Electrothermal bonding: shear bond strength of orthodontic brackets after two weeks.

Electrothermal bonding is based on acceleration of the setting reaction of a bonding: resin by the selective application of heat to the orthodontic bracket through the passage of a low voltage electric current. The purpose of this study was to compare the shear bond strength of nine resins comprising chemically-cured, light-cured, and glass ionomer types, 14 days after electrothermal and conventional bonding. Mean shear and bond strengths ranged from a low of 7.4 MPa for Sequence (electrothermally bonded) to a high of 15.4 MPa Concise (control). There was no statistically significant difference between the electrothermal and conventional bonding methods. All the resins produced bond strengths adequate for clinical orthodontics at 14 days.

Pulse oximetry in infants of < 1500 gm birth weight on supplemental oxygen: a national survey.

OBJECTIVE: To determine practices related to the use of pulse oximetry in monitoring infants of < 1500 gm birth weight on supplemental oxygen. STUDY DESIGN: A mailing list of all neonatal intensive care units with accredited Neonatal-Perinatal Fellowship programs was prepared. A questionnaire was prepared and mailed to collect information on the following: Method used for noninvasive monitoring of oxygen therapy, acceptable maximum and minimum arterial pulse oxygen saturation levels, high and low alarm settings, and whether oxygen was administered at a fixed or variable rate. RESULTS: A response rate of 70% to 85% was achieved for different items of the questionnaire. A wide variation exists regarding acceptable arterial pulse oxygen saturation levels and alarm settings. Many units accepted an arterial pulse oxygen saturation level of 100% or set the high alarm at 100%. CONCLUSION: There is a need for greater awareness of the potential for hyperoxemia that may result from accepting an arterial pulse oxygen saturation level of 100% or setting high alarms at 100%. We urge stricter adherence to published recommendations.

Assessment of cytotoxicity assays as predictors of ocular irritation of pharmaceuticals.

We have evaluated the use of cytotoxicity assays in vitro as an alternative to predicting ocular irritation potential in animals. Three different measures of cytotoxicity--leucine incorporation into protein, MTT dye reduction, and neutral red uptake--were measured in a presumed target cell, corneal epithelial cells from rabbit, as well as in a nontarget cell, V79 (Chinese hamster lung fibroblasts). An IC50 value was determined for each endpoint in one or both target cells for a series of 27 commercially available compounds and 56 in-house materials from a variety of chemical classes (carbonitriles, imidazoles, substituted benzenes, aromatic acids, peptides, phenols, esters, etc.). Analysis of the data by Spearman rho rank correlation and Pearson's correlation indicated that none of the endpoint-target cell combinations used here accurately predicts in vivo irritation potential for this group of compounds. The MTT dye reduction endpoint gave the best overall correlation, regardless of target cell, but still had a correlation coefficient below -0.5. We conclude that the measurement of cytotoxicity is of limited value as an alternative assay for the classes of materials studied here.

Single base mutation in the hormone binding domain of the thyroid hormone receptor beta gene in generalised thyroid hormone resistance demonstrated by single stranded conformation polymorphism analysis.

Thyroid hormone resistance is a syndrome of considerable clinical heterogeneity. Three mutations in the c-erb A beta gene encoding the human beta thyroid hormone receptor have been described in different kindreds. We report here, in a family affected with peripheral thyroid hormone resistance, a unique point mutation in the ligand binding domain of the c-erb A beta gene resulting in histidine replacement of an arginine residue at position 438. The region in which the mutation occurred was identified by single stranded conformation polymorphism analysis and confirmed by subcloning and sequencing of the mutant alleles from each of the affected members. Binding of tri-iodothyronine to isolated nuclei from family members was normal suggesting the mechanism of thyroid hormone resistance in this family is not mediated by abnormal binding of ligand and receptor.

Modulation of pteroylpolyglutamate concentration and length in response to altered folate nutrition in a comprehensive range of rat tissues.

For a range of rat tissue extracts, the concentrations of total folates and of short-chain pteroylpolyglutamates were assayed by Lactobacillus casei with and without conjugase treatment, respectively, and the concentration and chain length of H4PteGlnn and 5,10-CH2-H4PteGlnn together were assayed after binding to thymidylate synthase and tritiated fluorodeoxyuridylate. For rats fed a nonpurified diet and consuming 26 micrograms of folic acid daily, the respective concentrations of these total folates, short-chain folates and thymidylate synthase bindable folates were, in nmol/g, 10.2, 2.5 and 3.5 in liver, 3.9, 1.8 and 2.0 in kidney, 4.2, 1.2 and 1.0 in bone marrow, 2.3, 0.6 and 0.2 in adrenal, 2.1, 0.3 and 0.5 in spleen, 2.1, 0.9 and 0.8 in jejunal smooth muscle, 1.2, 0.9 and 0.2 in jejunal mucosa, 1.0, 0.3 and 0.6 in testis, 0.7, 0.1 and 0.2 in heart, 0.3, 0.1 and 0.1 in skeletal muscle, 0.5, 0.1 and 0.3 in brain and 0.7, 0.002 and 0 in erythrocytes. The predominant pteroylpolyglutamate chain length was 6 residues in all tissues except kidney, jejunal mucosa, skeletal muscle and brain, in which the value was 5 residues. A folate-deficient diet (30 ng/d) fed for 3 wk resulted in a depression in the total folate concentration of all tissues (except brain); the depression was generally greater for short-chain than for long-chain folates and was accompanied by a lengthening of the pteroylpolyglutamate chain. Opposite results followed folate excess of 4 to 5.4 mg/d. The fractional change in the folate concentration of the individual tissues, following perturbation of dietary folate, did not vary greatly among tissues.(ABSTRACT TRUNCATED AT 250 WORDS)