Pituitary-adrenal response in preterm very low birth weight infants after treatment with antenatal corticosteroids

Antenatal corticosteroids have been widely used for the prevention of respiratory distress syndrome in preterm neonates, yet little is known about their effects on the hypothalamic-pituitary-adrenal axis in these infants. We prospectively evaluated pituitary-adrenal function in 61 preterm (< 32 gestational weeks), very low birth weight (< 1500 g) infants on days 7 and 14 of life using the human CRH stimulation test. The baseline and poststimulation plasma ACTH and serum cortisol concentrations did not differ significantly between infants whose mothers received no antenatal corticosteroids, and those whose mothers received 1-2 doses or > 2 doses (mean 7.2 doses) of prenatal dexamethasone (P = > 0.12). The number of doses of dexamethasone and the time intervals between the last dose of drug and delivery did not significantly affect the pituitary-adrenal responsiveness on days 7 and 14 of life. Among infants who did not require mechanical ventilation at the time of the human CRH test, significantly higher plasma ACTH (P < 0.014) and lower serum cortisol concentrations (P < 0.02) were found on day 14 than on day 7. In contrast, none of the poststimulation hormone concentrations were significantly different in ventilated infants between days 7 and 14. The relationship between the blood hormone concentrations in each time epoch (day 7 and day 14) and possible confounding factors including gestational and postconceptional age, birth weight, sex, Apgar scores, mode of delivery, single or higher order births, and mode of ventilation were determined. Plasma ACTH concentrations on day 7 were found to be significantly higher in ventilated than in nonventilated infants (P = 0.006). However, none of the aforementioned factors correlated significantly with plasma ACTH concentrations on day 14. Serum cortisol concentrations on day 7 were significantly higher in infants of greater gestational age (P = 0.039) and birth weight (P = 0.013), with lower Apgar scores at 1 and 5 min (P = 0.021 and P = 0.049, respectively), and in those delivered vaginally (P = 0.047). Similarly, serum cortisol concentrations on day 14 were found to be significantly higher in infants with lower Apgar scores at 1 and 5 min (P = 0.011 and P = 0.014, respectively) and in infants requiring mechanical ventilation (P = 0.014). Our results suggest that single or multiple courses of antenatal dexamethasone have no long-lasting suppressive effects on pituitary-adrenal function in preterm, very low birth weight infants. Maturation of pituitary function appears to be more advanced than adrenal function. The organ's ability to respond appropriately to various stressful stimuli indicates that the pituitary-adrenal axis is highly responsive at these early gestational ages.

A substitute for facial replica in mannequin procedures

The use of mannequin exercises has been a teaching tool in the education of dental students. Various commercially available materials to simulate extraoral facial structure form part of this apparatus, also called a "phantom head." It is not always practical, with cost considerations, to replace this external component when unavoidable wear and tear occurs. An alternative that uses a recycled milk carton is presented as an inexpensive substitute.

Pituitary-adrenal suppression and recovery in preterm very low birth weight infants after dexamethasone treatment for bronchopulmonary dysplasia

High dose dexamethasone is frequently used for the treatment of neonatal respiratory conditions and to facilitate weaning from mechanical ventilation in preterm, very low birth weight infants. However, very little is known about the severity, site, and duration of steroid-induced hypothalamic-pituitary-adrenal axis suppression in this category of patients. Twenty-three preterm, very low birth weight infants who received a full 3-week dose-tapering course of dexamethasone were prospectively studied, with a human CRH stimulation test performed at three different times: before the start of steroid treatment (week 0), immediately after the course (week 3), and 4 weeks after stopping dexamethasone (week 7). Plasma ACTH and serum cortisol concentrations were measured at 0 (baseline), 15, 30, and 60 min. Immediately after the steroid course (week 3), both basal and poststimulation plasma ACTH and serum cortisol concentrations were markedly suppressed. The hormone concentrations at 0, 15, 30, and 60 min in week 3 were significantly lower than their corresponding levels in week 0 (P < 0.0001 for both ACTH and cortisol) and week 7 (P < 0.0001 and P < 0.005 for ACTH and cortisol, respectively). In contrast, when the hormone levels in week 7 were compared to their corresponding concentrations in week 0, only the 60 min serum cortisol concentration in week 7 was significantly lower (P = 0.02). The currently used dosage of dexamethasone caused severe pituitary-adrenal suppression immediately after treatment, but substantial recovery of the endocrine axis was observed 4 weeks after discontinuation of therapy. Although the recovery appeared to be earlier with the pituitary center, both pituitary and adrenal glands were capable of mounting a biochemically adequate response to exogenous human CRH stimulation at this stage. Steroid replacement therapy may be desirable at a time of stress in the immediate posttreatment period, but it would seem unnecessary 1 month after stopping dexamethasone treatment.

The role of a single formin isoform in the limb and renal phenotypes of limb deformity

BACKGROUND

Mutations of the murine limb deformity (ld) locus are responsible for a pleiotropic phenotype of completely penetrant limb malformations and incompletely penetrant renal agenesis and/or dysgenesis. The ld locus encodes a complex family of mRNA and protein isoforms.

MATERIALS AND METHODS

To examine the role of one of the more prominent of these isoforms, isoform IV, we specifically eliminated it by gene targeting.

RESULTS

Unlike other mutant ld mice, homozygous mice bearing this isoform IV disruption display incompletely penetrant renal agenesis, but have perfectly normal limbs. Whole mount in situ hybridization demonstrated that this targeted disruption was specific for isoform IV and did not interfere with the expression of other ld isoforms. The isoform IV-disrupted allele of ld does not complement the renal agenesis phenotype of other ld alleles, in a manner consistent with its penetrance, and like the isoform IV-deficient mice, these compound heterozygotes have normal limbs. Sequence analysis of formin isoform IV in other ld mutant alleles did not detect any amino acid changes relative to the strain of origin of the mutant allele.

CONCLUSIONS

Thus, the disruption of isoform IV is sufficient for the renal agenesis phenotype, but not the limb phenotype of ld mutant mice. Structural mutations in this isoform are only one of several genetic mechanisms leading to the renal phenotype, since amino acid changes in this isoform were not detected. These results demonstrate that this gene is limb deformity, and that variable isoform expression may play a role in generating the pleiotropic ld phenotype.

Potent, long-acting bradykinin antagonists for a wide range of applications

Actions of bradykinin (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg; BK) are mediated by constitutively expressed B2 receptors (which require the full BK peptide chain) and by B1 receptors (which require BK (1-8) as ligand) that are induced in inflammation. BK has many functions in normal and pathological physiology, including initiation of most, if not all, inflammation. BK also evidently functions as an autocrine stimulant for growth of small cell lung cancer (SCLC). A new group of BK antagonists containing the novel amino acid alpha-(2-indanyl)glycine (Igl) provides both broad-spectrum and selective antagonists for all these functions. As examples, D-Arg-Arg-Pro-Hyp-Gly-Igl-Ser-D-Igl-Oic-Arg (B9430) is an extremely potent and long-acting antagonist of both B1 and B2 receptors, is stable against endogeneous kininase enzymes, and is active in various in vivo models, including by intragastric administration. Acylation of B9430 with dehydroquinuclidine-2-carboxylic acid (Dhq) gives B9562, a highly selective B2 antagonist. In contrast, Lys-Lys-Arg-Pro-Hyp-Gly-Igl-Ser-D-Igl-Oic (B9858) is a highly potent and selective B1 antagonist. The dimer of B9430 linked at the amino terminus with suberimide is a potent selectively cytotoxic agent for SCLC cells. Results with these peptides suggest that a new generation of antiinflammatory and anticancer drugs may be at hand.

Potent, long-acting, orally-active bradykinin antagonists for a wide range of applications

Actions of bradykinin (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg; BK) are mediated by constitutively expressed B2 receptors, that require the full BK peptide chain, and by B1 receptors, induced in inflammation, that use BK(1-8) as ligand. In addition to many physiological and pathophysiological functions, the growth factor activity of BK evidently allows it to act as an autocrine stimulant for small cell lung cancer. A new group of BK antagonists containing the novel amino acid a-(2-indanyl)glycine provides extremely potent broad-spectrum as well as selective antagonists for all these functions.

FBP WW domains and the Abl SH3 domain bind to a specific class of proline-rich ligands

WW domains are conserved protein motifs of 38-40 amino acids found in a broad spectrum of proteins. They mediate protein-protein interactions by binding proline-rich modules in ligands. A 10 amino acid proline-rich portion of the morphogenic protein, formin, is bound in vitro by both the WW domain of the formin-binding protein 11 (FBP11) and the SH3 domain of Abl. To explore whether the FBP11 WW domain and Abl SH3 domain bind to similar ligands, we screened a mouse limb bud expression library for putative ligands of the FBP11 WW domain. In so doing, we identified eight ligands (WBP3 through WBP10), each of which contains a proline-rich region or regions. Peptide sequence comparisons of the ligands revealed a conserved motif of 10 amino acids that acts as a modular sequence binding the FBP11 WW domain, but not the WW domain of the putative signal transducing factor, hYAP65. Interestingly, the consensus ligand for the FBP11 WW domain contains residues that are also required for binding by the Abl SH3 domain. These findings support the notion that the FBP11 WW domain and the Abl SH3 domain can compete for the same proline-rich ligands and suggest that at least two subclasses of WW domains exist, namely those that bind a PPLP motif, and those that bind a PPXY motif.

Core structure of gp41 from the HIV envelope glycoprotein

The envelope glycoprotein of human immunodeficiency virus type 1 (HIV-1) consists of a complex of gp120 and gp41. gp120 determines viral tropism by binding to target-cell receptors, while gp41 mediates fusion between viral and cellular membranes. Previous studies identified an alpha-helical domain within gp41 composed of a trimer of two interacting peptides. The crystal structure of this complex, composed of the peptides N36 and C34, is a six-helical bundle. Three N36 helices form an interior, parallel coiled-coil trimer, while three C34 helices pack in an oblique, antiparallel manner into highly conserved, hydrophobic grooves on the surface of this trimer. This structure shows striking similarity to the low-pH-induced conformation of influenza hemagglutinin and likely represents the core of fusion-active gp41. Avenues for the design/discovery of small-molecule inhibitors of HIV infection are directly suggested by this structure.

A prospective randomized study of three types of platelet concentrates in patients with haematological malignancy: corrected platelet count increments and frequency of nonhaemolytic febrile transfusion reactions

We prospectively randomized 51 patients with haematological malignancy requiring platelet concentrates (PCs) to receive either single donor platelet-pheresis products (SD-PC), PCs made from pooled buffy coats (BC-PC) or pooled units of platelets made by the platelet-rich plasma method (PRP-PC). The leucocyte content of each type of PC was 0.33 (0.03-13.5), 5.68 (0.19-99.0) and 365 (65-910) x 10(6); median (range), respectively; P < 0.0001. All red cell transfusions were leucodepleted by filtration. Statistical comparison of the probability of the occurrence of a nonhaemolytic febrile transfusion reaction (NHFTR) following transfusion of PCs in patients in each group showed a significant decrease for the SD-PC and BC-PC groups (0.031 and 0.038, respectively) when compared with PRP-PC (0.171); P = 0.0001. The actual corrected platelet count increments (CCI) at 1-6 and 18-24 h post-transfusion for all three types of PC did not differ significantly. We conclude that transfusion of PRP-PC is associated with a significant increase in NHFTR.

The pituitary-adrenal responses to exogenous human corticotropin-releasing hormone in preterm, very low birth weight infants

To evaluate the pituitary-adrenal reserve and to standardize the methodology of performing the human CRH (hCRH) stimulation test, we performed the hCRH test on 14 preterm (< 32 gestational weeks), very low birth weight infants, who did not receive antenatal or postnatal corticosteroid treatment, on days 7 and 14 of life. Blood samples were obtained 0 (baseline), 15, 30, and 60 min after an iv dose of hCRH (1 microgram/kg). The plasma ACTH concentration rose from a basal value of 5.7 +/- 0.6 pmol/L (mean +/- SEM) to 11.9 +/- 2.1 pmol/L (P < 0.005), 9.2 +/- 1.2 pmol/L (P < 0.005), and 7.7 +/- 0.8 pmol/L (P < 0.005) at 15, 30, and 60 min, respectively. The corresponding rises in serum cortisol from a basal concentration of 396 +/- 67 nmol/L were 509 +/- 71 nmol/L (P < 0.0001), 647 +/- 62 nmol/L (P < 0.0001), and 578 +/- 60 nmol/L (P < 0.0001). The plasma ACTH concentration consistently peaked early at 15 min, whereas the maximum cortisol response occurred 30 min post-hCRH stimulation. No significant differences were detected between the hCRH tests performed on days 7 and 14 (P > 0.15). Mechanical ventilation, infant gender, and mode of delivery did not significantly influence the hormonal responses (P > 0.25). We have defined in this study the pattern, the magnitude of the pituitary-adrenal response, and the timing of the peak concentrations of plasma ACTH and serum cortisol in relation to a standard iv dose of hCRH. The hCRH test in very low birth weight infants appears to be safe and reproducible, and produces a pituitary-adrenal response comparable to that seen in older children and adults, indicating that pituitary-adrenal function is mature at these early stages of gestation.

The mouse formin (Fmn) gene: genomic structure, novel exons, and genetic mapping

Mutations in the mouse formin (Fmn) gene, formerly known as the limb deformity (ld) gene, give rise to recessively inherited limb deformities and renal malformations or aplasia. The Fmn gene encodes many differentially processed transcripts that are expressed in both adult and embryonic tissues. To study the genomic organization of the Fmn locus, we have used Fmn probes to isolate and characterize genomic clones spanning 500 kb. Our analysis of these clones shows that the Fmn gene is composed of at least 24 exons and spans 400 kb. We have identified two novel exons that are expressed in the developing embryonic limb bud as well as adult tissues such as brain and kidney. We have also used a microsatellite polymorphism from within the Fmn gene to map it genetically to a 2.2-cM interval between D2Mit58 and D2Mit103.

Submargination of a resin luting cement--a clinical case report

The purpose of this case report was to examine the marginal integrity of an indirect inlay and an onlay luted with resin luting cement over a four year period. A technique to seal the occlusal margins of the inlay restoration was reported. Over time, the occlusal margins of the inlay were noticeably submarginated due to wear degradation of the resin inlay cement. The onlay margins were less affected by wear. Clinical techniques to overcome submargination problems were discussed.

Paclitaxel enhances in vitro radiosensitivity of squamous carcinoma cell lines of the head and neck

Squamous cell carcinoma of the head and neck is the fourth most common cancer in the United States, and therapy for very advanced cases is relatively ineffective. Paclitaxel has activity against cancers of the breast, lung, prostate, cervix, and ovary. The activity of paclitaxel for squamous cell carcinoma of the head and neck is less certain, and results of its radiosensitization properties have been variable. The radiation responses of two squamous carcinomas, SCC-9 (oropharynx) and HEP-2 (larynx), were examined to determine the radiosensitizing potential of paclitaxel. In vitro exposures for 24 and 48 h with paclitaxel concentrations of 10(-4) to 6 x 10(-2) microg/ml were followed by irradiation of 0.1-10 Gy. Percent survival was calculated by colony count, and the paclitaxel-radiation interaction was quantitated by the median effect principle and the combination index method of Chou and Talalay. The paclitaxel-radiation combination resulted in multiphasic interactions in both 24 and 48 h paclitaxel pretreatment in SCC-9 and HEP-2 cell lines. In general there was slight synergism [combination index (CI) <1] at low dose-low effect levels (e.g., at a paclitaxel concentration of 0.002 microg/ml or lower and radiation of 0.1-0.3 Gy), moderate antagonism (CI >1) at median dose ranges and strong synergism (CI <<1) at high dose ranges (e.g., at a paclitaxel concentration of 0.012-0.06 microg/ml and radiation doses of 3-10 Gy), especially at a surviving fraction of <0.1, which is therapeutically relevant. The median effect principle and combination index method provided a simple way to quantitate the synergism or antagonism of a paclitaxel-radiation interaction under various conditions. This analysis demonstrated that paclitaxel-radiation synergy exists at doses that are readily achievable in the clinical scenario for both agents and that greater synergy occurred at high dose-high effect levels. These results suggest that the combination of both therapies should be explored further in clinical trials assessing the treatment of squamous cell carcinomas of the head and neck.

Genetic evidence that formins function within the nucleus

The murine limb deformity (ld) locus encodes a set of proteins, termed formins, that are required for embryonic limb and kidney development. Previous studies had indicated that these proteins are located in the nucleus and cytoplasm and have biochemical properties consistent with an action within the nucleus. To test the notion that nuclear localization is crucial for formin function, we carried out molecular and biochemical studies on three ld alleles. We show that two transgene-induced alleles, ldTgHd and ldTgBri, generate similar COOH-truncated formins that lack the terminal 110 amino acids, while a third allele, ldIn2, generates a less extensively truncated formin that lacks the terminal 42 amino acids. Using subcellular fractionation analysis, we find that wild-type formin is detected in both nuclear and cytosolic fractions; in contrast, the truncated formins encoded by ldTgHd and ldTgBri are strictly cytosolic. The less extensively truncated ldIn2 formin shows a similar, but less complete, localization defect. Consistent with this weaker cellular phenotype, hind limbs from ldIn2 mice have milder skeletal defects than those of ldTgBri mice. These observations define a small region in the carboxyl terminus that is required for nuclear localization and suggest that nuclear localization plays a role in formin action.

The effect of microabrasion on restorative materials and tooth surface

The effect of microabrasion on human enamel has been well documented; however, no information is available on its effect on dentin or restorative materials. The purpose of this study was to evaluate the effect of the microabrasion technique on the surface roughness of restorative materials and enamel and dentin surfaces. Flat disks of amalgam, composite resin, porcelain, and glass ionomer were evaluated. Labial enamel of three maxillary incisors and three molars that were flattened buccally to expose dentin were also tested. The Prema microabrasion compound was applied to each sample with a 10:1 gear-reduction, slow-speed handpiece for 5 seconds, then rinsed for 10 seconds. Roughness was determined with a profilometer. This procedure was repeated 20 times for each sample. A polyvinylsiloxane impression of the surface was taken after 0, 5, 10, 15, and 20 applications and examined under a scanning electron microscope. Enamel surface roughness did not improve as previously reported, suggesting that changes in optical characteristics may not be as important as removal of enamel in obtaining esthetic results. Dentin and glass ionomer exhibited an increase in roughness, such that their presence contraindicates the technique. Amalgam was essentially polished. Porcelain was most resistant to the effects of microabrasion. Judicious use of the technique, especially when restorative materials are present, is advised.

Formin binding proteins bear WWP/WW domains that bind proline-rich peptides and functionally resemble SH3 domains

The formins, proteins involved in murine limb and kidney development, contain a proline-rich region that matches consensus sequences for Src homology 3 (SH3) ligands. To identify proteins that interact with formins, we used this proline-rich region to screen mouse limb bud expression libraries for formin binding proteins (FBPs). As expected, we found one class of FBPs that contains SH3 domains, including two novel members of this class. In addition, however, we also found a novel class of FBPs that contains one or two copies of a 26 amino acid homology region that has been recently termed the WWP or WW motif. We demonstrate that WWP/WW domains as short as 26 amino acids can act as modular protein-binding interfaces that bind with high affinity to proline-rich sequences that are similar and, in some cases, identical to SH3 ligands. Furthermore, we find that the WWP/WW domain can compete with the Abl SH3 domain in binding a proline-rich peptide present in formin. Our results suggest that these novel protein interaction domains can perform functions similar to those of SH3 domains and, thus, might regulate SH3 interactions with target proteins through competitive binding.

Formin isoforms are differentially expressed in the mouse embryo and are required for normal expression of fgf-4 and shh in the limb bud

Mice homozygous for the recessive limb deformity (ld) mutation display both limb and renal defects. The limb defects, oligodactyly and syndactyly, have been traced to improper differentiation of the apical ectodermal ridge (AER) and shortening of the anteroposterior limb axis. The renal defects, usually aplasia, are thought to result from failure of ureteric bud outgrowth. Since the ld locus gives rise to multiple RNA isoforms encoding several different proteins (termed formins), we wished to understand their role in the formation of these organs. Therefore, we first examined the embryonic expression patterns of the four major ld mRNA isoforms. Isoforms I, II and III (all containing a basic amino terminus) are expressed in dorsal root ganglia, cranial ganglia and the developing kidney including the ureteric bud. Isoform IV (containing an acidic amino terminus) is expressed in the notochord, the somites, the apical ectodermal ridge (AER) of the limb bud and the developing kidney including the ureteric bud. Using a lacZ reporter assay in transgenic mice, we show that this differential expression of isoform IV results from distinct regulatory sequences upstream of its first exon. These expression patterns suggest that all four isoforms may be involved in ureteric bud outgrowth, while isoform IV may be involved in AER differentiation. To define further the developmental consequences of the ld limb defect, we analyzed the expression of a number of genes thought to play a role in limb development. Most significantly, we find that although the AERs of ld limb buds express several AER markers, they do not express detectable levels of fibroblast growth factor 4 (fgf-4), which has been proposed to be the AER signal to the mesoderm. Thus we conclude that one or more formins are necessary to initiate and/or maintain fgf-4 production in the distal limb. Since ld limbs form distal structures such as digits, we further conclude that while fgf-4 is capable of supporting distal limb outgrowth in manipulated limbs, it is not essential for distal outgrowth in normal limb development. In addition, ld limbs show a severe decrease in the expression of several mesodermal markers, including sonic hedgehog (shh), a marker for the polarizing region and Hoxd-12, a marker for posterior mesoderm. We propose that incomplete differentiation of the AER in ld limb buds leads to reduction of polarizing activity and defects along the anteroposterior axis.

Polydactylous limbs in Strong's Luxoid mice result from ectopic polarizing activity

Strong's Luxoid (1stD) is a semidominant mouse mutation in which heterozygotes show preaxial hindlimb polydactyly, and homozygotes show fore- and hindlimb polydactyly. The digit patterns of these polydactylous limbs resemble those caused by polarizing grafts, since additional digits with posterior character are present at the anterior side of the limb. Such observations suggest that 1stD limb buds might contain a genetically determined ectopic region of polarizing activity. Accordingly, we show that mutant embryos ectopically express the pattern-determining genes fibroblast growth factor 4 (fgf-4), sonic hedgehog (shh), and Hoxd-12 in the anterior region of the limb. Further, we show that anterior mesoderm from mutant limbs exhibits polarizing activity when grafted into host chicken limbs. In contrast to an experimentally derived polydactylous transgenic mouse, forelimbs of homozygotes show a normal pattern of Hoxb-8 expression, indicating that the duplication of polarizing tissue here occurs downstream or independently of Hoxb-8. We suggest that the 1st gene product is involved in anteroposterior axis formation during normal limb development.

The relationship between preparation convergence and retention of extracoronal retainers

PURPOSE

Although traditional ideal convergence (the sum of taper of the opposite sides) for crown preparation has been arbitrarily set at 4 degrees to 10 degrees, some believe absolute parallelism yields the highest retention. This study examined the relationship between the degree of convergence of a machined metal die and the retention of its casting.

MATERIALS AND METHODS

The method used was that of cementing cast metal crowns onto full crown preparations on brass dies with varying convergence angles, and then recording the force required to remove the crowns from the dies in a vertical direction using a Tate-Emery Testing Machine and Load Indicator.

RESULTS

It was found that retention (i.e., the force needed to remove the cemented castings from the die in their common long axis) increases from 0 degree convergence to peak between 6 degrees to 12 degrees convergence. It also seems that a critical film thickness does exist for optimum retention, and that film thicknesses smaller than the critical thickness may be responsible for the phenomenon that we have observed and directly related to the convergence angle itself.

CONCLUSIONS

There seems to be experimental data supporting the use of traditionally taught convergence. Our study found that convergence angles between 6 degrees and 12 degrees seem to be optimum for tooth crown preparation when one plans to use zinc phosphate cement. Convergence angles of less than 6 degrees may not be desirable even if they can be clinically achieved. The results of our study indicate that a relationship exists between the convergence angle and the critical cement thickness that is necessary to realize the maximum strength properties of zinc phosphate cement.

Caries protection after orthodontic band cementation with glass ionomer

This study evaluated the resistance of the enamel to an artificial caries challenge after removing orthodontic bands cemented with a glass ionomer cement (GIC). Ten extracted caries-free molars were cleaned with a slurry of pumice and randomly divided into 2 groups of 5 teeth each: Group 1: Cementation with GIC (Fuji) and Group 2: Cementation with a zinc phosphate cement (Mizzy). Both cements were handled according to manufacturer's instructions. Before cementing the bands, an area of S x S mm was masked with adhesive tape on the lingual surfaces of all teeth. The orthodontic bands were cemented over this adhesive tape. After band cementation, the occlusal and gingival margins of the band were delineated with a bur on the tooth surface. The teeth were thermocycled (200 cycles, 5-55 degrees C, 30-second dwell time) and stored in distilled water for 24 hours. Then, the bands and adhesive tape were removed and the teeth again stored in distilled water for a week, changing the water daily. The teeth were then varnished with the exception of a 5 x 5 mm window (including previously exposed and covered areas) on the buccal and lingual surfaces. All teeth were then placed in an acidified gel (pH 4.5) for 5 weeks to produce artificial caries. At least three sections from the exposed and covered areas were made from the buccal and lingual challenged areas. Sections were ground to approximately 100 microns. Polarized microscopy and image analysis were used to analyze the results.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparative study of three glass ionomer base materials

This study compared the compressive and diametral tensile strength, compressive modulus, shear bond strength to dentin and resin composite, marginal gap between the base and tooth in Class V cavity preparation, and fluoride release of three glass ionomer base materials. In general, visible light-cured (VLC) base materials outperform the autopolymerizing glass ionomer base Ketac-Bond. The compressive modulus is significantly less for the VLC glass ionomer materials Vitrebond and Fuji LC compared to Ketac-Bond. The Fuji LC had greater diametral tensile strength, compressive strength, bond to dentin and bond to resin composite than Vitrebond or Ketac-Bond. The fluoride release of Vitrebond was greater than Ketac-Bond or Fuji LC. The marginal gap at the tooth/base interface was significantly less with the Fuji LC compared to the other two materials.

Retention of Class 3 composite restorations: retention grooves versus enamel bonding

This study compared the tensile loads required to dislodge class 3 composite restorations with and without retention grooves. Thirty extracted human maxillary central incisors were divided into two groups of 15 teeth each. A C-shaped class 3 preparation with lingual access was cut into one approximal surface of each incisor to standardized dimensions using a #329 bur. A 0.5-1.0 mm 45 degrees bevel was prepared on the lingual and gingival enamel margins. In one group, an incisal retention point and a gingival retention groove were prepared with a #1/4 round bur to a depth of 0.25-0.5 mm; the other group had no retention grooves/points. A nonretentive 2 mm round "well" with diverging walls was cut 0.5-1.0 mm into the axial dentin to accommodate the head of a pin that was inserted prior to composite restoration. Each pin shaft extended approximally from its incisor. A bonding agent (Universal Bond 3 Primer and Adhesive, L D Caulk) was applied to each preparation, and composite resin (Prisma APH, L D Caulk) was inserted incrementally. Each increment was exposed to 40 seconds of polymerization light. Restoration surfaces were finished and polished with Sof-Lex disks (3M Dental Products). Specimens were thermocycled 6 to 60 degrees C, for 500 cycles, with a 30-second dwell time. They were then positioned in an aligning device, and pins were loaded in tension in an Instron Testing Machine at a head speed of 2 mm/minute to restoration failure. Mean (SD) failure loads in Newtons were: no grooves 83.6 (19.8); grooves 69.6 (18.1).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of a resin lining and rebonding on the marginal leakage of amalgam restorations

This in vitro study compared microleakage in Class V amalgam restorations with three different lining agents and with no lining agent, with and without resin rebonding of the margins. Eight groups of ten molars were divided into four pairs of groups. Class V preparations were cut in the facial surfaces of each molar so that the occlusal margin was in enamel and the gingival margin in dentine. The preparations in one pair of groups received no lining agent; the preparations in the remaining three pairs of groups were lined with one of the following: Copalite, Universal Bond 3 (UB3) Primer and Adhesive, or UB3 Primer only. The enamel walls of the preparations receiving the UB3 Primer and Adhesive were etched prior to applying the lining material. Amalgam was hand condensed into each preparation. In one of each pair of groups, the margins of restorations were treated with 37% phosphoric acid gel, rinsed and dried, and UB3 Adhesive was applied over amalgam and tooth margins and polymerized (rebonded). Specimens were thermocycled, stained and sectioned. Microleakage was graded using a stereomicroscope. Mean microleakage scores for occlusal and gingival margins were calculated and analysed. At enamel margins, non-rebonded Copalite and all rebonded specimens showed less microleakage than the other non-rebonded groups. The group lined with UB3 Primer only and rebonded showed significantly less (P < 0.01) microleakage at enamel margins than all the other groups except the group lined with Copalite and rebonded. At cementum/dentine margins, restorations lined with UB3 Primer and rebonded showed significantly less microleakage than the other groups.

Sensitive high-performance liquid chromatographic assay for the determination of chlorhexidine in saliva

A high-performance liquid chromatographic assay was developed to determine salivary chlorhexidine concentration. Saliva sample (200 microliters) was extracted into methylene chloride. Chromatographic separation was achieved with a C18 column using a mobile phase of acetonitrile-0.05 M sodium acetate and 0.005 M heptanesulfonic acid (40:60, v/v). The standard curve was linear from 0.051 to 20.48 micrograms/ml (r2 > or = 0.997). Intra-day and inter-day coefficients of variation were < 5.5 and < or = 9%, respectively. The assay is rapid, sensitive, simple, and successfully used for quantitating salivary chlorhexidine content released from a chlorhexidine-impregnated resin worn by patients.

Effect of rinse time on microleakage between composite and etched enamel

This study compared microleakage of composite bonded to etched flattened enamel in seven groups of five extracted maxillary molars. The facial enamel of the molars was ground flat and etched for 20 seconds with 37% phosphoric acid gel. In one group, etching gel was not rinsed but dried only. In four groups, gel was rinsed with an air/water spray for varying amounts of time. In the other two groups, gel was rinsed with water only for two different amounts of time. Etched surfaces were dried, and a liquid resin was applied and polymerized; a button of composite resin was polymerized to the flattened surface. Specimens were thermocycled, stained, then sectioned longitudinally. Microleakage was measured at the occlusal and gingival enamel margins and expressed as a percentage of the total length of interface. A mean (SD) percentage microleakage was determined at the occlusal and at the gingival margins for each group as follows: no rinse--89.60 (14.34); one second--water 0 (0), air/water 0 (0); three seconds--water 0.98 (1.34), air/water 0 (0); five seconds--air/water 0 (0); 20 seconds--air/water 0 (0). Because of abnormal distribution, data were analyzed using Wilcoxon two-sample tests. The no-rinse group had significantly more microleakage than any of the other groups (P = 0.0067), which were not significantly different from each other (P = 0.18). A one-second rinse with either water or air/water spray was as effective as a 20-second rinse with air/water spray in preventing microleakage at the resin-enamel interface.

Two-step provisional technique for onlay preparations

Compared to full crown temporization, direct autocured resin provisional technique for intracoronal onlay preparations is more complicated and less predictable. Clinical concerns include possible pulpal irritation, extra chair time for contouring proximal and marginal excess, and a critically short time constraint to remove the curing resin in the "rubbery stage" to avoid distortion or "locking" into the preparation. A two-step direct technique using two new light-cured provisional resins addresses these problems. First, a light-cured, elastic resin is condensed against the internal preparation walls and confined within a wedged metal matrix band. Then, using a clear template matrix, the elastic foundation is overlaid with a strong and esthetic light-cured provisional resin.

Elevated DT-diaphorase activity and messenger RNA content in human non-small cell lung carcinoma: relationship to the response of lung tumor xenografts to mitomycin Cł

The enzyme DT-diaphorase (DTD; NAD(P)H:quinone oxidoreductase, EC 1.6.99.2), is an obligate two electron reductase which catalyzes reduction of a broad range of substrates, including quinones. We report here variations in DTD concentrations among different classes of lung tumors known also to vary in their responsiveness to cytotoxic agents. Small cell lung carcinomas (SCLCs) and cell lines derived from them have the low DTD activities and mRNA content characteristic of normal human lung, whereas non-small cell lung carcinomas (NSCLCs) have greatly elevated levels. DTD activity was increased up to 80-fold in NSCLC tumors relative to normal lung and 20-35-fold in NSCLC relative to SCLC cell lines. Increased DTD activity appeared to be a function of the NSCLC phenotype rather than a result of derivation from a cell type rich in DTD, since all histological classes of NSCLC showed this phenotype. In addition, where transfection of SCLC cell lines with the v-Ha-ras protooncogene caused a transition to a NSCLC phenotype, DTD activity was also elevated. Neuroendocrine-positive cells (SCLC, carcinoids, and a few NSCLC lines) typically had far lower DTD activities than did cell lines which lacked neuroendocrine markers (most NSCLC cells and mesotheliomas). High DTD activity may be exploited in the design of drugs which undergo bioreductive activation by this enzyme. Consistent with this, xenografts derived from NSCLC cell lines with high DTD that were grown in athymic nude mice were more susceptible to the antitumor quinone, mitomycin C, than were xenografts derived from SCLC cells containing low DTD. These data provide a mechanistic basis for the rational design of more effective bioreductive antitumor agents for use against NSCLC.

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.