William J. O'Brien

Hardening of High-Fusing Gold Alloys

SYNOPSIS IN INTERLINGUA INDURAMENTO DE ALLIGATOS DE AURO A ELEVATE PUNCTO DE FUSION.—Esseva studiate le effecto indurante producite per le addition systematic de metallos vil (ferro, stanno, e indium) a alligatos de auro e palladium e de auro e platinum. Funditos specimen de iste alligatos esseva subjicite a duo cyclos de tractamento thermal: (1) refrigidation ab 1800 F (= 1060 C) e (2) invetulation ante le frigidation, durante 30 minutas a un serie de temperaturas inter 850 e 1600 F (=450 e 870 C). Le valores de duressa Brinell esseva registrate, e le microstructura esseva studiate post le tractamento thermal. Le addition del metallos vil al alligatos de auro e platinum (sed non de auro e palladium) resultava in un augmento significative del duressa in le condition invetulate. Evidentia de un precipitation o de un formation subgranular esseva obtenite in omne le systemas de auro e platinum in condition hyper-inventulate.

Surface energy of liquids isolated in narrow capillaries

Abstract This paper presents a conceptual and mathematical model for the surface tension of liquids in narrow capillaries isolated from a reservoir. A pure liquid is viewed as a two component system consisting of vacancies as well as the molecules of the liquid. Desorption of vacancies takes place at the solid-liquid interface. The attendent increase in vacancy concentration at the liquid-vapor interface results in a greater average intermolecular distance and higher attractive forces. The equation relating the change in surface tension at the liquid-vapor interface is, dγ dA SL = (F SV − F SL ) A LV . This relation is used to derive the Fisher equation for the strength of liquid bridges between two spheres without the use of the reduced pressure device. This approach considers the properties of a liquid in small capillaries as part of a composite system and the results support the work of Shereshefsky and Derjaguin who have observed the abnormal behavior of liquids in small capillaries.

Effect of an elastic lining on the retention of dentures

Abstract Denture retention was measured in each of ten patients who complained of poor retention. Eight of these dentures were restored to maximum retention by relining with a hydrophilic, soft-lining material. When new dentures were constructed, all ten patients obtained maximum retention. Retention levels were measurable up to the point at which each patient felt pain. In a concurrent laboratory study, improvements in wettability and in retention to glass with water were made by coating acrylic-resin disks with a layer of a hydrophilic, soft-lining material. Complete spreading of the soft-lining material was obtained with distilled water. Retention values obtained in vitro were more than twice those obtained with the uncoated disks. A mechanism requiring more energy was the cause of failure of the lined disks. A hypothesis was put forth that the soft elastic layer produced a more uniform distribution of stresses in the joint. Without the lining, the disks separated from the glass by a cantilever action. With the lining, an hourglass failure mechanism was observed.

Contact angles of drops of enamels on metals

A LTHOTJGH the area of enamel-metal dental restorations has seen the introduction of several new materials in the past ten years, relatively little has been published concerning their nature and properties. l-13 Generally, an enamel-metal system in dentistry consists of a vitreous material that is fused to a gold-platinum casting to produce veneered crowns, jacket crowns, and fixed partial dentures. An important aspect of this system is the adhesion between the enamel and the metal structure ; without true adhesion, the restoration will fail. Adhesion depends upon several factors, but the most important of these is the degree of attraction between the elementary particles of the enamel and the metal. Mechanical tests have been applied to test the strength of the interface between the enamel and metal. Shell and Nielsen1 applied a pull-through shear test, and Custer, Asgar, and Peyton2 employed a beam test for bond strength. O’brien and Ryge3 have reported on the wetting forces between one molten enamel and several materials. Substances have been suggested that are called “bonding agents” to be used in joining these enamels and metals. Although complete information is not available, these “bonding agents” contain compounds or colloidal dispersions of gold in an organic base. Manufacturers recommend that the metal to receive the enamel be coated with a layer of such a material and fired. During the firing operation, a layer of gold is deposited on the surface of the alloy. It was the purpose of this study to determine the degree of wetting by contact angle measurements between several commercial enamels and various metals. These data, in addition to other information, may be used to estimate the strength of the wetting forces involved in the .adhesion between these materials.

Empirical Equation for Estimating the Area of a Maxillary Edentulous Jaw

An empirical equation to calculate the surface area of the maxillary edentulous jaw was formulated. The values obtained by use of the equation were compared with the values determined by two methods of area measurements. Regression analysis and correlation coefficient computation showed good agreement between the calculated and the experimental values.

Animal Study of Adhesion and Leakage of a Carboxylate Cement

Recently, Smith (Brit Dent 1 125:381-384, 1968) has proposed the use of a polyacrylic acid solution and zinc oxide combination as a dental cement with adhesive properties. Since then, commercial products based on this formula have appeared for use as adhesives for orthodontic brackets and as restorative materials. The purpose of this study was to evaluate the adhesion of this type of cement to enamel and its sealing qualities as a restorative material. Thirty Class V cavities were prepared on the labial surfaces of the teeth of dogs. Five dogss were used in this study. The cavity surfaces were debrided and pretreated with ethyl alcohol and carbon tetrachloride followed by swabbirng with the cement liquid. Nine of the preparations received the polyacrylic acid cementJf The ten preparations in the control group were filled with the conventional acrylic cement.§ To test for marginal leakage, a small crystal of fiuorescein was placed on the pulpal axial wall of each preparation just before placing the restorations. Leakage was detected by use of an ultraviolet light to which fluorescein is sensitive (R. J. NELSON, R. B. WOLCOTT, and G. C. PAFFENBARGER, JADA 44:288-295, 1952). To study adhesion to enamel, stainless steel orthodontic brackets were bonded to the labial surfaces of maxillary teeth of dogs after the cleaning and surface treatments with alcohol,

Evolution of Gases from High-Fusing Gold Alloys

SYNOPSIS IN INTERLINGUA EVOLUTION DE GASES AB ALLIGATOS DE AURO A ALTE FusioN.-Con le objectivo de determinar le comparative quantitates de gas evolvite ab alligatos de auro empleate in le technica de porcellana fusionate a auro, un systema a vacuo esseva concipite pro mesurar le effecto de varie factores manipulative super le evolution de gas durante le coction e pro determinar le fonte de gases evolvite. Le magnitude comparative del quantitate de gas evolvite dependeva del tractamento del fundituras ante le contraplacation. Le evolution de gas esseva maximal post contamination digital, durante que nulle gas esseva detegite post un calefaction del specimens secundo le proponimentos del fabricantes. Ni magazinage ni depurgation con HF contribueva al evolution de gas. Apparentemente, le gas evolvite es un gas de superficie.