Identification of the in vivo promoters of bacteriophages S13 and phi X174 and measurement of their relative activities.

Regions of bacteriophages phi X174 and S13 that contain putative promoter sequences were amplified by the polymerase chain reaction (PCR) and cloned into the reporter vector pKO-1. Assays of galactokinase activity revealed in vivo promoter activity in those constructs containing the promoter sequences with transcription initiation (+1) sites at nucleotide positions 45, 982, 1823, and 5211. These were identical in location to sequences with in vitro promoter activity and to the three known promoters PA, PB, and PD. P5211 is the location of a new, fourth, promoter. A site with a +1 position at nucleotide 4876, previously shown to initiate RNA synthesis in an in vitro run-off transcription assay, had no in vivo promoter activity. To investigate whether flanking sequences had effects on promoter activity, restriction fragments of phi X174 and S13 that encompass the in vivo promoters were cloned into the reporter vector pKO-1. The PA and P5211 promoter constructs showed dramatic effects with increases in activity of up to 7 times that shown with the PCR-generated promoter constructs. The phi X174 PB promoter construct had a 50% decrease in activity compared with the PCR-generated PB clone. While the data showed that in most instances promoter activity is affected by the flanking sequences in which the promoter is embedded, no general pattern correlating flanking sequences and promoter activity could be discerned. Additional evidence that the promoter sequence regions were active in vivo promoters was obtained by S1 nuclease mapping experiments. Initiation of RNA synthesis was shown at positions 45, 982, and 5211.

The effect of film thickness on the bond strength of polycarboxylate cement.

This study examined the bond strength of polycarboxylate cement when used to cement gold alloy specimens to dentin. The film thickness was controlled and varied over a range of 10 to 150 microns. Tensile and shear bond strengths were measured and, contrary to anticipated results, there was an increase in bond strength as the film thickness increased. In this study, the bond strength of polycarboxylate cement as it relates to film thickness is evaluated in relationship to the clinically significant value of 50 microns over the thickness range of 150 microns.

Radiofrequency gas plasma (glow discharge) disinfection of dental operative instruments, including handpieces.

The radiofrequency-stimulated argon gas plasma (glow discharge) technique, already well-known for surface cleaning and activation of adhesion, was investigated for determination of its separate potential for rapid disinfection of dental operative instruments. Disinfection effectiveness was judged from diminished post-treatment recovery of viable organisms from the instruments agitated in saline. Streptococcus salivarius, Bacillus stearothermophilus, and Escherichia coli were used as primary contaminant organisms, dried from gelatin-thickened laboratory cultures onto the instruments and not subjected to any preliminary cleaning steps. Significant disinfection was obtained, with no sensible temperature increases, in under 10 minutes in laboratory apparatus consuming fewer than 5 Watts of power per cycle. Also, clinically used and deliberately-saliva-contaminated high-speed handpieces were gas-discharge-treated, with their resultant rapid disinfection noted by complete suppression of the viability of any transferred natural contaminant organisms within two minutes. With regard to preservation of instrument quality, it was also shown that this low-temperature gas-discharge method provides the noted substantial disinfection without deterioration of sharp edges. Work now in progress suggests that the method can provide cool, rapid, and complete sterilization when hydrogen peroxide vapors are present in the gas plasma used for treatment of instruments first given the normally recommended thorough pre-cleaning.

Physical and mechanical properties of elastomers in orthodontic positioners.

Elastomers for conventional Kesling-type tooth positioners are relatively inelastic and are primarily indicated as finishing devices. However, new materials, first described in the Japanese literature, with claims of a greater range of tooth movement warrant a comparison with conventional materials. Physical and mechanical property testing of positioner elastomers has not been reported in the orthodontic literature. This investigation compared properties of a high temperature vulcanizing (HTV) Japanese silicone (Orthocon) to three traditional polyurethane and vinyl-based polymers and five experimental silicone elastomers. Fourier transform infrared spectroscopy established the definitive chemical composition of the urethane and vinyl materials obtained from a commercial positioner laboratory. Tear strength, tensile strength, tensile stress at selected elongations, and ultimate elongation of all materials were evaluated at 37 degrees C in an aqueous environment. Hardness and water sorption values also were determined and an in vitro force measurement apparatus was fabricated to determine force levels exerted by positioner materials at low displacements. Orthocon was statistically different (Duncan's multiple range test, p less than 0.05) from the traditional commercial urethane and vinyl materials. Orthocon had lower tear strength than the traditional materials. It also demonstrated lower stress values below 100% elongation. The parameters of tensile stress at 50% elongation and ultimate elongation were statistically identical for Orthocon and one experimental silicone material.

Clinical and laboratory evaluation of visible light-cured denture base resins and their application to orthodontics.

A series of investigations is being conducted to examine the applicability of visible light-cured resins to orthodontics. The experimental vehicle is the Hawley retainer, which is made from autopolymerized (AP), heat-cured (HC), thermoplastic Biocryl 2 (BC), and Traid visible light-cured (VLC) resins. In all physical property testing, it was found that VLC resins met or exceeded required values as established by ADA Specification No. 12 for denture base polymers. In vitro bacterial adherence studies showed that more organisms adhered to heat-cured specimens than to the other specimens. In vivo studies using split-palate Hawley retainers demonstrated slightly less bacterial adherence to BC than to the other resins. Scanning electron microscopy (SEM) observations have shown the BC surface to be the smoothest, although surface chemistry also seems important. None of the materials being tested appears to cause any significant change in the subjacent subgingival bacterial flora. There was no adverse tissue reaction under any of the materials when observed clinically. Manipulation characteristics and time of fabrication appear to be dependent on the depth of the palate and the skill of the operator.

A new visible light-cured resin system applied to removable prosthodontics.

Preliminary studies of VLC resins have produced promising results; however, additional research is necessary to completely define qualities of this material. Biologic testing of VLC (Triad) resins indicated that they are nontoxic and biocompatible. They have a wide range of uses in all subdisciplines of prosthodontics. Advantages such as accuracy of fit, superior strength, complete polymerization without residual compounds, ease of fabrication and manipulation, patient acceptance, ability to bond with other denture base resins, and low bacterial adherence make this material an important addition to the choices available to dentists. As with many new materials, there are initial problems or hurdles that must be overcome before there is widespread use. Initial formulations of material had insufficient flexural strength and tended to fracture when flexed over uncut sites on a stone cast. This problem has been reduced by Dentsply International, Inc. with the introduction of the new improved formulation. The original VLC bonding agent did not provide sufficient bond strength with acrylic resin denture base materials, but this also has been improved with development of a new VLC bonding agent. The problem of microporosity and small voids produced when adapting VLC resin sheets against a stone cast may be overcome with pressure or vacuum adaptation techniques. A promising application of VLC resin material is in direct intraoral procedures such as relining of dentures. Physical and chemical properties are superior to autopolymerizing methacrylates. Preliminary studies have shown successful patient acceptance to this clinical procedure. It is of particular advantage to the patient not to be without dentures for the period of at least 1 day necessary for a laboratory-processed relining. Immediate light-curing is time-saving and convenient compared to indirect (heat-cured) relining. Until recently, most direct intraoral applications of autopolymerizing acrylic resin reliner material were considered temporary or expedient to a permanent procedure. The patient and dentist may now have another treatment choice. The release of residual methyl methacrylate, among other shortcomings of AP materials, is not a concern when using the VLC reliner material. Some patients may notice a nonobjectionable taste to the uncured material; however, they can be reassured that the taste will be only temporary until the material is completely polymerized in the curing unit. The flow of the material can be regulated by selection of appropriate viscosity, warming and cooling measures, and partial intraoral polymerization with hand-held curing lights.(ABSTRACT TRUNCATED AT 400 WORDS)

Gingival and alveolar bone reaction to marginal fit of subgingival crown margins.

Interproximal subgingival marginal discrepancies of full coverage restorations were compared with adjacent crevicular fluid flow and percentage radiographic periodontal bone loss. A total of 88 patients with 116 premolar crowns were evaluated. Patients were selected at random from student treatment records, Institute of Dental Prosthetics, Royal Dental College, Copenhagen, Denmark. Crevicular fluid collected on filter paper strips from the interproximal area was stained with 0.2% ninhydrin solution and the length of the area measured. Marginal fit was determined by measuring the marginal excess or deficit recorded in a polyether impression. The amount of bone around each crowned tooth was measured on five times magnified prints of radiographs. Percentage bone loss was calculated by dividing the distance from the alveolar crest to the most coronal level at which the periodontal space retained its normal width by the distance from the alveolar crest to the root apex. Correlating marginal fit with crevicular fluid within gingival index scores showed r = 0.32 (G.I.1) and r = 0.42 (G.I.2). Fit vs percentage bone loss showed r = 0.68 and r = 0.59, respectively (P less than or equal to 0.001). Differentiation was further made within the 0.0-0.2 mm range discrepancy by categorizing the data in four groups. Comparing fit relative to crevicular fluid and bone loss, most of these groups were significantly different when analyzed statistically using the Mann-Whitney U-Test. Small defects less than or equal to 0.050 mm were associated with significantly less fluid flow and bone loss than defects exceeding this value.

Determination of residual stresses in denture base polymers using the layer removal technique.

In order to study the influence of residual stresses on dimensional accuracy and mechanical properties of denture bases, an experimental model was devised for measurement of residual stresses in acrylic denture base polymers. Rectangular bar coupons were cut from resin plates heat processed by conventional dental methods. They included samples which had been slow and fast cooled after polymerization and had been stored in dry and wet environments. Uniaxial residual stress distributions for each coupon were disclosed by removing layers of known thicknesses and measuring the ensuing deflection of the specimens. Coupons of a commercial acrylic resin were annealed and used as controls. ANOVA and Scheffe's test were used to compare experimental conditions at the 95% confidence level. Dry specimens exhibited residual surface compressive stresses from 0.43-0.83 MPa (62-120 psi). Water-stored specimens showed higher stress levels, 2.86-3.24 MPa (414-470 psi). Slow cooled pigmented acrylic coupons which were dry showed higher residual stresses compared with other dry but nonpigmented specimens. No significant differences were found between pigmented or clear coupons which contained moisture.

Spectrometric analysis of the influence of metal substrates on the color of metal-ceramic restorations.

The development and use of ceramic alloys have created the potential for variation in the color of dental porcelain. In order to define the nature of the alterations, it is necessary to examine quantitatively the color of dental porcelain baked onto ceramic alloys. The purpose of this study was to examine spectrometrically where color differences occur in the fabrication process. One shade of Vita porcelain was baked onto coupons of three ceramic alloys (high gold, palladium-silver, base metal). Eight replications were made in each alloy at seven fabrication steps: prepared metal, oxide, first opaque, second opaque, first dentin, second dentin, and glaze. Spectrometric analyses were performed for each replication at each step. Data were tabulated every 10 nm over the recorded 380-750-nm range, for conversion to the CIE color measurement system. Tristimulus values X, Y, and Z and chromaticity coordinates x and y were calculated. Differences from spectrographic inspection were seen among the metal substrate series. The greatest variation appeared at the first dentin step between the palladium-silver and high-gold alloys and between the palladium-silver and base metal alloys. Mean tristimulus values were significantly different (p less than 0.0001) for all steps and alloys. The distribution of plotted values followed the same pattern of spectral changes throughout the seven fabrication steps. Analysis of these data shows that color differences of metal-ceramic coupons based on dissimilar metal substrates can be quantified, and that spectral reflectance values can be converted to CIE notation. As depicted spectrally, notable color differences appeared with the first dentin porcelain layer.

Measurement of spine morphology in children, ages 10-16.

Measurements of vertebral body diameters and spine lengths in 248 Swedish children, ages 10-16, who had structurally normal spines are reported. Spine slenderness factors were calculated from these data. The spines of girls were found to be significantly more slender than those of boys. There was little dependence of slenderness on age in either sex.

Punch shear testing of extracted vital and endodontically treated teeth.

Plano-parallel specimens of human dentin cut from vital and endodontically treated teeth were tested by the punch shear test. Shear strength values were found to positively correlate with approximate toughness values. Statistically significant differences were found between shear strength and toughness values for vital and endodontically treated teeth, the latter showing lower values. The clinical impression that endodontically treated teeth are weaker and more brittle than vital teeth has therefore been quantitated. Anatomically different teeth or the methods used to store and cut teeth could not be consistently correlated with punch shear and toughness values. When dentin slices were constrained during punching so that bending was prevented, the precision of the results was improved and higher values were recorded.

The importance of neonatal asphyxia and caesarean section as risk factors for neonatal respiratory disorders in an unselected population.

The risk of neonatal respiratory disorders was calculated in an unselected, total population together with the relative contributions of some factors found associated with an increased risk. Postnatal asphyxia, expressed as a low one minute Apgar score, and low gestational age were substantially, independent risk factors. Caesarean section added, though less markedly, to the risk of the above disorders.

Procedure for a simplified collarless metal-ceramic restoration using gold powder.

This technique describes a simple and practical approach to the fabrication of collarless metal-ceramic restorations. Instead of making a duplicate die from the master die, this technique conserves time by blocking out the undercut using impression modeling compound on the master die. The use of gold powder does not require special equipment and produces a precise porcelain abutted margin on the shoulder. Excluding the labial gold collar from the shoulder enhances the esthetic appearance of the restoration. This approach is effective with gold-based and silver-palladium alloys as materials for the metal-ceramic framework. The marginal fit of 10 collarless meta-ceramic crowns cemented on silver plated dies were evaluated by measuring sectioned specimens with a scanning electron microscope. The average gap at the porcelain butt margin was observed to be 30 to 50 mu (Fig. 10).

A critical evaluation of the acute systemic toxicity test for dental alloys using histopathologic criteria.

The A.D.A. acute systemic test for type II, class 11 materials defines compliance on the basis of fewer than 50% mortality at 2 weeks. Histopathologic criteria were developed from pilot study data to evaluate the effects of these materials. In this double blind study, the frequency of histopathological changes in lung, liver, small intestine, and kidney were rated at 2 and 5 weeks, for six dental crown and bridge alloys ranging from 44% to 97% (Au, Pt, and Pd). Two positive 360 mg/kg and 1 g/kg of cadmium and two negative, a blank capsule and untreated control groups were used. There was significant difference (chi square test, X2 = 0.95) between the positive and negative controls at 2 and 5 weeks. The lung, liver, kidney showed the highest level of histopathological changes. Significant changes occurred in the four tissues for all alloys at two and five weeks. At five weeks, alloys with a lower noble metal content (44-62%, Au, Pd, and Pt) elicited significant chronic changes, while higher noble metal content (78-97%) showed healing and no significant difference from the negative controls. Applying histopathologic criteria and statistical parameters independent examiners can examine experimental animals and arrive at conclusive and reproducible results.

Toothbrush abrasion of color-corrective porcelain stains applied to porcelain-fused-to-metal restorations.

Normal toothbrushing with a common dentifrice has the ability to wear away color-corrective porcelain stains applied to the surface of porcelain-fused-to-metal restorations in as few as 10 to 12 years unless a protective layer of clear glaze is applied over the stain. The additional layer of clear glaze more than doubled the time required to abrade the stain from the surface.

Metrizamide and metrizoate for cardioangiography in infants. Comparison of heart rate and arrhythmia.

The cardiotoxic effect of Isopaque Coronar (metrizoate 370 mg I/ml) and Amipaque (metrizamide 370 mg I/ml) was analysed in 52 infants weighing less than 5 kg. In each group of patients 37 injections of contrast medium were performed and the immediate side effects, extrasystoles and change in heart frequency, were recorded. Amipaque caused significantly less bradycardia and significantly fewer immediate extrasystoles than Isopaque Coronar. The results indicate a lower cardiotoxicity of Amipaque in cardioangiography in infants.