasmic reticulum, but not the Golgi. These data suggest that, in cultured rat hepatocytes, the majority of both molecular weight forms of apoB are localized in the endoplasmic reticulum, the initial site of VLDL assembly. The additional finding that proteolytic fragments of apoB are enriched in the microsomal fraction suggests that if the proteolysis occurs during subcellular fractionation, immature apoB is susceptible to proteolysis.(ABSTRACT TRUNCATED AT 400 WORDS)

A scanning electron microscopic study of enamel surfaces treated with topical fluoride agents in vivo

The morphological appearance of human enamel treated with topical fluoride (F) agents was studied. Maxillary acrylic appliances carrying the enamel sections were worn for 24 h following 5-min application of neutral NaF gel-drops, APF gel and Duraphat varnish. All F treatment induced surface coatings composed of globules, suggestive of CaF2. The sizes of the globules varied according to the F agents and, in general, were less than 1 micron in diameter. The globules formed following neutral NaF gel-drops and APF were spherical; while those produced by Duraphat were flattened, forming a sheet-like deposit. Irregular masses of organic-like material were seen on F- untreated enamel, which were exposed to the oral environment for 24 h (controls). The prolonged retention of a F-rich surface coating may act as a reservoir of F supplement to the enamel microenvironment, which thus contributes to remineralization.

Composite resin compatibility and bond longevity of a dentin bonding agent

The shear strength of a commercial dentin bonding agent was studied using human dentin in vitro. The agent was tested for compatibility with three proprietary composite resins. In addition, some samples were subjected to prolonged water immersion and thermocycling to determine effects on bond strength. There was no statistically significant difference in shear strengths when the three composite resins were used. In addition, there was no difference in shear strengths among those samples thermocycled or immersed for up to one year. The implications of this study are that the dentin bonding agent may be used with several composite resins with no significant difference in bond strengths, and that the bond seems stable when subjected to immersion or simulated intra-oral thermal stresses.

The role of the central globular domain of histone H5 in chromatin structure

Histone H5 contains three tyrosines in the central, apolar region of the molecule. All three tyrosines can be spin labeled at low ionic strength. When the central globular domain is folded at high ionic strength, only one tyrosine becomes accessible to the imidazole spin label. Spin labeling the buried tyrosines prevents the folding of the globular structure, which, in turn, affects the proper binding of the H5 molecule to stripped chromatin. Chromatin complexes reconstituted from such an extensively modified H5 molecule show a weaker protection of the 168 base pair chromatosome during nuclease digestion. However, when only the surface tyrosine of the H5 molecule is labeled, such a molecule can still bind correctly to stripped chromatin, yielding a complex very similar to that of native chromatin. Our data supports the idea that not just the presence of the linker histone H5, but the presence of an intact H5 molecule with a folded, globular central domain in essential in the recognition of its specific binding sites on the nucleosomes. Our data also show that during the chromatin condensation process, the tumbling environment of the spin label attached to the surface tyrosine in the H5 molecule is not greatly hindered but remains partially mobile. This suggests that either the labeled domain of the H5 molecule is not directly involved in the condensation process or the formation of the higher-order chromatin structure does not result is a more viscous or tighter environment around the spin label. The folded globular domain of H5 molecule serves in stabilizing the nucleosome structure, as well as the higher-order chromatin structure.

Effect of Tyrosyl modifications on nucleosome reconstitution: a spin-labeling study

An imidazole spin-label was used to study the role of tyrosyl residues in the reassociation process for the nucleosome core particle. The nucleosome core particle, containing 145 base pairs of DNA and a histone core (two each of the four histones H2S, H2B, H3, and H4), was isolated from chicken erythrocytes. Native particles were first dissociated in 2 M NaCl and labeled with varying concentrations of imidazole spin-label. The labeled histone core and endogenous DNA were then reassociated back by salt step dialysis. Reconstituted spin-labeled complexes, purified by an isokinetic sucrose gradient, were found to have physical properties identical with those of unlabeled native particles. Spin-labeling the surface tyrosines of the histone core did not interfere with proper reassociation of the nucleosome core complex. ESR spectra of the reconstituted nucleosomes core complex are not the strongly anisotropic type, suggesting that labeled surface tyrosines in the histone core are not involved in specific DNA-histone interaction nor does wrapping of DNA on the histone core involve very close contact with the label. When labeling was carried out under denaturing conditions following exposure of the histone core to urea, additional histone tyrosine residues were spin-labeled. The resulting histone-DNA complexes that formed after reassociation had physical properties different from those of the native nucleosomes core. This result suggested that some of the "buried" tyrosines are essential for specific histone-histone interactions that lead to stable histone core structures. Spin-labeling the buried tyrosines prevented to compact supercoiling of DNA into nucleosome core particle.

ESR spin label studies of the nucleosome core particle and histone core

An imidazole spin label has been used to study the accessibility and conformational state of tyrosines in both the nucleosome core particles and histone core extracted from chicken erythrocytes. About 40% of the tyrosyl residues in the histone core can be labeled under nondenaturing conditions. However, less than 15% of the tryosyls in the nucleosome core particle can be labeled even at 200- to 300-fold M excess of label. The effect of urea on the conformational state of the spin-labeled tyrosyls in both the nuclesome core particles and the histone core has been studied. Ionic effects on the spin-labeled nucleosome core have been investigated. Several conformational transitions are observed in the range of 1 mM NaCl to 2.5 M NaCl. Three major transitions are found at 0.1 M to 0.6 M, 0.7 M to 1.8 M and 2 M to 2.5 M NaCl, respectively. The observed changes can be interpreted as swelling and conformational change of the inner histone core, gradual separation of DNA from the histone core, and tightening of the histone core.

Conformational state of DNA in chromatin subunits. Circular dichroism, melting, and ethidium bromide binding analysis

This study compares some physical properties of DNA in native chromatin and mono-, di-, trinucleosomes obtained after mild micrococcal nuclease digestion. Melting curves and derivatives are shown to be very similar from one sample to another although a shift from 79 to 82 degrees C is observed between the mainly monophasic peak of multimers and chromatin. Careful analysis of the positive band of the circular dichroism spectra shows the appearance of a shoulder at 275nm, the intensity of which increases from the mono- to the di- and trinucleosome. This shoulder is maximum for native chromatin. At the same time binding isotherms of ethidium - bromide are characterized by two highly fluorescent binding sites for all the samples but the product KN of the apparent binding constant of the higher affinity binding sites by the apparent number of those sites increases from the mono- to the di- and trinucleosome. There again the valus is maximum for native chromatin. Such results strongly suggest that the native state of chromatin requires something more than the indefinite repeat of an elementary subunit.