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Heat treatment caused an increase in ductility. Aging caused an increase in strength and hardness with a decrease in ductility. Overaging caused decreases in strength and ductility. Solution treating resulted in a single phase. The precipitation of coherent intermetallic compounds caused maximum strengthening with minimum loss of ductility.

The σ phase is rich in Ta. When the Ta concentration is less than 14%, σ does not interfere with the slip mechanism; when the Ta concentration is more than 15%, σ interferes with the slip mechanism. The coherent α-Co 3Ta phase forms at Ta concentrations of less than 15%, whereas incoherent γ-Co 2Ta forms only at higher Ta concentrations. The interface between σ and the matrix is an important factor in the failure mechanism.

Crystal formations obtained from evaporating clear filtrates of dental stone mixed with various solutions were examined with an optical and scanning electron microscope. It was found that when K2SO4 was present in any concentration, a spherulitic structure dissimilar to that of CaSO4 2H2O and K2SO4 was dominant. It is concluded that syngenite (a complex compound of CaS04 and K2SO4) forms at the center of the nuclei of crystallization and is responsible for spherulitic formation. The use of K2SO4 solution and saturated CaSO 4 solution was also found to improve the strength both at one and 24 h.

Five different implant materials and three different geometries of ankylosed single-tooth implants were investigated. The stress distributions within and around the implants were determined by finite element analysis. Results show that the optimal combination of implant material and geometry can reduce implant and alveolar stresses by a factor of three when compared to an arbitrary implant design.

This study delineates the effects of varying the root length as well as incorporating a soft pseudo periodontal ligament on the overall stress distribution for each of five different implant materials and one implant design.

A microstructural study was conducted on 15 cobalt-chromium-nickel alloys of the basic composition 40 Co-30 Ni-30 Cr. The alloys were strengthened by the addition of tantalum and tantalum-rich regions were found at the interdendritic spaces. The increase in Ta concentration caused a decrease in the concentration of the β phase and an increase in the amounts of the a phase. Excessive amounts of Ta resulted in formation of the σ phase. The failure of the alloy occurred as a result of the interconnection of σ regions.

Cobalt-base alloys strengthened by intermetallic compounds of tantalum were prepared and tested. Some of the alloys were stronger and more ductile than conventional base-metal alloys.

X-ray diffraction analysis of the alloy system Co-Ni-Cr-Ta showed that the ternary alloy base consisted of three phases (a, β, and σ). Addition of Ta caused a decrease in the intensity of the β lines. Further Ta additions caused diffraction lines characteristic of the intermetallic compound α-Co3Ta. At higher Ta concentrations, the intensity of the lines characteristic of the σ phase increased and lines characteristic of Co2Ta appeared.

In Dentistry, a mixture of eugenol liquid (extract of oil of cloves) and zinc oxide powder enjoys many favored uses. The mixture is used as an obtunding temporary filling material, for temporarily cement­ ing dental inlays, crowns and bridges, for endodontic treatment and for taking impressions of edentulous cases. Despite this popularity of the material and its significance in dentistry, the hardening or setting mechanism of the material is not full y understood. Review of the literature 1 • 6 indicates that the major problem with respect to the setting of zinc oxide­ eugenol (ZOE) cement is whether zinc cugenolate crystals form as a result of the setting reaction and whether their formation causes the setting of the mix. The studies that dealt with the acceleration of ZOE 7 • 11 showed no systematic work to study the ef­ fect of an accelerator on the setting time of ZOE. The accelerator's efficiency was referred to its cation by some investigators 11 and to its anion3 by others. The purpose of this investigation was to study the effect of several accelerators when used in a powder form and as eugenol solutions on the setting time of ZOE; to study the relationship between the time of formation of eugenolate crystals and the setting time of ZOE; to illustrate whether the acceleration of ZOE is cationic or anionic in nature; and to study the effect of accelerator concentration 12 and eugenolate con­ centration on the compressive strength of ZOE.

Twenty-two materials, including 19 dental impression elastomers, were compared in their ability to replicate microscopic detail. Some polysulfide, silicone, and polyether materials performed well. Curiously, microscopic replication ability generally correlated inversely with that expected from the nominal consistency. The test method developed appears to be a suitable microreplication evaluation standard.

DOI: http://dx.doi.org/10.5915/18-3_4-12801 Among the factors claimed to affect the retention of full dentures is the shape of the supporting structure. Parametric evaluation through the adaption of Fourier Analysis to the surface of maxillary edentulous jaw is described in this study. lt has been established that alteration in the cosine coefficient of the expanded equation affects both the right and left ridges symmetrically. Alteration of the sine coefficient affected the two sides of the ridge asymmetrically. The analysis furnished in this study will be necessary to study the relationship between jaw shape or the symmetry of such shape and the retention of full dentures.

DOI: http://dx.doi.org/10.5915/15-1-12345 A simple and economical tensile test for measuring bond strength has been developed and utilized to compare the adherence of four composite resins. Specimen preparation is convenient, and conditioning treatments can be performed easily. Statistical analysis of the data obtained indicates that the test is useful for comparative adhesion studies.

The contourmeter was used to determine quantitatively the denture displacements caused by various impression materials and techniques during the relining of a maxillary denture. This study indicated the following conclusions. Tissue-conditioning material used with closed-mouth impression technique or light-bodied polysulfide used with either open- or closed-mouth technique caused the least denture displacement in the three dimensions when compared with regular-bodied polysulfide or zinc oxide and eugenol impression materials. Comparing the same impression materials used with either open- or closed-mouth technique showed no significant difference in maxillary denture displacements. A relined complete denture should be remounted on the articulator and the occlusion refined to eliminate occlusal mismatches resulting from three-dimensional denture displacements during relining.

Finite element analysis is used to determine the physiological stress values in the natural tooth and the underlying bone. In addition to modeling the periodontal ligament (PDL) as a continuous structure as considered in previous studies, the PDL is modeled more accurately in a novel fashion as a fibrous structure. The results indicate that the type of PDL modeling has a significant effect on the nature and magnitude of alveolar stresses, and that the fibrous PDL modeling shows higher and more widely distributed lateral tensile stresses in the alveolar bone than those resulting from the continuous PDL modeling.

Basic factors that influence the physical metallurgy and the mechanical properties of cobalt-base alloys are discussed in this study; these factors include the coherency of the interphase interface, the stacking fault energy, and the average electron hole number. Control of these factors and considerations of corrosion resistance and body compatibility determined the compositions for alloys that fulfill dental requirements.

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.

Macrosegregation refers to the inhomogeneous distribution of solute elements at the scale of cast product. It is a severe defect affecting the quality of cast product produced through Direct Chill (DC) casting process. Several casting parameters and transport mechanisms such as shrinkage induced flow, natural convection and equiaxed grain motion contribute to macrosegregation formation. Of these, equiaxed grain motion and its interplay with other transport mechanisms leading to macrosegregation formation is not well understood. The complexity increases when the grain morphology is accounted for which further influences macrosegregation formation. The goal of this work is to establish a numerical framework within which the effects of transport mechanisms with focus on grain motion and morphology on macrosegregation formation and, as an extension, modification can be studied. Furthermore, we move from 2D sheet ingot simulations to full scale 3D sheet ingot simulations. A previously published two-phase volume averaged solidification model is used to study the effect of the alloy elements (Mg, Cu and Zn) on macrosegregation formation in 2D sheet ingots by studying the transport mechanisms individually and in combination. It is shown that the alloy element influences the interplay of transport mechanisms leading to macrosegregation formation. The same model is used to conduct a comparison study of a simplified 3D and 2D sheet ingot simulation against experiment. A qualitative comparison is obtained between the three results. The two-phase model is extended to a simplified three-phase model, as a part of this work, to also account for grain morphology. The simplified three-phase model is novel in its approach as it solves for the grain growth kinetics accounting for three phases (solid, intragranular liquid and extragranular liquid) but solves for the macroscopic transport accounting for only two phases (solid and liquid), similar to the two-phase model. This model is also validated against experimental data for AA7050 on axis symmetric billets. Macrosegregation reduction or optimization is important to maintain ingot quality. The first step towards achieving this is by modifying macrosegregation by controlling process parameters. An attempt is made to complement recent experimental studies by numerically modifying macrosegregation by introducing an inlet jet. This qualitative study is conducted on axis symmetric billets and 3D sheet ingots using the simplified three-phase model. It is shown that macrosegregation modification due to grain resuspension is possible by using an inlet jet. The extent of modification depended on the grain morphology: globular or dendritic.