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.

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.

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.

Treatment and sequelae of angiographic complications in children.

Fourteen cases of thromboembolic complications appeared in 267 consecutive angiographies during a 7-yr period. The arterial circulation has been evaluated both clinically and with oscillometry. The complication rate was substantially higher after cut down then after percutaneous approach (56% vs. 2.7%). Seven patients with signs of total vascular obstruction were subjected to acute thromboectomy whereas three patients with milder clinical symptoms were treated nonoperatively with anticoagulants. Four patients have died during the examination period, the remaining ten patients have been subjected to long term follow-up (mean follow-up period 3 yr). Seven demonstrated normal findings clinically, as well as oscillographically, whereas three patients subjected ot thromboectomy after cut down were clinically normal but decreased oscillographic pulsations could be demonstrated.

Effect of methods of tooth enamel preparation on the retentive strength of acid-etch composite resins.

The effect of three procedures of preparing enamel surface on the retentive strengths of Concise Enamel Bond. Adaptic acid etch, Restodent and Nurva-Seal/Nurva-Fil was investigated. Resins using an unfilled-filled resin combination(Concise Enamel Bond, Adaptic acid etch, and Nurva-Fil) had a significantly higher retentive strength when the enamel was prepared with a coarse diamond bur than when the surface was unprepared or prepared with a carbide bur. The different procedures of tooth preparation did not affect the retentive strength of the resin when only filled resin was used (Restodent).

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.

Creep of dental amalgam.

The steady-state creep rates of dental amalgams were measured and the creep rates were correlated with the microstructure of the amalgams. The influence of manipulation variables on creep rate and microstructure are evaluated. The samples were either mechanically or hand triturated, hand condensed, and stored at 20 degrees C for 7 d. The specimens were subjected to a constant tensile load for 24 h, and the elongation was measured with a displacement transducer. The smallest creep rate was found on a spherical amalgam, and the highest on an amalgam made from a preamalgamated fine grain alloy. A correlation between microstructure and creep rate could be demonstrated. The amount of gamma2 phase did not seem to influence the creep rate. Amalgams that had large closely packed gamma particles surrounded by a small volume fraction of gamma1 phase exhibited a low creep rate. Amalgams that had small broken up gamma particles surrounded by a large volume fraction of gamma1 exhibited a high creep rate. Abusive manipulation of lathe-cut amalgam alloys resulted in high creep rates, small broken up gamma particles and a high volume fraction of gamma1.

Adherence of a nickel-chromium alloy and porcelain.

1. Surface oxide favors adherence. The results of this study do not support the hypothesis that chromium oxide has a deleterious effect on adherence as measured by the torsion test. 2. Gritblasting the surface before porcelain application improves adherence. Smooth uncoated specimens where oxide was removed before enameling developed insufficient amounts of oxide for bonding. 3. The particular coating agent used on this study indirectly promotes adherence, since additional oxide forms during its application. Also, it may be directly involved by its influence on the residual stress distribution in the interface porcelain. 4. The more extensive the reaction zone at the interface, the further away the fracture surface is from the interface.

Intra-arterial blood pressures at rest and during exercise after surgery for coarctation of the aorta.

Nineteen young men operated upon for coarctation of the aorta during childhood, between the ages of 6 and 14 yr, were studied. Twelve patients had a systolic hypertension in the right arm at rest, and generally during exercise, measured intra-arterially. All patients but 2 had systolic gradients between the right arm and leg at rest and even more so during exercise. There was no significant correlation between the degree of hypertension or gradient on the one hand and the width of the anastomosis, age at surgery or years since surgery on the other in this group of patients. No better correlation was found when the patients were studied during exercise. Thus, blood pressure measurements can not reveal whether a re- or rest-coarctation is at hand. It can be questioned whether an early operation could prevent postoperative hypertension in the long run.

Complications of angiography in children and means of prevention.

In 267 consecutive angiographic examinations in children 14 thromboembolic complications occurred: following surgical exposure 8 complications in 14 cases and 6 complications in 253 percutaneous angiographies. The origin of thrombus during angiography has recently been clarified. Technical advances such as thin walled catheters, systemic heparinization and lately heparinized catheters decreased the complication rate significantly, no complication occurred among the last 153 examinations.

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.

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)

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.

Tissue toxicity of intravenous solutions. A phlebographic and experimental study.

A phlebographic study in 32 children has shown that i.v. infusion of invertose, glucose, Vamine and Intralipid but not saline, damages the tissues as judged from changes in the vessel walls, oedema and disturbances in the venous circulation. The addition of Heparin to the solutions markedly reduced the frequency of these untoward reactions. The toxicity of invertose, glucose, Vamine and Intralipid was studied experimentally in a biologic tissue: the cheek pouch of the hamster. All solutions particularly Vamine caused some damage to the microcirculation. In this study the factor mainly responsible for thrombophlebitis was the toxicity of the solution infused. Other factors such as surgical trauma, site of entry, local infection, temperature of solutions etc. played only a minor role.

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.

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.

A comparison of Isopaque Coronar 370 and Amipaque in angiocardiography in infants.

Experimental studies and some clinical investigations have indicated that Amipaque (metrizamide) is less cardiotoxic than other contrast media in common use for angiocardiography. It, therefore, seemed motivated to find out whether these findings are valid in the high-risk group of neonates and small infants subjected to angiocardiography.

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.