Carl W. Fairhurst

Bond strength and mechanical properties of dental porcelain enamels

E nameled gold-alloy restorations potentially have the desirable and necessary properties of both metal and porcelain. In order to obtain the full benefit of both materials, and thus insure a successful restoration, the dentist must possess thorough knowledge of their properties. The purpose of this investigation was to gain some additional understanding of the mechanical properties of the metal-porcelain composite. Previous investigations by Shell and Nielsen,l and Custer, Asgar, and Peytor? reveal the effects of certain variables on the bond strength of porcelain fused to gold. The effects of such variables as bonding agents? and the atmosphere in which the porcelain is fused to the metal have not been studied. Specifically, this investigation was designed to study the effect of bonding agents and firing atmospheres on bond strength, to determine the tensile and compressive properties of the porcelains, and to study tensile properties of the metal after certain heat treatments.

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.

The contour meter: An apparatus for comparison of mucosal surface contour of impressions, models, and dentures

Abstract The contour meter is described, and problems in connection with the positioning procedure and the correction factors for recording of points on inclined surfaces are discussed. Experimental errors affecting the reproducibility of recordings have been studied, and limits of accuracy for the contour meter are given.

Strength and phase formation of dental amalgam.

Ten dental amalgam alloys from the American Dental Associations list of certified dental materials, purchased on the open market, were used for this study, together with a few model alloys. Furthermore, experimental alloys were furnished through the courtesy of the L. D. Caulk Co. and S. S. White Co. Ultimate compressive strength was determined on cylinders of 4 by 8 mm., packed in a steel mold. The amalgam alloys and mercury for the specimens were weighed. The proportions used were: 5 to 71/2, 5 to 8, 5 to 9, and 5 to 10. Trituration, from 5 to 60 seconds, was done in an S. S. White mechanical amalgamator without pestle. After amalgamation the amalgam was rolled in a cotton squeeze cloth to form a cylinder of about 3 mm. in thickness. In some experiments mulling was done for 45 or 90 seconds before the amalgam was shaped into a cylinder. For all specimens used for this report, packing of the test cylinders was done in 2 steps. The amalgam was placed in the mold in large increments by very light packing with a 4 mm. Sweeney plugger, care being taken to avoid expression of mercury at this stage. The mold was then transferred to a testing machine and a load calculated to produce 2,000, 5,000, or 8,000 pounds per square inch, was applied over a 10to 15-second interval and then maintained for 60 seconds. The mercury expressed during condensation was carefully collected and weighed. The part of the specimen exceeding 8 mm. in length was extruded and removed by a razor blade and weighed, after which the finished specimen was extruded from the mold and weighed. From the weights of the original alloy and mercury, the expressed mercury, the amalgam in excess of 8 mm., and the finished sample, it was possible to compute the weight of mercury and alloy in the sample, the per cent of residual

Heat treating porcelain-enameled restorations

Abstract Maximum physical properties of the restoration will be obtained by adding a heat treatment at the completion of the final firing cycle. This is accomplished by employing the following simple procedure. Upon completion of the glazing, remove the piece from the oven and place it under a covered glass. Next, allow the furnace to cool to 1,000 °F. At this time place the enameled restoration back into the furnace at this temperature for 15 minutes, followed again by cooling under glass. This procedure will routinely eliminate the variability or range in the physical properties of the cast piece which occurs after the method of firing as recommended by the manufacturer. In addition, the hardness properties exhibit a substantial increase.

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.